MUSCLE EXCITATION IN ELDERLY ADULTS - THE EFFECTS OF TRAINING

Muscle 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.