Masters Thesis

Electromyography of Shoulder Muscles during Upper Extremity Plyometrics

Plyometric exercises are often used to dynamically strengthen the shoulder muscles for overhead athletes. the purpose of this study was to examine differences in relative muscular activation of four shoulder muscles and four upper extremity plyometric exercises. It was hypothesized that the upper trapezius would be most active in the standing scaption exercise, that the lower trapezius and posterior deltoid would be most active in the prone external rotation exercise, and that the infraspinatus would be most active in the kneeling 90/90 exercise. 30 healthy, recreationally active subjects were tested using surface EMG during a five-repetition set of each of the four exercises: kneeling diagonal plyometric, kneeling 90/90 plyometric, prone ER plyometric, and standing scaption plyometric exercises using a 1kg soft plyoball. Electrodes were attached to the upper trapezius (UT), lower trapezius (LT), posterior deltoid (PD), and infraspinatus (IS) muscles. Normalized peak and mean EMG amplitudes were expressed as % MVIC. Results showed LT > UT for the kneeling diagonal, 90/90, and prone ER exercises. the highest peak and mean LT activation was in the prone ER exercise. Highest peak IS activation in the kneeling 90/90 and highest mean IS activation in the prone ER. the results demonstrated that body position affects muscle activation, and in the dynamic, overhead exercises, good LT:UT activation occurred.

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