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Muscle Nerve. 2014 Apr;49(4):575-83. doi: 10.1002/mus.23978. Epub 2014 Jan 6.

Synchronization of low- and high-threshold motor units.

Author information

1
University of Oklahoma, 1401 Asp Avenue, Norman, Oklahoma, 73019.

Abstract

INTRODUCTION:

We examined the degree of synchronization for both low- and high-threshold motor unit (MU) pairs at high force levels.

METHODS:

MU spike trains were recorded from the quadriceps during high-force isometric leg extensions. Short-term synchronization (between -6 and 6 ms) was calculated for every unique MU pair for each contraction.

RESULTS:

At high force levels, earlier recruited motor unit pairs (low-threshold) demonstrated relatively low levels of short-term synchronization (approximately 7.3% extra firings than would have been expected by chance). However, the magnitude of synchronization increased significantly and linearly with mean recruitment threshold (reaching 22.1% extra firings for motor unit pairs recruited above 70% MVC).

CONCLUSIONS:

Three potential mechanisms that could explain the observed differences in synchronization across motor unit types are proposed and discussed.

KEYWORDS:

Synchrony; common inputs; decomposition; motor neuron; recruitment threshold

PMID:
23893653
DOI:
10.1002/mus.23978
[Indexed for MEDLINE]

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