COOLING-INDUCED CHANGES IN MUSCULAR PERFORMANCE AND EMG ACTIVITY OF AGONIST AND ANTAGONIST MUSCLES

The effect of whole body cooling on the muscular performance and electromyographic (EMG) activity of agonist and antagonist muscles during dynamic exercise wets studied, Eleven slightly clothed male subjects were exposed to ambient temperatures of 27 degrees C and 10 degrees C for 60 min, After the exposures the subjects performed an overhead ball throwing test, Five balls, weighing from 0.3 kg to 3.0 kg were thrown and the velocity of the balls was measured, The EMG activity of two agonist-antagonist muscle pairs (m. triceps brachii - m. deltoideus and m. rectus abdominis - m. erector spinae) were measured during throwing, Cooling decreased mean skin temperature by 6.3 +/- 0.5 degrees C (mean +/- SE). The temperature of m. triceps brachii decreased by 4.0 +/- 1.6 degrees C and 1.8 +/- 0.6 degrees C from the depth of 20 rind 30 mm underneath the skin surface, respectively, The corresponding values of m. deltoideus were 5.1 +/- 0.4 degrees C and 3.2 +/- 0.8 degrees C, The cooling-induced decrement in ball velocity varied from 9.4 +/- 3.3% (0.3-kg hall) to 5.6 +/- 2.8% (3.0-kg ball) (p < 0.001-0.01), After cooling, the time to reach the maximal level of integrated electromyographic (IEMG) activity in m. triceps brachii (agonist) wets increased (30-42%, p < 0.05-0.001), Moreover, cooling decreased the mean IEMG activity m. triceps brachii, while the activity of m. deltoideus (antagonist) was increased, The alteration was significant (p < 0.05-0.001) with the three lightest balls, We conclude that cooling decreased muscular performance in dynamic upper body exercise, and the decrement was clearly pronounced with fast contraction velocities, Cooling also slowed the function of agonist muscle and decreased its IEMG activity, but increased the IEMG activity of the antagonist muscle.