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 dif ferent levels of body cooling and muscle performance decrement and to study the motor eo-ordination of the working agonist-antagonist muscle pair of the lower leg. Eight volunteer male subjects dropped from a 4 0-cm bench on to a force plate and performed a maximal rebound jump (s tretch-shortening cycle). The jumps were performed after 60-min exposu res to 27 degrees C, 20 degrees C, 15 degrees C and 10 degrees C. In c omparison to those at 27 degrees C, all the exposures to lower tempera tures decreased the flight time of the jump, average force production and take-off velocity in a dose-dependent manner. The changes in elect romyogram (EMG) activity also behaved in a dose-dependent manner. Duri ng preactivity and stretch phases the integrated EMG (iMEG) activity o f the agonist muscle (triceps surae) increased due to cooling (at 10 d egrees 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 de grees C, P < 0.05). Moreover, the activity of the antagonist muscle (t ibialis anterior) increased due to cooling (at 15 degrees C and 10 deg rees C. P < 0.01). The mean power frequency of the agonist muscle duri ng the shortening-phase was shifted from 124 (SEM 12) Wt (at 27 degree s C) to S1(SEM 7) Wt (at 10 degrees C, P < 0.01). We concluded that th ere was a dose-dependent response between the degree of cooling and th e amount of decrease in muscle performance as well as EMG activity cha nges. A relatively low level of cooling was sufficient to decrease mus cle performance significantly.