AN OVERVIEW OF THE ISSUES - PHYSIOLOGICAL-EFFECTS OF BED REST AND RESTRICTED PHYSICAL-ACTIVITY

Reduction of exercise capacity with confinement to bed rest is well re cognized. Underlying physiological mechanisms include dramatic reducti ons in maximal stroke volume, cardiac output, and oxygen uptake. Howev er, bed rest by itself does not appear to contribute to cardiac dysfun ction. Increased muscle fatigue is associated with reduced muscle bloo d flow, red cell volume, capillarization, and oxidative enzymes. Loss of muscle mass and bone density may be reflected by reduced muscle str ength and higher risk for injury to bones and joints. The resultant de conditioning caused by bed rest can be independent of the primary dise ase and physically debilitating in patients who attempt to reambulate to normal active living and working. A challenge to clinicians and hea lth care specialists has been the identification of appropriate and ef fective methods to restore physical capacity of patients during or aft er restricted physical activity associated with prolonged bed rest. Th e examination of physiological responses to bed rest deconditioning an d exercise training in healthy subjects has provided significant infor mation to develop effective rehabilitation treatments. The successful application of acute exercise to enhance orthostatic stability, daily endurance exercise to maintain aerobic capacity, or specific resistanc e exercises to maintain musculoskeletal integrity rather than the use of surgical, pharmacological, and other medical treatments for clinica l conditions has been enhanced by investigation and understanding of u nderlying mechanisms that distinguish physical deconditioning from the disease. This symposium presents an overview of cardiovascular and mu sculoskeletal deconditioning associated with reduced physical work cap acity following prolonged bed rest and exercise training regimens that have proven successful in ameliorating or reversing these adverse eff ects.