Rate of force development and rapid muscle activation characteristics of knee extensors in very old men
Abstract
The age-related decrease in neuromuscular performance is usually accentuated in very old age (> 80 yr) as evidenced by a marked reduction in maximal force production. However, little is known about the ability to rapidly produce force, which limits daily activities and increase the risk of falling. We aimed to assess rapid force production characteristics and rate of muscle activation of the knee extensors in 15 very old (82 +/- 1 yr) vs 12 young (24 +/- 4 yr) men. Maximal force (F-max) and maximal rate of force development (RFDmax) were determined during separated specific isometric contractions. EMG from the vastus lateralis was analyzed to assess the rate of EMG rise (RER). Finally, RFD and RER were examined at time intervals of 0-50, 50-100, 100-200, 0-200 ms and 0-30, 0-50, 0-75 ms, respectively. We reported lower F-max (414 +/- 91 N vs. 661 +/- 139 N) and absolute REDmax (8720 +/- 2056 N*s(-1) vs. 5700 +/- 2474 N*s(-1)) in the very old men compared to young men (P < 0.01). When normalized to F-max, RFD(max )was similar between groups. Normalized RFD at 0-50 and 0-200 ms were lower (- 34% and - 46%, P = 0.04) for the very old men, while no difference was observed at 50-100 ms and 100-200 ms. RER values were higher (similar to 346%, P < 0.01) for the young men at every time interval. These data suggest that the decline in REDmax is associated with the decrease in F-max. Impairments in RFD were accentuated in the first phase of the contraction, which has been associated in the literature with impairments in neural factors associated with aging.
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