Modeling Intermittent Cycling Performance in Hypoxia Using the Critical Power Concept

Purpose This study investigated the efficacy of an intermittent critical power (CP) model, termed the "work-balance" (W′_BAL) model, during high-intensity exercise in hypoxia (HYPO). Methods Eleven trained male cyclists (mean ± SD age, 27 ± 6.6 yr; VO_2peak, 4.79 ± 0.56 L·min^-1) completed a maximal ramp test and a 3-min "all-out" test to determine CP and work performed above CP (W′). On another day, an intermittent exercise test to task failure was performed. All procedures were performed in normoxia (NORM) and HYPO (FiO₂ ≈ 0.155) in a single-blind, randomized, and counter-balanced experimental design. The W′_BAL model was used to calculate the minimum W′ (W′_BALmin) achieved during the intermittent test. The W′_BALmin in HYPO was also calculated using CP + W′ derived in NORM (N + H). Results In HYPO, there was an 18% decrease in VO_2peak (4.79 ± 0.56 vs 3.93 ± 0.47 L·min^-1; P < 0.001) and a 9% decrease in CP (347 ± 45 vs 316 ± 46 W; P < 0.001). No significant change for W′ occurred (13.4 ± 3.9 vs 13.7 ± 4.9 kJ; P = 0.69; NORM vs HYPO). The change in VO_2peak was significantly correlated with the change in CP (r = 0.72; P = 0.01). There was no difference between NORM and HYPO for W′_BALmin (1.1 ± 0.9 kJ vs 1.2 ± 0.6 kJ). The N + H analysis grossly overestimated W′_BALmin (7.8 ± 3.4 kJ) compared with HYPO (P < 0.001). Conclusion The W′_BAL model produced similar results in HYPO and NORM, but only when model parameters were determined under the same environmental conditions as the performance task. Application of the W′_BAL model at altitude requires a modification of the model or that CP and W′ are measured at altitude.