Muscle Capacity, Adiposity And Change In Dynamic Function After Weight Loss In Older Women

Abstract

PURPOSE: Improving muscle capacity (strength or power) can improve lower-extremity physical function (LEPF); however, it is unclear how concomitant weight loss impacts this relationship. Exercise training during weight loss may have complicated implications for changes in LEPF due to changes in both muscle capacity and adiposity. This study aimed to determine if adiposity influences the relationship between change in muscle capacity and LEPF in inactive overweight older women following a weight loss and exercise program. METHODS: Inactive overweight/obese older women (n = 38; BMI = 30.0 ± 4.4 kg/m2; 69.3 ± 4.1 y) completed a 6-month weight loss and supervised exercise intervention. Maximal leg strength (STR) was measured via isokinetic dynamometry and leg power (POW) via leg extension power rig. Body composition was assessed via DXA. LEPF was assessed using the 6-minute walk (6MW) and 8-foot Up-and-Go (UPGO), which are both dynamic physical functional tests. RESULTS: Body weight (-9.6 ± 3.5%), fat mass (-6.8 ± 2.4 kg) and leg lean mass (-0.3 ± 0.5 kg) decreased (all p < 0.01). Muscle STR (19.7 ± 35.4 N-m) and POW (23.3 ± 39.1 watts) improved (both p < 0.01); 6MW (58.9 ± 33.7 m) and UPGO (-0.84 ± 0.74 s) also improved (both p < 0.01). Linear regression analysis (unstandardized betas) indicated: a) changes in STR predicted changes in 6MW (β = 0.505, R2 = 0.15, p < 0.05) and changes in UPGO (β = -0.012, R2 = 0.19, p < 0.05); and b) changes in POW predicted changes in 6MW (β = 0.310, R2 = 0.12, p < 0.05) but was not related to changes in UPGO (R2 = 0.05, p = 0.22). There was a strong trend for the addition of change in fat mass to the predictive model to improve the explained variance in LEPF outcomes by 7-10% (p = 0.053-0.06). CONCLUSIONS: Increases in muscle capacity, especially strength, improve dynamic measures of LEPF in response to a weight loss and exercise program in older women, even in the presence of leg lean mass loss. The influence of reductions in fat mass on measures of LEPF appears to be of lesser importance compared to improvements in muscle capacity given the relative amount of variance explained. More research is needed to inform best practice for exercise prescription to enhance LEPF in older adults, especially under weight loss conditions.