Effects of Environmental Heat Stress (35 °C) with Simulated Air Movement on the Thermoregulatory Responses during a 4‐km Cycling Time Trial

Abstract

The aim of the present investigation was to examine the influence of environmental heat stress (35 °C) on 4-km cycling time trial performance using simulated environmental conditions and facing air velocities that closely reflect competitive situations. Nine competitive cyclists (age 34 ± 5 years, maximal oxygen uptake 61.7 ± 8.6 ml · kg⁻¹ · min⁻¹) completed a simulated 4-km cycling time trial in laboratory ambient temperatures (dry bulb temperatures) of 35 °C and 13 °C (relative humidity 60 %, air velocity 5.6 m/s). Mean performance time was reduced in 35 °C (390.1 ± 19.6 s) compared to 13 °C (382.8 ± 18.2 s) (95 % CI of difference = 4.0 to 10.6 s; p < 0.01). This was consistent with a decline in mean power output throughout the duration of exercise in 35 °C compared with 13 °C (p < 0.01). Mean skin temperature and mean body temperatures were elevated at rest and throughout the duration of exercise in 35 °C (p < 0.01). A higher level of muscle temperature was also observed at the onset and cessation of exercise in 35 °C (p < 0.01). The rate of heat storage (35 °C, 413.6 ± 130.8 W · m⁻²; 13 °C, 153.1 ± 112.5 W · m⁻²) representative of the entire 4-km time trial was greater in the heat (p < 0.01). When expressed per kilometre, however, difference in the rate of heat storage between conditions declined during the final kilometre of exercise (p = 0.06). We conclude that the current decrements in self-selected work-rate in the heat are mediated to some extent through afferent feedback arising from changes in heat storage at rest and during the early stages of exercise which serve to regulate the subsequent exercise intensity in attempt to preserve thermal homeostasis.

Key words

heat storage - skin temperature - self chosen work‐rate

References

• 1 Adams W C, Mack G W, Langhans G W, Nadel E R. Effects of varied air velocity on sweating and evaporative rates during exercise.  J Appl Physiol. 1992;  73 2668-2674
• 2 Atkinson G, Nevill A M. Selected issues in the design and analysis of sport performance.  J Sports Sci. 2001;  19 811-827
• 3 Ansley L, Schabort E, St Claire Gibson A, Lambert M I, Noakes T D. Regulation of pacing strategies during successive 4-km time trials.  Med Sci Sports Exerc. 2004;  36 1819-1825
• 4 Ball D, Burrows C, Sargeant A J. Human power output during repeated sprint cycle exercise: the influence of thermal stress.  Eur J Appl Physiol. 1999;  79 360-366
• 5 Batterham A M, Atkinson G. How big does my sample need to be? A primer on the murky world of sample size estimation.  Phys Ther Sport. 2005;  6 153-163
• 6 Bishop D. Warm up II: performance changes following active warm up and how to structure the warm up.  Sports Med. 2003;  33 483-498
• 7 Borg G. Ratings of perceived exertion and heart rates during short-term cycle exercise and their use in a new cycling strength test.  Int J Sports Med. 1982;  3 153-158
• 8 Castle P C, Macdonald A L, Philp A, Webborn A, Watt P W, Maxwell N S. Precooling leg muscle improves intermittent sprint exercise performance in hot, humid conditions.  J Appl Physiol. 2006;  4 1377-1384
• 9 Dubois D, Dubois E F. A formulae to estimate the approximate surface area if height and weight be known.  Arch Intern Med. 1916;  17 831-836
• 10 Gonzalez-Alonso J, Teller C, Andersen S L, Jensen F B, Hyldig T, Nielsen B. Influence of body temperature on the development of fatigue during prolonged exercise in the heat.  J Appl Physiol. 1999;  86 1032-1039
• 11 Hopkins W G, Hawley J A, Burke L M. Design and analysis of research on sport performance enhancement.  Med Sci Sports Exerc. 1999;  31 472-485
• 12 Jackson A S, Pollock M L. Generalized equations for predicting body density of men.  Br J Nutr. 1978;  40 497-504
• 13 Kayser B. Exercise starts and ends in the brain.  Eur J Appl Physiol. 2003;  90 405-410
• 14 Kenney W L. Heat flux and storage in hot environments.  Int J Sports Med. 1998;  19 S92-S95
• 15 Lambert E V, St Claire Gibson A, Noakes T D. Complex system model of fatigue: integrative homeostatic control of peripheral physiological systems during exercise in humans.  Br J Sports Med. 2005;  39 52-62
• 16 Lee D T, Hayes E M. Exercise duration and thermoregulatory responses after whole body precooling.  J Appl Physiol. 1995;  79 1971-1976
• 17 Linnane D M, Bracken R M, Brooks S, Cox V M, Ball D. Effects of hyperthermia on the metabolic responses to repeated high-intensity exercise.  Eur J Appl Physiol. 2004;  93 159-166
• 18 Marino F E. Anticipatory regulation and avoidance of catastrophe during exercise-induced hyperthermia.  Comp Biochem Physiol B Biochem Mol Biol. 2004;  139 561-569
• 19 Marino F E, Lambert M I, Noakes T D. Superior performance of African runners in warm humid but not in cool environmental conditions.  J Appl Physiol. 2004;  96 124-130
• 20 Martin P G, Marino F E, Rattey J, Kay D, Cannon J. Reduced voluntary activation of human skeletal muscle during shortening and lengthening contractions in whole body hyperthermia.  Exp Physiol. 2005;  90 225-236
• 21 Mitchell J W, Nadel E R, Stolwijk J A. Respiratory weight losses during exercise.  J Appl Physiol. 1972;  32 474-476
• 22 Morrison S, Sleivert G G, Cheung S S. Passive hyperthermia reduces voluntary activation and isometric force production.  Eur J Appl Physiol. 2004;  91 729-736
• 23 Nielsen B. Heat stress and acclimation.  Ergonomics. 1994;  37 49-58
• 24 Noble B J, Metz K F, Pandolf K B, Bell C W, Cafarelli E, Sime W E. Perceived exertion during walking and running II.  Med Sci Sports Exerc. 1973;  5 116-120
• 25 Nybo L, Jensen T, Nielsen B, Gonzalez-Alonso J. Effects of marked hyperthermia with and without dehydration on VO(2) kinetics during intense exercise.  J Appl Physiol. 2001;  90 1057-1064
• 26 Parkin J M, Carey M F, Zhao S, Febbraio M A. Effect of ambient temperature on human skeletal muscle metabolism during fatiguing submaximal exercise.  J Appl Physiol. 1999;  86 902-908
• 27 Ramanathan N J. A weighting system for mean surface temperature of the human body.  J Appl Physiol. 1964;  19 521-533
• 28 Reilly T, Brooks G A. Exercise and the circadian variation in body temperature measures.  Int J Sports Med. 1986;  7 358-362
• 29 Sargreant A J, Dolan P. Effect of prior exercise on maximal short-term power output in humans.  J Appl Physiol. 1987;  63 1475-1480
• 30 Saunders A G, Dugas J P, Tucker R, Lambert M I, Noakes T D. The effects of different air velocities on heat storage and body temperature in humans cycling in a hot, humid environment.  Acta Physiol Scand. 2005;  183 241-255
• 31 Siri W E. Body composition from fluid spaces and density: analysis of methods. Berkeley, CA; University of California; Radiation Laboratory Report (UCRL 3349) 1956
• 32 Slater G J, Rice A J, Sharpe K, Tanner R, Jenkins D, Gore C J, Hahn A G. Impact of acute weight loss and/or thermal stress on rowing ergometer performance.  Med Sci Sports Exerc. 2005;  37 1387-1394
• 33 St Clair Gibson A, Baden D A, Lambert M I, Lambert E V, Harley Y X, Hampson D, Russell V A, Noakes T D. The conscious perception of the sensation of fatigue.  Sports Med. 2003;  33 167-176
• 34 St Clair Gibson A, Lambert E V, Rauch L H, Tucker R, Baden D A, Foster C, Noakes T D. The role of information processing between the brain and peripheral physiological systems in pacing strategies and perceptions of effort.  Sports Med. 2006;  36 705-722
• 35 St Clair Gibson A, Noakes T D. Evidence for complex system integration and dynamic neural regulation of skeletal muscle recruitment during exercise in humans.  Br J Sports Med. 2004;  38 797-806
• 36 Tatterson A J, Hahn A G, Martin D T, Febbraio M A. Effects of heat stress on physiological responses and exercise performance in elite cyclists.  J Sci Med Sport. 2000;  3 186-193
• 37 Thomas M M, Cheung S S, Elder G C, Sleivert G G. Voluntary muscle activation is impaired by core temperature rather than local muscle temperature.  J Appl Physiol. 2006;  100 1361-1369
• 38 Todd G, Butler J E, Taylor J L, Gandevia S C. Hyperthermia: a failure of the motor cortex and the muscle.  J Physiol. 2005;  563 621-631
• 39 Tucker R, Marle T, Lambert E V, Noakes T D. The rate of heat storage mediates an anticipatory reduction in exercise intensity during cycling at a fixed rating of perceived exertion.  J Physiol. 2006;  3 905-915
• 40 Tucker R, Rauch L, Harley Y X, Noakes T D. Impaired exercise performance in the heat is associated with an anticipatory reduction in skeletal muscle recruitment.  Pflugers Arch. 2004;  448 422-430
• 41 Ulmer H V. Concept of an extracellular regulation of muscular metabolic rate during heavy exercise in humans by psychophysiological feedback.  Experentia. 1996;  52 416-420