Respiratory quotient during exercise

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Abstract
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 ½12—4 min work. The rise of work RQ (ΔRQ) 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 γ = 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 δRQ represents the percentual participation of anaerobic glycolysis in the total energy expenditure rather than the fuel used during exercise. Submitted on January 26, 1961