AN EVALUATION OF EXERCISE AND TRAINING ON MUSCLE LIPID METABOLISM

Abstract

1746 To evaluate the hypothesis that endurance training increases intramuscular triglyceride (IMTG) oxidation, we studied leg net free fatty acid (FFA) and glycerol exchange 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, and 65% post-training ˙VO2peak, same relative intensity). Nine male subjects 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. Training significantly (p<0.05) decreased RER values at the same absolute workload (0.96±0.01 at 65% pre- vs. 0.93±0.01 post-training), but not the same relative workload(0.95±0.01 at REL). After training leg RQ was not significantly different at either the same absolute (0.98±0.02 pre- vs. 0.98±0.03 post-training) or relative workload (1.01±0.02 at REL). Net FFA uptake was not significantly different at the same absolute workload after training. At the same relative workload, net FFA uptake was greater for the first 5 minutes of exercise after training, but similar to pre-training for the last 45 minutes of exercise. FFA fractional extraction was not significantly different at any exercise intensity or following training. Likewise, net glycerol release did not change from rest to exercise, or at the same absolute and relative workloads after training. Simultaneous measurements of leg RQ, and net FFA uptake by working legs indicated no change in leg fat oxidation, FFA uptake, or IMTG oxidation during leg cycling exercise that elicits 65% pre-, and 54% post-training ˙VO2peak. The high RER at all work intensities indicate that FFA and intramuscular triglycerides are of secondary importance as fuels in moderate and greater intensity exercise.

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