Time Course of Performance Fatigability during Exercise below, at, and above the Critical Intensity in Females and Males.

Purpose: This study aimed to investigate the time course and amplitude of performance fatigability during cycling at intensities around the maximal lactate steady state (MLSS) until task failure (TTF).

Methods: Ten females and 11 males were evaluated in eight visits: 1) ramp incremental test; 2-3) 30-min constant power output (PO) cycling for MLSS determination; and 4-8) cycling to TTF at PO relative to the MLSS of (i) -15%, (ii) -10 W, (iii) at MLSS, and (iv) +10 W, and (v) +15%. Performance fatigability was characterized by femoral nerve electrical stimulation of knee extensors at baseline; minutes 5, 10, 20, and 30; and TTF.

Comparing muscle V̇o from near-infrared spectroscopy desaturation rate to pulmonary V̇o during cycling below, at, and above the maximal lactate steady state.

Muscle oxygen uptake (V̇o) evaluated from changes in the near-infrared spectroscopy oxygen desaturation slope during a 5-s arterial blood flow occlusion has been proposed as an estimation of the actual V̇o. However, its correspondence with pulmonary oxygen uptake (V̇o) during exercise remains unknown. This study investigated the V̇o and V̇o relationship in females and males in response to prolonged constant-load cycling exercise at different intensities.

The effects of exercise intensity and duration on the relationship between the slow component of V̇O and peripheral fatigue.

Aim: If the development of the oxygen uptake slow component (V̇O ) and muscle fatigue are related, these variables should remain coupled in a time- and intensity-dependent manner.

Methods: 16 participants (7 females) visited the laboratory on 7 separate occasions: (1) three 6-minutes moderate-intensity cycling exercise bouts proceeded by a ramp incremental test; (2-3) 30-minutes 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; (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.

Slight power output manipulations around the maximal lactate steady state have a similar impact on fatigue in females and males.

Neuromuscular fatigue (NMF) and exercise performance are affected by exercise intensity and sex differences. However, whether slight changes in power output (PO) below and above the maximal lactate steady state (MLSS) impact NMF and subsequent performance (time to task failure, TTF) is unknown. This study compared NMF and TTF in females and males in response to exercise performed at MLSS, 10 W below (MLSS) and above (MLSS).