Prediction of Critical Power and W′ in Hypoxia: Application to Work-Balance Modelling

Abstract

Purpose: Develop a prediction equation for critical power (CP) and work above CP (W′) in hypoxia for use in the work-balance (WBAL′) model.Methods: Nine trained male cyclists completed cycling time trials (TT; 12, 7, and 3 min) to determine CP and W′ at five altitudes (250, 1,250, 2,250, 3,250, and 4,250 m). Least squares regression was used to predict CP and W′ at altitude. A high-intensity intermittent test (HIIT) was performed at 250 and 2,250 m. Actual and predicted CP and W′ were used to compute W′ during HIIT using differential (WBALdiff′) and integral (WBALint′) forms of the WBAL′ model.Results: CP decreased at altitude (P < 0.001) as described by 3rd order polynomial function (R2 = 0.99). W′ decreased at 4,250 m only (P < 0.001). A double-linear function characterized the effect of altitude on W′ (R2 = 0.99). There was no significant effect of parameter input (actual vs. predicted CP and W′) on modelled WBAL′ at 2,250 m (P = 0.24). WBALdiff′ returned higher values than WBALint′ throughout HIIT (P < 0.001). During HIIT, WBALdiff′ was not different to 0 kJ at completion, at 250 m (0.7 ± 2.0 kJ; P = 0.33) and 2,250 m (−1.3 ± 3.5 kJ; P = 0.30). However, WBALint′ was lower than 0 kJ at 250 m (−0.9 ± 1.3 kJ; P = 0.058) and 2,250 m (−2.8 ± 2.8 kJ; P = 0.02).Conclusion: The altitude prediction equations for CP and W′ developed in this study are suitable for use with the WBAL′ model in acute hypoxia. This enables the application of WBAL′ modelling to training prescription and competition analysis at altitude.

The Critical Power Model as a Potential Tool for Anti-doping

“…The opposing responses of CP and W′ in this experiment may have been artifactually caused by the hyperbolic form of the model (see section below on “Model Bias and Artifacts”). In contrast, acute hypoxia treatment to simulate various altitudes decreases CP ( Parker Simpson et al, 2014 ; Townsend et al, 2017 ) in a dose-response manner consistent with observed decrements in O 2max ( Townsend et al, 2017 ). Specifically, CP decreased in proportion to simulated altitude, with significant reduction evident at 1,250 m. W′ was less sensitive to altitude change than CP as it was significantly reduced only at a simulated altitude of 4,250 m.…”

“…τ w′ was observed to increase (i.e., recovery took longer) as a function of the recovery intensity. Subsequent studies further revealed the sensitivity of τ w′ to work and recovery bout durations ( Skiba et al, 2014a ) and to environmental conditions ( Townsend et al, 2017 ).…”

“…First, the model takes as input W′, which is difficult to accurately estimate as discussed above. Furthermore, τ w′ is determined in part by CP, and both CP and W′ are sensitive to environmental conditions such as altitude ( Shearman et al, 2016 ; Townsend et al, 2017 ), which serve to reduce the accuracy of the W′ bal model if such factors are left unaccounted for. In addition, the depletion and recovery kinetics are dependent on task features such as work and rest durations ( Skiba et al, 2012 , 2014b ) and pacing strategy.…”

Methodological Approaches and Related Challenges Associated With the Determination of Critical Power and Curvature Constant

“…(61,63,79,91)). An alternative approach has been proposed by Hill (51), and recently adopted by some researchers (18,19,101), whereby the model producing the lowest standard error of estimate (SEE) is used. We therefore recommend that the P-T relationship should be characterised with the 2-parameter model that results in the lowest SEE.…”

Considerations on the Assessment and Use of Cycling Performance Metrics and their Integration in the Athlete's Biological Passport

“…These effects are observed on mountainous compared with flat stage races, despite the negative influence of altitude on cycling performance. Indeed, environmental conditions such as hypoxia and heat impair power production and their effects would need to be considered when comparing cycling performances (Nybo, 2010 ; Garvican-Lewis et al, 2015 ; Townsend et al, 2017 ). While research has attempted to predict the effects of acute hypoxia on exercise capacity (i.e., critical power), the effects of environmental heat on performance is not immediate and complicated by many factors including convective cooling, blood distribution, core, skin, and environmental temperature gradients.…”