Abstract

Alterations in enzyme activities involved in muscle energy metabolism and the muscle fiber type distribution were investigated in six subjects, ranging in age from 19-23 years, following short-term, high intensity exercise. Changes in the vastus lateralis muscle were studied prior to exercise and approximately 24 h after each of 2 consecutive days of supramaximal cycling exercise (120 VO2 max) performed intermittently as 1-min work to 4-min rest until fatigue. The results indicated that there were no changes in maximal in vitro activities for representative enzymes of beta-oxidation (3-hydroxyacyl CoA dehydrogenase, HAD), the citric acid cycle (succinic dehydrogenase, SDH), glucose phosphorylation (hexokinase, HK), glycogenolysis (total phosphorylase, PHOSPH), or glycolysis (phosphofructokinase, PFK; pyruvate kinase, PK; lactate dehydrogenase, LDH) in spite of the large increase in carbohydrate utilization and glycolytic flux rate. In addition, although no change in fiber type distribution was found in the pre-exercise biopsy between days, an acute reduction in type I fiber distribution occurred with exercise. It is concluded that supramaximal exercise performed on a short-term basis does not alter the enzymatic profile or the fiber type distribution when measured 24 h following the activity. Verf.-Referat