Oxygen uptake kinetics as a determinant of very‐heavy intensity exercise tolerance

The tolerance profile for very‐heavy intensity exercise is well described by a hyperbola with two parameters: a curvature constant (W′) and a power asymptote (CP). During cycle ergometry, where work efficiency is similar between subjects, the tolerable duration (t lim ) is highly dependent on the rate at which oxidative ATP synthesis rises to meet the demand. We were therefore interested in the relationship between pulmonary oxygen uptake (VO 2 ) kinetics and the power‐duration hyperbola. We hypothesized that CP (the upper limit for steady‐state VO 2 ) would relate to the fundamental VO 2 time‐constant (τ), and W′ to the slow component magnitude (ΔVO 2sc ). Eight males performed repeats of constant work‐rate (WR) cycle ergometry to t lim : 1) over a range of WRs to estimate CP and W′ and 2) with WR normalized to induce intolerance in 6 min (WR 6 ; for τ and ΔVO 2sc ). VO 2 was measured breath‐by‐breath using a turbine and mass spectrometer. Tolerance at WR 6 averaged 365 ± 17 s. CP (range 181–289 W) was inversely correlated (R 2 = 0.37) with τ (21.3‐30.5 s); and W′ (12.8‐27.3 kJ) was strongly and directly correlated (R 2 = 0.97) with ΔVO 2sc (370–940 ml/min). Therefore, a fast τVO 2 was associated with a high CP thereby maximizing the WR for a given O 2 deficit, whilst a high rate of anaerobiosis ‐ reflected in W′ ‐ resulted in a large ΔVO 2sc . Together, this suggests that VO 2 kinetics are a major determinant of tolerance during very‐heavy intensity exercise.