Modeling Intermittent Cycling Performance in Hypoxia Using the Critical Power Concept

Area of Science:

• Exercise physiology
• Environmental physiology
• Sports science

Background:

• High-intensity exercise performance is influenced by environmental factors such as hypoxia.
• Critical Power (CP) and work above CP (W') are key physiological determinants of endurance exercise capacity.
• The work-balance (W'BAL) model is an intermittent critical power model used to predict exercise duration.

Purpose of the Study:

• To investigate the efficacy of the W'BAL model during high-intensity exercise in hypoxia (HYPO).
• To compare W'BAL model performance when parameters are determined in normoxia (NORM) versus hypoxia.
• To assess the impact of hypoxia on CP and W' in trained cyclists.

Main Methods:

• Eleven trained male cyclists performed maximal ramp and 3-min all-out tests in both NORM and HYPO (FiO2 ≈ 0.155).
• An intermittent exercise test to task failure was conducted under both conditions.
• The W'BAL model was applied to calculate minimum W' (W'BALmin), with parameters measured in NORM and HYPO, and also using NORM-derived parameters for HYPO performance (N + H).

Main Results:

• Hypoxia significantly reduced V˙O2peak by 18% and CP by 9%, while W' remained unchanged.
• The W'BAL model yielded similar W'BALmin values in HYPO and NORM when parameters were condition-specific.
• The N + H analysis significantly overestimated W'BALmin in HYPO compared to the HYPO-specific analysis.

Conclusions:

• The W'BAL model is effective in hypoxia, provided that critical power (CP) and work above CP (W') are determined under the same environmental conditions as the exercise task.
• Applying the W'BAL model at altitude necessitates either modifying the model or measuring CP and W' at altitude.
• Accurate prediction of high-intensity exercise performance in hypoxia requires condition-specific physiological parameter determination.