Determinants of Endurance Exercise Capacity in the Heat in Prepubertal Boys

 

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Abstract

The goal of this study was to identify factors which limit exercise endurance in hot ambient conditions in prepubertal boys. Eight healthy non-acclimatized, highly physically active prepubertal boys performed steady load cycling at approximately 65 % peak V·O₂ to exhaustion in both cool (19.6 ± 0.6 °C, 66.4 ± 11.0 % relative humidity) and hot (31.0 ± 0.3 °C, 56.9 ± 2.0 % relative humidity) environmental conditions. Cardiac output, oxygen uptake, rectal temperature (T_re), rating of perceived exertion (RPE), blood pressure, and calculated arterial venous oxygen difference were obtained serially in each testing session, and percent dehydration was calculated from body weight loss. Endurance time was significantly shorter in the hot condition (29.30 ± 6.19 minutes versus 41.38 ± 6.30 minutes in the cool room). No significant differences in circulatory markers or hydration status were observed either during testing or between cycling thermal conditions. Rate of rise of T_re was greater during exercise in the heat, but no significant difference in T_re between conditions was observed at exhaustion. Mean values of RPE were consistently greater during exercise in the heat, but these differences did not reach statistical significance. These findings support the concept that rises in core temperature and/or brain perception (RPE) rather than circulatory insufficiency may be the critical factors defining limits to exercise in the heat.

References

• 1 Bar-Or O. Temperature regulation during exercise in children and adolescents. Gisolfi CV, Lamb DR Perspectives in Exercise Science and Sports Medicine. Vol. 2. Indianapolis; Benchmark Press 1988: 199-226
  Google Scholar
• 2 Cheung S S, McLellan T M. Influence of heat acclimation, aerobic fitness, and hydration effects on tolerance during uncompensable heat stress.  J Appl Physiol. 1988;  84 1731-1739
  PubMedGoogle Scholar
• 3 Cheung S S, Sleivert G G. Multiple triggers for hyperthermic fatigue and exhaustion.  Exerc Sports Sci Rev. 2004;  32 100-106
  PubMedGoogle Scholar
• 4 Cooper T, Willman V L, Hanlon C R. Cardiac and peripheral vascular responses to hyperthermia induced by blood stream heating.  J Thor Cardiovasc Surg. 1962;  44 667-673
  PubMedGoogle Scholar
• 5 Coyle E F, Gonzalez-Alonso J. Cardiovascular drift during prolonged exercise: new perspectives.  Exerc Sport Sci Rev. 2001;  29 88-92
  CrossrefPubMedGoogle Scholar
• 6 Drinkwater B L, Kepprat I C, Denton J E, Crist J L, Horvath S M. Response of prepubertal girls and college women to work in the heat.  J Appl Physiol. 1977;  43 1046-1053
  PubMedGoogle Scholar
• 7 Eston R G, Lamb K L, Bain A, Williams A M, Williams J G. Validity of a perceived exertion scale for children: a pilot study.  Percept Mot Skills. 1994;  78 691-696
  PubMedGoogle Scholar
• 8 Febbraio M A. Does muscle function and metabolism affect exercise performance in the heat?.  Exerc Sports Sci Rev. 2000;  28 171-176
  PubMedGoogle Scholar
• 9 Fuller A, Carter R N, Mitchell D. Brain and abdominal temperatures at fatigue in rats exercising in the heat.  J Appl Physiol. 1998;  84 877-883
  PubMedGoogle Scholar
• 10 Galloway S DR, Maughan R J. Effects of ambient temperature on the capacity to perform prolonged exercise in man.  J Physiol. 1995;  489 35-36
  PubMedGoogle Scholar
• 11 Gonzalez-Alonso J, Calbet J A, Nielsen B. Muscle blood flow is reduced with dehydration during prolonged exercise in humans.  J Physiol. 1998;  513 895-905
  CrossrefPubMedGoogle Scholar
• 12 Gonzalez-Alonso J, Mora-Rodriguez R, Below P R, Coyle E F. Dehydration reduces cardiac output and increases systemic and cutaneous vascular resistance during exercise.  J Appl Physiol. 1995;  79 1487-1496
  PubMedGoogle Scholar
• 13 Gonzalez-Alonso J, Mora-Rodriguez R, Below P R, Coyle E F. Dehydration markedly impairs cardiovascular function in hyperthermic endurance athletes during exercise.  J Appl Physiol. 1997;  82 1229-1236
  PubMedGoogle Scholar
• 14 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
  PubMedGoogle Scholar
• 15 Kayser B. Exercise starts and ends in the brain.  Eur J Appl Physiol. 2003;  90 411-419
  PubMedGoogle Scholar
• 16 Lamb K L. Children's ratings of effort during cycle ergometry: an examination of the validity of two effort-rating scales.  Pediatr Exerc Sci. 1995;  7 407-421
  PubMedGoogle Scholar
• 17 Marshall W A, Tanner J M. Variations in the pattern of pubertal changes in boys.  Arch Dis Child. 1970;  45 13-23
  PubMedGoogle Scholar
• 18 Moore F T, Marable S A, Ogden E. Contractility of the heart in abnormal temperatures.  Ann Thorac Surg. 1966;  2 446-450
  PubMedGoogle Scholar
• 19 Morrison S A, Sleivert G G, Cheung S S. Passive hyperthermia reduces voluntary activation and isometric force production.  Eur J Appl Physiol. 2004;  91 729-736
  CrossrefPubMedGoogle Scholar
• 20 Nielsen B, Hyldig T, Bidstrup F, Gonzalez-Alonso J, Christoffersen G R. Brain activity and fatigue during prolonged exercise in the heat.  Pflugers Arch. 2001;  442 41-48
  CrossrefPubMedGoogle Scholar
• 21 Nielsen B, Nybo L. Cerebral changes during exercise in the heat.  Sports Med. 2003;  33 1-11
  CrossrefPubMedGoogle Scholar
• 22 Nielsen B, Savard G, Richter S A, Hargreaves M, Saltin B. Muscle blood flow and muscle metabolism during exercise and heat stress.  J Appl Physiol. 1990;  69 1040-1046
  PubMedGoogle Scholar
• 23 Nybo L, Nielsen B. Hyperthermia and central fatigue during prolonged exercise in humans.  J Appl Physiol. 2001;  91 1055-1060
  CrossrefPubMedGoogle Scholar
• 24 Rivera Brown A M, Rowland T W, Ramirez-Marrero F, Santacama, Vann A. Exercise tolerance in hot and humid climates: comparison between active, heat-acclimated girls and women.  Med Sci Sports Exerc. 2003;  35 S198 (abstract)
  PubMedGoogle Scholar
• 25 Rowell L B. Human cardiovascular adjustments to exercise and thermal stress.  Physiol Rev. 1974;  54 75-159
  PubMedGoogle Scholar
• 26 Rowland T, Blum J. Cardiac dynamics during upright cycle exercise in boys.  Am J Hum Biol. 2000;  12 749-757
  CrossrefPubMedGoogle Scholar
• 27 Rowland T, Melanson E L, Popowski B, Ferrone L C. Test-retest reproducibility of maximal cardiac output by Doppler echocardiography.  Am J Cardiol. 1998;  81 1228-1230
  CrossrefPubMedGoogle Scholar
• 28 Rowland T, Obert P. Doppler echocardiography for the estimation of cardiac output with exercise.  Sports Med. 2002;  32 973-986
  CrossrefPubMedGoogle Scholar
• 29 Savard G, Nielsen B, Laszcynska I, Larsen B E, Saltin B. Muscle blood flow is not reduced in humans during moderate exercise and heat stress.  J Appl Physiol. 1988;  64 649-657
  PubMedGoogle Scholar
• 30 Tucker R, Rauch L, Harley Y XR, 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
  PubMedGoogle Scholar

M.D. Thomas Rowland

Department of Pediatrics
Baystate Medical Center

Springfield, MA, 01106

USA

Phone: + 4137947350

Fax: + 41 37 94 71 40

Email: thomas.rowland@bhs.org