Effect of altered physical loading on bone and muscle in the forearm

Cast immobilization of injured forearms is common clinical practice yet little is known about the effect of reduced skeletal loading in the absence of pathology. This study reports the changes in the forearms of nine healthy young adults owing to six weeks in a plaster cast followed by 1 year of either habitual activity or a strengthening program. Both groups exhibited similar patterns of change in wrist mobility, forearm muscle strength, and bone variables. Because of small sample size and poor compliance with the exercise protocol, no conclusions can be drawn about the effect of exercise. In all subjects, reduced loading caused a decrease in wrist mobility (p < 0.02) and grip strength (p = 0.01) with full recovery following 3 months of remobilization. Six months after removing the cast, bone size was reduced in the middle region of the radius (p = 0.02) and recovered after 1 year of remobilization. Given that radial bone mass tended to decrease while bone density was unchanged, we conclude that the effect of casting was modulated by changes in gross bone morphology rather than in material characteristics.Key words: bone mass, muscle strength, physical loading, radius, young adults.