Aging, regularity and variability in maximum isometric moments

This study examined the variability and regularity of maximum isometric moment production of the plantar flexors in young and old subjects. It was hypothesized that in the development of maximum isometric moments there would be greater regularity in the moment profiles for older subjects compared with young subjects, due to the reduced number of motor units present in elderly muscle. Two groups of subjects produced three maximal isometric plantar flexions (young: n=11, mean age 23.8±2.8 years, mean mass 81.2±10.4 kg, mean height 1.78±0.05 m; elderly: n=13, mean age 74.0±3.3 years, mean mass 78.5±3.4 kg, mean height 1.73±0.05 m). The plateau of the moment-time curve was analyzed for each trial. A repeat measures analysis of variance showed the young subjects produced statistically greater peak plantar flexion moments than the elderly subjects, but similar coefficients of variation. Signal regularity was determined by computing the signal's approximate entropy, which demonstrated that the older group had greater regularity in their generation of moment profiles. The hypothesis was accepted, with a potential explanation for this increased regularity in old age being the reduced number of motor units to coordinate.