Reliability and Validity of Portable Sweat Sodium Analyzers during Exercise in the Heat

We aimed to evaluate reliability and validity of MX3 and LAQUAtwin-Na-11 (LANa) analyzers in measuring sweat [Na+]. Nineteen healthy, active adults (9 females, 33±10 y) completed two matched, self-paced 60-minute cycling or running trials in warm-humid conditions (27.3±0.4℃, 50.9±1.8% RH). Sweat was collected from an absorbent patch on the left ventral forearm. Sweat was analyzed using MX3, LANa, and Medica analyzers. The accuracy of both portable analyzers was compared to Medica results. Reliability was assessed using coefficient of variation (CV) and intraclass correlation coefficient (ICC). MX3 demonstrated acceptable-to-high between-trial reliability (CV: 23%; ICC: 0.826), while LANa showed acceptable-to-moderate between-trial reliability (CV: 24%; ICC: 0.744). Validity was evaluated using CV and linear regression. Both analyzers demonstrated strong associations with the reference method (MX3: R² = 0.867; LANa: R² = 0.852), with good CV values (MX3: 17.5%; LANa: 13%). Overall, MX3 demonstrated higher reliability than LANa, and both analyzers provide good validity for laboratory-based sweat [Na⁺] assessment.