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Impaired exercise performance in the heat is associated with an anticipatory reduction in skeletal muscle recruitment

  • Exercise, Temperature Regulation
  • Published:
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Abstract

Exercise in the heat causes “central fatigue”, associated with reduced skeletal muscle recruitment during sustained isometric contractions. A similar mechanism may cause fatigue during prolonged dynamic exercise in the heat. The aim of this study was to determine whether centrally regulated skeletal muscle recruitment was altered during dynamic exercise in hot (35°C) compared with cool (15°C) environments. Ten male subjects performed two self-paced, 20-km cycling time-trials, one at 35°C (HOT condition) and one at 15°C (COOL condition). Rectal temperature rose significantly in both conditions, reaching maximum values at 20 km of 39.2±0.2°C in HOT and 38.8±0.1°C in COOL (P<0.005 HOT vs. COOL). Core temperatures at all other distances were not different between conditions. Power output and integrated electromyographic activity (iEMG) of the quadriceps muscle began to decrease early in the HOT trial, when core temperatures, heart rates and ratings of perceived exertion (RPE) were similar in both conditions. iEMG was significantly lower in HOT than in COOL at 10 and 20 km, while power output was significantly reduced in the period from 80% to 100% of the trial duration in the HOT compared with COOL condition. Thus, reduced power output and iEMG activity during self-paced exercise in the heat occurs before there is any abnormal increase in rectal temperature, heart rate or perception of effort. This adaptation appears to form part of an anticipatory response which adjusts muscle recruitment and power output to reduce heat production, thereby ensuring that thermal homeostasis is maintained during exercise in the heat.

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Acknowledgements

Funding for this experiment was provided by Medical Research Council of South Africa, the University of Cape Town Harry Crossley and Nellie Atkinson Staff Research Funds, Discovery Health and the National Research Foundation of South Africa through the THRIP initiative.

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Authors and Affiliations

  1. MRC/UCT Bioenergetics of Exercise Research Unit, University of Cape Town, Sports Science Institute of South Africa, PO Box 115, 7725, Newlands , South Africa

    Ross Tucker, Laurie Rauch, Yolande X.R. Harley & Timothy D. Noakes

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  1. Ross Tucker
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  2. Laurie Rauch
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  3. Yolande X.R. Harley
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  4. Timothy D. Noakes
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Correspondence to Ross Tucker.

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Tucker, R., Rauch, L., Harley, Y.X. et al. Impaired exercise performance in the heat is associated with an anticipatory reduction in skeletal muscle recruitment. Pflugers Arch - Eur J Physiol 448, 422–430 (2004). https://doi.org/10.1007/s00424-004-1267-4

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  • DOI: https://doi.org/10.1007/s00424-004-1267-4

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