Abstract
Antagonistic muscle pairs cannot be fully activated simultaneously, even with maximal effort, under conditions of voluntary co-contraction, and their muscular activity levels are always below those during agonist contraction with maximal voluntary effort (MVE). Whether the muscular activity level during the task has trainability remains unclear. The present study examined this issue by comparing the muscular activity level during maximal voluntary co-contraction for highly experienced bodybuilders, who frequently perform voluntary co-contraction in their training programs, with that for untrained individuals (nonathletes). The electromyograms (EMGs) of biceps brachii and triceps brachii muscles during maximal voluntary co-contraction of elbow flexors and extensors were recorded in 11 male bodybuilders and 10 nonathletes, and normalized to the values obtained during the MVE of agonist contraction for each of the corresponding muscles (% EMGMVE). The involuntary coactivation level in antagonist muscle during the MVE of agonist contraction was also calculated. In both muscles, % EMGMVE values during the co-contraction task for bodybuilders were significantly higher (P<0.01) than those for nonathletes (biceps brachii: 66±14% in bodybuilders vs. 46±13% in nonathletes, triceps brachii: 74±16% vs. 57±9%). There was a significant positive correlation between a length of bodybuilding experience and muscular activity level during the co-contraction task (r = 0.653, P = 0.03). Involuntary antagonist coactivation level during MVE of agonist contraction was not different between the two groups. The current result indicates that long-term participation in voluntary co-contraction training progressively enhances muscular activity during maximal voluntary co-contraction.
Highlights
Simultaneous voluntary contractions of antagonistic pairs produce resistive forces that act against each other to produce zero net torque [1]
A recent study [2] reported that a training program in which subjects performed voluntary co-contractions of elbow flexors and extensors produced significant increases in the strength capability of both muscle pairs without the use of an external load as resistance
The electromyogram (EMG) activities of elbow flexors and extensors during the co-contraction task performed at the elbow joint angle of 90–100 deg, expressed as the value relative to that during maximal voluntary effort (MVE) of agonist contraction (% EMGMVE), have been shown to be 40–60% and 60–75%, respectively [3,5,6]
Summary
Simultaneous voluntary contractions of antagonistic pairs (cocontraction) produce resistive forces that act against each other to produce zero net torque [1]. A recent study [2] reported that a training program in which subjects performed voluntary co-contractions of elbow flexors and extensors produced significant increases in the strength capability of both muscle pairs without the use of an external load as resistance. A recent study [6] showed that a 4-wk of maximal voluntary co-contraction training performed on elbow flexors and extensors did not change the muscular activity levels during the task. These findings tempt us to speculate that muscular activation levels during voluntary cocontraction are always below those during MVE of agonist contraction, even after subjects are familiarized with the task. To discuss the efficacy of voluntary co-contraction as a training modality for improving muscle function, this issue should be clarified
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