Estimating maximal metabolic steady state using critical power

which model is best?

Abstract

It has been advocated that critical power (CP) should be considered the gold standard to determine the maximal metabolic steady state (MMSS). However, the choice of the model affects the estimation of CP. The purpose of this study was to investigate which of the models, exponential (CP_exp), 3-parameter hyperbolic (CP_3-hyp), 2-parameter hyperbolic (CP_2-hyp), linear (CP_linear), and inverse of time (CP_1/time), estimates MMSS best. Eleven male participants (Age: 31±11 years, Body mass: 70.5±5.6 kg) performed three time-trials (12-, 6-, and 3-min long) to determine CP from the five models. On three subsequent visits, participants cycled for 30-min, or until task failure, at the CP estimated by each model. CP_exp estimated the highest CP (303 ±69 W), followed by CP_1/time (272 ±66 W), CP_linear (270±64 W), CP_2-hyp (266 ±65 W) and CP_3-hyp (262 ±63 W). Oxygen uptake (VO₂) stabilised at a significantly lower value than peak VO₂ (VO_2peak) during exercise at CP_linear, CP_2-hyp, and CP_3-hyp (94±5%, p=.041; 87±4%, p<.001; 86±4%, p<.001, respectively). VO₂ stabilisation was not significantly different to VO_2peak during exercise at CP_exp and CP_1/time (98±2%, p=1.000; 94±6%, p=.130, respectively). For all conditions, VO₂ did not increase significantly after stabilisation (p=1.000). Rate of perceived exertion significantly increased over time during exercise at CP_1/time (p < .001) and CP_linear (p=.006) but was unchanged between minute 15 and end-exercise during CP_2-hyp (p=.762) and CP_3-hyp (p = .569). Lactate increased significantly in the last 10, 15, and 20 minutes of the exercise for all models. No model had an increase of ≤1mmol·L^-1 from minute 10 to 30. These results suggest that CP_2-hyp or CP_3-hyp should be favoured when CP is used to assess MMSS.