Activities of rat muscle enzymes after acute exercise.

The enzyme activities of rat gastrocnemius and cardiac muscle were measured immediately and at varying intervals up to 5 days after exhaustive swimming to study the onset and duration of enzyme changes. Immediately after exercise a decrease in the activities of hexokinase and phosphofructokinase was found in gastrocnemius muscle. The activities of various glycolytic, hexose monophosphate shunt and oxidative enzymes were increased in both muscles 1 and 3 days and were returned to control levels after 5 days. A decrease in RNA content was obtained in cardiac muscle immediately after exercise and an increase in RNA was seen in both muscles the day after exercise. In gastrocnemius muscle glycogen overshoot was found. Glucose tolerance was increased 1 day after the exhaustive swimming. It is concluded that the intensity of exercise and the interval between exercise and enzyme analysis have to be considered when studying adaptive responses in muscle enzyme activities