Muscle excitation in elderly adults: The effects of training
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AbstractMuscle membrane excitability is thought to decline with aging; the extent of this decline may be noninvasively assessed by measurement of the electrically evoked compound muscle action potential (M‐wave). The intent of this study was two‐fold: (1) to compare the M‐wave in the brachioradialis (BR), tibialis anterior (TA), and thenar (TH) muscles of elderly (mean age = 66.3 ± 3.7 years) and young (mean age = 31.2 ± 4.9 years) adults, and (2) to determine the effects of 12 weeks of resistance training on M‐wave characteristics in elderly adults. Prior to training, the elderly subjects had significantly smaller (P < 0.05) resting M‐waves than the young adults in the BR (4.8 mV vs. 8.7 mV), TA (8.8 mV vs. 11.0 mV), and TH (5.2 mV vs. 10.2 mV) muscles. During a 2‐minute voluntary fatigue paradigm (3 seconds MVC per 2 seconds rest for 2 minutes), there was no evidence of excitability failure in either group. Following training, there was a significant increase (P < 0.05) in the size of the M‐wave of the TH (pretraining: 5.2 mV; posttraining: 8.96 mV) and BR (pretraining: 4.8 mV; posttraining: 6.1 mV), and a nonsignificant increase in the M‐wave of the TA, but there was no change in the relative behavior of the M‐wave during the 2‐minute voluntary fatigue paradigm, It is suggested that the decline in muscle membrane excitation with aging may be due, at least in part, to the effects of a decreased membrane potential on the muscle fiber action potential. Furthermore, our results suggest that exercise training may improve muscle excitability in elderly adults, possibly reflecting a training‐induced increase in the resting membrane potential due to an increased activity and/or concentration of the skeletal muscle Na+K+‐ATPase.
