Share this article on:


Backx, K1; van Someren, K A.1; Nevill, A M.1; Palmer, G S.1

Medicine & Science in Sports & Exercise: May 2003 - Volume 35 - Issue 5 - p S30
A-15O Free Communication/Poster Heat Stress and Dehydration

1University of Wolverhampton, ENGLAND

(Sponsor: John A. Hawley, FACSM)

Most research examining thermal stress during exercise relates to low-intensity, endurance efforts (< 70% VO2peak, > 2hr) with little study of high-intensity, moderate duration (> 80% VO2peak, −60 min) exercise.

Back to Top | Article Outline


To determine the effect of different ambient temperatures (Ta) on laboratory 1-h cycling time trial (TT) performance.

Back to Top | Article Outline


16 male, trained cyclists (VO2peak 63.4 ±6.4 ml/kg/min, peak power output 386 ±49 W) each undertook between 3 and 6 self-paced TT during which they were instructed to cover as much distance as possible, in an environmental chamber at a range of different Ta, (between 12 and 32 °C) with constant relative humidity (63 ±6%). Elapsed time, distance covered, power output, heart rate, skin and core temperature were recorded throughout a TT. Prior to all rides, subjects received 6 ml/kg BM of a 6% CHO beverage, and during TT efforts, water ad-libitum. A polynomial regression with a different intercept was generated for each participant and used to analyze the relationship between distance covered and Ta.

Back to Top | Article Outline


Using elementary differential calculus, the curvilinear relationship between Ta and performance predicted that the greatest distance was covered at 18.6 °C, with a predicted drop of 509m and 2155m at 12 and 32 °C respectively. The highest power outputs were predicted to be achieved at Ta of 21.3, 18.9, 18.0 and 17.5 °C for the 1 st to 4 th quarters of the TT respectively. A linear increase in HR, core temperature, mean body temperature, sweat loss and self-selected water intake was found with increasing Ta.

Back to Top | Article Outline


These findings are the first to show that optimal 1-h TT performance in the laboratory setting occurs at an Ta of approximately 19 °C. Whether similar performance and physiological responses would occur in a ‘field’ setting with higher convective heat losses has yet to be examined.

©2003The American College of Sports Medicine