MUSCULOSKELETAL ADAPTATIONS TO WEIGHTLESSNESS AND DEVELOPMENT OF EFFECTIVE COUNTERMEASURES

A Research Roundtable, organized by the American College of Sports Med icine with sponsorship from the National Aeronautics and Space Adminis tration, met in November 1995 to define research strategies for effect ive exercise countermeasures to weightlessness. Exercise was considere d both independently of and in conjunction with, other therapeutic mod alities (e.g., pharmacological, nutritional, hormonal, and growth-rela ted factors) that could prevent or minimize the structural and functio nal deficits involving skeletal muscle and bone in response to chronic exposure to weightlessness, as well as return to Earth baseline funct ion if a degree of loss is inevitable. Musculoskeletal deficits and co untermeasures are described with respect to: 1) muscle and connective tissue atrophy and localized bone loss, 2) reductions in motor perform ance, 3) potential proneness to injury of hard and soft tissues, and 4 ) probable interaction between muscle atrophy and cardiovascular alter ations that contribute to the postural hypotension observed immediatel y upon return from space flight. In spite of a variety of countermeasu re protocols utilized previously involving largely endurance types of exercise, there is presently no activity-specific countermeasure(s) th at adequately prevent or reduce musculoskeletal deficiencies. It seems apparent that countermeasure exercises that have a greater resistance element, as compared to endurance activities, may prove beneficial to the musculoskeletal system. Many questions remain for scientific inve stigation to identify efficacious countermeasure protocols, which will be imperative with the emerging era of long-term space flight.