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Effect of motor unit firing pattern on twitches obtained by spike‐triggered averaging
Author(s) -
Nordstrom Michael A.,
Miles Timothy S.,
Veale John L.
Publication year - 1989
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/mus.880120706
Subject(s) - motor unit , isometric exercise , electrophysiology , interval (graph theory) , motor unit recruitment , spike (software development) , electromyography , biomedical engineering , neuroscience , mathematics , computer science , medicine , biology , software engineering , combinatorics
The spike‐triggered averaging technique (STA) was used to determine the twitch profile of single motor units in human masseter during a voluntary isometric contraction. The effect of the immediate firing pattern of the unit on the twitch was assessed with a computer program which scanned the unit discharge records and selected valid trigger spikes for the averager on the basis of the interspike intervals preceding and following the trigger spike. Successive averages from the same data using different interval parameters revealed progressively more fusion of twitches as the instantaneous firing rate increased. When the data were averaged with interval parameters similar to those used in earlier studies, some fusion of the twitch profile was also evident. It is therefore likely that the degree of fusion of human motor unit twitches obtained by STA has been underestimated in the past. It is further concluded that masseter motor units are sufficiently fast‐contracting to allow a relatively unfused twitch profile to be obtained with STA, provided trigger spikes are subjected to appropriate rate control.