Electromyographic Analysis of the Shoulder Girdle Musculature During External Rotation Exercises.
Level 4 - case-series / case-control
Descriptive cross-sectional biomechanical/laboratory study in healthy subjects
PubMed 26740950 · doi:10.1177/2325967115613988
What was done
Electromyographic (EMG) activity was measured across 16 shoulder girdle muscles or muscle segments in 30 healthy subjects during 5 external rotation (ER) exercises: standing ER at 0° and 90° of abduction, standing ER with an underarm towel roll, prone ER at 90° of abduction, and side-lying ER with an underarm towel roll. Surface electrodes were used for 12 superficial muscles/segments (anterior, middle, and posterior deltoid; upper, middle, and lower trapezius; serratus anterior; teres major; upper and lower latissimus dorsi; upper and lower pectoralis major) and fine-wire electrodes for 4 deep muscles (supraspinatus, infraspinatus, subscapularis, rhomboid major). Amplitudes were normalized to EMG at maximum ER force in a standard position.
What was found
Muscular activity differed significantly across exercises (P < .05 to P < .001; exact percentage amplitudes were not reported in the abstract). Standing ER at 90° abduction elicited the greatest activation for anterior and middle deltoid, supraspinatus, upper trapezius, and serratus anterior. Side-lying ER with a towel roll maximized posterior deltoid, middle trapezius, and rhomboid activation. Prone ER at 90° abduction produced the highest activation for lower trapezius, upper and lower latissimus dorsi, subscapularis, and teres major. Standing ER with a towel roll showed highest activation for clavicular and sternal pectoralis major.
Why it matters
Identifying distinct activation profiles enables clinicians and trainers to selectively target or offload specific glenohumeral and scapular muscles during shoulder rehabilitation and athletic conditioning.
Limits
The study included only 30 healthy subjects, so activation strategies may differ in symptomatic individuals or those with shoulder pathology. Exact EMG amplitude numbers and exercise loads were not provided in the abstract.
Cited by
- partial When attempting to externally rotate the shoulder, elevating the elbow away from the torso shifts the muscular workload from the rotator cuff to the deltoid.