Muscle Metabolism and Enzyme Activities after Training in Boys 11–13 Years Old

Abstract The effect of training on the skeletal muscle metabolism of 11‐to 13‐year‐old boys was examined. In one experiment changes in blood lactate, and muscle lactate, CP, ATP, and glycogen were determined at rest and following exercise before and after 4 months of training. The concentrations of glycogen, CP and ATP at rest were higher (P<0.01) following training. Blood and muscle lactate were 23 and 56 % higher after maximal work following training. A greater reduction in muscle glycogen occurred during maximal work after training but the pattern for ATP and CP depletion was unchanged. In a second experiment boys trained by pedalling a bicycle ergometer an average of 30 min 3 times a week for 6 weeks. Biopsy samples of the vastus lateralis were examined for oxidative (succinate dehydrogenase) and anaerobic (phosphofructokinase) capacity before and after training. The fiber composition and relative oxidative capacity in the fibers was determined histochemically. Succinate dehydrogenase and phosphofructokinase activities increased 30 and 83 %, respectively, following training. Fiber distribution was unchanged by training but the oxidative capacity of both fiber types appeared to increase.