SUBSTRATE SUPPLY OF HUMAN SKELETAL MUSCLE AT REST DURING AND AFTER WORK

The arterial femoral venous differences for glucose, lactate, pyruvate, free fatty acids, and O2 pressure were measured in healthy adults at rest, during light and intensive physical exercise under steady-state conditions and during the recovery phase. The conception that the rise in lactate and the lactate/pyruvate ratio in blood during exercise is due to insufficient O2-supply cannot be reconciled with the following facts: the greatest lactate- and pyruvate delivery was observed following an interval of 3 min. after exercise, at this point, the O2 -pressure is significantly higher than the rest value in the femoral venous blood. The critical O2 -pressure no longer guaranteeing the oxidative energy gain was not reached in the blood emerging from the working musculature during heavy exercise. The lactate/pyruvate ratio during exercise is lower in the femoral venous blood than in the arterial blood. Consequently, the rise of the lactate pyruvate ratio cannot be explained by insufficient O2 -supply of the muscle. During the recovery phase the lactate/pyruvate ratio climbs in the femoral venous blood above the arterial value, although the femoral venous O2-pressure surpasses the rest value. Whereas at rest the extracted glucose is almost completely oxidized by the skeletal muscle, 2/3 of the extracted glucose is totally oxidized during strenuous exercise. One-third is decomposed to lactate and pyruvate and then discharged into the blood. In the 3rd min. of recovery the amount of the extracted glucose equals the amount of lactate and pyruvate discharged from the tissue. During intensive exercise glycolysis amounts to approximately 4-6% of the all energy production of the skeletal muscle. The role of the free fatty acids in energy gain of the muscle tissue increases during exercise.