Electromyographic analysis of the rotator cuff and deltoid musculature during common shoulder external rotation exercises.
Level 4 - case-series / case-control
Prospective single-group repeated-measures laboratory biomechanical study in healthy participants.
PubMed 15296366 · doi:10.2519/jospt.2004.34.7.385
What was done
Intramuscular electromyography (EMG) was evaluated in 10 healthy participants performing 7 shoulder external rotation exercises: prone horizontal abduction at 100° abduction with full external rotation (ER), prone ER at 90° abduction, standing ER at 90° abduction, standing ER in the scapular plane (45° abduction, 30° horizontal adduction), standing ER at 0° abduction, standing ER at 0° abduction with a towel roll, and sidelying ER at 0° abduction. Peak percentage of maximal voluntary isometric contraction (% MVIC) was recorded for the infraspinatus, teres minor, supraspinatus, middle deltoid, and posterior deltoid, and compared using a 1-way repeated-measures ANOVA (P < .05).
What was found
Muscle activation varied significantly across the 7 exercises (P < .05): - Sidelying ER at 0° elicited the highest EMG activity for the infraspinatus (62% MVIC) and teres minor (67% MVIC). - Prone horizontal abduction at 100° with full ER produced the highest EMG activity for the supraspinatus (82% MVIC), middle deltoid (87% MVIC), and posterior deltoid (88% MVIC).
Why it matters
This study identifies specific exercises that selectively maximize recruitment of posterior rotator cuff stabilizers versus the deltoid and supraspinatus, informing exercise selection in shoulder rehabilitation protocols.
Limits
The study is limited by a very small sample size (n = 10) of solely healthy subjects, which may not reflect activation patterns in injured or symptomatic shoulders. It measured only acute EMG amplitude under controlled conditions, not long-term strength development or clinical recovery.
Cited by
- context 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.