Introduction

Can you train the "upper glutes" and "lower glutes" separately? Few questions in fitness generate more content and less evidence. Social media is full of upper glute exercises promising a "shelf," lower glute exercises promising to lift the "underbutt," and programs claiming that the right combination of movements will grow each region on demand. The anatomy behind the question is real: the gluteus maximus is functionally segmented into upper and lower portions, with distinct nerve distribution, different contractile properties, and different activity during movement. The popular answer, however, is only half right, and the wrong half is the one selling programs.

This article is a systematic review of every study we could identify comparing upper and lower gluteus maximus activity, including fine-wire and surface EMG research on glute activation exercises, loaded resistance exercise (including the hip thrust vs. squat comparison), walking, stair climbing, sprinting, and the only training study to measure regional gluteus maximus growth. The findings support an asymmetric conclusion. The upper gluteus maximus can be biased: hip abduction and external rotation exercises (e.g., clams, side-steps, and single-limb stance positions) resulted in significantly higher upper gluteus maximus activity when compared to lower gluteus maximus activity. The lower gluteus maximus cannot: no identified exercise resulted in higher lower gluteus maximus activity when compared to upper gluteus maximus activity, and hip extension exercises (e.g., hip thrusts, squats, and bridges) recruited both portions similarly. Further, the best glute exercises for activation may not be the best exercises for growth: 9 weeks of hip thrust training and 9 weeks of back squat training resulted in statistically similar increases in upper, middle, and lower gluteus maximus size, despite higher EMG activity during hip thrusts.

The conclusions, recommendations, summary of research findings, and a complete annotated bibliography are below. As with all Brookbush Institute content, every claim is matched to the strength of the research supporting it, and every study was verified against the primary text.

Conclusions

Recommendations: You can preferentially recruit the upper portion, but not the lower portion of the gluteus maximus. If you are performing both hip abduction/external rotation exercises, conventionally labeled "gluteus medius exercises ", and multi-joint hip extension exercises like hip thrusts, squats, and lunges, you are doing as much as you can do to activate and strengthen the gluteus maximus.

Position Statement: Research demonstrates that the upper gluteus maximus exhibits higher EMG activity when compared to the lower gluteus maximus during exercises incorporating hip abduction and/or hip external rotation, that the upper and lower gluteus maximus exhibit similar EMG activity during exercises consisting primarily of hip extension, and that the lower gluteus maximus does not exhibit higher EMG activity during any identified exercise (excluding a single phase of a single exercise). If the intent is to bias the upper gluteus maximus, then optimal exercise selection includes hip abduction and external rotation exercises (e.g., clams, side-steps, and single-limb stance positions), especially with the hips flexed (e.g., clams). Hip extension exercises (e.g., barbell hip thrusts, unilateral bridges, and quadruped hip extensions) are likely to result in similar EMG activity of the upper and lower gluteus maximus. If the intent is to comprehensively improve activity and strength of the gluteus maximus, then both abduction/external rotation exercises and hip extension exercises are recommended. Last, gluteus maximus EMG activity may not be correlated with muscle growth: 9 weeks of hip thrust training and 9 weeks of back squat training resulted in statistically similar increases in upper, middle, and lower gluteus maximus cross-sectional area, despite higher EMG activity during hip thrusts. That is, selecting exercises for higher regional EMG activity may not result in more regional muscle growth.

Summary:

• If the intent is to bias the upper gluteus maximus, then optimal exercise selection includes hip abduction and external rotation exercises (e.g., clams, side-lying hip abduction, side-steps, hip hikes, and single-limb stance positions), and clams resulted in the highest upper gluteus maximus EMG activity of the exercises tested (43.6% of MVIC).
• Research demonstrates that none of the exercise biases lower gluteus maximus EMG activity when compared to upper gluteus maximus EMG activity; hip extension exercises (e.g., bridges, quadruped hip extensions, lunges, squats, and hip thrusts) recruit both portions similarly.
• If the intent is to increase gluteus medius and upper gluteus maximus activity with less TFL activity, then optimal exercise selection includes clams, side-steps, unilateral bridges, and quadruped hip extensions.
• If the intent is to achieve the highest gluteus maximus EMG activity during loaded exercise, then barbell hip thrusts resulted in significantly higher upper and lower gluteus maximus EMG activity than back squats, with the highest activity occurring near full hip extension under load.
• EMG activity may not predict hypertrophy: hip thrust training and back squat training resulted in statistically similar growth in all 3 gluteus maximus regions, and exercise selection for gluteus maximus hypertrophy should not be based on EMG comparisons alone.

Caption: Glute bridges and hip thrusts result in similar activation of the upper and lower portions of the gluteus maximus.

Summary of Research Findings

Exercise Demand Comparisons: Hip Abduction and External Rotation Compared to Hip Extension

Summary Statement: Exercises incorporating hip abduction and/or hip external rotation resulted in significantly higher upper (superior) gluteus maximus EMG activity when compared to lower (inferior) gluteus maximus EMG activity, and exercises consisting primarily of hip extension resulted in statistically similar upper and lower EMG activity. This pattern was demonstrated with fine-wire recording, replicated with surface recording in 3 additional independent samples, and extended to single-limb stance and abduction at various hip flexion angles. The practical interpretation is conservative but useful: the upper gluteus maximus may be biased with frontal plane and rotational demands (e.g., clams, side-lying hip abduction, side-steps, hip hikes, and single-limb stance positions), whereas the lower gluteus maximus cannot be meaningfully isolated; hip extension exercises recruit both portions similarly.

• Hip Abduction and External Rotation Exercises: Side-lying hip abduction, clams, hip hikes, side-steps, and forward step-ups resulted in significantly higher superior gluteus maximus EMG activity when compared to inferior gluteus maximus EMG activity, with the highest superior EMG activity occurring during clams (43.6% of MVIC). Clams and side-lying hip abduction also resulted in significantly higher superior than inferior gluteus maximus activity in a separate sample using surface recording during all phases of both exercises, regardless of whether abdominal bracing was performed. A wall touch single-limb stance, performed with the stance hip in external rotation, resulted in significantly higher superior than inferior gluteus maximus EMG activity, and the difference between portions grew as exercises demanded more frontal plane and rotational control.
• Hip Extension Exercises: Bilateral bridges, unilateral bridges, both quadruped hip extension variations, forward lunges, and squats resulted in statistically similar activity in both portions of the gluteus maximus. The inferior portion exhibited the highest amplitude during unilateral bridges (36.7% of MVIC); however, this value was not significantly higher than the superior portion. Only 1 finding in this literature resulted in higher inferior than superior gluteus maximus EMG activity: inferior gluteus maximus activity was significantly higher than superior activity during the concentric phase of prone hip extension, and only when participants did not receive core activation instructions. Note that the bias toward the inferior portion required isolating a single phase of a single exercise, whereas the bias toward the superior portion is demonstrated for all phases during a variety of exercises.
• The Step-Up (Conflicting Findings): During forward step-ups, fine-wire recording demonstrated significantly higher upper gluteus maximus EMG activity when compared to lower gluteus maximus EMG activity. During 10-inch step-ups, surface recording in a different sample demonstrated statistically similar upper and lower activity. Note that the step-up sits at the boundary of the 2 exercise categories, because the movement is primarily hip extension, but the single-limb support phase adds a frontal plane demand. Until additional research resolves this conflict, the step-up should not be cited as an exercise that biases the upper gluteus maximus, or as an exercise that recruits both portions similarly.
• Hip Flexion Angle and Contraction Intensity During Isometric Hip Abduction: During isometric hip abduction, upper and lower gluteus maximus EMG activity increased significantly as the hip moved into flexion (tested at 0°, 20°, 40°, 60°, and 80°), and the effect grew as contraction intensity increased (tested at 20%, 40%, 60%, and 80% of each participant's maximal abduction force, matched using visual feedback of force output). The upper gluteus maximus exhibited its highest amplitude (85.7% of MVC) at 80° of hip flexion and 80% of maximal abduction force, and upper gluteus maximus activity was higher than lower gluteus maximus activity at every angle and intensity; however, the study did not statistically compare the portions to one another. Gluteus medius activity did not differ across hip flexion angles. Note that these findings suggest the upper gluteus maximus contributes more to abduction as the hip flexes, which may partly explain why the clam (performed with the hips flexed to 45°) resulted in higher upper gluteus maximus activity than side-lying hip abduction (performed with the hips at 0°) in the exercise research below.
• The Upper Portion Is a Secondary Abductor: During side-lying hip abduction and hip hikes, upper gluteus maximus EMG activity was significantly lower than tensor fasciae latae (TFL) EMG activity. In contrast, during side-lying hip abduction, gluteus medius EMG activity was significantly higher than TFL activity, and during hip hikes, gluteus medius and TFL activity were statistically similar. Note that this implies that during both side-lying hip abduction and hip hikes, the upper fibers of the gluteus maximus were significantly less active than the TFL, and likely less active than the gluteus medius. That is, abduction results in more upper gluteus maximus activity when compared to the lower gluteus maximus, but the upper gluteus maximus remains a supporting abductor when compared to the gluteus medius and TFL. If the intent is to increase gluteus medius and upper gluteus maximus activity with less TFL activity (highest gluteal-to-TFL activation index values), then optimal exercise selection includes clams, side-steps, unilateral bridges, and quadruped hip extensions.

Regional Function During Gait, Stairs, Running, and Sprinting

Summary Statement: Fine-wire gait analysis demonstrated that the upper and lower gluteus maximus exhibit different EMG activity during locomotion, with the upper portion behaving like a hip abductor (matching the gluteus medius in timing and intensity) and the lower portion behaving as a hip extensor (matching the activity of the adductor magnus). Higher-intensity functional activities (sprinting and climbing) resulted in significantly higher upper and lower gluteus maximus EMG activity when compared to walking, and an experimental increase in trunk control demand (additional forward lean) during running resulted in higher lower gluteus maximus activity specifically. These findings support the functional division of the muscle; however, they should be applied to exercise recommendations with caution. These locomotion studies used normalization methods that cannot be compared with the %MVIC values used in the exercise studies.

• Walking and Stairs: During walking, the upper gluteus maximus and the gluteus medius exhibited the same activity pattern (a peak during the loading response - heel strike), and the lower gluteus maximus exhibited the same activity pattern as other hip extensors, including the adductor magnus. During stair ascent, the lower gluteus maximus was the primary hip extensor during the loading response and mid-stance. During stair descent, the upper gluteus maximus and gluteus medius remained active, and the lower gluteus maximus was nearly silent. Note that this may imply that the 2 portions can behave independently: stair descent likely requires more frontal-plane support of the pelvis and hip abductor recruitment than hip extensor recruitment for eccentric deceleration of hip flexion.
• Running, Sprinting, and Climbing: During sprinting, both portions exhibited the highest activity recorded (more than 5 times walking activity for the upper gluteus maximus). During ladder climbing, both portions exhibited activity similar to running. Note that this implies both portions are recruited heavily during powerful, whole-body tasks, and neither portion is excluded from high-intensity activity.
• Trunk Control Perturbation: During running with a device that attempted to increase forward trunk lean, lower gluteus maximus EMG activity increased significantly, while no other measured muscle activity changed. During walking with the same device, gluteus medius activity increased, but neither portion of the gluteus maximus exhibited a significant increase in activity. During running with a device that decreased the demand to control forward trunk lean, muscle activity did not significantly decrease for any of the muscles measured.. Note that this is the only identified study in which an imposed demand during a functional activity resulted in a significant difference in EMG activity in one portion of the gluteus maximus and not the other, and it is likely the strongest evidence available that the portions can be influenced separately. However, this finding only supports the functional division of the muscle and the potential effects of a forward lean on muscle activity during running, and likely cannot be generalized to a specific technique for increasing gluteus maximus activity during running.

Trunk Rotation and the Effects of Low Back Pain

Summary Statement: During standing isometric trunk rotation to the left, the right upper and lower gluteus maximus and the left latissimus dorsi exhibited increased EMG activity, and during trunk rotation to the right, the pattern reversed (the left gluteus maximus and the right latissimus dorsi exhibited increased activity). Note that this pairing may imply force transfer between the trunk and the opposite hip through the thoracolumbar fascia (Posterior Oblique Subsystem ). During left trunk rotation, participants with chronic low back pain exhibited significantly higher EMG activity in the left and right biceps femoris, the left and right erector spinae, and the left upper and lower gluteus maximus when compared to matched controls; latissimus dorsi activity was statistically similar between groups during all conditions. Note that this implies participants with low back pain performed the same submaximal rotation task with higher activity across the hip and trunk extensor muscles bilaterally, including muscles on the side not producing the rotation force, while activity of the primary rotation-producing muscle (the latissimus dorsi) did not differ. This is the only identified study of upper and lower gluteus maximus activity in a symptomatic population, and low back pain was associated with increased activity in both portions rather than a change in one portion when compared to the other.

Loaded Resistance Exercise Comparisons

Summary Statement: Barbell hip thrusts resulted in significantly higher upper gluteus maximus EMG activity when compared to American and band hip thrust variations; however, lower gluteus maximus EMG activity was statistically similar during all 3 hip thrust variations. Barbell hip thrusts also resulted in significantly higher upper and lower gluteus maximus EMG activity when compared to back squats, during both dynamic repetitions and isometric holds. Further, front, full, and parallel squats resulted in statistically similar upper and lower gluteus maximus EMG activity. Note that these comparisons should be interpreted with caution. All 4 publications drew from a single sample of 13 resistance-trained females, and none statistically compared the upper and lower portions of the gluteus maximus. That is, this research compared EMG activity during various exercises, but did not compare upper gluteus maximus EMG activity to lower gluteus maximus EMG activity. These findings should not be cited as evidence that any loaded exercise biases one portion relative to the other; however, the pattern is consistent with the abduction and external rotation research above: some comparisons resulted in a statistically significant difference in upper gluteus maximus EMG activity while lower gluteus maximus EMG activity remained statistically similar.

• Why Can't This Data Set Compare Portions? Note that a %MVIC value is a ratio: EMG activity during the exercise divided by EMG activity during a maximal reference contraction, recorded at the same electrode site. Comparing 2 exercises at the same site compares 2 ratios with the same denominator; comparing the upper site to the lower site compares 2 ratios with different denominators. That is, a higher %MVIC value at the lower site only implies more recruitment if the reference contraction captured the true maximum of each portion. These publications normalized each site to the higher of 2 reference contractions, and the same research group demonstrated that 1 of these reference positions (the standing glute squeeze) lowers the reference value for the lower gluteus maximus by approximately 10%, without changing the reference value for the upper gluteus maximus. That is, the higher values exhibited by the lower gluteus maximus in these publications may partly reflect the reference contractions used for normalization, and not a difference in recruitment between the portions.
• Hip Thrusts Compared to Squats: During dynamic repetitions with 10-RM loads, barbell hip thrusts resulted in significantly higher upper gluteus maximus, lower gluteus maximus, and biceps femoris EMG activity when compared to back squats, and vastus lateralis activity was statistically similar. During isometric holds with the same loads, barbell hip thrusts (held in full hip extension) resulted in significantly higher upper and lower gluteus maximus EMG activity (87.1% and 115.7% of MVIC) when compared to back squats held in hip flexion (10.1% and 20.9% of MVIC). Note that this may imply that gluteus maximus activity is dependent on hip position, with the highest activity occurring near full hip extension under load.
• Hip Thrust Variations: Barbell hip thrusts resulted in significantly higher mean upper gluteus maximus EMG activity when compared to American hip thrusts (69.5% compared to 57.4% of MVIC) and band hip thrusts (49.2% of MVIC), and lower gluteus maximus EMG activity was statistically similar during all 3 variations. That is, every statistically significant difference in EMG activity during the hip thrust variations occurred in the upper gluteus maximus. Note that the band-variation loads were matched to force plate data rather than to 10-RM estimates, and the barbell-to-band load differences are the most questionable load comparisons in this research.
• Squat Variations: Front, full, and parallel squats resulted in statistically similar upper and lower gluteus maximus EMG activity, despite parallel squats using 35.5% heavier loads than front squats. This may imply that matching relative loads to each variation (10-RM loads for each) results in similar gluteal demands across squat depths and bar positions.

Regional Hypertrophy Following Training

Summary Statement: In the only training study to measure multiple gluteus maximus regions, 9 weeks of hip thrust training and 9 weeks of back squat training resulted in statistically similar increases in upper, middle, and lower gluteus maximus cross-sectional area. Despite first-session EMG activity being significantly higher during hip thrusts at every gluteal recording site, acute EMG amplitudes did not consistently correlate with regional muscle growth. Note that the study compared exercises within each region, but did not compare growth of one region to growth of another.

• Growth by Region and Exercise: After 9 weeks of volume-matched training to volitional failure, upper, middle, and lower gluteus maximus cross-sectional area increased in both groups, and the increases were statistically similar between the hip thrust and back squat groups for all 3 regions. In contrast, quadriceps and adductor cross-sectional area increased significantly more in the back squat group, and hamstrings cross-sectional area exhibited little change in either group. Note that this may imply that hip thrusts and back squats provide a similar growth stimulus to the gluteus maximus, while back squats provide a larger growth stimulus for the thigh muscles.
• Strength Transfer: Back squat 3-RM strength increased significantly more in the back squat group, and hip thrust 3-RM strength increased significantly more in the hip thrust group. Deadlift 3-RM strength (15 - 16%) and isometric wall push force (7.6 - 10%) increased similarly in both groups. Note that this may imply that strength gains are largest in the trained exercise, while transfer to untrained tasks is similar between these 2 exercises.

Supporting Research

• Whole-Muscle Corroboration: During 3-RM lifts in trained males, barbell hip thrusts results significantly higher whole-muscle gluteus maximus EMG activity than back squats and split squats. Note that this replicated the hip thrust findings above in a different sample, sex, load, and laboratory; however, the 4 electrode sites were averaged for analysis, and this study cannot support any comparison of the upper and lower gluteus maximus. Further, sprint velocity correlated with force production during hip thrusts and during sprinting, and gluteus maximus EMG activity did not correlate with sprint velocity.
• The Gluteal Region as a Continuum: During walking, a multi-electrode array spanning the TFL, gluteus medius, and gluteus maximus demonstrated that activation characteristics change gradually across the gluteal region, rather than switching abruptly at muscle borders. Note that this may support interpreting the upper gluteus maximus as a functional partner of the gluteus medius. However, the electrodes were set from anterior to posterior at a single height/level; therefore, this study cannot be used to support differences in upper and lower gluteus maximus EMG activity.
• Physiological and Anatomical Basis: Evoked contraction time was longest in the upper segment of the gluteus maximus and shortest in the lower segment, and contractile properties were statistically similar between medial and lateral sites within each segment. That is, the contractile gradient of the muscle runs along the superior-to-inferior axis. Further, cadaveric nerve staining demonstrated distinct nerve-dense zones in the upper, middle, and lower segments. Note that these findings establish that regional recording is anatomically justifiable; however, the proposal that the upper segment contains more slow-twitch fibers is an inference from contraction time and has not been verified with muscle biopsy.
• Historical Sources (Pending Verification): The association between hip abduction and the upper gluteus maximus was first reported in 1965, and the earliest statistical comparison of the portions during gait was reported in 1980; however, the primary texts of these studies have not been retrieved, and their findings are excluded from the conclusions above until verified.

Caption: Squats are a great hip extension exercise, recruiting both the upper and lower portions of the gluteus maximus.

Table 1. Relevant Research: Direct Comparisons of Upper and Lower Gluteus Maximus Activity or Growth

(rows follow the order of Section 1)

Study

Method and regions

Normalization

Key outcome

Cross-study caution

Selkowitz et al. (2013 and 2016) (1 dataset) — Section 1.1

Fine wire; superior and inferior portions (2016); superior only with gluteus medius and TFL (2013); 11 therapeutic exercises

Highest of 4 MVIC positions

Superior activity was significantly higher than inferior during the 5 exercises incorporating hip abduction and/or external rotation (side-lying abduction, clams, hip hikes, side-steps, step-ups); the portions were statistically similar during the 6 primarily hip extension exercises. Superior activity was highest during clams (43.6% of MVIC); inferior activity was highest during unilateral bridges (36.7% of MVIC). The superior portion was significantly less active than the TFL during side-lying abduction and hip hikes

2 publications report 1 data collection; multi-position normalization produces lower %MVIC values than single-position studies

Chan et al. (2017) — Section 1.1

Surface; upper and lower portions; prone hip extension, clams, side-lying abduction, with and without abdominal bracing

Manual muscle testing MVICs

Upper activity was significantly higher than lower during all phases of clams and side-lying abduction; lower activity was significantly higher than upper during the concentric phase of prone hip extension under the natural core condition (the only lower-higher-than-upper finding identified)

MMT reference; mean-substitution for invalid trials; Tables 1 and 5 pending retrieval

Rani et al. (2023) — Section 1.1

Surface; upper and lower portions; step-ups, unsupported wall squats, wall touch single-limb stance

Standing glute squeeze MVIC

The upper-minus-lower difference increased with frontal-plane and rotational demand (statistically significant only during the wall touch single-limb stance, 24.6% of MVIC); the portions were statistically similar during step-ups

Surface step-up finding conflicts with Selkowitz et al.'s fine wire step-up finding (superior significantly higher); the wall touch exercise overlaps the normalization task

Fujisawa et al. (2014) — Section 1.1

Surface, ultrasound confirmed; upper and lower portions with gluteus medius and TFL; isometric abduction at 5 hip flexion angles and 4 effort levels

Single MVC trial per position

Upper and lower activity increased significantly with hip flexion angle (upper: to 85.7% of MVC; lower: to 38.2% of MVC, with the angle effect gated by effort level); gluteus medius activity did not differ across angles; TFL activity decreased with flexion

Source of the electrode convention used by Contreras and Plotkin; single MVC trial; no between-portion statistical test

Lyons et al. (1983) — Section 1.2

Fine wire; upper and lower portions with 5 other hip muscles; walking (2 speeds), stair ascent and descent

Manual muscle test or dynamometer maximum

The upper portion matched the gluteus medius pattern across all gait conditions; the lower portion behaved as a hip extensor and was the primary hip extensor during stair ascent loading response and mid-stance; during descent, the upper portion (15%) and gluteus medius (20%) were active while the lower portion was nearly silent (5%)

Manual muscle test reference; values not comparable to modern %MVIC; source of the insertion-site convention used by Selkowitz and Pirouzi

Bartlett et al. (2014) — Section 1.2

Surface; superior and inferior portions with gluteus medius and hamstrings; walking, running, sprinting, climbing, and trunk pitch perturbations

Unperturbed walking or running (not MVIC)

Sprinting produced the highest activity in both portions; climbing equaled running; increased forward trunk pitch demand during running increased inferior activity (23%) without changing superior activity (the only experimentally produced dissociation identified; speed-dependent and one-directional)

Values are changes relative to gait; no unit shared with any %MVIC study

Pirouzi et al. (2006) — Section 1.3

Surface; upper and lower portions with trunk and thigh muscles; submaximal standing trunk rotation; chronic low back pain and matched controls

Submaximal reference contractions (gluteals); maximal (latissimus dorsi, biceps femoris)

The low back pain group exhibited significantly higher upper and lower gluteus maximus, hamstring, and erector spinae activity; both portions acted as contralateral trunk rotation agonists; upper activity was descriptively higher than lower in both groups (not statistically tested)

Different normalization references for different muscles within the study; within-muscle upper compared to lower comparison is descriptive only

Contreras et al. (2015 and 2016, 4 publications) (1 dataset) — Section 1.4

Surface; upper and lower sites per Fujisawa et al.; squats, hip thrusts, and variations; MVIC position comparison

Higher of 2 MVIC positions (or highest 1,000 ms window, PeerJ)

Hip thrusts produced higher upper and lower activity than back squats (dynamic and isometric); squat variations were statistically similar at both portions; hip thrust variations differed at the upper portion only (barbell higher than American and band); the 2 MVIC positions were statistically similar for the upper portion, with a trend favoring prone hip extension for the lower portion

1 sample of 13 trained females across all 4 publications; 2 publications share recorded squat data; the authors treated the lower site as a middle-fiber proxy; no between-portion statistical tests

Plotkin et al. (2023) — Section 1.5

Surface EMG (3 sites) and MRI (3 slice-anchored regions); 9 weeks of hip thrust or squat training, volume-matched RCT

MVIC (EMG); cm² (MRI)

Upper, middle, and lower gluteus maximus CSA increases were statistically similar between exercises; quadriceps and adductor growth significantly favored squats; first-session EMG was higher during hip thrusts at all gluteal sites yet did not consistently correlate with hypertrophy

EMG labels are not interchangeable with the study's own MRI labels or other studies' labels; no statistical comparison of growth among regions

Table 2. Supporting Research: Context That Informs Interpretation but Cannot Support Regional Claims

(rows follow the order of Section 2)

Study

Method and scope

Key contribution

Role and status in this bibliography

Williams et al. (2021) — Section 2.1

Surface EMG; upper and lower sites recorded bilaterally, averaged for analysis; 3-RM squats, split squats, hip thrusts; sprint correlations

Hip thrusts produced higher combined gluteus maximus activity than back squats and split squats in trained males; sprint velocity correlated with hip thrust force, not squat force; gluteus maximus activity did not correlate with sprint velocity

Whole-muscle evidence only (4 sites averaged; no regional findings exist); independently corroborates the Contreras hip thrust finding in a different sample, sex, load, and laboratory

Anders et al. (2017) — Section 2.2

Surface array, 8 anterior-to-posterior positions at a single height; TFL, gluteus medius, and gluteus maximus territory; walking at 3 speeds in healthy older adults

Anterior positions (TFL, gluteus medius) exhibited higher amplitudes than posterior (gluteus maximus) positions at all speeds, with activation timing shifting continuously across the region; the authors conclude the gluteals behave as an intermuscular functional unit

Resolves the anterior-to-posterior axis, not superior-to-inferior; supports the regional-continuum concept; no regional gluteus maximus conclusions may cite it

McAndrew et al. (2006) — Section 2.3

Laser mechanomyography of evoked twitches; upper, middle, and lower segments, each with medial and lateral sites

Evoked contraction time was longest in the upper segment and decreased significantly toward the lower segment; medial and lateral portions were statistically similar within segments (the contractile gradient runs along the superior-to-inferior axis only)

Physiological basis for regional analysis; evoked rather than voluntary; fiber-type claims are inference, not histology; deep fibers not analyzed

Yi et al. (2024) — Section 2.3

Cadaveric Sihler whole-nerve staining; upper, middle, and lower segments (20 muscles)

Intramuscular nerve endings were concentrated in the central portion of each segment's span from origin to insertion, supporting anatomically distinct segments and central injection or recording targets

Anatomical basis for regional recording; innervation topography does not establish independent neural control

Stern (1972) — Section 2.4

Comparative anatomy of human and ape gluteals (specimen numbers not verified)

The superior portion is the distinctly human enlargement, with extensive fascia lata attachment (as characterized by citing authors)

Anatomical context for the introduction only; pending primary verification; not activation evidence and not relevant to recommendations

Stern et al. (1980) — Section 2.4

Gait EMG (methods not verified)

Superior activity was reported as significantly higher than inferior during walking and slow running (as characterized by Bartlett et al.)

Historical lineage only; pending retrieval; excluded from vote counts until verified

Karlsson & Jonsson (1965) — Section 2.4

EMG of gluteus maximus function (methods not verified)

Earliest identified source associating hip abduction with the upper portion; also cited for gluteus maximus quiescence during relaxed standing

Historical priority citation only; journal discontinued, interlibrary loan required; excluded from all vote counts and recommendations

Caption: Side Plank with Resisted Abduction may bias the upper portion of the gluteus maximus (as well as target the gluteus medius).

Annotated Bibliography

SECTION 1: RELEVANT RESEARCH - Direct Comparisons of Upper and Lower Gluteus Maximus Activity or Growth

1.1 Exercise Demand Comparisons: Hip Abduction and External Rotation Compared to Hip Extension

Hip abduction and external rotation exercises result in significantly higher superior than inferior gluteus maximus EMG activity; hip extension exercises result in statistically similar activity in both portions

Selkowitz et al. compared 20 healthy males and females (10 males, 10 females) (age: 27.9 ± 6.2 years; range: 18 - 50 years; height: 170.5 ± 11.1 cm; body mass: 67.7 ± 14.1 kg) with no orthopedic injuries of the trunk or lower extremities, neurological disorders, or current pregnancy. All participants performed 11 exercises with the dominant leg (the leg used to kick a ball), in random order, during 1 session: side-lying hip abduction (to approximately 30°, heel sliding along a wall), clams with elastic resistance around the distal thighs (hips flexed to 45°, knees flexed to 90°, raising the top knee to 30° of hip abduction with heels together), bilateral bridges (from hook-lying with hips at 45° of flexion, raising the pelvis to 0° of hip flexion), unilateral bridges, quadruped hip extension on the elbows with the knee extending (to 0°), quadruped hip extension on the elbows with the knee flexed (maintained at 90°), forward lunges with an erect trunk, squats (to approximately 90° of hip and knee flexion with slight hip external rotation and abduction), side-steps with elastic resistance around the distal thighs in a squatted position, hip hikes (standing on a platform, raising and lowering the pelvis), and forward step-ups (to a step height producing approximately 90° of knee flexion). The exercise protocol included 5 reps/exercise (side-steps: 3 cycles of 2 strides in each direction), paced by a metronome at 40 beats/min (side-steps at 80 beats/min) with 1 beat of rest between reps, and a short (2 min) rest between exercises; all participants practiced the exercises before data collection. Outcome measures included fine wire EMG (50 micron nickel-chromium wires, placement per Delagi and Perotto and per Lyons et al., confirmed by electrical stimulation and by observing the EMG signal during voluntary contractions, and re-verified by repeating the MVIC procedure after the exercises) of the superior portion of the gluteus maximus (wires inserted superior and lateral to the midpoint of the line from the PSIS to the posterior greater trochanter) and the inferior portion (wires inserted inferior and medial to the midpoint of the same line, 2.5 - 5.0 cm above the gluteal fold), expressed as the mean root mean square across the concentric and eccentric phases of all 5 reps, and normalized to the highest value obtained across 4 MVIC positions performed in random order: resisted hip extension with the hip at 45° of flexion and the knee at 90°, resisted hip extension fully prone with the knee at 90°, resisted hip abduction side-lying at 30° of abduction with the knee extended (pelvis perpendicular to the table, scapulae and pelvis against a wall), and resisted hip abduction and internal rotation side-lying at 30° of abduction and 45° of hip flexion (joint angles measured with a goniometer, with verbal encouragement during each test). The findings demonstrated a significant portion by exercise interaction. EMG activity of the superior portion was significantly higher than the inferior portion during the 5 exercises incorporating hip abduction and/or hip external rotation: side-lying hip abduction (23.7% compared to 5.2% of MVIC), clams (43.6% compared to 14.3% of MVIC), hip hikes (17.7% compared to 5.4% of MVIC), side-steps (27.4% compared to 19.9% of MVIC), and forward step-ups (22.8% compared to 15.7% of MVIC). EMG activity of the superior and inferior portions was statistically similar during the remaining 6 exercises, which primarily involved hip extension: bilateral bridges (17.4% compared to 22.3% of MVIC), unilateral bridges (34.6% compared to 36.7% of MVIC), quadruped hip extension with the knee extending (28.5% compared to 31.2% of MVIC), quadruped hip extension with the knee flexed (30.1% compared to 34.3% of MVIC), forward lunges (20.1% compared to 18.5% of MVIC), and squats (12.9% compared to 10.5% of MVIC). Additionally, the superior portion exhibited its highest activity during clams, and the inferior portion exhibited its highest activity during unilateral bridges (36.7% of MVIC), followed by quadruped hip extension with the knee flexed (34.3% of MVIC) and with the knee extended (31.2% of MVIC). Note that bilateral bridges exhibited a trend toward higher inferior than superior activity (mean difference: -4.9% of MVIC; 95% CI: -9.9 to 0.0; P = .052) (the trend failed to reach statistical significance), the only exercise in which the difference favored the inferior portion by this margin. Note that the authors conclude the superior portion is active as a hip extensor, abductor, and external rotator and the inferior portion is active primarily as a hip extensor; the exercises were not kinematically analyzed, so the attribution of differences to abduction and external rotation demands is based on exercise classification rather than measured joint mechanics, which the authors state as a limitation. Note that the authors state activation differences were observed between the portions even though the entire muscle is innervated by the inferior gluteal nerve, and propose nonuniform distribution or asynchronous recruitment of motor units as explanations. Note that the authors state there was considerable variability among participants, with not all individuals demonstrating activation patterns consistent with the cohort means, and caution against overgeneralizing. Note that this study and Selkowitz et al. (2013) report identical participant numbers, sex distributions, and demographics, the same laboratory, fine wire methodology, and 11 exercise protocol, and this study's appendix reprints the exercise descriptions and photographs from the 2013 publication with permission; the 2 publications report the same data collection and are treated as 1 dataset for evidence counting (??)

• Selkowitz, D. M., Beneck, G. J., & Powers, C. M. (2016). Comparison of electromyographic activity of the superior and inferior portions of the gluteus maximus muscle during common therapeutic exercises. Journal of Orthopaedic & Sports Physical Therapy, 46(9), 794-799. https://doi.org/10.2519/jospt.2016.6493

Related citation, not a regional comparison: superior gluteus maximus portion only. The clam, sidestep, unilateral bridge, and both quadruped hip extension exercises produce the highest gluteal-to-TFL activation index values; the superior gluteus maximus is significantly less active than the TFL during side-lying hip abduction and hip hikes

Selkowitz et al. compared 20 healthy males and females (10 males, 10 females) (age: 27.9 ± 6.2 years; range: 18 - 50 years) recruited from 2 university communities, with no reported musculoskeletal disorders of the trunk or lower extremities and no neurological conditions. All participants performed 11 exercises with the dominant leg, in random order, during 1 session: side-lying hip abduction (to approximately 30°), clams with elastic resistance around the distal thighs (hips flexed to 45°, knees flexed to 90°, raising the top knee to 30° of hip abduction with heels together), bilateral bridges (hips at 45° of flexion to a 90° knee flexion bridge position), unilateral bridges, quadruped hip extension on the elbows with the knee extending (to 0°), quadruped hip extension on the elbows with the knee flexed (maintained at 90°), forward lunges with an erect trunk, squats (feet at approximately 15° of toe-out, descending to approximately 90° of hip and knee flexion), side-steps with elastic resistance around the distal thighs in a squatted position, hip hikes (standing on a platform, raising and lowering the pelvis), and forward step-ups. The exercise protocol included 5 reps/exercise (side-steps: 3 cycles of 2 strides in each direction), paced by a metronome at 40 beats/min (side-steps at 80 beats/min) with 1 beat/phase and 1 beat of rest between reps, and a short (2 min minimum) rest between exercises. Outcome measures included fine wire EMG (50 micron wires, placement per Delagi and Perotto and per Lyons et al., confirmed by electrical stimulation; superior gluteus maximus wires inserted superior and lateral to the midpoint of the line from the PSIS to the posterior greater trochanter) of the superior gluteus maximus (only), gluteus medius (middle portion), and tensor fasciae latae (TFL), normalized to the highest value obtained across MVIC positions (1 trial/muscle/position, 5 second contractions; the superior gluteus maximus was tested in 2 resisted hip extension positions: prone with the hip at 45° of flexion and the knee at 90°, and fully prone with the knee at 90°), and a descriptive gluteal-to-TFL activation index combining the amplitude of each gluteal muscle with its ratio to the TFL. The findings demonstrated that both the gluteus medius and superior gluteus maximus were significantly more active than the TFL during 7 exercises: unilateral bridges (30.9% and 34.6% compared to 18.1% of MVIC), bilateral bridges, both quadruped hip extension variations, clams (26.7% and 43.6% compared to 11.4% of MVIC), side-steps, and squats. During side-lying hip abduction, gluteus medius activity was significantly higher than the TFL (43.5% compared to 32.3% of MVIC); however, superior gluteus maximus activity was significantly lower than the TFL (23.7% of MVIC). During hip hikes, gluteus medius activity was statistically similar to the TFL (37.7% compared to 31.4% of MVIC), and superior gluteus maximus activity was significantly lower than the TFL (17.7% of MVIC). Muscle activity was statistically similar among all 3 muscles during lunges and step-ups. The gluteal-to-TFL activation index ranged from 18 to 115, and was highest for the clam (115), followed by the sidestep (64), the unilateral bridge (59), and both quadruped hip extension exercises (50 each); the authors conclude these 5 exercises are most appropriate for preferentially activating the gluteal muscles while minimizing TFL activation, as each also produced amplitudes above 25% of MVIC for both gluteals and below 20% of MVIC for the TFL. The superior gluteus maximus amplitude was highest during the clam (43.6% of MVIC) and second highest during the unilateral bridge (34.6% of MVIC), which the authors attribute to the greater hip external rotation and extension components of these exercises. The authors state that the superior gluteus maximus may act as a secondary hip abductor relative to the gluteus medius and TFL during side-lying hip abduction and hip hikes, with less activation required, particularly at submaximal loads. Additionally, muscle activity did not differ between males and females. Note that this study recorded the superior portion of the gluteus maximus only and is therefore not a regional comparison; its exercise findings describe the superior portion and should not be attributed to the gluteus maximus as a whole. Note that the gluteal-to-TFL activation index is a descriptive analysis, and the authors state it can be artificially high when one gluteal muscle's amplitude is high and should only be interpreted for exercises in which both gluteal muscles exceeded the TFL by statistical testing. Note that the elastic resistance for the clam and sidestep was not quantified in absolute or relative terms, which the authors state as a limitation, and both exercises with elastic resistance ranked in the index's top 2. Note that this study and Selkowitz et al. (2016) report identical sample sizes, sex distributions, age ranges, laboratories, fine wire methodologies, and 11-exercise protocols; whether the 2 publications report the same data collection requires confirmation against the 2016 full text, and if confirmed, the 2 Selkowitz publications should be treated as 1 dataset for evidence counting.

• Selkowitz, D. M., Beneck, G. J., & Powers, C. M. (2013). Which exercises target the gluteal muscles while minimizing activation of the tensor fascia lata? Electromyographic assessment using fine-wire electrodes. Journal of Orthopaedic & Sports Physical Therapy, 43(2), 54-64. https://doi.org/10.2519/jospt.2013.4116

Upper gluteus maximus EMG activity was significantly higher than lower gluteus maximus EMG activity during all phases of clams and side-lying hip abduction, for both natural core and cued abdominal bracing conditions. Prone hip extensions resulted in similar upper and lower gluteus maximus EMG activity during both core conditions, except higher lower gluteus maximus EMG activity during the concentric phase without core bracing.

Chan et al. compared 20 healthy males and females (10 males, 10 females) recruited from a university population (specific ages not reported in the participant description; verify against Table 1) with no history of musculoskeletal or neurological disorders of the lower back or lower extremities. All participants performed clams (side-lying, hips flexed to 45°, knees flexed to 90°, with 30° of combined hip abduction and external rotation), side-lying hip abduction (knee extended, abduction to 30°), and prone hip extensions (knee flexed to 90°, extension to 20°), in random order, during a natural core activation condition and an enhanced core activation condition, during 1 session. The natural core condition included no instruction or correction. The enhanced core condition included a voluntary abdominal wall bracing maneuver ("navel up and in toward the spine, then tightening the abdominal wall without changing lumbar spine position"), trained for approximately 15 min under therapist guidance, and verified during every trial with real-time surface EMG of the bilateral internal obliques (threshold of more than 20% of MVIC) and palpation to confirm bracing without pelvic or lumbar movement. The exercise protocol included 3 trials/exercise, with concentric, isometric, and eccentric phases of 3 seconds each (metronome paced at 60 beats/min), 3 seconds rest between trials, and a short (1 min) rest between exercises. Note, trials in which internal oblique activity missed the condition threshold were replaced with series means, which the authors acknowledge as a statistical limitation. Outcome measures included surface EMG of the bilateral internal obliques, and the upper gluteus maximus, lower gluteus maximus, gluteus medius, and biceps femoris of the dominant leg, normalized to manual muscle testing MVICs. The findings demonstrated that upper gluteus maximus EMG activity was significantly higher than lower gluteus maximus EMG activity during all phases of clams and side-lying hip abduction, for both core conditions. Upper and lower gluteus maximus EMG activity was similar during most phases of prone hip extensions, for both core conditions; however, lower gluteus maximus EMG activity was significantly higher than upper gluteus maximus EMG activity during the concentric phase of prone hip extensions under the natural core condition. Additionally, internal oblique EMG activity was significantly higher during the cued bracing condition during all phases of all 3 exercises, which confirmed the condition threshold. When compared to the natural core condition, the cued bracing condition resulted in significantly higher upper gluteus maximus EMG activity during all phases of prone hip extensions; significantly higher lower gluteus maximus EMG activity during the eccentric phases of all 3 exercises and the isometric phase of prone hip extensions; significantly higher gluteus medius EMG activity during all phases of clams, the eccentric phase of side-lying hip abduction, and the concentric and isometric phases of prone hip extensions; and significantly higher biceps femoris EMG activity during all phases of all 3 exercises, except the eccentric phase of prone hip extensions. Note, the differences in hip muscle activity between core conditions were small (0.7 - 9.4% of MVIC), and the authors state the clinical significance of differences of this magnitude has not been established.

• Chan, M. K., Chow, K. W., Lai, A. Y., Mak, N. K., Sze, J. C., & Tsang, S. M. (2017). The effects of therapeutic hip exercise with abdominal core activation on recruitment of the hip muscles. BMC Musculoskeletal Disorders, 18(1), 313. https://doi.org/10.1186/s12891-017-1674-2

Wall touch single-limb stance results in the largest difference between upper and lower gluteus maximus EMG activity when compared to step-ups and unilateral wall squats.

Rani et al. compared 24 healthy males and females (17 males, 7 females) (age: 21.8 ± 2.2 years) not participating in regular resistance training or sport, and with no history of lower extremity or spine injury, surgery, or deformity, patellofemoral pain syndrome, neuromuscular disorders, or current pregnancy. Note, 7 additional females were excluded because gluteal adipose tissue interfered with surface EMG recording. All participants performed step-ups, unilateral wall squats, and wall touch single-limb stance exercises, in random order, during 1 session. The step-up protocol included stepping up onto a 10 inch box, leading with the dominant leg (heel contacting the posterior edge of the box), by extending the leading hip and knee until the rear leg was placed on the box. The unilateral wall squat protocol included standing with the back and head against a wall, in a single-limb stance on the dominant leg (heel placed approximately 1 foot from the wall), with the non-dominant hip flexed and knee extended to hold the leg off the floor, squatting down as far as possible and returning to the start position while keeping the trunk upright and against the wall. The wall touch single-limb stance protocol included standing upright facing 45° to a wall, in a single-limb stance on the dominant leg positioned in hip external rotation, with the non-dominant hip and knee flexed to 90° and the knee touching the wall, and elongating the trunk (cued as "trying to appear taller" without a heel raise) while maximally contracting the gluteals isometrically. The exercise protocol included 3 reps/exercise, 5 - 6 second contractions/rep, and a long (3 min) rest between exercises. Outcome measures included surface EMG of the upper and lower gluteus maximus of the dominant leg, normalized to a standing glute squeeze MVIC, and perceived exertion (Borg CR10 scale). The findings demonstrated that upper and lower gluteus maximus EMG activity was highest during the wall touch single-limb stance (137% and 112.5% of MVIC), followed by unilateral wall squats (93.2% and 80.2% of MVIC), and lowest during step-ups (70.4% and 65.3% of MVIC); however, EMG activity was statistically similar for step-ups and unilateral wall squats. Additionally, upper gluteus maximus EMG activity was significantly higher than lower gluteus maximus EMG activity during the wall touch single-limb stance; upper activity was higher than lower activity during unilateral wall squats and step-ups, but these differences failed to reach statistical significance. Last, perceived exertion was lowest during step-ups (0.5/10), followed by the wall touch single-limb stance (2.4/10), and highest during unilateral wall squats (4.8/10).

Additional information regarding this study:

The difference between upper and lower gluteus maximus activity grew as the exercises demanded more frontal plane and rotational control. The difference was smallest during step-ups (5.1% of MVIC), which load the stance leg briefly and primarily in the sagittal plane. The difference was larger during unilateral wall squats (13.0% of MVIC), which require a sustained single-limb stance; however, the wall supports the trunk, and this difference failed to reach statistical significance. The difference was largest during the wall touch single-limb stance (24.6% of MVIC), which combines a sustained single-limb stance, an externally rotated hip, and an unsupported trunk, and only this difference reached statistical significance. For this reason, the gradient across the 3 exercises may be reported as a descriptive pattern, and a bias toward the upper gluteus maximus may only be claimed for the wall touch single-limb stance.

A potential confound should be considered before this study is cited as support for the abduction and external rotation hypothesis. The wall touch single-limb stance instructions included a maximal voluntary contraction of the gluteal muscles, and the reference contraction used for normalization was a standing glute squeeze. That is, the exercise is nearly the same task as the normalization contraction, with external rotation, a single-limb stance, and trunk elongation added. This overlap explains why recorded values exceeded 100% of MVIC, and it raises the possibility that the bias toward the upper gluteus maximus reflects a maximal contraction performed in external rotation, rather than the postural demands of the exercise alone. However, Contreras et al. (2015) demonstrated that a bilateral standing glute squeeze resulted in similar upper and lower gluteus maximus activity (92.0% and 85.1% of the highest value). A maximal squeeze alone does not appear to produce the bias, which implies the external rotation position and the single-limb stance are the more likely contributors.

This study supports the hypothesis that hip abduction and external rotation demands result in higher upper gluteus maximus activity, and extends the hypothesis to a new condition: exercises in which the femur is fixed and the pelvis moves (or is stabilized) on the femur. During the wall touch single-limb stance, the stance femur is fixed to the floor in external rotation, and the gluteal muscles must hold the pelvis and trunk in position over the femur. The single-limb stance also adds a frontal plane demand: the hip abductors must generate an abduction moment to prevent the opposite side of the pelvis from dropping. The exercise therefore loads both of the motions associated with an upper gluteus maximus bias, even though neither motion is visible as limb movement. The study authors note the external rotation position, but do not distinguish between movement of the femur on the pelvis and stabilization of the pelvis on the femur. This distinction may be important, because Selkowitz et al. (2016) identified the hip hike, a pelvis-on-femur exercise, among the exercises that biased the upper portion.

• Rani, B., Sharma, S., Berwal, P., Shree, R., & Dhillon, M. S. (2023). A novel wall touch-single limb stance exercise for dynamic activation of gluteus maximus - a cross sectional study. Journal of Orthopaedics, 41, 33-38. https://doi.org/10.1016/j.jor.2023.05.005

Upper and lower gluteus maximus EMG activity increases significantly with increasing hip flexion angle during isometric hip abduction, and the increase grows with effort level; gluteus medius activity does not differ across hip flexion angles, and tensor fasciae latae activity decreases with increasing hip flexion

Fujisawa et al. compared 27 healthy males (age: 21.5 ± 1.2 years; height: 172.8 ± 5.0 cm; body mass: 64.6 ± 2.3 kg) with no history of hip joint problems. All participants performed isometric hip abduction of the right hip at 5 hip flexion angles (0°, 20°, 40°, 60°, and 80°) and 4 effort levels (20%, 40%, 60%, and 80% of maximum abduction strength) during 1 session. Testing was performed supine, with a low-friction sheet under the lower extremity, the pelvis fixed to the table with a belt, the knee maintained in neutral, and the ankle fixed in neutral with a brace; the table was manipulated to achieve each hip flexion angle. Maximum abduction strength was measured at 0° of hip flexion with a strain gauge sensor placed between the resistance belt and the lateral epicondyle of the femur (130.5 ± 16.9 Nm), and participants controlled abduction effort to each indicated level for 3 second contractions using visual biofeedback on a display. Outcome measures included integrated surface EMG (calculated from the steady middle 2 seconds of each contraction) of the upper gluteus maximus, lower gluteus maximus, gluteus medius, and tensor fasciae latae (TFL), normalized to MVC (upper and lower gluteus maximus tested during prone hip extension with the knee flexed; gluteus medius and TFL tested during side-lying hip abduction at 0° of hip flexion; 3 second contractions, measured once). Electrode placement was confirmed with ultrasound imaging of each muscle belly: upper gluteus maximus electrodes 2 finger widths above the line from the posterior superior iliac spine (PSIS) to the greater trochanter, lower gluteus maximus electrodes below the same line, TFL electrodes between the anterior superior iliac spine (ASIS) and the greater trochanter, and gluteus medius electrodes between the upper gluteus maximus and TFL electrodes. The findings demonstrated that upper gluteus maximus EMG activity increased significantly with each increase in hip flexion angle and effort level, with a significant interaction: the effect of hip flexion angle grew with each increase in effort (4.6% of MVC at 0° and 20% effort, increasing to 85.7% of MVC at 80° and 80% effort). Lower gluteus maximus EMG activity also increased significantly with hip flexion angle and effort level, with a significant interaction; however, the effect of hip flexion angle was not significant at the lowest effort level (20% of maximum strength), and significant increases from 0° occurred only at 60% and 80% effort (38.2% of MVC at 80° and 80% effort). Gluteus medius EMG activity increased significantly with effort level; the main effect of hip flexion angle was significant, but post hoc testing revealed no significant differences among angles, and there was no interaction (58.6 - 66.1% of MVC across angles at 80% effort). TFL EMG activity increased with effort level and decreased significantly with increasing hip flexion angle (69.8 - 71.0% of MVC at 0° - 20° of flexion, decreasing to 45.1% of MVC at 80° of flexion, at 80% effort). Note, the published abstract states the highest TFL value occurred at 40° of hip flexion; the results table places that value (71.0% of MVC) at 20° of hip flexion. Additionally, upper gluteus maximus activity was descriptively higher than lower gluteus maximus activity in every angle and effort condition (85.7% compared to 38.2% of MVC at the highest condition); however, the study did not statistically compare the portions to one another, standard deviations were large (± 80.8% for the upper portion at the highest condition), and normalization referenced a single MVC trial per position. Last, the authors state cross-talk from adjacent muscles and electrode movement with hip flexion as limitations, and conclude that abduction in hip flexion is desirable for strengthening the upper gluteus maximus, whereas abduction in hip extension is desirable for strengthening the TFL (??)

• Fujisawa, H., Suzuki, H., Yamaguchi, E., Yoshiki, H., Wada, Y., & Watanabe, A. (2014). Hip muscle activity during isometric contraction of hip abduction. Journal of Physical Therapy Science, 26(2), 187-190. https://doi.org/10.1589/jpts.26.187

1.2 Locomotion and Perturbation: Regional Function During Gait, Stairs, Running, and Sprinting

During walking and stair ambulation, the upper portion of the gluteus maximus functions as a hip abductor (paralleling the gluteus medius), and the lower portion functions as a hip extensor; the lower portion is the primary hip extensor during the loading response and mid-stance of stair ascent

Lyons et al. compared 11 healthy males and females (5 males, 6 females) (age: 25 - 34 years; mean: 27.6 years) with no observable gait abnormalities and no leg length discrepancy of more than 1 cm. All participants walked at self-selected free and fast velocities on a 15 m walkway (the middle 6 m designated as the steady-state data segment by photoelectric cells), and ascended and descended a 4 step staircase (15 cm risers, 27 cm depth), during 1 session; 3 runs were recorded per condition, the middle stride of each run was analyzed, and each trial was repeated once to accommodate the 7 channel recording system. Outcome measures included fine wire EMG (50 micron wires inserted with Basmajian's single needle technique, placement confirmed by electrical stimulation and re-verified by repeated muscle tests after the trials) of the left upper gluteus maximus (inserted superior and lateral to a line drawn between the PSIS and the posterior greater trochanter), lower gluteus maximus (inserted inferior and medial to the same line), gluteus medius, tensor fasciae latae (TFL), semimembranosus, long head of the biceps femoris, and adductor magnus, expressed in 2% increments of the gait cycle as a percentage of maximum effort. Normalization used the highest integrated EMG registered over 2 consecutive seconds during maximum effort testing with manual resistance and with a dynamometer (2 efforts/position, 4-second holds, with a long (3 min minimum) rest between trials); manual muscle testing produced the higher value in 77% of the 73 trials analyzed. Note: 6 muscle samples were excluded due to reduced signal amplitude on repeat testing, including 2 wire insertions that were pulled out during stair ascent. The findings demonstrated that the upper portion of the gluteus maximus and the gluteus medius exhibited the same activity pattern during free walking: minimal activity at the end of swing, a strong peak during the first 10% of the gait cycle (the loading response), and a low level of continued action into mid-stance. The lower portion of the gluteus maximus exhibited the hip extensor pattern, registering its greatest activity during the loading response alongside the adductor magnus, with minimal swing phase action. Peak activity was approximately 30% of maximum for most muscles during free walking, and fast walking produced earlier onset in swing, higher peaks (approximately 50% of maximum), and briefer stance action; however, the hip abductor muscles did not significantly change intensity as gait velocity increased, which the authors interpret as the abductors controlling the swinging limb's position rather than responding to loading demand. During stair ascent, the upper and lower gluteus maximus, gluteus medius, and adductor magnus began activity in late swing and continued at a high level through the loading response, and the lower portion of the gluteus maximus was the primary hip extensor during the loading response and mid-stance; although both portions lengthened their period of activity during ascent, only the upper portion exhibited a notable increase in EMG intensity, similar to the gluteus medius. Stair ascent produced the highest EMG activity for the upper gluteus maximus, lower gluteus maximus, gluteus medius, and TFL; stair descent produced the lowest activity for all muscles, with the gluteus medius (20% of maximum) and upper gluteus maximus (15% of maximum) active from terminal swing through the loading response while the lower gluteus maximus registered only 5% of maximum, indicating that limb support during descent depends on hip abductor action and not hip extension. The authors conclude that the gluteus maximus is functionally divided, with the upper portion acting as an abductor, like the gluteus medius, and the lower portion providing hip extension. Note, the authors also state that because lower gluteus maximus peak activity consistently occurred during the loading response, when hip posture changes very little, isometric extensor support of the flexed hip appears to be this portion's role, and that activity intensity remained below 50% (generally below 30%) of maximum, consistent with the aerobic endurance demands of repetitive gait (??)

• Lyons, K., Perry, J., Gronley, J. K., Barnes, L., & Antonelli, D. (1983). Timing and relative intensity of hip extensor and abductor muscle action during level and stair ambulation. An EMG study. Physical Therapy, 63(10), 1597-1605. https://doi.org/10.1093/ptj/63.10.1597

Sprinting results in the highest superior and inferior gluteus maximus EMG activity; running and ladder climbing result in similar activity; increased forward trunk pitch demand during running increases inferior gluteus maximus EMG activity without changing superior gluteus maximus activity

Bartlett et al. conducted 2 experiments comparing separate samples of avid recreational runners free of current musculoskeletal injury. Experiment 1 compared 10 healthy males and females (5 males, 5 females) (age: 31 ± 9 years). All participants performed 4 locomotion conditions in increasing order of intensity during 1 session: treadmill walking (1.25 m/s), treadmill running (3.0 m/s), ladder climbing (a standard extension ladder anchored at 75°, rungs 20.3 cm apart, climbed at a quick pace to a center-of-mass height of 3 m while maintaining 3 points of contact), and 5 maximal 30 m sprints from a standing start (5.28 ± 0.42 m/s; the fastest trial was analyzed). Experiment 2 compared 9 different healthy males and females (5 males, 4 females) (age: 27 ± 5 years). All participants walked (1.25 m/s) and ran (3.0 m/s) during 3 conditions in random order: a control condition (a hip belt with lead strips matching the device masses), a condition increasing forward trunk pitch demand (a 2.27 kg disk on a vertical pole 1.41 m above the hip joint, increasing the torso's moment of inertia about the hip by 70%), and a condition decreasing hip extension demand (a 2.27 kg disk on a horizontal 61 cm bar positioned 0.71 m posterior to the hip at approximately L4, applying a static 22 Nm hip extensor torque). Outcome measures included surface EMG of the right superior gluteus maximus, inferior gluteus maximus, and gluteus medius (Experiment 1), with the biceps femoris and semitendinosus/semimembranosus added in Experiment 2; peak stance phase activity (100 millisecond moving average) was averaged across 4 strides and normalized to the unperturbed walking condition (Experiment 1) or the unperturbed running condition (Experiment 2). The findings of Experiment 1 demonstrated that superior and inferior gluteus maximus EMG activity was significantly higher during running (166% and 111% higher), climbing (250% and 216% higher), and sprinting (562% and 451% higher) when compared to walking, and sprinting activity was significantly higher than running activity for all 3 gluteal muscles; gluteus medius activity was similar for running and walking, but was significantly higher during climbing (70% higher) and sprinting (299% higher). Climbing and running produced statistically similar activity for all 3 gluteal muscles. Additionally, EMG activity was similar for males and females during all conditions, and peak sprinting activity remained constant across the first 6 steps. The findings of Experiment 2 demonstrated that increased forward trunk pitch demand during running significantly increased inferior gluteus maximus EMG activity (23% increase); superior gluteus maximus, gluteus medius, biceps femoris, and semitendinosus/semimembranosus activity did not change. Decreased hip extension demand during running did not significantly change activity in any muscle. During walking, increased trunk pitch demand significantly increased gluteus medius activity (30% increase), and decreased hip extension demand significantly decreased biceps femoris activity (12% decrease). The authors conclude that only the inferior gluteus maximus aids trunk pitch control, and only when the demand is extreme, and that the large size of the gluteus maximus reflects its multifaceted role during rapid and powerful movements rather than an adaptation for a single submaximal task such as endurance running. Note that EMG activity was normalized to unperturbed gait rather than to an MVIC; all values in this study are changes relative to walking or running, and cannot be compared to the %MVIC values reported by other studies in this bibliography. Note that the published participant numbers contain inconsistencies: the text describes 9 volunteers for Experiment 2 while also stating 1 participant's electrodes dislodged with 9 remaining, and the Experiment 1 figure caption reports N = 9 despite 10 described participants; these inconsistencies should be noted if participant numbers are quoted (??)

Additional information regarding this study:

This is the only study identified that changed a mechanical demand and demonstrated that one portion of the gluteus maximus responded while the other did not. This design deserves attention, because it provides a stronger form of evidence than the exercise comparisons in this bibliography. When 2 exercises result in different activity, many variables differ between the exercises at once, and the variable responsible for the difference must be inferred. In this study, the researchers added a single demand (a weighted pole that increased the difficulty of controlling forward trunk lean), held the task otherwise constant, and observed which muscles responded. Only the inferior gluteus maximus increased activity. A response isolated to one portion, produced by a single imposed demand, is direct evidence that the portions can be controlled separately.

The dissociation depended on speed. During running, the added trunk demand increased inferior gluteus maximus activity, and no other measured muscle responded. During walking, the same device increased gluteus medius activity instead, and neither portion of the gluteus maximus responded. That is, the body solved the same problem with different muscles at different speeds: the abductors at a walk, and the inferior gluteus maximus at a run. A statement citing this study should therefore attribute the trunk control role of the inferior portion to running specifically, and not to gait in general.

The evidence is also limited to one direction of loading. Increasing the demand increased inferior gluteus maximus activity; however, decreasing the demand (a posterior counterweight that assisted trunk control) did not significantly decrease activity in any muscle. The dissociation therefore rests on the increased-demand condition alone. The demand was also large: the device increased the torso's resistance to forward rotation by 70%, and the authors state that the inferior portion aids trunk control "only when the demand is quite extreme." A statement citing this study should include this qualifier, because the finding does not demonstrate that ordinary running trains the inferior portion through trunk control; it demonstrates that an unusually large trunk demand recruits the inferior portion specifically.

• Bartlett, J. L., Sumner, B., Ellis, R. G., & Kram, R. (2014). Activity and functions of the human gluteal muscles in walking, running, sprinting, and climbing. American Journal of Physical Anthropology, 153(1), 124-131. https://doi.org/10.1002/ajpa.22419

1.3 Trunk Integration and Symptomatic Populations

Chronic low back pain results in significantly higher upper and lower gluteus maximus, hamstring, and erector spinae EMG activity during submaximal isometric trunk rotation; trunk rotation activates the contralateral upper and lower gluteus maximus as agonists, and contralateral upper gluteus maximus activity is descriptively higher than lower gluteus maximus activity (no within-muscle statistical comparison was performed)

Pirouzi et al. compared 30 females with chronic low back pain (age: 27.3 ± 8.1 years) of more than 6 months duration that limited functional activity, with or without referral to the lower limb (pain intensity on the testing day: 25.8 ± 13.3 mm on a visual analog scale; Roland Morris Disability Index: 4.4 ± 2.5), and 30 healthy pain-free females matched for age, height, weight, and BMI (age: 27.5 ± 7.9 years). Exclusion criteria included previous lumbar surgery, neuromuscular or joint disease, signs of nerve root compression, systemic disease, carcinoma, pregnancy (current or within 2 years), and any sports or fitness training involving the back or hip muscles within the previous 3 months; all participants were right-handed. All participants performed isometric trunk rotation efforts to the left and right at 25% of maximum voluntary contraction (standardized from pilot data for women of different BMI categories), standing upright in a trunk rotation device (an adapted isokinetic dynamometer) with the chest, pelvis, and lower limbs stabilized by a thoracic pad, pelvic restraint, and thigh and knee straps, using visual torque feedback (reaching the target within 5 seconds and holding for 5 more seconds), with 3 reps of alternating left and right rotation per condition. Four support conditions were tested in randomized order: arms across the chest without pelvic support, arms across the chest with pelvic support (the traditional testing position), an isometric upper limb lifting task (push-up position on a bar) without pelvic support, and the lifting task with pelvic support. Outcome measures included bilateral surface EMG of the latissimus dorsi, erector spinae, upper gluteus maximus (electrodes placed per Lyons et al.), lower gluteus maximus, and biceps femoris (representing the hamstrings), analyzed as the 1 second epoch at maximum torque and normalized to voluntary reference contractions. The findings demonstrated that participants with chronic low back pain exhibited significantly higher EMG activity, with a main effect of group during left rotation in 3 of 4 support conditions and during right rotation in 1 condition, and planned contrasts identified significantly higher activity in the left and right biceps femoris, left and right erector spinae, and left upper and lower gluteus maximus (the lifting task conditions produced the greatest number of significant differences, and removing pelvic support highlighted the differences in the hip extensors). In both groups, trunk rotation to one side activated the latissimus dorsi on the same side and the upper and lower gluteus maximus on the opposite side as agonists, consistent with the posterior oblique sling model of load transfer through the thoracolumbar fascia. Additionally, contralateral upper gluteus maximus activity was descriptively higher than contralateral lower gluteus maximus activity during rotation in both groups and all support conditions (approximately 27 - 39% compared to 13 - 21% of the reference contraction during left rotation). Note that the study compared groups within each muscle and did not statistically compare the upper and lower gluteus maximus to one another; the characterization by Selkowitz et al. (2016) that the contralateral superior gluteus maximus was more active than the inferior during ipsilateral trunk rotation corresponds to this descriptive pattern and not to a statistical finding. Note that the upper gluteus maximus, lower gluteus maximus, and erector spinae were normalized to submaximal reference contractions (the weight of the leg or trunk against gravity, chosen to avoid pain invalidating the reference in the low back pain group), whereas the latissimus dorsi and biceps femoris were normalized to maximal contractions; the authors state that using different normalization procedures for different muscles can affect between-muscle comparisons, and these values cannot be compared to the %MVIC values of other studies in this bibliography. Note that the authors state the increased gluteus maximus activation in the low back pain group was an unexpected finding, as prior research had reported increased fatigability and delayed activation, and they interpret the elevated activity as a compensatory antagonist stabilization strategy (??)

• Pirouzi, S., Hides, J., Richardson, C., Darnell, R., & Toppenberg, R. (2006). Low back pain patients demonstrate increased hip extensor muscle activity during standardized submaximal rotation efforts. Spine, 31(26), E999-E1005. https://doi.org/10.1097/01.brs.0000250076.74366.9d

1.4 Loaded Resistance Exercise Comparisons (1 Dataset: 13 Resistance-Trained Females)

Barbell hip thrusts result in higher upper and lower gluteus maximus EMG activity than back squats with estimated 10-RM loads, during both dynamic repetitions and isometric holds (held in full hip extension compared to hip flexion)

Contreras et al. compared 13 healthy resistance-trained females (age: 28.9 ± 5.1 years) with 7.0 ± 5.8 years of resistance training experience, familiarity with both the back squat and barbell hip thrust, and no history of musculoskeletal or neuromuscular injuries, pain, or illness (screened with the Physical Activity Readiness Questionnaire), who refrained from lower body training for 72 hours before testing. All participants performed back squats and barbell hip thrusts, and 3-second isometric holds of both exercises, in randomized and counterbalanced order, during 1 session. All participants performed a 10 min general warm-up (dynamic stretches) and 3 progressively heavier specific warm-up sets/exercise; 10-RM loads were then estimated from a maximum-repetition set (Baechle and Earle table, corresponding to approximately 75% of estimated 1-RM loads; back squats: 53.2 ± 17.0 kg; barbell hip thrusts: 87.4 ± 19.3 kg). The dynamic protocol included 1 set/exercise, 10 reps/set, with estimated 10-RM loads, a self-selected tempo (selected to mimic typical training conditions), and a very long (5 min) rest between sets; back squats were performed to a parallel-thigh depth with feet slightly wider than shoulder width, and barbell hip thrusts were performed with the upper back on a 16 inch bench, a padded barbell over the hips, and a neutral spine and pelvis. The isometric protocol included 1 hold/exercise, 3-second holds, with the same estimated 10-RM loads, and a very long (5 min) rest between holds; back squats were held at the parallel-thigh position (hips flexed), and barbell hip thrusts were held at lockout (hips fully extended). Outcome measures included mean and peak surface EMG of the right upper gluteus maximus, lower gluteus maximus, biceps femoris, and vastus lateralis, with gluteus maximus activity normalized to the higher of 2 MVIC positions (prone bent-knee hip extension against manual resistance, or a standing glute squeeze). The findings demonstrated that mean and peak EMG activity during the dynamic protocol was significantly higher during barbell hip thrusts when compared to back squats for the upper gluteus maximus (mean: 69.5% compared to 29.4% of MVIC; peak: 172% compared to 84.9% of MVIC), the lower gluteus maximus (mean: 86.8% compared to 45.4% of MVIC; peak: 216% compared to 130% of MVIC), and the biceps femoris (mean: 40.8% compared to 14.9% of MVIC; peak: 86.9% compared to 37.5% of MVIC); however, vastus lateralis EMG activity was similar during both exercises. Similarly, mean and peak EMG activity during the isometric holds was significantly higher during barbell hip thrusts (held in full hip extension) when compared to back squats (held in hip flexion) for the upper gluteus maximus (mean: 87.1% compared to 10.1% of MVIC), the lower gluteus maximus (mean: 115.7% compared to 20.9% of MVIC), and the biceps femoris (mean: 42.5% compared to 7.4% of MVIC); however, vastus lateralis EMG activity was similar during both holds. Note, both portions of the gluteus maximus exhibited the same direction of effect with comparable effect sizes during both protocols (dynamic mean effect sizes: 1.55 for the upper portion and 1.64 for the lower portion); however, the study did not statistically compare the upper and lower portions to one another, so this parallel response is descriptive. Additionally, the authors state that in their comparison table with prior whole-muscle back squat research, the lower gluteus maximus values were assumed to best represent the middle gluteus maximus fibers, which is relevant to reconciling regional nomenclature across studies.

• Contreras, B., Vigotsky, A. D., Schoenfeld, B. J., Beardsley, C., & Cronin, J. (2015). A comparison of gluteus maximus, biceps femoris, and vastus lateralis electromyographic activity in the back squat and barbell hip thrust exercises. Journal of Applied Biomechanics, 31(6), 452-458. https://doi.org/10.1123/jab.2014-0301

Barbell hip thrusts result in higher mean upper gluteus maximus EMG activity than American and band hip thrusts, and higher peak upper gluteus maximus EMG activity than band hip thrusts; lower gluteus maximus EMG activity is similar during all 3 variations

Contreras et al. compared 13 healthy resistance-trained females (age: 28.9 ± 5.1 years) with 7.0 ± 5.8 years of resistance training experience, at least 3 years of consistent training at least 3 times/week, familiarity with the hip thrust, and no current musculoskeletal or neuromuscular injuries, pain, or illness (screened with the Physical Activity Readiness Questionnaire), who refrained from lower body training for 72 hours before testing. All participants performed barbell hip thrusts, American hip thrusts, and band hip thrusts, in counterbalanced and randomized order, during 1 session. All participants performed a 10 min general warm-up (dynamic stretches) and 3 progressively heavier specific warm-up sets; 10-RM loads were estimated from a maximum-repetition set (Baechle and Earle table; barbell hip thrusts: 87.4 ± 19.3 kg; American hip thrusts: 91.9 ± 18.5 kg), and band hip thrust loads were matched to the barbell condition by equating peak ground reaction forces from unpublished pilot force plate data, with adjustments from participant feedback. The exercise protocol included 1 set/variation, 10 reps/set, with estimated 10-RM loads, a self-selected tempo (selected to represent true training conditions), a consistent hip range of motion across variations, and a very long (5 min) rest between sets. Barbell hip thrusts were performed with the upper back on a 16-inch bench, feet slightly wider than shoulder width, a padded barbell over the hips, a neutral spine and pelvis, and a full range of motion (barbell touching the ground to full hip extension). American hip thrusts were performed with the bench contact lowered to the inferior angle of the scapulae, combining anterior pelvic tilt and hip flexion during the eccentric phase with posterior pelvic tilt and hip extension during the concentric phase, and reversing the movement in mid-air (the barbell does not touch the ground). Band hip thrusts were performed identically to barbell hip thrusts, with elastic band resistance replacing the barbell. Outcome measures included mean and peak surface EMG of the right upper gluteus maximus, lower gluteus maximus, biceps femoris, and vastus lateralis, with gluteus maximus activity normalized to the higher of 2 MVIC positions (prone bent-knee hip extension against manual resistance, or a standing glute squeeze). The findings demonstrated that mean upper gluteus maximus EMG activity was significantly higher during barbell hip thrusts (69.5% of MVIC) when compared to American hip thrusts (57.4% of MVIC) and band hip thrusts (49.2% of MVIC); mean upper gluteus maximus activity was statistically similar for American and band hip thrusts. Peak upper gluteus maximus EMG activity was significantly higher during barbell hip thrusts (172% of MVIC) when compared to band hip thrusts (120% of MVIC); peak upper gluteus maximus activity was statistically similar for barbell and American hip thrusts (157% of MVIC), and for American and band hip thrusts. Mean and peak EMG activity of the lower gluteus maximus (mean: 86.7%, 89.9%, and 79.2% of MVIC; peak: 216%, 200%, and 185% of MVIC for the barbell, American, and band variations), the biceps femoris, and the vastus lateralis were statistically similar during all 3 variations. Additionally, 11 of 13 participants (84.6%) exhibited their highest mean upper gluteus maximus activity during barbell hip thrusts, whereas the variation producing the highest lower gluteus maximus activity was distributed across participants (barbell: 6; American: 5; band: 2), and 9 of 13 participants (69.2%) exhibited their highest mean biceps femoris activity during American hip thrusts. Note that the band loads were approximately, but not exactly, 10-RM (matched by force plate rather than estimated by the same method as the other variations), which the authors state as a limitation; the barbell compared to band differences are the least load-controlled comparisons in the study. Note that every statistically significant difference in this study occurred in the upper gluteus maximus, and the lower gluteus maximus did not discriminate between variations; the study did not statistically compare the upper and lower portions to one another, so this differential sensitivity is descriptive. Note that the American hip thrust produced lower mean upper gluteus maximus activity than the barbell hip thrust despite a slightly heavier load, which the authors attribute to the shorter moment arm created by the lower bench contact position. Note that a consistent descriptive pattern appears across the 3 Contreras publications: the lower electrode site produced higher values than the upper site during every squat and hip thrust condition, whereas the upper site produced higher values during the abduction and external rotation exercises in Part 1; however, no study statistically compared the portions to one another, so this reciprocal pattern is descriptive.

• Contreras, B., Vigotsky, A. D., Schoenfeld, B. J., Beardsley, C., & Cronin, J. (2016). A comparison of gluteus maximus, biceps femoris, and vastus lateralis electromyography amplitude for the barbell, band, and American hip thrust variations. Journal of Applied Biomechanics, 32(3), 254-260. https://doi.org/10.1123/jab.2015-0091

Front, full, and parallel squats with estimated 10-RM loads result in similar upper and lower gluteus maximus EMG activity, despite heavier absolute loads during parallel squats

Contreras et al. compared 13 healthy resistance-trained females (age: 28.9 ± 5.1 years) with 7.0 ± 5.8 years of resistance training experience, at least 3 years of consistent training, familiarity with the front, full, and parallel squat, and no current musculoskeletal or neuromuscular injuries, pain, or illness (screened with the Physical Activity Readiness Questionnaire), who refrained from lower body training for 72 hours before testing (no recruited participants were excluded). All participants performed front squats, full squats, and parallel squats, in randomized and counterbalanced order, during 1 session. All participants performed a 10 min general warm-up (dynamic stretches) and 3 progressively heavier specific warm-up sets/variation; 10-RM loads were estimated for each variation from a maximum-repetition set (Baechle and Earle table; front squats: 39.2 ± 15.6 kg; full squats: 46.7 ± 17.1 kg; parallel squats: 53.1 ± 17.0 kg). The exercise protocol included 1 set/variation, 10 reps/set, with estimated 10-RM loads, a self-selected tempo (selected to mimic typical training conditions), and a very long (5 min) rest between sets. All variations were performed with feet slightly wider than shoulder width, and toes pointed forward or slightly outward. Front squats were performed with the barbell across the anterior deltoids and clavicles, elbows fully flexed, and upper arms parallel to the floor, descending until the knees were maximally flexed. Full squats were performed with the barbell in the high bar position, descending until the knees were maximally flexed. Parallel squats were performed with the barbell in the high bar position, descending until the tops of the thighs were parallel with the floor. Outcome measures included mean and peak surface EMG of the right upper gluteus maximus, lower gluteus maximus, biceps femoris, and vastus lateralis, with gluteus maximus activity normalized to the higher of 2 MVIC positions (prone bent-knee hip extension against manual resistance, or a standing glute squeeze). The findings demonstrated that mean and peak EMG activity of the upper gluteus maximus (mean: 29.4%, 29.6%, and 29.2% of MVIC; peak: 84.9%, 88.1%, and 84.6% of MVIC for the parallel, full, and front squats), the lower gluteus maximus (mean: 45.3%, 42.2%, and 43.9% of MVIC; peak: 129.6%, 124.8%, and 134.6% of MVIC), and the biceps femoris was statistically similar during all 3 variations. Mean vastus lateralis EMG activity was also statistically similar during all 3 variations; peak vastus lateralis EMG activity exhibited a significant main effect (parallel: 243.9%; full: 280.5%; front: 302.6% of MVIC), but post hoc testing revealed no significant pairwise differences, and the authors state the study may have been underpowered for this outcome. Additionally, the similar gluteus maximus activity across variations occurred despite parallel squats using 12.8% heavier loads than full squats and 35.5% heavier loads than front squats, which is consistent with relative-load matching rather than absolute-load matching. Note that full squat depth was not standardized to a measured joint angle; participants were instructed to descend as low as possible while maintaining proper form, which the authors state as a limitation. Note that the lower gluteus maximus produced higher mean and peak values than the upper gluteus maximus during every squat variation; however, the study did not statistically compare the portions to one another, so this pattern is descriptive. Note that the parallel squat values in this study (all 8 upper and lower gluteus maximus values) are identical to the back squat values reported by Contreras et al. (2015); the 2 publications report the same recorded squat data, and the Contreras publications should be treated as 1 dataset for evidence counting.

• Contreras, B., Vigotsky, A. D., Schoenfeld, B. J., Beardsley, C., & Cronin, J. (2016). A comparison of gluteus maximus, biceps femoris, and vastus lateralis electromyography amplitude in the parallel, full, and front squat variations in resistance-trained females. Journal of Applied Biomechanics, 32(1), 16-22. https://doi.org/10.1123/jab.2015-0113

Prone bent-knee hip extension and standing glute squeeze MVIC positions result in similar upper gluteus maximus EMG activity; lower gluteus maximus EMG activity exhibits a trend toward higher activity during prone hip extension

Contreras et al. compared 13 healthy resistance-trained females (age: 28.9 ± 5.1 years) with 7.0 ± 5.8 years of resistance training experience and at least 3 years of consistent resistance training, free of musculoskeletal or neuromuscular injuries, pain, or illness (inclusion required an age of 20 - 40 years), who refrained from lower body training for 72 hours before testing. All participants performed a 10 min general warm-up (dynamic stretches) and practiced each testing position until comfortable. All participants then performed MVIC trials in 2 positions, in randomized and counterbalanced order (alternating between positions), during 1 session. The prone position was performed lying prone on a bench with the knee flexed to 90°, extending the hip against manual resistance applied to the distal thigh. The standing glute squeeze was performed standing with feet slightly wider than shoulder width and the hips slightly externally rotated, squeezing the glutes while focusing on externally rotating and extending the hips. The protocol included 3 trials/position, 5-second contractions/trial, a cue to contract "as hard as possible," and a long (3 min) rest after each pair of trials. Outcome measures included peak surface EMG of the right upper and lower gluteus maximus (electrodes placed per Fujisawa et al.: upper electrodes 2 finger widths above the line from the PSIS to the greater trochanter, lower electrodes below the same line), with peak values taken from the highest 1,000 millisecond window within each contraction. The findings demonstrated that peak upper gluteus maximus EMG activity was similar during both positions (91.9% compared to 92.0% of the highest value; effect size: 0.005). Peak lower gluteus maximus EMG activity exhibited a trend toward higher activity during prone hip extension (94.5% compared to 85.1%; effect size: 0.41) (the trend failed to reach statistical significance). Additionally, prone hip extension produced the highest peak amplitude for the upper gluteus maximus in 7 of 13 participants (53.8%), and for the lower gluteus maximus in 10 of 13 participants (76.9%), and the authors recommend using multiple MVIC positions given this individual variation. Note that this may suggest, although without a statistically significant finding, that the upper gluteus maximus is recruited for abduction and external rotation and the lower gluteus maximus is recruited for extension. Note that the authors state that although the approximately 9% difference for the lower gluteus maximus failed to reach statistical significance, it could be considered practically meaningful: normalizing to the standing glute squeeze alone would inflate normalized lower gluteus maximus values by approximately 10% when compared to normalizing to the prone position. Note that the authors state that the statistical analysis was not designed to assess whether the upper and lower portions differed from one another during either position, and that the 2 positions differed simultaneously in knee angle, pelvic position, hip range of motion, kinetic chain, and resistance type, which prevents attribution of the result to any single variable. Note that the authors hypothesized (from pilot data) that the standing glute squeeze would produce higher upper gluteus maximus activity; the findings did not support this hypothesis (??)

• Contreras, B., Vigotsky, A. D., Schoenfeld, B. J., Beardsley, C., & Cronin, J. (2015). A comparison of two gluteus maximus EMG maximum voluntary isometric contraction positions. PeerJ, 3, e1261. https://doi.org/10.7717/peerj.1261

1.5 Regional Hypertrophy Following Training

9 weeks of hip thrust or back squat training results in statistically similar increases in upper, middle, and lower gluteus maximus cross-sectional area between exercises; back squat training results in significantly higher quadriceps and adductor growth; acute EMG amplitudes did not consistently correlate with hypertrophy

An RCT by Plotkin et al. compared 34 untrained males and females who completed the study, randomly assigned to a hip thrust group (5 males, 13 females) (age: 22 ± 3 years; BMI: 24 ± 3 kg/m²) or a back squat group (6 males, 10 females) (age: 24 ± 4 years; BMI: 23 ± 3 kg/m²). Inclusion required an age of 18 - 30 years, a BMI below 30 kg/m², minimal resistance training experience (1 day/week or less, averaged over the previous 5 years), no structured endurance training of more than 2 days/week over the previous 6 months, no known cardiovascular or metabolic disease, no creatine or hormone-affecting supplements within the previous 2 months, no MRI contraindications, and no milk protein intolerance. All participants were provided a daily whey protein serving (29 g protein) to reduce inadequate protein intake as a confounder, and food logs revealed no significant group by time differences in dietary intake. The training protocol included 9 weeks of supervised training (15 - 17 total sessions; 1 session in week 1, then 2 sessions/week on non-consecutive days) of only the allocated exercise, with 3 sets/session in week 1, 4 sets/session in week 2, 5 sets/session in weeks 3 - 6, and 6 sets/session in weeks 7 - 9, 8 - 12 reps/set to volitional failure (loads adjusted to maintain the range), and an approximately (1 s concentric: 2 s eccentric) tempo. Squats were performed to the lowest achievable depth during training, and hip thrusts were performed on an apparatus with a 21-inch bench, from plate contact with the ground to full hip extension. Outcome measures included muscle cross-sectional area (CSA) of the upper, middle, and lower gluteus maximus (bilateral, summed) and the combined gluteus medius and minimus (measured with MRI, 71 slices at 4 mm with no gap, acquired by an investigator blinded to group assignment; the middle gluteus maximus was standardized to the slice at the top of the femur, the upper region 10 slices above, and the lower region 18 slices below), the combined quadriceps, adductor, and hamstrings CSA, 3-RM strength of the back squat, barbell hip thrust, and deadlift, isometric wall push force (force plate), and mean and peak surface EMG of the right upper, middle, and lower gluteus maximus and gluteus medius during 1 set of 10 reps with estimated 10-RM loads of both exercises during the first session, normalized to MVIC (prone bent-knee hip extension for the gluteus maximus sites; side-lying abduction for the gluteus medius). The findings demonstrated that gluteus maximus CSA increased for both groups at the upper, middle, and lower regions, and the increases were statistically similar between groups at all 3 regions (between-group estimates: upper -0.5 ± 2.6 cm²; middle -0.5 ± 1.7 cm²; lower -1.6 ± 2.1 cm²). Combined gluteus medius and minimus CSA and hamstrings CSA changes were small for both groups and statistically similar between groups. Quadriceps CSA (3.6 ± 1.5 cm²) and adductor CSA (2.5 ± 0.7 cm²) increased significantly more in the back squat group. Back squat 3-RM strength increased significantly more in the squat group (44% compared to 17%), hip thrust 3-RM strength increased significantly more in the hip thrust group (63% compared to 34%), and deadlift 3-RM strength (15 - 16%) and wall push force (7.6 - 10%) increases were statistically similar between groups. Additionally, during the first-session EMG comparison, mean EMG activity at all 4 gluteal sites was significantly higher during hip thrusts than back squats; peak EMG activity was significantly higher during hip thrusts for the upper and middle gluteus maximus, and statistically similar for the lower gluteus maximus and gluteus medius sites. EMG amplitudes did not consistently correlate with hypertrophy across participants, regions, or exercises. Note that the study reported training outcomes as between-group effect estimates with bootstrapped 95% confidence intervals and did not calculate within-group significance tests; "statistically similar" above indicates a between-group confidence interval crossing zero, "significantly more" indicates an interval excluding zero, and within-group increases were reported without statistical testing. Note that negative between-group estimates indicate values in the direction of the hip thrust group. Note that the only across-subject EMG-to-hypertrophy correlation whose confidence interval excluded zero was mean upper gluteus maximus EMG (r = 0.50; 95% CI 0.03 to 0.81); all other correlations ranged from r = -0.03 to r = 0.32 with intervals crossing zero. Note that the study did not statistically compare hypertrophy among the 3 gluteus maximus regions; the regional statistics are between-group comparisons within each region, so this study supports statistically similar growth between exercises at every region and does not establish which region grew most. Note that the regional EMG nomenclature in this study is unique: the upper and middle gluteus maximus electrodes were placed per Fujisawa et al.'s upper and lower convention (the authors relabeled Fujisawa's lower site as middle), and the lower gluteus maximus electrodes were placed at a novel site 1 inch (2.54 cm) above the most medial gluteal fold, which no other study in this bibliography used; the EMG region labels are therefore not interchangeable with this study's own MRI region labels, with the labels of Contreras et al., or with the labels of Fujisawa et al.

• Plotkin, D. L., Rodas, M. A., Vigotsky, A. D., McIntosh, M. C., Breeze, E., Ubrik, R., ... & Roberts, M. D. (2023). Hip thrust and back squat training elicit similar gluteus muscle hypertrophy and transfer similarly to the deadlift. Frontiers in Physiology, 14, 1279170. https://doi.org/10.3389/fphys.2023.1279170

SECTION 2: SUPPORTING RESEARCH - Context That Informs Interpretation but Cannot Support Regional Claims

Note: The sources in this section are secondary sources, mechanistic studies, or cadaveric studies. Per BI citation policy, they are used only when necessary; statements supported by them should clearly indicate the source type, and they should not be cited in the same statement as primary experimental sources.

2.1 Whole-Muscle Corroboration

Barbell hip thrusts with 3-RM loads result in higher mean and peak gluteus maximus EMG activity than back squats and split squats; back squats and split squats result in similar gluteus maximus EMG activity (upper and lower electrode data were averaged; no region-specific findings can be derived from this study)

Williams et al. compared 12 male team sport athletes (age: 25.0 ± 4.0 years) with 4.0 ± 1.0 years of strength training experience, at least 3 years of resistance training experience, experience with all 3 exercises, and the ability to safely perform each exercise with external load (inclusion required an age of 18 - 35 years). All participants performed 3-RM testing of the back squat, split squat, and barbell hip thrust in randomized order during an initial session (barbell hip thrusts: 157 ± 29 kg; back squats: 117 ± 39 kg; split squats: 68 ± 23 kg; all loads significantly different from one another). During the testing session, all participants performed a 3-RM set of each exercise, in randomized and counterbalanced order, with a moderate (4 min) rest between exercises (split squat sets were performed on both legs). Back squats were performed with the barbell across the upper trapezius, feet slightly wider than shoulder width, descending until the thighs were parallel with the floor (continually cued by the researcher). Split squats were performed with the barbell positioned in the same position in a split stance, with the front foot flat on the floor and the rear knee slightly flexed, heel raised. Barbell hip thrusts were performed with the upper back against a 17-inch bench, feet slightly wider than shoulder width, and the barbell positioned across the hips. Outcome measures included mean and peak surface EMG of the upper and lower gluteus maximus of both legs (averaged across all 4 electrode sites for analysis), normalized to a standing glute squeeze MVIC, peak ground reaction force of each leg (force plates), and peak velocity, horizontal force, and vertical force during a maximal sprint (non-motorized treadmill). The findings demonstrated that mean and peak gluteus maximus EMG activity were significantly higher during barbell hip thrusts than during back squats and split squats; gluteus maximus EMG activity was similar for back squats and split squats, despite split squats producing a higher summed load across the front limbs relative to body mass. Peak ground reaction force was significantly lower during barbell hip thrusts when compared to both squat exercises. Additionally, peak sprint velocity correlated significantly with peak anterior-posterior horizontal force during sprinting and with peak ground reaction force during barbell hip thrusts; correlations with peak force during back squats and split squats failed to reach statistical significance, and gluteus maximus EMG activity during the exercises did not correlate with peak sprint velocity. Note that although electrodes were placed on the upper and lower gluteus maximus of both legs, the data were averaged across the 4 sites, and the authors state this prevented determining how the upper and lower fibers relate to sprinting independently; the findings of this study describe combined gluteus maximus activity and cannot be attributed to either portion. Additionally, EMG activity was normalized to a standing glute squeeze only, and prior research has demonstrated that this position may result in lower peak values for the lower gluteus maximus than prone hip extension, which limits comparison of these values with studies using other normalization positions.

• Williams, M. J., Gibson, N. V., Sorbie, G. G., Ugbolue, U. C., Brouner, J., & Easton, C. (2021). Activation of the gluteus maximus during performance of the back squat, split squat, and barbell hip thrust and the relationship with maximal sprinting. Journal of Strength and Conditioning Research, 35(1), 16-24. https://doi.org/10.1519/JSC.0000000000002651

2.2 The Gluteal Region as a Continuum (Adjacent Axis)

Walking results in higher EMG amplitude at the anterior gluteal positions (TFL and anterior gluteus medius) than the posterior positions (gluteus maximus) at all speeds, with activation timing shifting continuously from posterior to anterior across the gluteal region; the authors conclude the gluteal muscles behave as an "intermuscular functional unit" rather than independently acting muscles

Anders et al. compared 54 healthy older adults (25 males, 29 females) (age: males 61.3 ± 7.0 years; females 63.7 ± 6.8 years) with verified normal hip mobility and no relevant orthopedic or neurological disorders, knee or hip joint replacement, pain during locomotion, or clinical signs of knee or hip osteoarthritis, recruited as an age-matched control cohort for future total hip arthroplasty research. All participants performed 10-15 trials on a 10 m walkway at self-selected slow, normal, and fast walking speeds (0.89, 1.46, and 1.74 m/s) during 1 session, with a minimum of 50 steady-state strides analyzed per speed. Outcome measures included bilateral surface EMG from 8 equally spaced, vertically oriented bipolar channels arranged along a horizontal line at mid-distance between the iliac crest and greater trochanter, covering 17.5 cm from the most anterior position (P1) to the most posterior position (P8) (the authors' terms: ventral to dorsal); positions P1 - P2 represented the TFL, P3 - P5 the gluteus medius, and P6 - P8 the gluteus maximus (assignments confirmed by cadaveric dissection), and amplitude was quantified as root mean square with cumulative muscle activity per distance calculated as amplitude divided by walking speed (values were not normalized to MVIC; only intra-individual comparisons were performed). The findings demonstrated that EMG amplitude was not influenced by gender or side, and mean amplitude was significantly higher at the anterior positions (P1 - P5; TFL and gluteus medius) than the posterior positions (P6 - P8; gluteus maximus) at all walking speeds. Two amplitude peaks occurred during the stance phase (load acceptance at approximately 5% and hip stabilization at approximately 35% of the gait cycle), and both peaks exhibited a continuous time shift across the region, occurring earliest at the most posterior (gluteus maximus) position and latest at the most anterior (TFL) position. The ratio of the first to second peak increased continuously from anterior to posterior, and mean amplitude increased significantly at all positions with increasing walking speed, whereas cumulative muscle activity per distance was highest at the slow speed (indicating slow walking is energetically unfavorable). The authors conclude that the superficial gluteal muscles behaved as a functionally coupled "intermuscular functional unit" with gradually changing activation across the region, rather than as independently activated, anatomically defined muscles. Note that the electrode array was oriented horizontally (anterior to posterior) at a single height, so this study resolves position across the gluteal region and does not resolve the superior-to-inferior axis of the gluteus maximus that is the subject of this bibliography; the gluteus maximus positions sample the region adjacent to the gluteus medius (the superior portion's territory). Additionally, the authors state that only positions P1, P4/P5, and P8 can be reliably assigned to the TFL, gluteus medius, and gluteus maximus, respectively, with intermediate positions subject to cross-talk from neighboring muscles, and that the amplitude values cannot be compared across individuals or studies because no MVIC normalization was performed.

• Anders, C., Patenge, S., Sander, K., Layher, F., Biedermann, U., & Kinne, R. W. (2017). Detailed spatial characterization of superficial hip muscle activation during walking: A multi-electrode surface EMG investigation of the gluteal region in healthy older adults. PLoS ONE, 12(6), e0178957. https://doi.org/10.1371/journal.pone.0178957

2.3 Physiological and Anatomical Basis for Regional Analysis

Mechanomyography: evoked contraction time is longest in the upper gluteus maximus segment and decreases significantly toward the lower segment; contractile properties are similar between the medial and lateral portions within each segment

McAndrew et al. compared 10 healthy young males (age: 21 years; range: 18 - 25 years) recruited from a university student population, free from musculoskeletal injury and pathology of the back, hips, and lower limbs. Muscle segment boundaries were established from the pelves of 6 human cadavers (age: 72 - 92 years) examined in situ, dividing the gluteus maximus into 3 segments (upper, middle, and lower; the authors' terms: cranial, middle, and caudal), each with a medial and a lateral portion (6 sites total), with segment origins normalized along a line from the anterior superior iliac spine (ASIS) to the coccyx along the iliac crest, and segment insertions normalized along a line from the iliac crest through the hip joint to the lateral epicondyle of the femur; the cadavers were also used to estimate muscle tissue depth at the center of each portion. All participants lay prone, secured to a plinth with straps across the lower back and mid-thigh, while maximal single-twitch percutaneous neuromuscular stimulation was delivered to each of the 6 sites (bipolar surface electrodes, 2 cm apart, parallel to the muscle fiber direction), and a laser mechanomyography (MMG) sensor (sensitivity: 0.002 mm) positioned 10 cm from the skin between the stimulating electrodes measured the lateral displacement of the muscle belly during the development of maximal isometric tension. Outcome measures included motor unit contractile properties of each site derived from the MMG waveform, including segment contraction time. The findings demonstrated that motor unit contractile properties varied significantly between the 3 segments and were statistically similar between the medial and lateral portions within each segment. Segment contraction time decreased significantly from the upper segment to the lower segment (longest in the upper segment and shortest in the lower segment). The authors inferred that the upper segment may contain a higher proportion of slow-twitch fibers and may be more involved in postural tasks, and that the lower segment may contain a higher proportion of fast-twitch fibers and may be more involved in dynamic tasks. Note that the stimulation was electrically evoked rather than voluntary, so these findings describe intrinsic contractile properties of the stimulated motor units and not voluntary recruitment strategies. Note that the fiber-type claim is an inference from contraction time; no biopsy or histological fiber-typing was performed. Note that the deep fibers of the gluteus maximus attached to the gluteal tuberosity were not analyzed, and the segment boundaries were derived from cadavers aged 72 - 92 years and applied to participants aged 18 - 25 years (??)

• McAndrew, D., Gorelick, M., & Brown, J. M. M. (2006). Muscles within muscles: a mechanomyographic analysis of muscle segment contractile properties within human gluteus maximus. Journal of Musculoskeletal Research, 10(1), 23-35. https://doi.org/10.1142/S0218957706001704

Cadaveric Sihler staining: the gluteus maximus is segmented into upper, middle, and lower portions (the authors' terms: cranial, middle, and caudal) with intramuscular nerve endings concentrated in the central portion of each segment's span from origin to insertion

A cadaveric study by Yi et al. examined 20 gluteus maximus muscles from 10 embalmed Korean cadavers (5 males, 5 females) (age: 81.7 years; range: 74 - 87 years), with 1 additional non-embalmed cadaver used for ultrasound validation. Each gluteus maximus was divided into upper, middle, and lower segments (the authors' terms: cranial, middle, and caudal), and each segment was further divided into 10 equal parts along its width from origin to insertion; intramuscular nerve arborization was visualized with modified Sihler whole-nerve staining (which renders muscle transparent while staining nerves), and the presence of nerve endings in each part was recorded across all 20 specimens. Ultrasound images were then obtained from the non-embalmed cadaver using surface landmarks (the PSIS to greater trochanter line marking the upper segment; the coccyx to ischial tuberosity line marking the lower segment; a middle line between them), and ultrasound-guided blue dye injections were delivered to the central region of each segment and verified by dissection. The findings demonstrated that intramuscular nerve endings were concentrated in the central regions of the muscle belly: nerve endings were present in all 20 specimens in the 20 - 70% sections of the upper segment, the 40 - 70% sections of the middle segment, and the 30 - 70% sections of the lower segment, with lower nerve-ending frequency in the sections closest to the origin and insertion. The ultrasound-guided injections using the proposed landmarks were confirmed by dissection to reach the central areas of all 3 segments. The authors state that previous EMG research has often treated the gluteus maximus as a unified entity, overlooking segmentation into 3 segments, and propose the central nerve-dense areas as the safest and most efficient locations for botulinum toxin injection and EMG procedures. Note that the abstract and discussion state the nerve endings are "mainly located" in the 40 - 70% range of the upper segment and the 30 - 60% range of the middle segment, which does not exactly match the results table (100% presence in the 20 - 70% and 40 - 70% ranges, respectively); the table values are reported above. Note that the methods report a cadaver age range of 74 - 87 years while the limitations section states 65 - 79 years; this inconsistency in the published text should be noted if ages are quoted. Note that innervation topography establishes that regional recording and injection are anatomically justifiable; it does not establish independent neural control of the segments, and the functional and fiber-type characterizations of the segments in this study's introduction are citations of McAndrew et al.'s contraction-time inference rather than findings of this study.

• Yi, K.-H., Kim, D. C., Lee, S., Lee, H.-J., & Lee, J.-H. (2024). Intramuscular neural distribution of the gluteus maximus muscle: Diagnostic electromyography and injective treatments. Diagnostics, 14(2), 140. https://doi.org/10.3390/diagnostics14020140

2.4 Historical and Anatomical Sources Pending Primary Verification

Anatomical basis: the superior portion of the gluteus maximus is the distinctly human enlargement, with attachments into the fascia lata; the inferior portion attaches to the ascending tendon and lateral intermuscular septum

[Abstract/secondary: Reached through Bartlett et al. (2014); the characterizations below reflect the citing authors and require primary source verification]

A comparative anatomical study by Stern examined the gluteus maximus of humans and extant apes (specimen numbers not verified). As characterized by Bartlett et al. (2014), the human gluteus maximus originates from the surface of the ilium behind the posterior gluteal line, the fascia of the gluteus medius, the thoracolumbar fascia, the erector spinae aponeurosis, the dorsal sacroiliac ligament, the sacrotuberous ligaments, and portions of the sacrum and upper coccyx, and is described as having superior (cranial) and inferior (caudal) portions. The superior portion attaches extensively to the fascia lata and the ascending tendon, whereas the inferior portion attaches to the ascending tendon and the lateral intermuscular septum. Apes possess a gluteus superficialis muscle in which the caudal fibers comprise the greatest proportion of the musculature; the human gluteus maximus is relatively larger than the ape musculature owing to an expanded cranial portion, and Stern first proposed that enlargement of these cranial fibers (the superior gluteus maximus in humans) comprises the unique morphological specialization of the human gluteus maximus, describing the muscle as a hallmark of bipedality. Note that this citation establishes the anatomical frame for regional analysis: the superior portion (the portion associated with hip abduction, external rotation, and frontal plane control in the EMG literature in Parts 1 - 4) is the portion that distinguishes human gluteal anatomy from the apes, and its extensive fascia lata attachment is consistent with an abductor-stabilizer contribution alongside the gluteus medius and tensor fasciae latae. Additionally, the differing distal attachments of the 2 portions (fascia lata compared to the lateral intermuscular septum) provide an anatomical rationale for differing mechanical actions; however, all characterizations above are secondhand and require primary verification before publication (??)

• Stern, J. T., Jr. (1972). Anatomical and functional specializations of the human gluteus maximus. American Journal of Physical Anthropology, 36(3), 315-339. https://doi.org/10.1002/ajpa.1330360303

Walking and slow running result in higher superior than inferior gluteus maximus EMG activity (findings pending primary retrieval)

Stern et al. compared participants (number, gender, and age not verified) during walking, slow running, and other rapid and complex locomotor behaviors (complete activity list not verified). Outcome measures included EMG of the superior and inferior portions of the gluteus maximus (electrode type and normalization method not verified). As characterized by Bartlett et al. (2014), EMG activity of the superior gluteus maximus was significantly higher than that of the inferior gluteus maximus during walking and slow running, and the authors suggested that the superior portion may play a greater role in hip abduction during climbing, uphill walking, and running. Note: this citation is the earliest identified report of significantly higher superior than inferior gluteus maximus activity during level gait, predating Lyons et al. (1983), and it originates from the same research group (Stern's laboratory) that established the anatomical basis for regional analysis of the gluteus maximus; primary retrieval is required before these findings can be repeated (??)

• Stern, J. T., Jr., Paré, E. B., & Schwartz, J. M. (1980). New perspectives on muscle use during locomotion: electromyographic studies of rapid and complex behaviors. Journal of the American Osteopathic Association, 80(4), 287-291.

Hip abduction results in higher upper gluteus maximus EMG activity, and the gluteus maximus is largely quiescent during relaxed standing (earliest identified regional source; findings pending primary retrieval)

[Abstract/secondary: Reached through Contreras et al. (2015), Bartlett et al. (2014), and Lieberman et al. (2006); all findings sentences reflect the citing authors' characterizations and require primary verification. The journal is discontinued and the full text is not digitized; retrieval likely requires an interlibrary loan]

Karlsson and Jonsson compared participants (number, gender, and age not verified) during electromyographic testing of gluteus maximus function across multiple postures and resisted movements (complete condition list not verified). Outcome measures included EMG of the gluteus maximus, including separate recording of the upper portion (electrode type and normalization method not verified). As characterized by Contreras et al. (2015), hip abduction better targeted the upper gluteus maximus. As characterized by Bartlett et al. (2014) and Lieberman et al. (2006), the gluteus maximus was "largely quiescent"; that is, near-silent, with perhaps occasional low-level bursts during relaxed bipedal standing. Note that this is the earliest identified source for the association between hip abduction and the upper portion, predating Stern et al. (1980) by 15 years and Lyons et al. (1983) by 18 years, and it should be cited for priority once verified. Additionally, the quiescent-standing characterization is corroborated by multiple independent citing authors and by contemporaneous research (Basmajian and De Luca describe gluteus maximus activity during abduction against heavy resistance with the thigh flexed, and inactivity during relaxed standing), whereas the regional abduction characterization traces to a single citing source (Contreras et al.) and carries the same single-source verification risk this project has already identified twice in this literature.

• Karlsson, E., & Jonsson, B. (1965). Function of the gluteus maximus muscle: an electromyographic study. Acta Morphologica Neerlando-Scandinavica, 6, 161-169.