Effect of endurance training on glycerol kinetics during strenuous exercise in humans.

Glycerol kinetics were evaluated during high-intensity exercise in five untrained and five endurance-trained subjects. Glycerol rate of appearance (Ra) in plasma was determined by infusing [2H5]glycerol during rest and 60 minutes of cycle ergometer exercise performed at 70% V02 peak. Mean plasma glycerol concentration was greater in trained than untrained subjects throughout exercise (P<.05). The average glycerol Ra during exercise and the integrated lipolytic response to exercise, expressed as total glycerol Ra above baseline, were both greater in trained (7.85 +/- 0.72 micromol x kg(-1) x min(-1) and 289 +/- 50 micromol x kg(-1) x h(-1), respectively) than in untrained (5.68 +/- 0.90 micromol x kg(-1) x min(-1), and 198 +/- 31 micromol x kg(-1) x h(-1), respectively) subjects (P<.05). We conclude that whole-body lipolytic rates are greater in endurance-trained athletes than in sedentary controls during high-intensity exercise performed at the same relative intensity.