Age-related Site-specific Thigh Muscle Loss And Daily Physical Activity Profile In Middle-aged And Older Women

Abstract

It is known that muscle mass loss with increased age is often greater in the anterior thigh than in the posterior thigh, which is defined as site-specific thigh muscle loss. However, it is unknown whether the site-specific thigh muscle loss is associated with participants’ physical activity (intensity and duration) profile. PURPOSE: To examine the relationships between accelerometer determined light, moderate and vigorous physical activity and muscle thickness distribution of the thigh in middle-aged and older women. METHODS: Eighty-eight women aged 47 to 83 years had their muscle thickness (MT) measured by B-mode ultrasound at two sites on the anterior and posterior aspects of the mid-thigh. The ratio of anterior to posterior thigh (A50:P50) MT was calculated to evaluate site-specific thigh muscle loss. Daytime physical activity was measured using an accelerometer on 30 consecutive days and the total duration at each level of exercise intensity [light-PA (<3.0 METs), moderate-PA (3.0-6.0 METs) and vigorous-PA (>6.0 METs)] and average daily step counts were determined. Relationships of each variable with A50:P50 MT ratio were determined with and without partialling out the effect of age. Significance was set at p≤0.05. RESULTS: Age was inversely correlated with A50 MT (r=−0.292, p=0.006), but not with P50 MT (r=0.074). Light-PA and moderate-PA were not significantly (p>0.05) correlated with either A50 MT (r=0.108 and r=0.193, respectively) or P50 MT (r=−0.068 and r=−0.001, respectively). However, moderate plus vigorous-PA (r=0.234, p=0.028) and vigorous-PA (r=0.231, p=0.030) were positively correlated with A50 MT, but not P50 MT. There were significant correlations between A50:P50 MT ratio and age (r=−0.281, p=0.008), average step count (r=0.225, p=0.035), moderate plus vigorous-PA (r=0.223, p=0.036) and vigorous-PA (r=0.356, p=0.001). After adjusting for age, A50:P50 MT ratio was significantly correlated to vigorous-PA (r=0.333, p=0.002), but not average step counts (r=0.157, p=0.148), light-PA (r=0.085, p=0.434), or moderate-PA (r=0.068, p=0.532). CONCLUSION: This cross-sectional analysis suggests that vigorous physical activity (>6.0 METs) may be necessary for lowering the risk of age-related site-specific thigh muscle loss.