Background and aims: It is unknown if the site-specific muscle loss of ageing muscle is associated with accelerometer-determined daily step count and/or intensity of physical activity. The purpose of this study was to examine the relationships between accelerometer- determined physical activity and lower body muscle size in women.
Methods: Forty-eight women aged 52 to 76 years had their muscle thickness (MTH) measured by B-mode ultrasound at seven sites on the anterior and posterior aspects of their upper- and lower-leg. Daytime physical activity was measured using an accelerometer on 30 consecutive days and the total duration of each level of exercise intensity (light-PA, moderate-PA and vigorous-PA), average step count, and physical activity-related energy expenditure were calculated.
Results: Age was inversely correlated with anterior 30% upper-leg MTH (r=-0.296, p<0.05), but not with other measured MTH sites. Light-PA was not significantly (p>0.05) correlated with measured lower body MTH. However, moderate-PA was correlated (p<0.05) with lower-leg MTH, while vigorous-PA was correlated (p<0.05) with lower-leg and anterior 30% upper- leg MTH. Following adjustment for confounding factors, the anterior and posterior lower-leg MTH was positively correlated (p<0.05) with duration of moderate- PA and vigorous-PA, as well as average step count.
Conclusions: Thus daily moderate and vigorous physical activity was associated with higher muscle mass in the lower leg, but not in the upper-leg muscle, suggesting that the site-specific upper-leg muscle loss may not be prevented or attenuated by daily physical activity.