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

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 ### Competing Interest Statement The authors have declared no competing interest.