Relative exercise intensity and core temperature in lean and obese children

Abstract

Leites et al1Leites G.T. Sehl P.L. Cunha Gdos S. Detoni Filho A. Meyer F. Responses of obese and lean girls exercising under heat and thermoneutral conditions.J Pediatr. 2013; 162: 1054-1060Abstract Full Text Full Text PDF PubMed Scopus (27) Google Scholar reported greater changes in rectal temperature (Tre) in lean compared with obese girls cycling at the same percentage of maximum oxygen uptake (%VO2max). A study published from our laboratory2Jay O. Bain A.R. Deren T.M. Sacheli M. Cramer M.N. Large differences in peak oxygen uptake do not independently alter changes in core temperature and sweating during exercise.Am J Physiol Regul Integr Comp Physiol. 2011; 301: R832-R841Crossref PubMed Scopus (104) Google Scholar and basic biophysical calculations suggest that, despite its widespread use in thermoregulatory studies over the past 40-plus years,3Saltin B. Hermansen L. Esophageal, rectal, and muscle temperature during exercise.J Appl Physiol. 1966; 21: 1757-1762Crossref PubMed Scopus (433) Google Scholar the employed %VO2max protocol may have introduced inherent experimental bias leading to the observed differences in Tre. Jay et al2Jay O. Bain A.R. Deren T.M. Sacheli M. Cramer M.N. Large differences in peak oxygen uptake do not independently alter changes in core temperature and sweating during exercise.Am J Physiol Regul Integr Comp Physiol. 2011; 301: R832-R841Crossref PubMed Scopus (104) Google Scholar demonstrated that high (60 mL/kg per minute) and low (40 mL/kg per minute) VO2max groups matched for total body mass exhibit identical changes in Tre when exercising at a metabolic heat production (Hprod) of 540 W despite large differences in %VO2max (40% vs 58%). On the other hand, exercise at 60%VO2max yielded far greater changes in Tre in the fit group by virtue of their greater Hprod per unit mass (10.7 vs 7.7 W/kg).2Jay O. Bain A.R. Deren T.M. Sacheli M. Cramer M.N. Large differences in peak oxygen uptake do not independently alter changes in core temperature and sweating during exercise.Am J Physiol Regul Integr Comp Physiol. 2011; 301: R832-R841Crossref PubMed Scopus (104) Google Scholar Taken together, these data show that in adults, VO2max does not fundamentally alter heat dissipation in compensable conditions, and changes in Tre during exercise are primarily dependent on Hprod and body mass, not VO2max. In the study by Leites et al,1Leites G.T. Sehl P.L. Cunha Gdos S. Detoni Filho A. Meyer F. Responses of obese and lean girls exercising under heat and thermoneutral conditions.J Pediatr. 2013; 162: 1054-1060Abstract Full Text Full Text PDF PubMed Scopus (27) Google Scholar the lean group was fitter than the obese group (44.9 vs 36.0 mL/kg per minute); therefore, exercise prescribed at ∼55% VO2max would have yielded4Nishi Y. Measurement of thermal balance in man.in: Cena K. Clark J. Bioengineering, thermal physiology and comfort. Elsevier, New York, NY1981: 29-39Crossref Scopus (110) Google Scholar (assuming an respiratory exchange ratio of 0.85) an Hprod of ∼8.4 W/kg in the lean group but only ∼6.7 W/kg in the obese group. Potential differences in thermoregulatory function between obese and lean girls may have therefore been obscured. To isolate the influence of adiposity on changes in core temperature during exercise from the confounding effects of Hprod and mass, future studies should administer exercise eliciting a fixed Hprod per unit body mass in both lean and obese groups, regardless of any differences in %VO2max. Responses of Obese and Lean Girls Exercising under Heat and Thermoneutral ConditionsThe Journal of PediatricsVol. 162Issue 5PreviewTo compare thermoregulatory and perceptual responses between lean and obese girls during and after exercise under heat (HC) and thermoneutral (TC) conditions. Full-Text PDF ReplyThe Journal of PediatricsVol. 163Issue 5PreviewMorris and Jay's criticism of the prevalent use of the maximum oxygen uptake (%VO2max) protocol as a potential experimental bias to compare thermoregulatory responses between groups of different fitness/body mass is pertinent. The suggestion is to clarify results from a heat production (Hprod) perspective. We considered this when recruiting obese and lean girls with similar physical activity and acclimatization levels. Their resulting VO2max per kg body mass, although expected to be higher in the lean girls (44.9 ± 8.5 vs 36.0 ± 8.5 mL/kg per minute), was similar when corrected by total muscle mass or even by leg muscle mass (60 ± 10 and 70 ± 10 mL/kg total muscle mass per minute and 184 ± 34 and 192 ± 33 mL/kg leg muscle mass per minute, respectively). Full-Text PDF