Scientific Programme
Physiology & Nutrition
IS-PN07 - Application of the Critical Power Concept to High-Intensity Intermittent Exercise in Normoxia and Hypoxia: Updates on Work-Balance Modeling
Date: 10.07.2026, Time: 08:00 - 09:15, Session Room: Auditorium C (STCC)
Description
The 2-parameter CP model is a simple mathematical description of the curvilinear power-duration relationship within the severe intensity domain i.e. at workrates above the maximum metabolic steady state (MMSS), yet below near maximal exercise intensities in which neuromuscular factors set the upper limit of sustainable performance (the so-called ‘extreme’ intensity domain). Within the severe domain, corresponding to maximal efforts of approximately 2-15 min in duration, performance is determined by a combination of CP, which is now known to be a reliable estimate of MMSS, and the work-capacity that can be performed above CP until exhaustion occurs (denoted as Wꞌ). The parameter Wꞌ is assumed to act akin to a battery which can be depleted and reconstituted, however the 2-parameter CP model is limited in scope since it does not include terms which describe these kinetics, and therefore cannot be applied to high-intensity interval exercise (HIIE). The introduction of the Work-Balance model overcomes this limitation, however questions remain over its validity when applied to various forms of HIIE. The first presentation will provide an overview of the validity and reliability of CP and Wꞌ estimation. This will lead into an update of Work-Balance modeling approaches and associated challenges in the second presentation. And lastly, the practical application of work-balance modeling will be discussed with special attention to HIIE in acute hypoxia.
Chair(s)
Nathan Townsend
Hamad Bin Khalifa University, College of Health and Life Sciences
Qatar
Speaker A
Bettina Karsten
University of Greenwich, School of Human Science, UK, Institute for Lifecourse Development, School of Human Sciences, Centre for Exercise Activity and Rehabilitation, University of Greenwich, London, United Kingdom
United Kingdom
Read CVECSS Lausanne 2026: IS-PN07 [14888]
Re-evaluating the Variability of W′: Implications for the Reliability of the Two-Parameter Power–Duration Relationship
The two-parameter power–duration relationship posits that exercise intensities within the severe domain (i.e., above the critical power; CP) predominantly rely on a so called ‘finite capacity for work’ that can be performed above CP, termed W′ (W prime). This capacity primarily reflects anaerobic energy contribution. Several methodologies have been described in the literature for determining CP and W′, including multiple constant-load time-to-exhaustion trials, distinct time trials of varying durations, and the 3-minute all-out test. Regardless of the specific testing protocol employed, research consistently demonstrates that CP exhibits a relatively low coefficient of variation (CoV; typically 2–5%), whereas W′ shows substantially greater variability, with reported CoV values typically ranging between 10% and 15%. This greater variability renders W′ a comparatively less reliable parameter within the power–duration relationship. A closer examination of the error comprised within the power–duration relationship suggests that the composite error attributable to both CP and W′ provides a more nuanced representation than evaluating the variability of W′ independently. Therefore, the influence of the comparatively low reliability of W′ on performance may be overestimated when the CoV of W′ is considered as a separate discrete measure. Consequently, when performing maximal efforts within the severe intensity domain, the combined CoV derived from both CP and W′ yields a smaller overall value than the CoV of W′ considered in isolation. Notably, this combined CoV aligns more closely with the variability typically observed in performance measures of comparable durations. For short maximal efforts (e.g., ~90 s), during which W′ can be almost fully expended, the variability associated with W′ exerts a proportionally greater influence on total performance variability. Nevertheless, even under such conditions, the combined CoV remains lower than the CoV of W′ alone. Conversely, for longer-duration efforts within the severe domain (e.g., ~5 min), the relatively large CoV of W′ contributes minimally to overall performance variability once integrated with the more stable CP component. This suggests that the two-parameter power–duration relationship provides a highly robust and accurate predictor of performance across the severe intensity domain. This session will re-evaluate previously published values and demonstrate that the CoV of W′ has only a small effect on mean power output, as total power output is predominantly determined by CP, even at intensities exceeding CP.
Speaker B
Philip Skiba
Advocate Lutheran General Hospital, Sports Medicine
United States
Read CVECSS Lausanne 2026: IS-PN07 [18029]
Adaptations to the CP and W’ Balance Model
The 2-parameter critical power (CP) model mathematically codifies the power-duration relationship in the severe intensity domain. It consists of 2 terms: the CP (an asymptote) and W’ (a curvature constant). The CP and W’ can be leveraged to understand performance during intermittent exercise using the “W’-Balance” (Wꞌbal) model. Several modifications of the original integrating model (Skiba et al 2012) have been proposed, including differential and biexponential forms. Each form has unique strengths and weaknesses. This presentation will cover two interrelated ways of potentially improving W’bal model performance: alternative formulations of the power-duration relationship (Puchowicz and Skiba, 2025), and alternative formulations of the W’bal model itself. With respect to the first possibility, we will examine the insights provided by functional principal component analysis (FPCA) of crowd-sourced cycling data. This technique indicates that variation in the power-duration relationship can be largely explained by 3 factors: a gain term (overall ability), a bias term (sprint vs. endurance), and a third term conferring middle distance ability. With respect to the second possibility, in light of recent physiological advances, we can re-cast the W’bal model in a matter analogous to Arsac’s (2001) treatment of PCr kinetics. Collectively, the above alterations in understanding and technique suggest new avenues of research into both the physiology and practicalities of performance during intermittent exercise. Moreover, these novel mathematics can provide new insights into both patient and athlete populations.
Speaker C
Nathan Townsend
Hamad Bin Khalifa University, College of Health and Life Sciences
Qatar
Read CVECSS Lausanne 2026: IS-PN07 [20986]
Application of Work-Balance Modelling to High-Intensity Interval Exercise (HIIE): Insights from Acute Hypoxia
The 2-parameter critical power (CP) model is a simple mathematical description of the power-duration relationship within the severe intensity domain. Whilst this model provides valuable insight into high-intensity performance, its applicability is limited to continuous exercise. This limitation led to development of the “Work-Balance” (Wꞌbal) model, which considers the intermittent nature of many sports and training methods characterised by high intensity work bouts above CP, interspersed with periods of recovery below CP. This presentation will build upon the previous two and discuss the practical application of work-balance modelling with special reference to exercise in hypoxia. The history and evolution of HIIE dates back over 100 years and today has become a mainstay of endurance training regimes. Moreover, there are a wide variety of sporting events that are characterized by intermittent high-intensity efforts such as racquet and team sports (e.g. tennis, football, basketball, hockey), or involve frequent and abrupt changes in pace (e.g. cycling, middle distance running). In each case, hypoxia and/or altitude training methods have emerged as a key environmental strategy associated with successful performance outcomes. A key assumption of the Wꞌbal model is that the work-capacity above CP (Wꞌ) depletes with linear kinetics when power (P) > CP, whereas reconstitution of Wꞌ occurs in a curvilinear fashion when CP > P. During exercise in acute hypoxia, there is a predictable decline in CP whereas Wꞌ remains similar to normoxic conditions. Thus, the change in CP must be accounted for in the parameters of the Wꞌbal model, but furthermore, since CP can be manipulated independently of Wꞌ, hypoxia represents a useful experimental intervention to dissociate the metabolic stress of high-intensity exercise from the mechanical workrate in a predictable and repeatable manner. This presentation covers the practical application of the Wꞌbal model to HIIE in hypoxia. Data will be presented which illustrates the relationship between Wꞌbal and physiological responses to HIIE in both normoxia and hypoxia, and guidelines for prescribing HIIE and workload monitoring in acute hypoxia will be discussed.