The effect of lifelong physical (in)activity on knee extensor force control

Abstract It is well-documented that older adults exhibit a greater magnitude and decreased complexity of muscle force fluctuations in comparison to young adults. To date, however, research on this age-related loss of force control has focused on heterogeneous groups of inactive/moderately active older adults, despite accumulating evidence that high levels of lifelong physical activity (such as that exhibited by Masters athletes) has a protective effect on neuromuscular function and morphology. The present study compared healthy young adults (aged < 35; n = 14), healthy but inactive older adults (aged > 55; n = 13) and Masters athletes (aged > 55; n = 14) in order to discern the effects of lifelong physical (in)activity on muscle force control. Force control was assessed during isometric knee extension contractions at 10, 20 and 40% maximal voluntary contraction (MVC) and was quantified according to the magnitude (coefficient of variation [CV]) and complexity (approximate entropy [ApEn]; detrended fluctuation analysis [DFA] α) of force fluctuations. Inactive older adults exhibited significantly greater CV, indicative of poorer force steadiness, than young adults and Masters athletes during contractions at 10, 20 and 40% MVC (all P < 0.001). There were no significant differences in CV between the young adults and Masters athletes. These results indicate that lifelong physical activity has a protective effect against the age-related loss of muscle force control and suggest that, up to this point, our understanding of the age-related loss of muscle force control has been confounded by the effects of physical inactivity. Key points Ageing is associated with a decrease in muscle force control (i.e., poorer steadiness and adaptability), though to date this has largely been studied in inactive older adults Lifelong physical activity, such as that exhibited by Masters athletes, has a protective role against many age-related decrements in neuromuscular physiology and function This study compared force control, during contractions at intensities typical of the requirements of activities of daily living, in healthy young adults, healthy but inactive older adults and age-matched Masters athletes Masters athletes exhibited significantly better force steadiness than their inactive counterparts and no difference in steadiness compared to young adults Lifelong physical activity appears to modulate the age-related loss of force control, indicating that our current understanding of this loss of force control may be contaminated by the negative effects of inactivity