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.
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
Inclusion Criteria:
Exclusion Criteria
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| Outcome Measures | Reference peak EMG signal amplitude for maximal voluntary isometric contraction (MVICs) obtained using manual muscle testing positions
EMG activity of LT and SA obtained in four different exercises using surface electrodes
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| Results |
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| 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. |
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
© 2016 Brent Brookbush
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