Educção fisica

Pflugers Arch - Eur J Physiol (2004) 448: 422–430
DOI 10.1007/s00424-004-1267-4

EXERCI SE, TEMPERATURE REG U LAT I ON

Ross Tucker . Laurie Rauch . Yolande X.R. Harley . Timothy D. Noakes
Impaired exercise performance in the heat is associated with an anticipatory reduction in skeletal muscle recruitment

Received: 6 August 2003 / Accepted: 20 November 2003 / Published online: 8 May 2004
# Springer-Verlag 2004

Abstract Exercise in the heat causes “central fatigue”, associated with reduced skeletal muscle recruitment during sustained isometric contractions. A similar mech- anism may cause fatigue during prolonged dynamic

Keywords Exercise . Heat . Fatigue . Brain . Electromyography . Cycling time-trial . Thermoregulation . Teleoanticipation

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 exer- cise in the heat occurs before there is any abnormal increase in rectal temperature, heart