The Application of Critical Power, the Work Capacity above Critical Power (W′), and Its Reconstitution: A Narrative Review of Current Evidence and Implications for Cycling Training Prescription

Abstract

The two-parameter critical power (CP) model is a robust mathematical interpretation of the power–duration relationship, with CP being the rate associated with the maximal aerobic steady state, and W′ the fixed amount of tolerable work above CP available without any recovery. The aim of this narrative review is to describe the CP concept and the methodologies used to assess it, and to summarize the research applying it to intermittent cycle training techniques. CP and W′ are traditionally assessed using a number of constant work rate cycling tests spread over several days. Alternatively, both the 3-min all-out and ramp all-out protocols provide valid measurements of CP and W′ from a single test, thereby enhancing their suitability to athletes and likely reducing errors associated with the assumptions of the CP model. As CP represents the physiological landmark that is the boundary between heavy and severe intensity domains, it presents several advantages over the de facto arbitrarily defined functional threshold power as the basis for cycle training prescription at intensities up to CP. For intensities above CP, precise prescription is not possible based solely on aerobic measures; however, the addition of the W′ parameter does facilitate the prescription of individualized training intensities and durations within the severe intensity domain. Modelling of W′ reconstitution extends this application, although more research is needed to identify the individual parameters that govern W′ reconstitution rates and their kinetics.

Exercise Intensity and Pacing Pattern During a Cross-Country Olympic Mountain Bike Race

“…The observations from this study showed frequent bouts with various degrees of W' expenditure ( Figures 1B , 4 ), tending to a lower degree of W' expended in later rounds ( Figure 4 ; Table 2 ). The mechanisms, and even the descriptive kinetics, of W' recovery are still to be clarified, but possibly reflect a complex interplay of biochemical pathways, including restoration of blood and muscle oxygen stores, high-energy phosphates, and the ability to proceed with anaerobic glycolysis ( Miura et al, 2000 ; Jones et al, 2010 ; Chidnok et al, 2013 ; Chorley and Lamb, 2020 ). Recent evidence points toward a bi-phasic recovery, enabling rapid recovery of one fraction of W ', followed by a slower recovery of the remaining fraction ( Caen et al, 2021 ).…”

One-Week High-Dose β-Alanine Loading Improves World Tour Cyclists’ Time-Trial Performance

“…An incremental cycling test to exhaustion performed one week before was employed to assess training status of participants and determine each volunteer’s critical power to quantify the individualised training load. Previous studies showed a good correlation between power output at the respiratory compensation point or ventilatory threshold 2 (WVT2) and the critical power [ 15 , 16 , 17 ], which demarcate the heavy from severe exercise intensity domains. Methods, equipment and repeatability measures were the same as described elsewhere [ 18 ], but fixing was without wheels, pedalling always with road cycling shoes, and the incremental ramp test consisted of a 4 min warm-up at 100 W, followed by ramp test with 5 W increments every 12 s (25 W per minute).…”

Can Popular High-Intensity Interval Training (HIIT) Models Lead to Impossible Training Sessions?

“…The CP models are considered simple, robust, and promising [ 20 , 24 ]. The parameters ( CP and W′ ) are presumed to be associated with physiological responses to exercise [ 20 , 25 , 26 , 27 ]. On the other hand, the CP concept is also widely criticized and referred to as a purely mathematical artifact with very few practical applications [ 28 , 29 ].…”

“…On the other hand, the CP concept is also widely criticized and referred to as a purely mathematical artifact with very few practical applications [ 28 , 29 ]. The Skiba model is yet to be adopted by endurance coaches [ 25 ]. The W′ reconstitution requires further work and individual adjustments [ 19 , 25 , 30 , 31 ].…”

“…The Skiba model is yet to be adopted by endurance coaches [ 25 ]. The W′ reconstitution requires further work and individual adjustments [ 19 , 25 , 30 , 31 ]. At the foundation of the Skiba HIIT model, the continuous exercise hyperbolic model relies on a specific set of assumptions [ 25 ] restricting its validity to limited intensity and duration windows [ 32 ].…”