Modeling intermittent cycling performance in hypoxia using the critical power concept

Abstract

Purpose: Recently, a novel model derived from the critical power (CP) concept was developed to determine W’

balance (W’BAL) during variable intensity exercise. The purpose of this study was to investigate the effect of hypoxia on the efficacy of the W’BAL model during high-intensity intermittent exercise.

Methods: Eleven trained, male cyclists (mean±SD; age 27±6.6 years, VO2peak 4.79±0.56) completed a maximal incremental ramp test and a 3 min “all out” test to determine end power (EP) and work performed above EP (W’EP). On another day an intermittent test to task failure was performed. All procedures were performed in normoxia (NORM) and hypoxia (HYPO; FiO2 ≈ 0.155). The experimental condition was single-blinded, randomized and counter-balanced, and the W’BAL model was used to calculate the minimum W’ (W’BALmin) achieved during the intermittent test. W’BALmin in HYPO was also calculated using model parameters derived in NORM (N+H).

Results: In HYPO there was a significant decline in VO2peak (4.79±0.56 vs 3.93±0.47 L.min-1; P<0.001) and EP (353±46 vs 319±49W; P<0.001), whereas no change occurred for W’EP (12.6±4.1 vs 13.3±5.3kJ; P=0.34; NORM vs HYPO). The change in VO2peak was significantly correlated with the change in EP (r = 0.72; P<0.05). There was no difference between NORM and HYPO for W’BALmin (1.7±0.9kJ vs 1.3±0.8kJ). The N+H analysis revealed a gross overestimation of W’BALmin (8.3±3.2kJ) and compared with HYPO (P<0.001). Figure 1 shows an example of modeled W’BAL for a typical subject.

Conclusion: The W’BAL model behaves similarly in hypoxic conditions equivalent to ≈2450m as previously reported for normoxia, but only when the model parameters (CP and W’) are determined under the same environmental conditions as the performance task is completed. The practical application of the W’BAL model for altitude training and performance monitoring, thus requires CP and W’ to be measured at altitude.