Article ID Journal Published Year Pages File Type
4065511 Journal of Electromyography and Kinesiology 2006 7 Pages PDF
Abstract

Motoneurons demonstrate a type of self-sustained firing behavior that seems to be produced by a prolonged period of depolarization caused by intrinsic long-term changes in the motoneuron. Such self-sustained firing behavior has previously been reported in human motor units. The purpose of the present study was to investigate the occurrence of self-sustained firing behavior in older adults. Eight young (mean age 24 yrs) and eight older (mean age 73 yrs) individuals participated in the investigation. While subjects produced light dorsiflexion contractions, a brief vibration stimulus was applied to the tibialis anterior muscle. Motor unit recordings were also obtained from the tibialis anterior muscle. Self-sustained firing behavior was evidenced by the appearance of new motor unit recruitment following vibration, even as the motor units that fired before the vibratory stimulus maintained a steady firing rate. The proportion of motor units exhibiting self-sustained firing activity was similar in both young and older adults (approx. 23% of trials). We conclude that self-sustained firing behavior is a ubiquitous phenomenon that does not seem to be affected by the aging process.

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