Electromyographic study during isometric exercise of the shoulder in head-out water immersion.

Water exercises are used for early rehabilitation programs after shoulder injury such as rotator cuff tear, yet no literature discusses the muscle activity of such rehabilitation programs in water. The purpose of this study was to analyze the electromyographic activity from 8 volunteers during isometric exercises in water and on land. Nine isometric exercises were studied: with 30 degrees, 60 degrees, and 90 degrees shoulder flexion and abduction, and 3 positions of shoulder rotation at 0 degrees abduction (both maximal internal and external rotation and mid-position). Nine parts of 6 muscles were studied: the supraspinatus, infraspinatus, subscapularis, 2 parts of the pectoralis major (clavicular and costal), 3 parts of the deltoid (anterior, middle, and posterior), and the latissimus dorsi. The electromyographic signals were low-pass filtered, full-wave rectified, and integrated for 5 seconds. The electromyographic activity was quantified as a percentage of the maximal manual muscle test. The results showed that supraspinatus activity at 90 degrees abduction significantly decreased from 22.3+/-15.8 on land to 3.9+/-3.3% manual muscle test in water (P < .01). Other muscle activities in water also decreased remarkably compared with those on land. These results provide valuable information for the safety of water exercise for early rehabilitation programs after shoulder injury such as rotator cuff tear.