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 (NH 3 ) and a lower sweat pH. Four groups (15 girls, 18 boys, 8 women, 8 men) cycled in the heat (42ºC, 20% relative humidity) at 50% VO 2max 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 NH 3 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 NH 3 transport from plasma to sweat as accounted for by a significant correlation between sweat NH 3 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.

The relationship between exercise intensity and the sweat lactate excretion rate

“…However, numerous studies [1,4,[9][10][11][12] have shown the exact opposite. For example, Falk et al [9] reported a correlation of r = -0.57 between sweat rate and [lactate] sweat in 36 boys exercising in the heat.…”

“…Thus, [lactate] sweat should theoretically reflect glycolytic ATP production supporting sweat formation and secretion in eccrine glands [7,9,10]. Interestingly, however, numerous studies [1,4,[9][10][11][12] have reported an inverse relationship between [lactate] sweat and exercise intensity. The inverse relationship is most likely the result of increased sweat production causing a dilution effect on the [lactate] sweat [11,[13][14][15], thus limiting its ability to accurately indicate the metabolic activity of the sweat gland.…”

Children and guns: The detection of recent contact with firearms on children's hands by the PDT reagent

“…Furthermore, it was found that in children, the acid salts are stable relatively to the esters as a function of time and temperature. Perhaps an even more relevant difference between children's and adults' sweat composition is the acidity: children's sweat pH is considerably lower (more acidic) than that of adolescents (girls: 5.4, boys: 5.0 vs. women: 6.2, and men: 6.2) [31,32]. Since the mechanism by which iron traces are transferred from the weapon to the hand is a chemical one [21], we assume that iron dissolution is enhanced by the more acidic sweat so that larger amounts of iron migrate to children's hands and hence the more intense PDT marks.…”

Opportunities and challenges of using ion-selective electrodes in environmental monitoring and wearable sensors

“…The current focus on point-of-care and self diagnostics encourages the use of ISEs for these applications [9,20,24]. There are many analytes in sweat and saliva whose monitoring would be extremely important [24][25][26][27][28][29][30][31][32][33][34] and hereafter few examples are reported.…”