European Journal of Applied Physiology

, Volume 111, Issue 11, pp 2873–2881 | Cite as

Sweat sodium concentration during exercise in the heat in aerobically trained and untrained humans

  • Nassim Hamouti
  • Juan Del Coso
  • Juan F. Ortega
  • Ricardo Mora-Rodriguez
Original Article

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 (\( \dot{V}{\text{O}}_{{2{\text{peak}}}} \) = 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% \( \dot{V}{\text{O}}_{{2{\text{peak}}}} \)). Whole-body (SRWB) and back sweat rates (SRBACK) were measured. At the conclusion of the study, Na+ in sweat and blood samples was analyzed to calculate Na+ secretion and reabsorption rates. SRWB and SRBACK were highly correlated in Tr and UTr (r = 0.74 and 0.79, respectively; P < 0.0001). In both groups, SRBACK 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% \( \dot{V}{\text{O}}_{{2{\text{peak}}}} \) (~22 mmol L−1 higher; P = 0.06). However, when normalized for SRBACK, [Na+]sweat was not different between groups. In both groups, Na+ secretion and reabsorption rates increased with the increases in SRBACK (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.

Keywords

Training status Exercise intensity Sweat sodium secretion Sweat sodium reabsorption Blood serum sodium 

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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • Nassim Hamouti
    • 1
  • Juan Del Coso
    • 1
  • Juan F. Ortega
    • 1
  • Ricardo Mora-Rodriguez
    • 1
  1. 1.Exercise Physiology Laboratory at ToledoUniversity of Castilla-La ManchaToledoSpain

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