Ventilatory thresholds during a graded exercise test.

38 healthy male volunteers were administered a graded exercise test during which selected respiratory gas exchange variables were monitored. In each case, two distinct ventilatory thresholds were observed. The first threshold was detected by the power output at which the VE/VO2 ratio and FEO2 reached a minimum. The mathematical relationship between these two variables was such that at power outputs above this threshold, hyperventilation with respect to oxygen consumption had to occur. The second threshold was detected by the power output at which the VE/VCO2 ratio reached a minimum and the FECO2 reached a maximum. These two variables were related in a manner such that at power outputs above this threshold, hyperventilation with respect to carbon dioxide production had to occur.