title: Effect of age and gender on sweat lactate and ammonia concentrations during exercise in the heat.
abstract: The dependence of sweat composition and acidity on sweating rate (SR) suggests that the lower SR in children compared to adults may be accompanied by a higher level of sweat lactate (Lac-) and ammonia (NH3) and a lower sweat pH. Four groups (15 girls, 18 boys, 8 women, 8 men) cycled in the heat (42 degrees C, 20% relative humidity) at 50% VO2max for two 20-min bouts with a 10-min rest before bout 1 and between bouts. Sweat was collected into plastic bags attached to the subject's lower back. During bout 1, sweat from girls and boys had higher Lac- concentrations (23.6 +/- 1.2 and 21.2 +/- 1.7 mM; P < 0.05) than sweat from women and men (18.2 +/- 1.9 and 14.8 +/- 1.6 mM, respectively), but Lac- was weakly associated with SR (P > 0.05; r = -0.27). Sweat Lac- concentration dropped during exercise bout 2, reaching similar levels among all groups (overall mean = 13.7 +/- 0.4 mM). Children had a higher sweat NH3 than adults during bout 1 (girls = 4.2 +/- 0.4, boys = 4.6 +/- 0.6, women = 2.7 +/- 0.2, and men = 3.0 +/- 0.2 mM; P < 0.05). This difference persisted through bout 2 only in females. On average, children's sweat pH was lower than that of adults (mean +/- SEM, girls = 5.4 +/- 0.2, boys = 5.0 +/- 0.1, women = 6.2 +/- 0.5, and men = 6.2 +/- 0.4 for bout 1, and girls = 5.4 +/- 0.2, boys = 6.5 +/- 0.5, women = 5.2 +/- 0.2, and men = 6.9 +/- 0.4 for bout 2). This may have favored NH3 transport from plasma to sweat as accounted for by a significant correlation between sweat NH3 and H+ (r = 0.56). Blood pH increased from rest (mean +/- SEM; 7.3 +/- 0.02) to the end of exercise (7.4 +/- 0.01) without differences among groups. These results, however, are representative of sweat induced by moderate exercise in the absence of acidosis.
authors.affiliation: Laboratório de Pesquisa do Exercício, Escola de Educação Física, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brasil.
authors.forename: F
authors.initials: F
authors.lastname: Meyer
authors.forename: O
authors.initials: O
authors.lastname: Laitano
authors.forename: O
authors.initials: O
authors.lastname: Bar-Or
authors.forename: D
authors.initials: D
authors.lastname: McDougall
authors.forename: G J F
authors.initials: GJ
authors.lastname: Heigenhauser
authors.forename: G J F
authors.initials: GJ
authors.lastname: Heingenhauser
mesh_terms: D000328:Adult; D000367:Age Factors; D000641:Ammonia / Q000032:analysis*; D002648:Child; D015444:Exercise / Q000502:physiology*; D005260:Female; D006358:Hot Temperature; D006801:Humans; D007773:Lactates / Q000032:analysis*; D008297:Male; D012737:Sex Factors; D013542:Sweat / Q000737:chemistry*
chemical_list: D007773:Lactates; D000641:Ammonia