Increased voltage of the muscle action potential of normal subjects after local cooling.

The compound muscle action potential (MAP) and the isometric twitch force of the adductor pollicis of 25 normal subjects were registered after local cooling. Intramuscular temperature ranged from 36.6 to 18.0 degrees C. The amplitude of the MAP increased while the twitch force decreased at lower temperatures. The increase of the MAP could be caused by the effect of cooling directly at the muscle cell membrane. The decreased twitch force probably is due to an affect on the contractile apparatus.