Comparing Whole Body Sweat Rate Estimates Between Commercial Sweat Patches And Body Mass Change Methods

PURPOSE: Hydration status impacts performance and safety during physical activity in the heat. However, sweat rate testing - to inform practice and mitigate the risks of hypohydration - is not common outside of high-performance or research settings. The purpose of this study was to compare sweat rate estimates during exercise in the heat between a commercially-available, sweat testing patch (PATCH) and a corrected, body mass loss estimate (SwR) - common in research. METHODS: Participants (n = 8; female = 4; aged 24 ± 3 y) completed exercise in an environmental chamber (35.9 ± 1.9 0C; 34.9 ± 3.1% RH) in fasted, euhydrated state (USG ≤ 1.020). The participants completed 20 minutes of walking at ≈ 6 METs (69.68 m·min-1 and 8.5% grade) followed by 10 minutes of seated recovery. Sweat rate was estimated two ways. PATCH required participants to wear a patch on their forearm and a photo of the patch was uploaded to a smart-phone application post-exercise. PATCH reported a sweat rate range from which an average was calculated. Second, SwR used participants’ post-exercise body mass subtracted from their pre-exercise body mass, adjusted for fluid consumed during exercise. The difference in mass was recorded to the nearest 0.1 kg. Both methods required transforming data to L · h-1 to compare sweat rates. A paired-samples, t-Test (p ≤ 0.05) was used to investigate differences between SwR and PATCH; and Pearson’s correlation was used to explore their relationship. RESULTS: SwR (0.6 ± 0.3 L · h-1) was lower than the PATCH (1.2 ± 0.3 L · h-1; p < 0.001) but highly correlated (r = 0.76). Of note, SWR was less than PATCH for all observations (range = 28-78% lower). CONCLUSIONS: Sweat testing is logistically difficult. The benefits that can be gleaned from commercially-available, wearable technology is promising. However, within this design, a sweat patch overestimated sweat rate when compared to methods that use body-mass change during this short exercise session in the heat.