title: Sweat sodium concentration during exercise in the heat in aerobically trained and untrained humans.
abstract: The purpose of this study was to determine whether sweat sodium concentration ([Na(+)](sweat)) during exercise in the heat differs between aerobically trained and untrained individuals. On three occasions, ten endurance-trained (Tr) and ten untrained (UTr) subjects (VO2peak = 4.0 ± 0.8 vs. 3.4 ± 0.7 L min(-1), respectively; P < 0.05) cycled in a hot-ventilated environment (36 ± 1°C; 25 ± 2% humidity, airflow 2.5 m s(-1)) at three workloads (i.e., 40, 60, and 80% VO2peak). Whole-body (SR(WB)) and back sweat rates (SR(BACK)) were measured. At the conclusion of the study, Na(+) in sweat and blood samples was analyzed to calculate Na(+) secretion and reabsorption rates. SR(WB) and SR(BACK) were highly correlated in Tr and UTr (r = 0.74 and 0.79, respectively; P < 0.0001). In both groups, SR(BACK) increased with the increases in exercise intensity (P < 0.05). Likewise, [Na(+)](sweat) increased with the exercise intensity in both groups (P < 0.05) and it tended to be higher in Tr than in UTr at 60 and 80% VO2peak (~22 mmol L(-1) higher; P = 0.06). However, when normalized for SR(BACK), [Na(+)](sweat) was not different between groups. In both groups, Na(+) secretion and reabsorption rates increased with the increases in SR(BACK) (P < 0.05). However, Na(+) reabsorption rate was lower in the Tr than in the UTr (mean slope = 48 vs. 82 ηmol cm(-2) min(-1); P = 0.03). In conclusion, using a cross-sectional study design, our data suggest that aerobic fitness level does not reduce sweat Na(+) secretion or enhance Na(+) reabsorption during prolonged exercise in the heat that induced high sweat rates.
authors: Exercise Physiology Laboratory at Toledo, University of Castilla-La Mancha, Avda. Carlos III, s/n. 45071, Toledo, Spain.
authors: Nassim
authors: N
authors: Hamouti
authors: Juan
authors: J
authors: Del Coso
authors: Juan F
authors: JF
authors: Ortega
authors: Ricardo
authors: R
authors: Mora-Rodriguez
mesh_terms: D000293:Adolescent; D000328:Adult; D000332:Aerobiosis / Q000502:physiology; D001831:Body Temperature / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005260:Female; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D006813:Humidity; D008297:Male; D009994:Osmolar Concentration; D010806:Physical Education and Training / Q000379:methods*; D010809:Physical Fitness / Q000502:physiology; D012964:Sodium / Q000032:analysis* / Q000378:metabolism; D013542:Sweat / Q000737:chemistry* / Q000378:metabolism; D014882:Water-Electrolyte Balance / Q000502:physiology; D055815:Young Adult
chemical_list: D012964:Sodium