RESUMEN
PURPOSE: Both cognitive motor dual-tasks (CMDT) protocols and hypoxic environments have been associated with significant impairments in cognitive and physical performance. We aimed to determine the effects of hypoxia on cognitive performance and neuromuscular fatigue during a highly physically demanding CMDT. METHODS: Fifteen young adults completed a first session involving a cognitive task (CTLCOG) followed by cycling exercise (CTLEX) in normoxia. After that, they randomly participated in CMDT sessions in normoxia (DTNOR) and hypoxia (DTHYP). The physical exercise consisted of 20 min cycling at a "hard" perceived effort, and the cognitive task consisted of 15 min sustained attention to response time task (SART). Concurrent psycho-physiological measurements included: quadriceps neuromuscular fatigue (peripheral/central components from femoral nerve electrostimulation), prefrontal cortex (PFC) oxygenation by near-infrared spectroscopy, and perception of effort. RESULTS: SART performance significantly decreased in DTNOR (-15.7 ± 15.6%, P < 0.01) and DTHYP (-26.2 ± 16.0%, P < 0.01) compared to CTLCOG (-1.0 ± 17.7%, P = 0.61). Peripheral fatigue similarly increased across conditions, whereas the ability of the central nervous system to activate the working muscles was impaired similarly in DTNOR (-6.1 ± 5.9%, P < 0.001) and DTHYP (-5.4 ± 7.3%, P < 0.001) compared to CTLEX (-1.1 ± 0.2%, P = 0.52). Exercise-induced perception of effort was higher in DTHYP vs. DTNOR and in DTNOR vs. CTLEX. This was correlated with cognitive impairments in both normoxia and hypoxia. PFC deoxygenation was more pronounced in DTHYP compared to DTNOR and CTLEX. CONCLUSION: In conclusion, performing a sustained attention task together with physically challenging cycling exercise promotes central neuromuscular fatigue and impairs cognitive accuracy; the latter is particularly noticeable when the CMDT is performed in hypoxia.
RESUMEN
PURPOSE: Repeated sprint ability is an integral component of team sports. This study aimed to evaluate fatigability development and its aetiology during and immediately after a cycle repeated sprint exercise performed until a given fatigability threshold. METHODS: On an innovative cycle ergometer, 16 healthy males completed an RSE (10-s sprint/28-s recovery) until task failure (TF): a 30% decrease in sprint mean power (Pmean). Isometric maximum voluntary contraction of the quadriceps (IMVC), central alterations [voluntary activation (VA)], and peripheral alterations [twitch (Pt)] were evaluated before (pre), immediately after each sprint (post), at TF and 3 min after. Sprints were expressed as a percentage of the total number of sprints to TF (TSTF). Individual data were extrapolated at 20, 40, 60, and 80% TSTF. RESULTS: Participants completed 9.7 ± 4.2 sprints before reaching a 30% decrease in Pmean. Post-sprint IMVCs were decreased from pre to 60% TSTF and then plateaued (pre: 345 ± 56 N, 60% 247 ± 55 N, TF: 233 ± 57 N, p < 0.001). Pt decreased from 20% and plateaued after 40% TSTF (p < 0.001, pre-TF = - 45 ± 13%). VA was not significantly affected by repeated sprints until 60% TSTF (pre-TF = - 6.5 ± 8.2%, p = 0.036). Unlike peripheral parameters, VA recovered within 3 min (p = 0.042). CONCLUSION: During an RSE, Pmean and IMVC decreases were first concomitant to peripheral alterations up to 40% TSTF and central alterations was only observed in the second part of the test, while peripheral alterations plateaued. The distinct recovery kinetics in central versus peripheral components of fatigability further confirm the necessity to reduce traditional delays in neuromuscular fatigue assessment post-exercise.