Intermuscular Adipose Tissue, Muscle Quality and Physical Function Following Weight loss in Overweight Older Women

Abstract

PURPOSE: Exercise and diet-induced weight loss are recommended to improve physical function in overweight and obese older adults, but the physiologic factors associated with improvements in physical function are unclear. This study examined the effects of exercise and weight loss on thigh composition, muscle quality and physical function, and the relationships between changes in these outcomes, in overweight and obese older women. METHODS: Twenty-five overweight/obese (BMI = 29.0 ± 3.2 kg/m2) postmenopausal (age = 68.5 ± 3.8 y) women completed a 6-month exercise and weight loss intervention designed to facilitate a 10% loss of initial body weight. The intervention was comprised of a) three 75-minute sessions per week that integrated cardiorespiratory, resistance, and balance training and b) recommendations to reduce energy intake by ~500 kcal/d. Whole-body composition was measured via dual-energy X-ray absorptiometry and thigh composition was determined using magnetic resonance imaging. Muscle quality (N-m/cm2) was defined as isokinetic knee torque divided by thigh muscle cross-sectional area. Physical function was measured using the 6-minute walk and 30-s chair stand. RESULTS: At 6 months, overall weight loss was 7.6 ± 3.1 kg (−9.9 ± 3.9%, p < 0.01). There was a 16.3 ± 8.8% reduction in thigh intermuscular adipose tissue (−2.9 ± 2.0 cm2, p < 0.01) and 18.0 ± 7.7% decrease in subcutaneous adipose tissue (-18.3 ± 8.4 cm2, p < 0.01), while muscle area did not change (-1.0 ± 2.7 cm2, p = 0.12). Muscle quality (+0.11 ± 0.20 N-m/cm2, p < 0.01) and measures of physical function improved (+9.7-58.7%, p < 0.01). Reduction in thigh intermuscular adipose tissue was the strongest independent predictor of a change in performance on the 30-s chair stand (standardized β = −0.80, p < 0.01) accounting for 34% of the variance. In contrast, change in muscle quality was the strongest independent predictor of change in 6-minute walk distance (β = 0.48, p < 0.05) accounting for 24% of the variance. CONCLUSIONS: Changes in intermuscular adipose tissue and muscle quality are both independent predictors of improved physical function following exercise and weight loss in overweight/obese older women; however, their relative importance may vary according to the functional task. Funded in part by The Beef Checkoff: co-PIs; Evans & Johnson