Fulltext

Combining heat stress and moderate hypoxia reduces cycling time to exhaustion without modifying neuromuscular fatigue characteristics

Girard, Olivier ; Racinais, Sébastien

In: European Journal of Applied Physiology, 2014, vol. 114, no. 7, p. 1521-1532

Aggiungi alla tua lista
    Titre
    • Combining heat stress and moderate hypoxia reduces cycling time to exhaustion without modifying neuromuscular fatigue characteristics
    Auteur
    • Girard, Olivier. Athlete Health and Performance Research Centre, Aspetar, Qatar Orthopaedic and Sports Medicine Hospital, PO Box 29222, Doha, Qatar
    • Racinais, Sébastien. Athlete Health and Performance Research Centre, Aspetar, Qatar Orthopaedic and Sports Medicine Hospital, PO Box 29222, Doha, Qatar
    Type de document
    • Postprint
    Langue
    • Inglese
    Publié dans
    • European Journal of Applied Physiology, 2014, vol. 114, no. 7, p. 1521-1532. Springer Berlin Heidelberg
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:325691
    Summary
    Purpose: This study investigated the isolated and combined effects of heat [temperate (22°C/30% rH) vs. hot (35°C/40% rH)] and hypoxia [sea level (FiO2 0.21) vs. moderate altitude (FiO2 0.15)] on exercise capacity and neuromuscular fatigue characteristics. Methods: Eleven physically active subjects cycled to exhaustion at constant workload (66% of the power output associated with their maximal oxygen uptake in temperate conditions) in four different environmental conditions [temperate/sea level (control), hot/sea level (hot), temperate/moderate altitude (hypoxia) and hot/moderate altitude (hot+hypoxia)]. Torque and electromyography (EMG) responses following electrical stimulation of the tibial nerve (plantar-flexion; soleus) were recorded before and 5min after exercise. Results: Time to exhaustion was reduced (P<0.05) in hot (−35±15%) or hypoxia (−36±14%) compared to control (61±28min), while hot+hypoxia (−51±20%) further compromised exercise capacity (P<0.05). However, the effect of temperature or altitude on end-exercise core temperature (P=0.089 and P=0.070, respectively) and rating of perceived exertion (P>0.05) did not reach significance. Maximal voluntary contraction torque, voluntary activation (twitch interpolation) and peak twitch torque decreased from pre- to post-exercise (−9±1, −4±1 and −6±1% all trials compounded, respectively; P<0.05), with no effect of the temperature or altitude. M-wave amplitude and root mean square activity were reduced (P<0.05) in hot compared to temperate conditions, while normalized maximal EMG activity did not change. Altitude had no effect on any measured parameters. Conclusion: Moderate hypoxia in combination with heat stress reduces cycling time to exhaustion without modifying neuromuscular fatigue characteristics. Impaired oxygen delivery or increased cardiovascular strain, increasing relative exercise intensity, may have also contributed to earlier exercise cessation.