Sweat Sodium Concentration Accuracy For A Wearable Fabric Sensor And Two Hydration Monitors During Running

INTRODUCTION: Endurance athletes may encounter hydration issues due to improper electrolyte and water intake during exercise. Sweat sodium concentration ([Na+]) can be a valid indicator of whole body sweat Na + loss. A wearable fabric sensor (WFS) that directly measures sweat Na + could be beneficial in developing exercise hydration plans. PURPOSE: Determine accuracy of two hydration monitors (HM1 and HM2) and a pre-commercial WFS that measure sweat [Na+]. METHODS: Subjects (n = 24, ages 18-60 yrs.) completed a 90 minute treadmill run at moderate intensity while wearing a WFS prototype and either HM1 or HM2. Macroducts collected samples during exercise. Samples were analyzed for [Na+] using a commercial sweat Na + analyzer (SSA) and a flame photometer (FP). [Na+] results from WFS and HM were evaluated for accuracy compared to SSA and FP measurements. Bland-Altman analysis was used to compare all four measurement methods. RESULTS: Average sweat [Na+] measured during exercise: SSA = 55 mM+/-22 mM; FP = 53 mM+/-29 mM. Average sweat [Na+]measured from the wearable devices: WFS = 49 mM+/-22 mM, HM1 = 54 mM+/-11 mM, and HM2 = 92+/-15 mM. Average accuracy of WFS to SSA: 89%, p = 0.49, R2 = 0.87; HM1 to SSA: 61%, p = 0.47, R2 = 0.88; HM2 to SSA: 49%, p = 0.005, R2 = 0.58. When compared to FP, the accuracy of WFS = 78%, p = 0.71, R2 = 0.80; HM1 = 44%, p = 0.29, R2 = 0.85, HM2 = 0%, p = 0.004, R2 = 0.51. Bland-Altman analysis showed an average concentration difference between WFS and SSA of 0.26 mM, with 93% of data points between +/- 1.96 times the standard deviation (SD). The average concentration difference between HM1 and SSA was -6.67 mM, with 100% of data points between +/- 1.96 times the SD. The average concentration difference between HM2 and SSA was 36.83 mM, with 100% of data points between +/- 1.96 times the SD. The average concentration difference between WFS and FP was -6.00 mM, with 92% of data points between +/- 1.96 times the SD. The average concentration difference between HM1 and FP was -10.27 mM, with 88% of data points between +/- 1.96 times the SD. The average concentration difference between HM2 and FP was -38.09 mM, with 100% of data points between +/- 1.96 times the SD. CONCLUSIONS: The WFS more accurately predicted [Na+] when compared to HM1 and HM2 while worn for 90 minutes during a treadmill run. Supported by: National Science Foundation [grant number 2111983]