MUSCLE FUNCTION AT THE WRIST FOLLOWING 9-D OF IMMOBILIZATION AND SUSPENSION

The purpose of this study was to evaluate the effects of 9 d of immobi lization and partial suspension on muscle function at the wrist. Twelv e female subjects (19-27 yr) wore a cast suspended from the neck by a sling that immobilized muscles acting on the wrist. Atrophy, muscle da mage indicators, isometric and isokinetic strength, reaction time, spe ed of movement, and fatigability were assessed. Forearm muscle cross-s ectional area decreased by 4.1% following immobilization and suspensio n. There was no indication that significant muscle degeneration occurr ed during immobilization or when muscles resumed normal function. Isom etric strength for flexion and extension decreased by 29.3 and 32.5%, respectively. Concentric strength decrements for flexion, extension, p ronation, and supination ranged from 8.9-21.7% at 2.11 and 3.16 rad.s( -1). Eccentric strength decrements at 2.11 rad.s(-1) for the same move ments ranged from 12. 5-18.5%. Fatigability was unaffected. Greater re lative strength losses compared to decreased muscle cross-sectional ar ea may be the result of a decrease in contractile protein density or u nidentified neural factors following immobilization and partial suspen sion. However, neuromuscular control of reaction time was not affected .