ALTERATIONS IN VENTILATION AND GAS-EXCHANGE DURING EXERCISE-INDUCED CARBOHYDRATE DEPLETION

The relationships between ventilation (V̇E), oxygen consumption (V̇O2), and carbon dioxide production (V̇CO2) during work were studied in four trained males during exercise-induced carbohydrate depletion. Repeated bouts of heavy treadmill exercise (6 min at 95% V̇O2max) were performed once per hour for 24 hr in order to promote a shift in energy substrate from carbohydrate to fat. Measurements of V̇O2 and V̇CO2 recorded during each minute indicated that V̇O2 was unaffected by the number of runs, whereas V̇CO2 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 V̇E occurred between any of the runs. It is concluded that during heavy, repeated, muscular exercise, reductions in V̇CO2, strongly suggestive of an increased fat oxidation, are not accompanied by a corresponding change in ventilation.