Habitual physical activity levels do not predict leg strength and power in healthy, active older adults

Abstract

Physical activity is considered crucial in attenuating losses in strength and power associated with ageing. However, in well-functioning, active older adults the relationship between habitual physical activity and muscle function is surprisingly unclear. Leg press velocity, force, and power, were compared between 50 older and 30 younger healthy individuals, and associations with habitual physical activity explored. An incremental power test was performed on a pneumatic leg press, with theoretical maximum velocity, force, and power calculated. Vastus lateralis muscle thickness was measured by ultrasound, and participants wore a combined accelerometer and heart rate monitor for 6-days of free-living. Older individuals produced lower absolute maximum velocity, force, and power, than younger individuals. When accounting for smaller muscle size, older individual's maximum force and power remained markedly lower. Both groups were active, however using age specific thresholds for classifying physical activity, the older individuals engaged in twice the amount of moderate-to-vigorous physical activity in comparison to the younger individuals. There were no associations between any characteristics of muscle function and physical activity. These data support that the ability to generate force and power deteriorates with age, however habitual physical activity levels do not explain inter-individual differences in muscle function in active older individuals.

Fig 1. Velocity, force, and power is significantly lower in healthy older individuals than younger individuals.

Mean ± SD extrapolated peak A) veolcity (V_max), B) force (F_max), and C) interpolated peak power (P_max) for 65–80 vs 20–35 yr olds. The older individuals are represented by circles and the younger individuals by squares. **denotes significant difference between age groups (P < 0.01).

Fig 2. Relative force and power are significantly lower in healthy older individuals than younger individuals.

Mean ± SD extrapolated peak force (F_max:VL) and interpolated peak power (P_max:VL) relative to vastus lateralis muscle thickness for 65–80 vs 20–35 yr olds. The older individuals are represented by circles and the younger individuals by squares. **denotes significant difference between age groups (P < 0.01).

Fig 3. Habitual physical activity level was not associated muscle function in healthy older or younger individuals.

Pearson’s correlations between daily physical activity level (PAL) (ratio of total energy expenditure to basal metabolic rate) to A) extrapolated maximum velocity (V_max), B) extrapolated maximum force (F_max), and C) interpolated maximum power (P_max) for 65–80 and 20–35 year olds. The older individuals are represented by circles and the younger individuals by squares. No significant relationships between PAL and muscle function characteristics were identified for either group.