Alterations in ventilation and gas exchange during exercise-induced carbohydrate depletion.

The relationship between ventilation (VE), oxygen consumption (VO2), and carbon dioxide production (VCO2) during work were studied in four trained males during exercise-induced carbohydrate depletion. Repeated bouts of heavy treadmill exercise (6 min at 95% VO2 max) were performed once per hour for 24 h in order to promote a shift in energy substrate from carbohydrate to fat. Measurements of VO2 and VCO2 recorded during each minute indicated that VO2 was unaffected by the number of runs, whereas VCO2 showed a progressive reduction which amounted to 24% during the final run. A corresponding decline of 19% was observed in the respiratory exchange ratio. No significant change in VE occurred between any of the runs. It is concluded that during heavy, repeated, muscular exercise, reductions in VO2, strongly suggestive of an increased fat oxidation, are not accompanied by a corresponding change in ventilation.