Poster Communications Year : 2025

EFFECT OF TEMPERATURE ON THE KINETICS OF NaCl CONCENTRATION IN SWEAT DURING SUB-MAXIMAL EXERCISE

Effet de la température ambiante sur l'évolution de la concentration en NaCl dans la sueur lors d'un exercice sous maximal

Abstract

Purpose: The human body primarily regulates core temperature through evaporation sweat loss, especially during physical activity. Previous studies suggested that an increased sweat rate (SR) leads to higher sweat-related sodium chloride (NaCl) concentration due to reduced NaCl reabsorption in sweat glands. In the heat, a rise in body core temperature and loss of body water via sweating are consequences of prolonged exercise. However, current methods for assessing SR and NaCl concen-tration in sweat do not allow real-time measurement, limiting the ability to make immediate adjust-ments in hydration or electrolyte management. This study aimed to compare the impact of ambient temperature on the evolution of SR and NaCl concentration in sweat using the BeOne armband, a device that continuously measures sweating throughout exercise in real time. Methods: 45 well-trained male athletes 45 male athletes (22±5 y ; 1.77±0.06 m ; 71±13 kg ; VO2 max : 66±11 ml.min-1.kg-1) performed a 45-minute cycling exercise at 50% of power output at which VO₂max was reached under two environmental conditions: a thermos-neutral climate (N: 24 ± 1°C, 30.0 ± 3% RH) and a hot climate (H: 35 ± 1°C, 30 ± 3% RH). During sessions NaCl concentration was continuously monitored using the BeOne armband, while whole-body SR was assessed via body mass changes. Core temperature (Tc), skin temperature (Ts), heart rate (HR), and heat production (indirect calorimetry) were also measured. Results: An increase in ambient temperature led to a shorter sudation delay from the armband sensor and a higher sweat rate (T-test). NaCl concentrations were time-normalized relative to the individual sweat measurement duration. ANOVA revealed a significant increase in sweat NaCl concentration starting from 30% of the sweat measurement period. In addition, core temperature, skin temperature, heart rate, RPE and thermal sensations increased with hot temperature. Conclusion: Higher ambient temperature led to faster sweating, increased sweat rate, and elevated NaCl concentration in sweat. Real-time, continuous measurement of NaCl concentration suggests that sweat rate increases progressively during the session. This study confirms the relationship between sweat rate and NaCl concentration, suggesting that higher sweat rate is associated with reduced NaCl reabsorption. Continuous monitoring of these variables in real time may provide more precise insights into athletes’ thermoregulatory capacity.

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Dates and versions

hal-05142169 , version 1 (03-07-2025)

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  • HAL Id : hal-05142169 , version 1

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A Ferrari, G Baquet, M Rance, M Sorg, Serge Berthoin, et al.. EFFECT OF TEMPERATURE ON THE KINETICS OF NaCl CONCENTRATION IN SWEAT DURING SUB-MAXIMAL EXERCISE. ECSS, Jul 2025, Rimini, France. ⟨hal-05142169⟩
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