Rafael de Almeida Azevedo, Daniel A. Keir, Jonas Forot, Danilo Iannetta, Guillaume Y. Millet, Juan M. Murias

Jan 5, 2022
Acta physiologica
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ABSTRACT Aim If the development of the oxygen uptake slow component (V̇O2SC) and muscle fatigue are related, these variables should remain coupled in a time‐ and intensity‐dependent manner.
Method Sixteen participants (7 females) visited the laboratory on seven separate occasions: 1) three 6‐min moderate‐intensity cycling exercise bouts proceeded by a ramp incremental test; 2‐3) 30‐min constant power output (PO) exercise bout to determine the maximal lactate steady state (MLSS); 4‐7) constant‐PO exercise bouts to task failure (TTF), pseudorandomized order, at (i) 15% below the PO at MLSS; (ii) 10 W below MLSS; (iii) MLSS; and (iv) 10 W above MLSS (first intensity and randomized order thereafter). Neuromuscular fatigue was characterized by isometric maximal voluntary contractions and femoral nerve electrical stimulation of knee extensors to measure peripheral fatigue at baseline, at min 5, 10, 20, 30, and TTF. Pulmonary oxygen uptake (V̇O2) was continuously recorded during the constant‐PO bouts and V̇O2SC was characterized based on each individual V̇O2 kinetics during moderate transitions.
Result The development of V̇O2SC and peripheral fatigue were correlated across time (r2adj range of 0.64‐0.80) and amongst each exercise intensity (r2adj range of 0.26‐0.30) (all p < 0.001). Also, TTF was correlated with V̇O2SC and neuromuscular fatigue parameters (r2adj range of 0.52‐0.82, all p < 0.001).
Conclusion The V̇O2SC and peripheral fatigue development are correlated throughout the exercise in a time‐ and intensity‐dependent manner, suggesting that the V̇O2SC may depend on muscle fatigue even if the mechanisms of reduced contractile function are different amongst intensities.

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