Neuromuscular fatigue of prolonged exercises in normoxia and hypoxia revisited: methodological developments and fatigue etiology
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2018-07-11
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Abstract
The understanding of knee extensor function under fatigue due to whole-body exercise was until recently limited due to short-term recovery. Indeed, subjects needed to be moved from a treadmill/cycle ergometer to an isometric chair, which may underestimate fatigue. This thesis addressed this issue thanks to an innovative ergometer where fatigue can be induced and measured on the same bike, allowing to revisit fatigue etiology in hypoxia and after endurance training. Also, to assess central fatigue, VATMS is traditionally assessed by delivering transcranial magnetic stimulation during three voluntary contractions, each interspersed with 5-10 s of rest (TRADI). In study 1, we assessed whether TRADI methodology resulted in central fatigue underestimation when compared to a continuous approach, with no rest in between voluntary contractions. Post-fatigue, VATMS was heavily underestimated with TRADI. Thus, we propose the continuous method to assess central fatigue. In addition of the lag time explained above, fatigue in hypoxia is poorly understood because of (i) the lack of control in arterial saturation and (ii) different exercise durations in hypoxia vs. normoxia. In study 2, fatigue was assessed on the new cycle ergometer during cycling and right at exhaustion (EXH) in normoxia, moderate and severe hypoxia at relative and absolute workloads. The relative sessions performed in hypoxia were shorter than in normoxia and yet presented lower peripheral fatigue at EXH. This suggests a brain-hypoxic effect that may not only happen in severe hypoxia as previously suggested but also in moderate hypoxia. In study 3, the innovative ergometer was used to revisit the effects of cycling training on neuromuscular fatigue measured during and immediately after cycling exercise. After training, peripheral fatigue was either similar or attenuated at EXH compared to pre-training. The lower or similar fatigue after endurance training suggests that, unlike previously suggested, fatigue may not be upregulated after training.
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Bartolomeu de Mira, J. M. (2018). Neuromuscular fatigue of prolonged exercises in normoxia and hypoxia revisited: methodological developments and fatigue etiology (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/32704