Comparison of Sweat Sodium Concentration From Absorbent Patch and Macroduct During Exercise in the Heat

The most common way to collect sweat during exercise is through application of an absorbent patch to the skin. Alternative to a patch, a macroduct with one-way valve and microtubing can be used to collect sweat and analyze sweat [Na + ]. However, research has not investigated potential differences in sweat [Na + ] between an absorbent patch and macroduct. PURPOSE: To compare sweat [Na + ] collected from a Tegaderm+ patch and macroduct (ELITechGroup Biomedical Systems) during exercise in the heat, and to quantify day-to-day variability for each method. HYPOTHESIS: We hypothesized that the Tegaderm+ patch would have greater sweat [Na + ] than the macroduct, suggesting potential contamination. METHODS: Nineteen healthy, active participants (9 females; 33 ± 10 y; 170.5 ± 10.9 cm; 69.8 ± 13.9 kg) participated in this study. Participants completed two matched trials, separated by 48 hours. Prior to exercise, a Tegaderm+ patch and a macroduct were applied to the left forearm after cleaning. Participants completed trials in an environmental chamber (27°C; 50% RH) where one hour of exercise (matched between trials) was performed on a treadmill or cycle-ergometer at a self-selected pace. Sweat samples were analyzed for sweat [Na + ] using a lab grade ion-selective electrolyte analyzer (Easylyte, Medica). Data were analyzed using paired samples t-tests, coefficients of variation (CV), mean bias, and 95% limits of agreement (LoA) to assess reliability and agreement between methods. RESULTS: Ambient conditions were consistent between trials (T1 temperature: 27.3 ± .1°C, T2 temperature: 27.2 ± .1°C, p = .18; T1 RH: 50.7 ± .2%, T2 RH: 50.1 ± 0.6%, p = 0.43). Exercise workload and duration did not differ between trials (T1 HR: 128 ± 29 bpm, T2 HR: 129 ± 28 bpm, p = .50; T1 RPE: 10 ± 2, T2 RPE: 10 ± 2, p = .47). Sweat [Na + ] for the patch on Day 1 was 41 ± 11 mmol•L-1 and 41 ± 9 mmol•L-1 on Day 2 (mean bias = -1 ± 5 [95% LoA: -11, 9]; CV: 7.4 ± 0.1%). Macroduct sweat [Na + ] for Day 1 was 37 ± 14 mmol•L-1 and 34 ± 10 mmol•L-1 on Day 2 mean bias = -3 ± 8 [95% LoA: -18, 12]; CV: 11.0 ± 0.1%). The macroduct produced lower sweat [Na + ] compared to the patch (40 ± 10 vs 37 ± 11 mmol•L-1, p=0.0005; mean bias = -3 ± 4 mmol•L-1 [95% LoA = -10, 4]). CONCLUSIONS: The Tegaderm+ patch showed lower day-to-day variability, but produced greater sweat [Na + ] compared to the macroduct. This finding suggest that the higher sweat [Na + ] observed with the patch, when compared to the macroduct, may indicate pre-sample collection contamination at the skin and should be taken into account when interpreting patch-based measurements. Future research should continue to investigate differences between the absorbent patch and macroduct. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.