Phosphagen and Carbohydrate Metabolism during Exercise in Trained Middle-Aged Men

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Abstract
Phosphagen (ATP and CP) stores, glycogen, and lactate were determined in muscle samples obtained from the thigh as well as the arterio-venous glucose difference over the leg in 7 well-trained 52–59-year-old men at rest, during 8 min of bicycle exercise at 5 submaximal and at one maximal work load. ATP and CP stores were reduced in direct proportion to oxygen uptake up to maximal levels of exercise. At submaximal work loads requiring less than 60% of VO2 max, almost no lactate accumulated in the muscles. At higher work intensities the increase was more pronounced, but maximal lactate concentration in the muscle was only 13.7 mmol/kg. Muscle glycogen was 86 mmol/kg at rest and was reduced only very little during submaximal work. Glucose uptake by the leg was related to work intensity and could account for up to 25% of the total energy output. The present subjects' reaction to exercise was very similar to that found in younger men, and it is most likely the optimal response that can be seen in middle-aged men.