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RELIABILITY AND VARIABILITY OF FIELD-BASED SWEAT ASSESSMENT TOOLS

Abstract

Monitoring sweat rate and composition helps develop individualized athlete hydration strategies to prevent dehydration and its physiological effects. PURPOSE: This study evaluated the variability and reliability of four low-cost, field-based sweat assessment tools for measuring sweat rate and sweat sodium concentration. METHODS: A 28-year-old endurance-trained female completed 10 trials. Each 60-minute cycling trial was conducted at 145 watts in an 80°F, 30% humidity chamber. Sweat rate and sodium concentration were assessed via Whole Body Displacement Method (WBDM, sweat rate only), GX Patch, Nix Biosensor, Hdrop Sensor, and Horiba Laqua Twin (sodium only). Measurements were analyzed for inter-device variability and test-retest reliability using Bland-Altman plots, Intraclass Correlation Coefficients (ICC), and Coefficient of Variation (CV). RESULTS: Fluid loss CV was lowest with the GX patch (3.9%), while WBDM (23.9%), Nix (18.4%), and Hdrop (13.7%) had higher variability. For sodium, Horiba was the most reliable (10.1%), while Nix (27.9%), Hdrop (20.7%), and GX (14.1%) showed greater variability. Bland-Altman analysis showed GX best agreed with Horiba (mean diff: -32.8, LOA: -204.5 to 138.8). Hdrop showed the largest sodium discrepancies vs. Nix (-1498.6, LOA: -2298.9 to -698.2) and Horiba (-1571.9, LOA: -2471.4 to -672.4). The best fluid agreement was Nix vs. Hdrop (mean diff: -182.2, LOA: -758.3 to 393.9), while the weakest was WBDM vs. Hdrop (-762.4, LOA: -1168.6 to -356.3). ICC showed poor agreement overall, with WBDM and Nix highest for fluid (0.47), and GX and Horiba for sodium (0.28), though not statistically significant. CONCLUSION: Some tools offer more consistent, reliable measurements. GX showed the best consistency for fluid (CV 3.9%), and Horiba for sodium (CV 10.1%). ICC results suggest limited agreement between tools. This study highlights the need to understand the accuracy of low-cost sweat assessment tools used in athlete hydration planning.

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