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Does Age Influence Dynamic Stability and Muscular Power Following Neuromuscular Fatigue in Women?

Abstract
Older adults, especially older women, produce less muscular power than young adults, due primarily to slower maximal contractile velocity. These decrements may lead to increased fall risk in older women and can be exacerbated by fatigue. Recently, a 32 min walking task (32MWT) was shown to elicit fatigue in older women. The purpose of this study was to determine whether knee extensor (KE) maximal velocity is related to dynamic stability (margin of stability, MoS) in young and older women pre- and post-32MWT. METHODS: Nine young (Y; 24.3+1.1years, mean±SE) and 17 older (O; 71.1±1.1years) healthy women completed 2 testing sessions on separate days: 1) electrically-stimulated and voluntary KE muscle characteristics were measured to determine rates of force development and relaxation (RFD, RFR) and half-relaxation times (T1/2) as well as peak isometric torque, power generated at 270 deg∙s-1, and maximal contractile velocity of the dominant leg; 2) MoS was measured using a forward fall test at 25% body weight; 10 baseline trials were performed. On both testing days, the 32MWT was performed following baseline measures. All variables of interest were then collected during 30 min of recovery. RESULTS: MoS was higher in young than older women (Y: 0.044±0.021m, O: -0.130±0.033m, p=0.001) and increased over the 10 baseline trials in both groups (p=0.01). Post-32MWT, both groups showed decreased isometric torque (Y: p=0.04, O: p-1 (Y: p=0.05, O: p=0.01), and unaltered MoS (Y: p=0.34, O: p=0.52) and maximal velocity (Y: p=0.22, O: p=0.54). Additionally, T1/2 was lower post-32MWT in older (p20.32) or post-32MWT (r20.22) in either group. CONCLUSIONS: The 32MWT elicited fatigue in some contractile variables, but improved or had no effect on others. Maximal KE contractile velocity was not associated with MoS in young or older women. Future studies are needed to determine other potential mechanisms of lower MoS in older than young women. The increase in MoS over 10 baseline trials should be considered by researchers when using the forward fall test to evaluate real-world fall risk.
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