Loading dose of physical activity is related to muscle strength and bone density in middle-aged women.

The aim of the current study was to investigate the association between loading dose of physical activity, muscle strength and bone density in middle-aged women. Thirty four healthy women (mean age=49.8±7.5years) were recruited. They were requested to wear an accelerometer for a period of 10h (from 9am to 7pm) on a day to record the acceleration. On a separate day their knee extension torque (KET) was measured using an isokinetic dynamometer and broadband ultrasound attenuation (BUA) at the heel by an ultrasound bone scanner. The loading dose of physical activity was calculated at four intensity categories - very light, light, moderate, and vigorous (intensities of <5BW/s, 5-10BW/s, 10-15BW/s and >15BW/s) and for three frequency bands - 0.1-2Hz, 2-4Hz, and 4-6Hz. Correlation analysis was used to examine the association between loading dose and age, KET, and BUA. With the increase of age, there tended to be a decrease in the loading dose of vigorous activity in 2-4 and 4-6Hz frequency bands (Kendall's tau=-.22, p<.1). The increase of loading dose in all three frequency bands in moderate or vigorous activity was associated with higher BUA (Kendall's tau=.27-.41, p<.05). The increase of loading dose in all frequency bands in light, moderate, or vigorous activity was associated with higher KET (Kendall's tau=.30-.45, p<.05). It is concluded that physical activity, especially that at high intensity level and high frequency range, may have beneficial effect on muscle strength and bone density in middle-aged women.