Muscle performance and electromyogram activity of the lower leg muscles with different levels of cold exposure.

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 degrees C, 20 degrees C, 15 degrees C and 10 degrees C. In comparison to those at 27 degrees 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 pre-activity and stretch phases the integrated EMG (iEMG) activity of the agonist muscle (triceps surae) increased due to cooling (at 10 degrees C, P < 0.05). In contrast, during the shortening phase iEMG of the agonist muscle decreased due to cooling (at 15 degrees C and 10 degrees C, P < 0.05). Moreover, the activity of the antagonist muscle (tibialis anterior) increased due to cooling (at 15 degrees C and 10 degrees 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 degrees C) to 82 (SEM 7) Hz (at 10 degrees 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.