Comparison of Muscle Activity of the Lower Trapezius and Serratus Anterior Muscles during Various Arm Elevation Exercises

Comparison of Muscle Activity of the Lower Trapezius and Serratus Anterior Muscle in Different Arm Lifting Scapular Posterior Tilt Exercises

By Alex Howard PT, DPT, CSCS

Edited by Brent Brookbush DPT, PT, COMT, MS, PES, CES, CSCS, ACSM H/FS

Original Citation: Ha, Sung-min., Kown, Oh-yum., Cynn, Heon-seock., Lee, Won-hwee., Park, Kyue-nam., Kim, Si-hyun., & Jun, Do-young. (2012) Comparison of electromyographic activity of the lower trapezius and serratus anterior muscle in different arm-lifting scapular posterior tilt exercises. Physical Therapy in Sport, 13, 227-232. ARTICLE

Why is this relevant?:

Scapula posterior tilt (SPT) must occur at end range shoulder elevation (flexion, scaption, abduction) to allow the humeral head and rotator cuff tendons to clear the anterior aspect of the acromion. The lower trapezius (LT) and serratus anterior (SA) are the prime movers of SPT. Poor activation and coordination of these muscles at end range shoulder elevation can lead to compensatory patterns of motion that may lead to conditions such as subacrominal impingement and glenohumeral instability. This study investigates the level of muscle activity of the LT and SA in four different arm lifting exercises.

Caption: Dr. Brookbush demonstrates a Serratus Anterior Manual Muscle Test with palpation of the inferior angle of the scapula on an athletic female.

Serratus Anterior Manual Muscle Test

Study Summary

Study Design	Cohort Study
Level of Evidence	Level IV - Evidence from well-designed case control or cohort study
Subject Demographics	Characteristics: 20 subjects Gender: Male (10) and Female (10) Age: 23.1 (+ 1.8 years) Weight 54.4 kg (+ 6.8 kg) Height 168 cm (+ 6.3 cm) Inclusion Criteria: Ability to perform full flexion in sagittal plane, full abduction in front plane, and full scaption in scapular plane Normal muscle length of the pectoralis minor, levator scapulae and rhomboids Exclusion Criteria Current shoulder pain or shoulder surgery History of neurolgical, musculoskeletal or cardiopulmonary disease that interfere with shoulder motion
Outcome Measures	Reference peak EMG signal amplitude for maximal voluntary isometric contraction (MVICs) obtained using manual muscle testing positions Lower Trapezius (LT): prone with arm diagonally overhead in line with muscle fibers, arm in external rotation. Resistance applied distal to elbow Serratus Anterior (SA): seated, shoulder internally rotated, abducted to 125 degrees in scapular plane. Resistance applied proximal to elbow EMG activity of LT and SA obtained in four different exercises using surface electrodes Target bar used to control amount of shoulder flexion in each exercise Dominant arm used for all EMG testing (right arm in all subjects) Three trials, 2 min rest between trials and 3 min rest between each exercise Wall facing arm lift (WAL): subjects stand facing wall with both arms in contact at 90/90 position with wall. Slide arms up the wall until 145 degrees of shoulder abduction. Then lift both arms until radial aspect of right wrist touches the target bar. Prone arm lift (PAL): prone position, non dominant hand under forehead, dominant arm in 145 degrees of shoulder abduction. Lift arm till radial aspect of wrist touches the target bar Backward rocking arm lift (BRAL): quadruped position, rock back until sitting on heels. Non dominant hand under forehead. Dominant arm placed in 180 degrees of shoulder abduction. Lift arm until radial aspect of wrist touches the target bar. Backward rocking diagonal arm lift (BRDAL): quadruped position, rock back till sitting on heels. Non dominant hand under forehead. Dominant arm placed in 145 degrees of shoulder abduction. Lift arm until radial aspect wrist touches the target bar.
Results	LT muscle activity significantly greater during the BRDAL exercise (63.50% + 23.92) LT muscle activity increase in order of WAL < BRAL < PAL < BRDAL SA muscle activity significantly greater during the BRAL exercise (60.04% + 28.04) SA muscle activity did not differ significantly among WAL, PAL and BRDAL exercises
Conclusions	This study provides evidence on the levels of muscle activity of the LT and SA in four different exercises. These findings can be helpful for exercise selection to specifically target the LT and SA during SPT.
Conclusions of the Researchers	From the EMG activity measured during four different arm lifting SPT exercises, LT muscle activity was significantly greater during the BRDAL exercise while SA muscle activity was significantly greater during the BRAL exercise.

Caption: Cadaver Dissection dipicting the trapezius muscle (especially the lower trapezius), with labels.

Trapezius Muscle - By Anatomist90 - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=17900189

Review & Commentary:

The authors of this study examined muscle activity, using EMG, of the lower trapezius (LT) and the serratus anterior (SA) during four different exercises that included scapular posterior tilt (SPT).

There were many strengths to the methodology of this study. The use of the target bar helped to ensure that the amount of shoulder flexion was the same in each exercise, and for each participant. The authors had the subjects touch the bar, rather than push into the bar, to better replicate the "normal" amount of muscle activity during tasks that include end range arm elevation (flexion, scaption, abduction). Last, the authors use of three exercises performed at 145° of abduction allowed for ease of comparison between exercises, and demonstrates how a change in body position can have an affect muscle activation, and how 145° of abduction differs from shoulder flexion to 180°.

There were several limitations to this study. First, as with any study using surface EMG, there is potential for cross-talk from neighboring muscles. Second, the objective of the study was to measure muscle activity during scapular posterior tilting (SPT); however, the amount of scapula posterior tilt was not measured directly. It was assumed the level of scapular posterior tilt changed with arm elevation, but this does not account for variations in shoulder and thoracic spine mobility between participants that may have allowed for various degrees of posterior tilting at the set level of elevation. Further, there may have been significant differences in scapular motion between the three exercises performed at 145° of abduction versus the one exercise at 180°. Motion capture and kinematic data may have provided better information. Third, three of the exercises were performed against gravity ((PAL, BRAL, BRDAL), which may have had an impact on muscle activity by simply increasing the relative load imparted on the posterior tippers. Last, bilateral activation versus unilateral activation may also have an impact on relative EMG activity. In the three prone based exercises (PAL, BRAL, BRDAL) only the dominant arm was elevated, and in the WAL exercise both arms muscles were lifted.

Why is this study important?

This study investigated the amount of muscle activity of the lower trapezius (LT) and serratus anterior (SA) at the end range of four upper extremity exercises. The authors provide evidence that the SA had greatest activation during an exercise performed at 180° of shoulder abduction compared with the three exercises performed at 145° of abduction. They also provide evidence that the LT had the greatest activation in the backward rocking position, it is hypothesized that this is due to stabilization of the spine. These findings highlight the importance of body position and arm position relative to activation of the SA and LT .

How does it affect practice?

The findings of this study show that the backward rocking position and 180° of shoulder abduction/flexion resulted in greater EMG activity of the lower trapezius (LT) and serratus anterior (SA) . These results may highlight the importance of exercise selection, body position and form. Further, the backward rocking position generally yielded neuromuscular activation greater than the 40-60% necessary for gains in muscle strength and hypertrophy; which may imply these exercises should be the goal of exercise progressions designed to increase SA and LT activity.

How does it relate to Brookbush Institute Content?

In the Brookbush Institute's predictive model of Upper Body Dysfunction (UBD) the lower trapezius (LT) and serratus anterior (SA) are implicated as long and under-active due to a maladaptive compensatory pattern that includes excessive downward rotation and anterior tipping of the scapula. These muscles are often addressed with activation and integration techniques in an attempt to optimize activity and length. The techniques investigated in this research study are similar to techniques recommended by the Brookbush Institute; however, the backward rocking position will need to be explored further. This may represent an additional progression that has yet to be included in the current corrective exercise library.

Below you will find videos demonstrating manual muscle testing of the SA and LT and a few sample activation exercises. Explore more techniques and progressions for activation of these muscles in the articles Lower Trapezius Activation and Serratus Anterior Activation .

Lower Trapezius Manual Muscle Testing (MMT) for an Active Population:

Serratus Anterior Manual Muscle Testing (MMT)

Serratus Anterior Activation

Serratus Anterior Activation Progressions

Trapezius Activation

Lower Trapezius Kinesiology Taping

Questions, comments, and criticisms are welcomed and encourage

Comparison of Muscle Activity of the Lower Trapezius and Serratus Anterior Muscles during Various Arm Elevation Exercises

Comparison of Muscle Activity of the Lower Trapezius and Serratus Anterior Muscle in Different Arm Lifting Scapular Posterior Tilt Exercises

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