![]() Just below the CP, muscle phosphocreatine (PCr), inorganic phosphate (P i) and pH reached stable values within ∼2 min of the onset of exercise, whereas, above the CP, these variables exhibited non‐steady‐state responses (Jones et al. The CP has been defined as a critical threshold of intramuscular metabolic control on the basis of 31phosphorous magnetic resonance spectroscopy ( 31P‐MRS) assessment of muscle phosphorous‐containing metabolites during single‐leg knee‐extension exercise (Jones et al. After ∼2 min of all‐out cycling against a fixed resistance, the W′ is essentially reduced to zero such that the greatest power output that can be maintained by maximum effort over the final 30 s of the 3 min test closely approximates the CP (Vanhatalo et al. The observation that the magnitude of the W′ remains fixed irrespective of the rate of its expenditure has given rise to an all‐out 3 min sprint protocol for a time‐efficient method to estimate the CP and W′ (Burnley et al. The curvature constant of this hyperbola, termed the W′, represents a fixed amount of work that can be performed >CP before exhaustion ensues (Chidnok et al. The consistent attainment of V ˙ O 2 max in the severe domain enables very accurate prediction of exercise tolerance based on the hyperbolic relationship between time‐to‐exhaustion ( T lim) and work‐rate ( P) (Jones et al. ![]() ![]() The CP reflects the bioenergetic characteristics of highly oxidative type I muscle fibres, such that a muscle metabolic steady‐state is attainable below and not above CP.Īttainment of the maximal rate of O 2 uptake ( V ˙ O 2 max ) during exhaustive, constant work rate (CWR) exercise above the critical power (CP) defines the range of the severe exercise intensity domain (Poole et al. These data indicate a mechanistic link between the bioenergetic characteristics of different muscle fibre types and the power–duration relationship. There was no relationship between W′ (19.4 ± 6.3 kJ) and muscle fibre type. The CP (234 ± 53 W) was correlated with muscle type I ( r = 0.67, P = 0.025) and inversely correlated with muscle type IIx fibre proportion ( r = −0.76, P = 0.01). Eleven men performed 3 min all‐out tests and donated muscle biopsies to test the second hypothesis. ![]() Four men and four women performed a 3 min all‐out cycling test for the estimation of CP and constant work rate (CWR) tests slightly >CP until exhaustion ( T lim), slightly CP T lim isotime to test the first hypothesis. We hypothesized that: (1) the critical power (CP) will represent a boundary separating steady‐state from non‐steady‐state muscle metabolic responses during whole‐body exercise and (2) that the CP and the curvature constant ( W′) of the power–time relationship for high‐intensity exercise will be correlated with type I and type IIx muscle fibre distributions, respectively. ![]()
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