Respiratory quotient during exercise

¹ Division of Research, Lankenau Hospital, Philadelphia, Pennsylvania

O₂ uptake and CO₂ output were determined during exercise on the bicycle ergometer. During moderate and heavy work three phases could be distinguished in the time course of RQ: a) initial increase, b) secondary drop followed by c) a continuous rise to a steady state which was reached after 3 –4 min work. The rise of work RQ (RQ) above an assumed metabolic RQ of 0.75 (or 0.83) showed an approximately logarithmic increase as work load increased. In the same subject there was a straight-line correlation between "nonmetabolic" excess CO₂ (= total CO₂ minus 0.75 x O₂) and the increase of blood lactate level (P < 0.001). In pooled calculations, a correlation coefficient = 0.92 was found. Whereas the respiratory minute volume plotted against O₂ uptake or CO₂ output showed a relative hyperventilation as the subject approached maximal aerobic capacity, excess CO₂ increased with the ventilation in a straight-line fashion. It was concluded that the RQ represents the percentual participation of anaerobic glycolysis in the total energy expenditure rather than the fuel used during exercise.