Pflügers Archiv

, Volume 448, Issue 4, pp 422–430

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

  • Ross Tucker
  • Laurie Rauch
  • Yolande X.R. Harley
  • Timothy D. Noakes
Exercise, Temperature Regulation

DOI: 10.1007/s00424-004-1267-4

Cite this article as:
Tucker, R., Rauch, L., Harley, Y.X. et al. Pflugers Arch - Eur J Physiol (2004) 448: 422. doi:10.1007/s00424-004-1267-4

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.

Keywords

ExerciseHeatFatigueBrainElectromyographyCycling time-trialThermoregulationTeleoanticipation

Copyright information

© Springer-Verlag  2004

Authors and Affiliations

  • Ross Tucker
    • 1
  • Laurie Rauch
    • 1
  • Yolande X.R. Harley
    • 1
  • Timothy D. Noakes
    • 1
  1. 1.MRC/UCT Bioenergetics of Exercise Research Unit, University of Cape TownSports Science Institute of South AfricaNewlands South Africa