Muscle performance and electromyogram activity of the lower leg muscles with different levels of cold exposure
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The purpose of this study was to evaluate the relationship between different levels of body cooling and muscle performance decrement and to study the motor co-ordination of the working agonist–antagonist muscle pair of the lower leg. Eight volunteer male subjects dropped from a 40-cm bench on to a force plate and performed a maximal rebound jump (stretch–shortening cycle). The jumps were performed after 60-min exposures to 27°C, 20°C, 15°C and 10°C. In comparison to those at 27°C, all the exposures to lower temperatures decreased the flight time of the jump, average force production and take-off velocity in a dose-dependent manner. The changes in electromyogram (EMG) activity also behaved in a dose-dependent manner. During preactivity and stretch phases the integrated EMG (iEMG) activity of the agonist muscle (triceps surae) increased due to cooling (at 10°C, P < 0.05). In contrast, during the shortening phase iEMG of the agonist muscle decreased due to cooling (at 15°C and 10°C, P < 0.05). Moreover, the activity of the antagonist muscle (tibialis anterior) increased due to cooling (at 15°C and 10°C, P < 0.01). The mean power frequency of the agonist muscle during the shortening phase was shifted from 124 (SEM 12) Hz (at 27°C) to 82 (SEM 7) Hz (at 10°C, P < 0.01). We concluded that there was a dose-dependent response between the degree of cooling and the amount of decrease in muscle performance as well as EMG activity changes. A relatively low level of cooling was sufficient to decrease muscle performance significantly.
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