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Purpose: Supraspinatus strengthening is an important part of shoulder rehabilitation programs. Because of the force-couple relationship between supraspinatus and deltoid during shoulder abduction, it has been proposed that the optimal exercise to strengthen supraspinatus is one that would maximize supraspinatus activity while minimizing surrounding muscle activity, particularly deltoid. The aim of this study was to simultaneously examine all exercises known to recruit supraspinatus at high levels and to compare the level of recruitment in supraspinatus, deltoid, and infraspinatus.

Methods: Using a combination of surface and intramuscular electrodes, EMG recordings were taken from supraspinatus, infraspinatus, and the three parts of deltoid of 15 subjects with normal dominant shoulder function during maximal isometric contractions in "empty can," "full can," prone elevation, pendant external rotation, and prone external rotation exercise positions.

Results: There was no significant difference in the level of supraspinatus activation for all exercise positions examined. No significant difference was found in activation levels across all muscles during the "can" exercise positions. The exercise positions using external rotation were found to activate parts of deltoid significantly less than the "can" and prone elevation positions. Infraspinatus was activated at greater levels than supraspinatus during the external rotation exercises.

Conclusions: Using the criteria that the optimal exercise to strengthen supraspinatus should maximize supraspinatus activity while particularly minimizing deltoid activity, this study has shown that the pendant external rotation and prone external rotation exercises are more valid than the "can" and prone elevation exercises for supraspinatus strengthening in subjects with normal dominant shoulder function.

(C)2009The American College of Sports Medicine