Characterizing the impact of muscle quality on lower-extremity physical function in overweight and obese older women following a weight loss and exercise intervention
Straight, Chad Richard
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The population of older women living in the United States continues to grow rapidly and aging is accompanied by an increased risk for physical limitations. Muscle quality, which is traditionally defined as muscle strength or power per unit of muscle size, is a salient determinant of physical function in older adults and thus a potential target for intervention. Therefore, in the context of a 6-month exercise and diet-induced weight loss intervention for overweight and obese (BMI ≥ 25.0 kg/m2) older (65-80 y) women, the primary aims of this dissertation were three-fold: 1) to examine the relative contributions of changes in muscle quality and body composition to changes in lower-extremity physical function (LEPF), 2) to determine the specific functional improvements associated with changes in various indices of whole-muscle performance, and 3) to examine the effects on midthigh composition, and the interrelationships among changes in intermuscular adipose tissue (IMAT), muscle quality and LEPF. For primary aim 1 (n=38), our linear regression model indicated that change in muscle quality (standardized β = 0.64, p < 0.01) was the strongest independent predictor of change in a composite LEPF Z-score; however, change in body weight (β = -0.30, p < 0.05) was also a significant contributor. For primary aim 2 (n=38), a 1 N-m increase in knee muscle strength consistently predicted improvements in 6-minute walk distance (unstandardized β range = 0.310 to 0.505, p < 0.05) and 8-foot up-and-go time (β range = -0.010 to -0.012, p < 0.05), although leg power was more important for tasks requiring the transfer of body weight (e.g., sitting-to-standing). With regard to primary aim 3 (n=25), a reduction in midthigh IMAT area was the strongest independent predictor of a change in performance on the 30-s chair stand (standardized β = -0.80, p < 0.01) while change in muscle quality was a significant predictor of change in 6-minute walk distance (β = 0.48, p < 0.05). Changes in muscle quality and whole-body and regional composition significantly predict improvements in LEPF tests among overweight and obese older women following exercise and diet-induced weight loss.