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This Article Full Text Full Text (PDF) All Versions of this Article: 103/3/995    most recent 00018.2007v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Timmons, B. W. Articles by Riddell, M. C. Search for Related Content PubMed PubMed Citation Articles by Timmons, B. W. Articles by Riddell, M. C.

Energy substrate utilization during prolonged exercise with and without carbohydrate intake in preadolescent and adolescent girls

Brian W. Timmons,¹ Oded Bar-Or,^1, and Michael C. Riddell²

¹Children's Exercise and Nutrition Centre, McMaster University, Hamilton, Ontario; and ²School of Kinesiology and Health Science, Faculty of Science and Engineering, York University, Toronto, Ontario, Canada

Submitted 4 January 2007 ; accepted in final form 28 June 2007

Little information is available on energy metabolism during exercise in girls, particularly the contribution of exogenous carbohydrate (CHO_exo). The purpose of this study was to determine substrate utilization during exercise with and without CHO_exo intake in healthy girls. Twelve-yr-old preadolescent (YG; n = 12) and 14-yr-old adolescent (OG; n = 10) girls consumed flavored water (WT) or ¹³C-enriched 6% CHO (CT) while cycling for 60 min at 70% maximal aerobic power (O_2max). Substrate utilization was calculated for the final 15 min of exercise. CHO_exo decreased fat oxidation by 50% in YG but not in OG (P < 0.001) and decreased endogenous CHO oxidation by 15% in OG but not in YG (P = 0.006). Endogenous CHO oxidation was lower in YG than in OG regardless of trial (P 0.01), whereas fat oxidation was higher in YG only during WT (P < 0.001). CHO_exo oxidation rate was similar between YG and OG (7.1 ± 0.5 and 6.8 ± 0.4 mg·kg^–1·min^–1, respectively, P = 0.67), contributing 19% to total energy expenditure. Serum estradiol levels in all girls correlated with fat (r = –0.50 to –0.59, P = 0.03 to 0.005) and endogenous CHO oxidation (r = 0.50 to 0.63, P = 0.03 to 0.005) but not with CHO_exo oxidation (r = –0.09, P = 0.71). We conclude that CHO_exo influences endogenous substrate utilization in an age-dependent manner in healthy girls but that total CHO_exo oxidation during exercise is not different between YG and OG. Our results also point to potential sex-related differences in energy substrate utilization even during childhood.

children; cycling; energy metabolism; stable isotope tracers