Fatigue Responses in Exercise under Control of V·O₂

Abstract

To examine the fatigue response during an exhaustive heavy exercise performed under control of oxygen uptake (SS@V·O₂Δ50) or power output (SS@pΔ50), eleven trained male subjects performed an incremental test to determine the peak of the oxygen uptake value (V·O_2peak) and lactate threshold and two exhaustive steady-state cycling exercises at the intermediate value between the lactate threshold and V·O_2peak (SS@V·O₂Δ50 and SS@pΔ50). The control of V·O₂ induced an oscillation of the power output, which lowered the average power output (276 ± 47 vs. 315 ± 40 W, p = 0.004) and cancelled the slow component of oxygen kinetics. However, all subjects reached maximal cardiac output (CO) and heart rate (HR) values which were sustained almost two times longer in SS@V·O₂Δ50 compared to SS@pΔ50 (979 ± 854 vs. 475 ± 236 s, p = 0.046 for CO and 1050 ± 890 vs. 513 ± 288 s, p = 0.037 for HR). Furthermore, SS@pΔ50 elicited V·O_2peak but not SS@V·O₂Δ50 (4963 ± 434 vs. 4723 ± 460 mL · min^-1, p = 0.026). Finally, the time spent at the maximal CO and HR values is correlated with time to exhaustion at V·O₂Δ50. In conclusion, the cause of fatigue does not seem to have the same origin during exhaustive supra-lactate threshold exercise under control of V·O₂ (V·O₂Δ50) compared to constant power output (pΔ50), while both elicit the maximal HR and CO values.

V·O₂ kinetics - cardiac output - cycling exercise - heart rate - heavy intensity - stochastic exercise

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