Bedrest induces a loss of muscle mass and function at the whole-muscle and single-cell levels, and ultimately a loss in physical function. We have consistently shown that muscle loading with resistance exercise during bedrest or unloading for 12-90 days can offset this loss of muscle mass and function. Currently, the standard of care for bedresting elderly is to perform loading equivalent to their body weight through a small amount of walking each day. The efficacy of this recommendation, however, has not been systematically examined at the whole-muscle and cellular levels. In fact, the incidence of falls in the elderly is significantly increased in the first month after discharge from a hospital stay. The goal of this project is to document the influence of bedrest on muscle mass and function at the whole-muscle and single-myofiber levels, as well as muscle protein metabolism in the elderly. An additional goal is to compare the influence of the standard-of-care walking exercise with that of a resistance training regimen known to be effective at preserving muscle mass, function, and metabolism during bedrest. We propose to study three groups of older (65-80 years) women and men who complete 10 days of bedrest: (1) those who do not complete any formal exercise during the bedrest period (BR), (2) those who complete resistance exercise (RE) three times during bedrest (BR+RE), and (3) those who perform the standard-of-care walking exercise (WE) daily (BR+WE). We will examine whole-muscle strength and size (by magnetic resonance imaging), fractional rate of muscle protein synthesis (FSR), and single-fiber contractile characteristics (size, strength, and power) before and after 10 days of bedrest. We hypothesize that whole-muscle and single-myofiber strength and size, as well as FSR, will be decreased with BR. We also hypothesize that these variables will be preserved with resistance exercise (BR+RE) but will not be maintained with the standard-of-care exercise (BR+WE). The investigators in this project have an extensive amount of experience in all of the proposed methodologies, specifically as they relate to bedrest. This investigation will provide important information for clinicians and physical therapists, as well as for older individuals, about the underlying basis of the loss of physical function that occurs as a result of bedrest in the elderly, and about the role of exercise in the treatment of bedrested elderly.
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