NET GLUCOSE UPTAKE AND GLUCOSE KINETICS AFTER ENDURANCE TRAINING IN MEN

Abstract

506 We evaluated the hypotheses that alterations in glucose disposal rate (Rd) due to endurance training are the result of changed net glucose uptake in active muscle, and that blood glucose is shunted to working muscle during exercise requiring high relative power output. We studied leg net glucose uptake during one hour of cycle ergometry at two intensities before training (45% and 65% VO2peak) and after training (65% pre-training VO2peak, same absolute workload (ABT), and 65% post-training VO2peak, same relative workload (RLT). Nine male subjects (178.1±2.5 cm, 81.8±3.3 kg, 27.4±2.0 yr) were tested before and after 9 weeks of cycle ergometer training, 5x/week at 75% VO2peak. The power output that elicited 66.0±1.1% of VO2peak prior to training elicited 54.0±1.7% after training due to a 14.6±3.1% increase in VO2peak. Whole body glucose Rd decreased post-training at the same absolute (5.45±0.31mg/kg/min at 65% pre-training to 4.36±0.44 mg/kg/min at ABT), but not the same relative workload (5.94±0.47 mg/kg/min). Net glucose uptake was attenuated post-training at the same absolute (1.87±0.42 mmol/min at 65%pre, and 0.54±0.33 mmol/min at ABT), but not the same relative workload (2.25±0.81 mmol/min at RLT). The decrease in leg net glucose uptake at ABT was of similar magnitude as the drop in glucose Rd and thus could explain dampened glucose flux after training. Glycogen degradation also decreased post-training at the same absolute, but not the same relative workload. Leg net glucose uptake accounted for 61% of blood glucose flux before training and 81% after training at the same relative (65% VO2peak) workload, and only 38% after training at the same absolute workload. We conclude that: 1) alterations in active muscle glucose uptake with training determine changes in whole body glucose kinetics, 2) muscle glucose uptake decreases for a given, moderate intensity task after training, and 3) hard exercise (65% VO2peak) promotes a glucose shunt from inactive tissues to active muscle.