Relationship Of Body Composition And Physical Activity To Muscle Performance In Women Across The Lifespan

Abstract

The relationship between body composition and physical function is an emerging area of research within the aging literature. In particular, changes with aging are poorly understood with respect to the relationship of muscle performance, body composition, and physical activity. PURPOSE: The primary aim of this study was to investigate the relationship between body composition and physical activity to leg strength and fatigue in women across the lifespan. METHODS: Seventy-two women were grouped into one of two age groups: Young (20-30 years; n=37) or Old (61-84 years; n=35). Each participant performed 25, maximal leg extensions (EXT) and flexions (FLX) at 180° sec-1. For each leg, a fatigue index (FI%) was determined from the peak and ending torque. Peak torque (TQ) was subsequently normalized to leg mineral free lean mass (MFLM) and used for age and limb comparisons of maximal strength. Body fat (BF%) and MFLM were measured using DXA and physical activity (STEPS) was assessed for 7 days using a step counter. RESULTS: The Young had significantly (p<0.05) lower BF% and greater STEPS, MFLMTOTAL, and MFLMLEG compared to Old. Repeated measures ANOVA indicated that although there was no difference in FI% and TQ between limbs (dominant vs. non-dominant), there was a significant main effect for age (collapsed across limb) where the Young group had lower EXT-FI%, FLX-FI%, and greater EXT-TQ, FLX-TQ than the Old. Correlation analysis suggested that EXT-TQ and EXT-FI% had the highest correlation to AGE (r=-0.61 and 0.34) while FLX-TQ had highest correlation with STEPS (r=0.33). EXT-TQ was also correlated to BF% (r=-0.39), MFLMLEGS (r=0.39), and STEPS (r=0.27). FLX-TQ was also correlated to AGE (r=-0.31 and BF% (r=-0.24), and EXT-FI% was also correlated to %BF (r=0.30). When controlling for AGE, no significant correlations were found. CONCLUSIONS: The results indicate significant age-related differences in body composition, strength, and physical activity. However, once AGE is accounted for, body composition and physical activity can not fully explain the age-related changes in muscle function. Thus, it is possible that other factors such as muscle activation and/or muscle composition may contribute to the age-related changes in function observed. Supported by: UIUC Research Board (PI: Ebersole).