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


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.


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



The authors wish to thank the subjects for their invaluable contribution to the study. Nassim Hamouti and Juan Del Coso were supported by a pre-doctoral fellowship from the Castilla-La Mancha government in Spain. Juan F. Ortega was supported by a Latin-American grant from the Gatorade Sports Science Institute.

Ethical standards

The authors of this study declare that the experiments comply with the current laws of the country in which they were performed. The study was approved by the local Hospital Research Ethics Committee and conducted in accordance with the guidelines of the revised Declaration of Helsinki.

Conflict of interest

The authors of this study declare that they have no financial, professional or other personal interest of any nature in any product, service and/or company that could be construed as influencing the position presented in this manuscript.


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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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