CHANGES IN MUSCULOSKELETAL STRUCTURE AND FUNCTION WITH PROLONGED BED REST

Prolonged bed rest produces profound changes in muscle and bone, parti cularly of the lower limb. This review first addresses the various mod els used by researchers to study disuse-induced changes in muscle and bone as observed during prolonged bed rest in humans. Dramatic change in muscle mass occurs within 4-6 wk of bed rest, accompanied by decrea ses of 6 to 40% in muscle strength. Immobilization studies in humans s uggest that most of this lost muscle mass and strength can be regained with appropriate resistance training within several weeks after a per iod of disuse. Significant decrements in bone mineral density of the l umbar spine, femoral neck, and calcaneus observed in able-bodied men a fter bed rest are not fully reversed after 6 months of normal weightbe aring activity. Importantly, the lost bone mass is not regained for so me weeks or months after muscle mass and strength have returned to nor mal, further contributing to the risk of fracture. Those who enter a p eriod of bed rest with subnormal muscle and bone mass, especially the elderly, are likely to incur additional risk of injury upon reambulati on. Practical implications for exercise professionals working with ind ividuals confined to bed rest are discussed.