Gas exchange kinetics during constant-load exercise were measured to investigate the possibility that excess CO₂ output during exercise might not be dependent on hyperventilation. Five healthy males performed twelve minutes of cycle exercise, including two minutes of 0 W pedaling, at 20, 40, 50, 60, 70, and 80% of their maximal work rate (WRmax) determined on the basis of preliminary ramp exercise of 30 W/min. Minute ventilation, O₂ uptake, and CO₂ output were measured breath-by-breath. Excess CO₂ output and CO₂ stores were calculated, assuming that the respiratory quotient (RQ) in tissue is constant during constant-load exercise and that the respiratory exchange ratio at the mouth level is equal to the RQ during the steady-state phase. Excess CO₂ output was observed at levels of WR greater than 40% WRmax after initial CO₂ storage, where VC_O2/V_E decreased gradually as though in parallel with the kinetics of CO₂ storage. VO₂/V_E, however, appeared to be constant after the initial peak. These data suggest that V_E is closely correlated with V_O2 rather than V_CO2 during constant-load exercise, indicating that excess CO₂ output to compensate lactate production is independent of hyperventilation.

A study was conducted to ascertain the relationship between oxygen uptake (Vo₂) and vertical velocity using a pedal-stepping stair simulator. Ten healthy volunteers performed fbur kinds of graded exercise using a stair simulator (SS), whose pitches were set at 80, 100, and 120 beat⋅min^-1, and also an electrically braked bicycle ergometer (BE) . Work rate on the SS was detemined on the basis of the vertical pedal velocity, in accord with the climbingvelocity for stairs. The incremental rate was set at 0.34 W⋅kg^-1 every 3 min. Heart rate and Vo₂ were measured during the final minute of every stage. Both heart rate and Vo₂ during SS were significantly lower than those on BE at the same level of work intensity. Regression equations between Vo₂ (ml⋅kg^-1⋅min^-1) and velocity (v: m⋅s^-1) were as follows;
pitch 80: Vo₂=1.00×v+0.06
pitch 100: Vo₂=0.88×v+1.58
pitch 120: Vo₂=0.84×v+2.13
These equations give a lower value of Vo₂ than the previous equation based on stair-climbingvelocity reported by the American College of Sports Medicine. Although the individual relationship between Vo₂ and heart rate was closely linear, there was a significant effect ofexercise mode and stepping pitch. These results indicate that the work intensity of pedalstepping exercise with a stair simulator is overestimated if it is calculated based on theprevious equation for stair-climbing.