Squat Depth Recommendations: Based on All Available Research

This article and systematic research review are excerpts from the course:

• Lower Body Exercise Progressions

How Deep Should You Squat?

What is the optimal range of motion (ROM) for squats? "Ass to Grass" has become the battle cry of every self-proclaimed "strength coach", but are deep squats really better? Deep squats are definitely harder, and they require a significant amount of work and dedication to perform well. Training with deep squats is certainly necessary for sports that require deep squatting (powerlifting and Olympic lifting). However, the body of research on squat ROM suggests that "squat deep" may be the most over-rated cue in fitness and performance training.

Note, you do not need to take our word for it. We have attempted to locate every relevant research study and included those studies in the systematic narrative research review below. Please feel free to read the research and develop your own conclusions (and if you know of additional peer-reviewed, published, original research studies, please leave them in the comments; we will add them). We hope that you find the following conclusions to be a reasonably objective summary of all research findings.

Squat Depth Research Quick Summary

Brookbush Institute’s Research-based Position on Squat Depth: Squats at any depth are beneficial for strength, hypertrophy, and power. Movement impairment may significantly influence squat depth. Squat depth should not be prioritized over optimal alignment or pain.

• Brookbush Institute’s Position Statement on ROM: Exercise (including squats) should be performed through the largest range of motion (ROM) that can be attained with good form and without pain.

Quick Summary of Research Findings:

• Force vs. Work: Because more load can often be lifted with less range of motion (ROM), it is likely that more force will be produced with shallower squats. However, because deeper squats involve more vertical displacement, more work will be performed with deeper squats (note that "work" is defined as force x distance).
• Depth vs. Load: It is likely that increases in depth have a larger influence than load on knee torque, increases in load have a larger influence than depth on ankle torque, and depth and load seem to affect hip torque equally.
• EMG Activity is Mixed: Deeper squats likely increase the EMG activity of the gluteus maximus, rectus femoris, erector spinae, and tibialis anterior, and may not significantly alter the EMG activity of the vastus lateralis, biceps femoris, and gastrocnemius. Additionally, the gluteus maximus, biceps femoris, and soleus may exhibit larger increases in EMG activity with the increases in load possible during shallower squats.
• Hypertrophy: Deeper squats likely result in larger improvements than shallower squats in muscle hypertrophy; however, these differences are likely small, as demonstrated by a lack of consistent findings in the available research.
• Strength: Squat strength is ROM specific, with deeper squats resulting in an increase in strength over a larger range, but the largest increases for a squat ROM resulting from training with that ROM.
• Power: The effect of training with different squat depths on power (e.g. box jumps, sprints, etc.) is inconclusive, with studies demonstrating larger improvements from both shallower and deeper squats.
• Inexperienced Exercisers: Deeper squats may result in larger improvements in hypertrophy, strength, and power for inexperienced or deconditioned individuals. It may be hypothesized that inexperienced or deconditioned individuals do not exhibit a significant difference in load when comparing 1-RM strength for different squat depths due to other limiting factors (e.g., neuromuscular coordination).
• Movement Impairment: Research has demonstrated that movement impairments, including changes in muscle EMG activity, a loss of hip flexion ROM, a loss of hip internal rotation ROM, and especially a loss of dorsiflexion ROM, can significantly decrease squat depth.

Caption: Should everyone squat this deep? What are the advantages and disadvantages?

A Better Squat Depth Recommendation

The research on deep squats implies that we need a more nuanced recommendation for squat ROM than "squat deep." There are several benefits that may be achieved via deep squats, and deep squats are obviously necessary for sports that require deep squatting (powerlifting and Olympic lifting). However, the research suggests that the benefits of squatting can be achieved with quarter-squats, half-squats, parallel squats, or deep squats. Further, due to the relationship between load (and potentially velocity), total work, and range of motion-specific strength, it is likely that the best recommendations will consider the client's goal, form (compensation), pain/discomfort, and risk of injury. Although there are more variables to consider, the recommendation does not need to be complicated. The following is our recommendation for exercise range of motion, which we believe to be a very moderate/conservative (scientifically conservative, not a political statement) position that implies ROM can be challenged, but not at the expense of form or pain.

• Brookbush Institute’s Position Statement on ROM: Exercise (including squats) should be performed through the largest range of motion (ROM) that can be attained with good form and without pain.

We define "good form" below, to aid in clarifying our definition above. Note, the Brookbush Institute's definition of good form (optimal posture) may appear a bit complex, but it is essential that the definition reflects the body of research, and is robust and measurable so that it may be tested in a research setting.

• Brookbush Institute's Definition of Optimal Posture (a.k.a. good form): A mean range of segment alignment that is absent of signs correlated with dysfunction, pain, or an increased risk injury. Additionally, "good form" may include alignment recommendations influenced by optimal length-tension relationships, biomechanical advantage, or force generation capacity.

And, just for a little humor here is a funny definition we created for the deep squat die-hards who have decided that evidence and reason have no place at the altar of the "squat deep or die" religion.

• "Ass to Grassholes" - A group of individuals who think squat depth is more important than alignment, pain-free motion, or the client’s goals.

Caption: Comparing squat form, the hip morphology myth, and the strange assumption that foot position and hip morphology are related.

If you think the squat on the left looks better than the squat on the right, you may be jumping to conclusions. The individual on the left is clearly exhibiting knee varus, feet turn out (tibial external rotation), and excessive pronation. All of which are compensations that have been correlated with pain and injury.

The individual on the right is a basketball player with a history of microdiscectomy. He is squatting as far as he can without compensation or pain (note the near-perfect trunk and lower extremity alignment). Are we going to take squats away from him because he cannot achieve "ass to grass" ROM? The research suggests that quarter-and-half squats are very beneficial for performance.

Ridiculous “coaching” tips we have heard:

“If you can’t get deep, it doesn’t count”

• As the research implies, in general squatting is very effective, and depth does not seem to have a large effect on any outcome.

“Just go lighter, work on your depth, and then you can add load.”

• This rarely if ever works. For example, how would lighter weight improve a dorsiflexion restriction?

“If you can’t squat deep, work on your flexibility.”

• Not all mobility issues are related to flexibility (at least, in the sense that you should "stretch more"). Motor control, joint stiffness, apprehension, and various injuries can influence ROM. And, mobility intervention recommendations should be based on a reliable, objective movement assessment .

“Just put your feet wider and turn them out.”

• This is both an excuse for individuals too lazy to learn corrective interventions, and willful dismissal of research demonstrating that excessive pronation, feet turn out, and knee varus are correlated with pain, dysfunction, and an increased risk of injury.

"You must be a terrible coach if you or your clients cannot squat deep."

• Coaches are not magicians. Squat depth should be recommended based on the client's goals and mobility, and not the coach’s goals or biases.

Caption: Are half-squats deep enough?

Squat Depth Research Summary

Single-session Comparison

• Force and Velocity: Because more load can often be lifted with less ROM, it is likely that more force will be produced with shallower squats. However, because deeper squats involve more vertical displacement, more work will be performed with deeper squats (note that in physics, "work" is defined as force x distance). Interestingly, it is likely that increases in depth have a larger influence on knee torque than load, increases in load have a larger influence on ankle torque than depth, and depth and load seem to affect hip torque equally.
• Electromyographic (EMG) Activity:
  • Comparing Depths with the Same Load: When squatting with the same absolute load (e.g. body weight), vastus medialis recruitment comprises a larger proportion of quadriceps muscle EMG activity closer to terminal knee extension, EMG activity of the tibialis anterior and gluteus maximus may increase with squat depth, and EMG activity of the vastus lateralis, biceps femoris and gastrocnemius may not be significantly influenced by squat depth.
  • Comparing Depths with Different Loads: When a similar relative load (e.g., 10-RM load) is determined for each squat depth, muscle EMG activity is likely similar for all depths; however, there may be some evidence that gluteus maximus, biceps femoris, and soleus EMG activity increase more with load, and rectus femoris and erector spinae EMG activity increase more with depth.

Comparing Training Periods with Quarter, Half, and Deep Squats

• Power
  • Relatively Inexperienced Exercisers: For relatively inexperienced individuals, deeper squats are likely to result in larger improvements in strength and may result in larger improvements in jump height; however, the jump height findings were mixed.
  • Experienced Exercisers: Studies demonstrate contradictory findings, including Pallarés et al. (11) demonstrating that half and deep squats result in larger increases in power performance, and Rhea et al. (12) demonstrating that quarter squats result in larger increases in power performance.
• Hypertrophy and Cross-sectional Area (CSA): Studies demonstrate deep squats may result in larger increases in the CSA of the anterior thigh, adductors, and gluteus maximus; however, for each of these findings, there is a study demonstrating that CSA was similar following deep and shallow squats, and one study demonstrating that shallow squats resulted in a larger increase in posterior thigh muscle CSA. These studies likely imply that deep squats result in larger increases in hypertrophy; however, the differences are likely small.
• Strength
  • Strength is ROM-Specific: Research demonstrates that training with quarter-squats will result in the largest improvements in quarter-squat 1-RM strength, that half-squats will result in the largest improvements in half-squat 1-RM strength, and that full-squats will result in the largest improvements in full squat 1-RM strength. It is important to consider that less ROM generally allows for significant increases in load.
  • Deep Squats Improve Strength for a Larger ROM: Larger ROM squats will result in increases in strength throughout a larger ROM, and may improve the amount of strength maintained during de-training.
  • Deep Squats Result in More Strength for All ROM: Full ROM squats may be superior for increasing full and partial ROM 1-RM strength. The findings of these studies contradict the studies demonstrating that strength is ROM-specific; however, this may be correlated with the inexperience or deconditioning of the participants. It may be hypothesized that inexperienced or deconditioned individuals do not exhibit a significant difference in load when comparing 1-RM strength for different squat depths due to other limiting factors (e.g., neuromuscular coordination). As mentioned previously, deeper squats with a similar absolute load (e.g., body weight or 20kg) result in larger increases in EMG activity.

Dysfunction Correlated with a Loss of Squat Depth: Changes in muscle EMG activity, a loss of hip flexion ROM, a loss of hip internal rotation ROM, and especially a loss of dorsiflexion ROM can significantly decrease squat depth.

Single-session Comparison

Force and Velocity

Two studies compared force, power, and velocity during sets of squats at a variety of depths. Drinkwater et al. compared 10 healthy male recreational rugby players (age: 21.4 ±1.14 years) with at least 1 year of squat training experience, who practiced at least 2 sessions/week, were involved in resistance training 2–3 sessions/week, and had no recent history of injuries. All participants performed squats with a partial range of motion (hips and knee in the horizontal plane) or a full range of motion (ROM) (120° of knee flexion), with 67% of 1-RM loads for 10 reps/set or 83% of 1-RM loads for 5 reps/set, in random order, 1 protocol/session, at least 3 days rest between sessions, with all sessions performed within 14 days. All protocols included 4 sets, with a moderate (90 sec) rest between sets and a tempo determined by the participant. The findings demonstrated that the highest peak force and peak power were exhibited during the partial ROM squats with 83% of 1-RM loads, and the largest amount of work and highest concentric velocity was performed during full ROM squats with 83% of 1-RM loads (1). Bryanton et al. compared 10 healthy, strength-trained females (age: 22.5 ± 2.1 years) with a minimum of 1 year of experience performing the high-bar back squat, able to perform a deep squat with a minimum barbell load of their body weight, with no history of musculoskeletal injuries. All participants performed back squats for 2 sessions. In the first session, the participants performed back squats for 5 sets, 3 reps/set, progressive increase in load from 50-90% 1RM, with a long (3-5 min) rest between sets. In the second session, the participants performed back squats for 3 sets, 2 reps/set, at 30°, 60°, and 90° joint angles at the hip and knee, and 5°, 15°, and 25° joint angles at the ankles. The findings were calculated based on relative muscular effect (RME), which was determined as the ratio of net joint moment to maximum voluntary torque, measured with a dynamometer matched to joint angles determined by motion analysis. The findings demonstrated that knee extensor RME significantly increased with increases in squat depth but not increases in load, and the ankle plantar flexor RME significantly increased with load but not squat depth. Hip extensor RME increased with both greater squat depth and load (2). In summary, because more load can often be lifted with less ROM, it is likely that more force will be produced with shallower squats. However, because deeper squats involve more vertical displacement, more work will be performed with deeper squats (note that in physics, "work" is defined as force x distance). Interestingly, it is likely that increases in depth have a larger influence on knee torque than load, increases in load have a larger influence on ankle torque than depth, and depth and load seem to affect hip torque equally.

Electromyographic (EMG) Activity

Comparing Depths with the Same Load:

Two studies compared the EMG activity of several lower extremity exercises during squats at partial, parallel, and full-depth with the same load. Caterisano et al. compared 10 healthy, resistance-trained males (age: 24.3 ± 5.6 years) with at least 5 years of free weight training experience. All participants performed a standardized warmup of "non-resistant movements, light-weighted squats, and stretching," followed by back squats to partial, parallel, and full depth for 1 set, 3 reps/set, with between 100 and 125% of the participant’s body weight (same load for each condition), with a long (3 min) rest between sets. The findings demonstrated that only the gluteus maximus exhibited a significant difference in EMG activity with different squat depths, exhibiting significantly more EMG activity during the deep squat. The vastus medialis obliquus exhibited more EMG activity as a proportion of thigh muscle activity during partial squats when compared to parallel and full-depth squats; however, the difference was not statistically significant. The vastus lateralis and biceps femoris did not exhibit a significant difference in EMG activity at any squat depth (3). Han et al. compared 15 healthy female college students with no history of musculoskeletal impairment, surgery, or orthopedic disease. All participants performed squats to 70°, 90°, and 100° of knee flexion on stable (ground) and unstable surfaces (foam pad) during 1 session. The squat protocol included bodyweight squats with arms held in front of the body and shoulders flexed to 90°, feet shoulder-width apart, eyes forward, and back straight for 3 sets, 5-sec hold/set, with a long (5 min) rest between sets. The findings demonstrated that the vastus medialis exhibited a significant increase in EMG activity at all angles, with the most activation at 90° and 100° while on stable ground. The tibialis anterior also exhibited a significant increase in EMG activity at all angles, with the most activation at 100° while on stable ground. Biceps femoris and gastrocnemius EMG activity was not significantly different at any joint angle. None of the muscles assessed exhibited a significant difference between stable and unstable surfaces (4). In summary, when squatting with the same absolute load (e.g. body weight), vastus medialis recruitment comprises a larger proportion of quadriceps muscle EMG activity closer to terminal knee extension, EMG activity of the tibialis anterior and gluteus maximus may increase with squat depth, and EMG activity of the vastus lateralis, biceps femoris and gastrocnemius may not be significantly influenced by squat depth.

Comparing Depths with Different Loads

Additional studies have compared the EMG activity of various muscles during squats of different depths with relative loads determined for each squat depth. Contreras et al. compared 13 healthy, resistance-trained women (age: 28.9 ± 5.1 years) with no history of pain, musculoskeletal injuries, neuromuscular injuries, or illness. All participants performed front, full, and parallel squats in a randomized order and counterbalanced fashion, with the feet slightly wider than shoulder-width apart and the toes pointed forward or slightly outward. Participants maximally flexed the knees during the descent (eccentric) phase of the front and full squat and flexed the knees until the tops of the thighs were parallel to the floor for the parallel squats, for 1 set each, 10 reps/set, using their estimated 10 RM (estimated separately for each condition), without a predetermined tempo, and a long rest (5 min) between variations. The findings indicated that all 3 variations of the squat resulted in significant and similar increases in mean and peak EMG activity of the vastus lateralis, upper gluteus maximus, lower gluteus maximus, and biceps femoris (5). Gorsuch et al. compared 20 healthy male and female Division I cross-country runners (age: 19.2 ± 0.4 years) with at least 4 years of significant running and resistance training experience. All participants performed partial squats and parallel squats in a randomized order. The squat protocol included 1 set of partial squats to 45° knee flexion and a set of parallel squats to 90° of knee flexion, 6 reps/set, with a 10 RM load (determined separately for each condition), a long (5 min) rest between sets, at a moderate (1:0:1) tempo for the partial squat, and a moderate (2:0:2) tempo for the parallel squat. All participants performed a warm-up protocol, including stationary cycling for 3 min, followed by parallel squats for 2 sets, 10 reps/set, at 50 - 75% of 10 RM loads, with long (3 min) rest between sets. The findings demonstrated that the rectus femoris and erector spinae exhibited significantly higher EMG activity during the parallel squats; however, the biceps femoris and gastrocnemius exhibited similar muscle activity during both squat conditions (6). Da Silva et al. compared 15 healthy, resistance-trained males (age: 26 ± 5 years) with no history of lower back injury, lower extremity surgery, or sensations of pain or "giving way" in the lower extremities within the previous year. All participants performed both partial and full ROM back squats with the feet hip-width apart and the barbell in the high-bar position, one set each, 10 reps/set, with a 10-RM load (significantly heavier loads for partial ROM squats), at a self-determined tempo, with a 30-minute rest between sets. Note that a 5-minute cycling warm-up at 70 rpm preceded both squat conditions. The findings demonstrated that both conditions resulted in significant and similar EMG activity for the vastus lateralis, vastus medialis, rectus femoris, semitendinosus, and erector spinae. However, the partial ROM squat resulted in significantly greater EMG activity of the gluteus maximus, biceps femoris, and soleus (likely due to a significantly heavier load lifted) (7). These studies suggest that when a similar relative load (e.g., 10-RM load) is determined for each squat depth, muscle EMG activity is likely similar for all depths; however, there may be some evidence that gluteus maximus, biceps femoris, and soleus EMG activity increase more with load, and rectus femoris and erector spinae EMG activity increase more with depth.

Comparing Training Periods with Quarter, Half, and Deep Squats

Power

Relatively Inexperienced Exercisers

Three studies have compared relatively inexperienced individuals training with different squat depths and the effects on power. Bloomquist et al. compared 17 healthy males (age: 25 ± 6 years) who had not participated in squat training more than 1 session/week or participated in strength or power sports in the previous 6 months. Participants were randomly assigned to a deep squat group or a shallow squat group for 12 weeks, 3 sessions/week, for a total of 36 sessions. The deep squat protocol included barbell back squats to 120° of knee flexion for 3-5 sets, 3-10 reps/set, at 3-10 RM loads (calculated separately for each group/depth), with a moderate (2-4:0:maxV) tempo (note that maxV = maximum velocity). The shallow squat protocol was performed to 60° of knee flexion with the same protocol used for deep squats. Participants performed a warm-up for 10 min/session, including 1-3 reps of submaximal squats (shallow or deep according to the training group). The findings demonstrated that increases in strength were ROM-specific. Counter-movement jump (CMJ) heights increased significantly for both groups; however, the deep squat group exhibited larger increases in CMJ height. Further, only the deep squat group exhibited significant improvements in jump squat heights (8). An RCT by Hartmann et al. compared 59 healthy males and females (age: 24.11 ± 2.88 years) who did not miss more than 2 training sessions. Participants were randomly assigned and counter-balanced based on their counter-movement jump height to a control group (no training intervention), a deep back squat group, a deep front squat group, or a quarter-back squat (120° of knee extension) group for 10 weeks, 2 sessions/week for a total of 20 sessions. The exercise protocol included the assigned squat movement for 5 sets, 2-10 RM/set (load determined independently for each group/depth), and a long (5 min) rest between sets. The findings demonstrated that increases in strength were ROM specific; however, the deep front squat group and deep back squat group exhibited significant and similar increases in vertical jump height (measured with a force plate), and the quarter-back squat group and controls did not (9). An RCT by Weiss et al. compared 19 healthy males and females (age: 23.7 ± 6.1 years) who had not participated in a formal strength development program for at least 1 year prior to the study. Participants were randomly assigned to a control group (no exercise), a deep squat group, or a shallow squat group for 9 weeks, 3 sessions/week for a total of 27 sessions. All participants performed Bear Machine and Nautilaus Plate-loaded squats in a daily undulated program of 2-5 sets, 1-10 RM/set (determined individually for each squat depth). Note that week 5 of the training protocol was a designated active rest week with no training. The findings demonstrated that the deep squat group was the only group to exhibit a significant increase in deep and shallow squat 1-RM strength when compared to controls. Neither exercise group exhibited significant increases in the height of depth jumps or restricted vertical jumps (measured with a Vertec device) (10). These studies suggest that for relatively inexperienced individuals, deeper squats are likely to result in larger improvements in strength and may result in larger improvements in jump height; however, the jump height findings were mixed.

Experienced Exercisers

Two additional studies compared the effects of squat depth on the power of experienced exerciers. Pallarés et al. compared 53 experienced male exercisers (age: 23.0 ± 4.4 years) randomly assigned to a control group (no training), a half-squat group, a parallel-squat group, and a full-squat group. All exercisers completed 10 weeks of periodized squat training, 2 sessions/week, 4-5 sets/session, 4-8 reps/set, with 60-80% of 1 RM loads, long (4 min) rest between sets, and a maximum velocity (maxV) concentric tempo. The findings demonstrated that the full-squat group exhibited an increase in 1-RM strength for all ranges; however, each group improved most for the ROM they trained. The full squat and parallel-squat group exhibited significant and similar improvements during the re-assessment of the counter-movement jump (CMJ) and Wingate performance tests; however, the half-squat group did not exhibit significant improvements (11). Rhea et al. compared 28 healthy male college athletes (age: 21.4 ± 3.2 years) with more than 2 years of consistent resistance training experience. Participants were randomly assigned to a quarter squat group (knee flexion between 55-65°), a half squat group (knee flexion between 85-95°), and a full squat group (knee flexion greater than 110°) for 16 weeks, 4 sessions/week for a total of 64 sessions. The exercise protocol included a split routine of lower body exercises on Monday and Thursday (squats, power cleans, lunges, reverse hamstring curls, and step-ups) for 4-8 sets of squats/session, 2-4 sets of cleans/session, 1-3 sets of other exercisers/session, 2-8 RM/set, and a long (3 min) rest between sets. Upper body exercises were performed on Tuesdays and Fridays (upper body exercises were not reported). The findings demonstrated that all groups exhibited significant increases in 1 RM strength that correlated with the ROM trained, and all groups exhibited significant increases in jump height and sprint speed; however, the largest increase in jump height and sprint speed was exhibited by the quarter squat group (12). These studies demonstrated contradictory findings, including Pallarés et al. (11) demonstrating that half and deep squats result in larger increases in power performance, and Rhea et al. (12) demonstrating that quarter squats result in larger increases in power performance.

Hypertrophy and Cross-sectional Area (CSA)

Several studies have compared training periods with various squat depths, and the effect on hypertrophy. As mentioned above, Bloomquist et al. compared 17 healthy males (age: 25 ± 6 years) who had not participated in squat training more than 1 session/week or participated in strength or power sports in the previous 6 months. Participants were randomly assigned to a deep squat group or a shallow squat group for 12 weeks, 3 sessions/week, for a total of 36 sessions. The findings demonstrated that increases in 1-RM strength were ROM-specific. Anterior thigh muscle cross-sectional area (CSA) (measured with MRI) increased at 2 sites for the shallow squat group, 3 sites for the deep squat group, and the increases were larger for the deep squat group. Conversely, only the shallow squat group exhibited a significant increase in posterior thigh muscle CSA, but only at one site. Only the deep squat group reached statistically significant increases in lean body mass; however, changes in body mass were not significant for either group. The pennation angle of the anterior thigh muscles significantly changed for both groups; however, patellar tendon CSA did not (13). An RCT by McMahon et al. compared 26 healthy males and females (age: 19 ± 3.4 years) with no history of musculoskeletal, neurological, inflammatory, or metabolic disorders. Participants were randomly assigned to a control group (no additional activity), a short ROM group (50° knee flexion), or a large ROM group (90° knee flexion) for 8 weeks, 3 sessions/week (including 1 home session) for a total of 24 sessions. All participants performed the same lower body resistance training protocol with either 50° or 90° knee flexion during back squats, knee extensions, Bulgarian split squats, bilateral and unilateral Sampson chair (a.k.a. wall sits), leg press, and dumbbell lunges for 3 sets, 10 reps/set, 80% of 1-RM loads, with a moderate (60-90 sec) rest between sets, and a moderate (1:2:1) tempo. The findings demonstrated that both exercise groups exhibited significant increases in ROM-specific 1-RM strength, muscle CSA, and pennation angle (measured with ultrasonography). The large ROM group exhibited a trend toward larger increases; however, following 4 weeks of detraining, both groups had returned to baseline values similar to the control group. Additionally, both groups exhibited a significant and similar decrease in subcutaneous fat (measured with ultrasonography) that persisted during the detraining period (14). Kubo et al. compared 17 healthy, physically active males (age: 20.9 ± 0.8 years) who had not participated in any regular exercise for at least 1 year. Participants were randomly assigned to a full squat group or a half squat group for 10 weeks, 2 sessions/week for a total of 20 sessions. The full squat protocol included full ROM squats to approximately 140° knee flexion. The half squat protocol included a half ROM squat to approximately 90° knee flexion. The exercise protocol included 3 sets, 10 reps/set at 60% of 1-RM loads in the first week; 3 sets, 8 reps/set at 70% 1-RM loads in the 2nd week; 3 sets, 8 reps/set at 80% of 1-RM loads in the 3rd week; and 3 sets, 8 reps/set at 90% of 1-RM loads at the beginning of the 4th week. If the participants were able to perform 3 sets of 8 reps then the load was increased by 5 kg during the next session. The findings demonstrated that both groups significantly increased 1-RM strength for both squat variations, with the full squat group exhibiting significantly larger increases. Additionally, both groups exhibited significant increases in adductor muscle and gluteus maximus muscle volume (measured with MRI); however, the full squat group exhibited larger increases in muscle volume. Both groups exhibited significant and similar increases in quadriceps muscle volume, and neither group exhibited significant changes in hamstring muscle volume (15). In summary, these studies demonstrate deep squats may result in larger increases in the CSA of the anterior thigh, adductors, and gluteus maximus; however, for each of these findings, there is a study demonstrating that CSA was similar following deep and shallow squats, and one study demonstrating that shallow squats resulted in a larger increase in posterior thigh muscle CSA. These studies likely imply that deep squats result in larger increases in hypertrophy; however, the differences are likely small.

Strength

Strength is ROM-Specific

The majority of studies demonstrate that increases in strength are ROM-specific. As mentioned above, Bloomquist et al. compared 17 healthy males (age: 25 ± 6 years) who had not participated in squat training more than 1 session/week or participated in strength or power sports in the previous 6 months. Participants were randomly assigned to a deep squat group or a shallow squat group for 12 weeks, 3 sessions/week, for a total of 36 sessions. The findings demonstrated that the 1-RM strength of partial and full-range squats increased significantly for both groups. However, shallow squat 1-RM strength increased more for the shallow squat group, and deep squat 1-RM strength increased more for the deep squat group. Further, maximal isometric knee extensor torque at 75˚ and 105˚ knee flexion increased significantly for both groups; however, the deep squat group exhibited larger improvements at 105˚ knee flexion (8). Also mentioned above, an RCT by Hartmann et al. compared 59 healthy males and females (age: 24.11 ± 2.88 years) who did not miss more than 2 training sessions. Participants were randomly assigned and counter-balanced based on their counter-movement jump height to a control group (no training intervention), a deep back squat group, a deep front squat group, or a quarter-back squat (120° of knee extension) group for 10 weeks, 2 sessions/week for a total of 20 sessions. The findings demonstrated that each group exhibited larger improvements in strength for the squat protocol they trained with (e.g., increases in strength were ROM-specific) (9). Last, Rhea et al. was also mentioned previously and compared 28 healthy male college athletes (age: 21.4 ± 3.2 years) with more than 2 years of consistent resistance training experience. Participants were randomly assigned to a quarter squat group (knee flexion between 55-65°), a half squat group (knee flexion between 85-95°), and a full squat group (knee flexion greater than 110°) for 16 weeks, 4 sessions/week for a total of 64 sessions. The findings demonstrated that the quarter squat group exhibited the largest improvements in 1-RM strength for quarter squats, the half-squat group showed the largest improvement in 1-RM strength for half-squats, and the full-squat group showed the largest improvements in 1-RM strength for full squats (12). These studies demonstrate that strength is ROM-specific. It is important to consider that less ROM generally allows for significant increases in load.

Deep Squats Improve Strength for a Larger ROM

Two of the studies mentioned above demonstrate that deeper squats improve strength over a larger ROM.As mentioned above, Pallarés et al. compared 53 experienced male exercisers (age: 23.0 ± 4.4 years) randomly assigned to a control group (no training), a half-squat group, a parallel-squat group, and a full-squat group for 10 weeks. The findings demonstrated that the full-squat group exhibited an increase in 1-RM strength for all ROM squats; however, each group improved most for the ROM trained (11). Also mentioned above, An RCT by McMahon et al. compared 26 healthy males and females (age: 19 ± 3.4 years) with no history of musculoskeletal, neurological, inflammatory, or metabolic disorders. Participants were randomly assigned to a control group (no additional activity), a short ROM group (50° knee flexion), or a large ROM group (90° knee flexion) for 8 weeks, 3 sessions/week (including 1 home session) for a total of 24 sessions. The findings demonstrated that both groups exhibited significant increases in ROM-specific strength (measured with a dynamometer), with the larger ROM group exhibiting an increase in strength over a larger ROM and maintaining more of the strength increases during the de-training period (14). These studies imply that larger ROM squats will result in increases in strength for a larger ROM, and may improve the amount of strength maintained during de-training.

Deep Squats Result in More Strength for All ROM

Last, 2 of the studies mentioned above suggest that deeper squats are superior to shallower squats for increasing strength, even when comparing 1-RM strength for shallower squats. As mentioned above, an RCT by Weiss et al. compared 19 healthy males and females (age: 23.7 ± 6.1 years) who had not participated in a formal strength development program for at least 1 year prior to the study. Participants were randomly assigned to a control group (no exercise), a deep squat group, or a shallow squat group for 9 weeks, 3 sessions/week for a total of 27 sessions. The findings demonstrated that the deep squat group was the only group to exhibit a significant increase in deep and shallow squat 1-RM strength when compared to controls (10). Kubo et al. compared 17 healthy, physically active males (age: 20.9 ± 0.8 years) who had not participated in any regular exercise for at least 1 year. Participants were randomly assigned to a full squat group or a half squat group for 10 weeks, 2 sessions/week for a total of 20 sessions. The full squat protocol included full ROM squats to approximately 140° knee flexion. The half squat protocol included a half ROM squat to approximately 90° knee flexion. The findings demonstrated that both groups significantly increased 1-RM strength for both squat variations, with the full squat group exhibiting significantly larger increases (15). In summary, these studies imply that full ROM squats may be superior for increasing full and partial ROM 1-RM strength. The findings of these studies contradict the studies demonstrating that strength is ROM-specific; however, this may be correlated with the inexperience or deconditioning of the participants. It may be hypothesized that inexperienced or deconditioned individuals do not exhibit a significant difference in load when comparing 1-RM strength for different squat depths due to other limiting factors (e.g., neuromuscular coordination). As mentioned above, deeper squats result in larger increases in EMG activity when comparing similar loads.

Dysfunction Correlated with a Loss of Squat Depth

Considering the research above, it is important to consider the issues that may contribute to an inability to squat deep. Although a comprehensive review of the signs correlated with dysfunction is beyond the scope of this publication, two studies were located that specifically demonstrate a correlation between dysfunction and a loss of squat depth. Kim et al. compared 101 healthy males and females (age: 25.69 ± 5.93 years) with no history of lower extremity injuries, surgery, or neurological disorders in the previous 6 months. All participants performed a bodyweight squat, both hands clasped behind the head, looking straight ahead, with the feet at hip width, and descending as low as possible without heel-off, for 1 rep, held for 5 sec. The findings demonstrated that a decrease in squat depth (measured with a digital camera) was correlated with a decrease in ankle dorsiflexion ROM, hip flexion ROM, hip internal rotation ROM (measured with a goniometer), and/or dorsiflexor strength (measured with a dynamometer). However, a decrease in squat depth was not correlated with a decrease in hip external rotation ROM or hip flexor strength (16). Macrum et al. compared 30 healthy males and females (age: 18-30 years) who engaged in 30 minutes of physical activity/day for at least 3 sessions/week with no history of lower extremity injury in either leg in the past 3 months or surgery within the past year. Participants were randomly assigned to a wedge group or a non-wedge group for 1 session. Both groups performed double-leg squats in a standardized start position with feet shoulder-width apart, toes facing straight ahead, arms overhead, and heels on the floor for 7 reps using bodyweight (tempo was not discussed). The wedge group performed squats on a wedge, inducing 12° dorsiflexion. The findings demonstrated that the wedge group exhibited decreased knee flexion, increased knee valgus, dorsiflexion, and medial knee displacement (measured with Motion Monitor software). Additionally, the wedge group exhibited significant increases in muscle activation (measured with surface electromyography) of the soleus and decreased activation of the vastus lateralis and vastus medialis obliquus. No group exhibited significant changes in muscle activation of the lateral gastrocnemius (17). These studies demonstrate that changes in muscle EMG activity, a loss of hip flexion ROM, a loss of hip internal rotation ROM, and especially a loss of dorsiflexion ROM can significantly decrease squat depth.

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