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 immobilization and partial suspension on muscle function at the wrist. Twelve female subjects (19-27 yr) wore a cast suspended from the neck by a sling that immobilized muscles acting on the wrist. Atrophy, muscle damage indicators, isometric and isokinetic strength, reaction time, speed of movement, and fatigability were assessed. Forearm muscle cross-sectional area decreased by 4.1% following immobilization and suspension. There was no indication that significant muscle degeneration occurred during immobilization or when muscles resumed normal function. Isometric strength for flexion and extension decreased by 29.3 and 32.5%, respectively. Concentric strength decrements for flexion, extension, pronation, 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 movements ranged from 12.5-18.5%. Fatigability was unaffected. Greater relative strength losses compared to decreased muscle cross-sectional area may be the result of a decrease in contractile protein density or unidentified neural factors following immobilization and partial suspension. However, neuromuscular control of reaction time was not affected.