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] ) 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 pointsO_LIAgeing 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 C_LIO_LILifelong physical activity, such as that exhibited by Masters athletes, has a protective role against many age-related decrements in neuromuscular physiology and function C_LIO_LIThis 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 C_LIO_LIMasters athletes exhibited significantly better force steadiness than their inactive counterparts and no difference in steadiness compared to young adults C_LIO_LILifelong 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 C_LI