Validity and Reliability of At-Home Sweat Rate and Sodium Patches

Introduction: Hydration recommendations encourage athletes to know their sweat rate and sweat electrolyte concentrations, and novel devices are now available for at-home testing. This study aims to determine the validity and reliability of an at-home sweat rate and Na + loss device. Methods: Eleven males (78.5 ± 8.7 kg, 55.0 ± 13.7 mL·kg −1 ·min −1 ) and 11 females (62.4 ± 7.3 kg, 37.6 ± 10.3 mL·kg −1 ·min −1 ) completed two matched cycling trials (~60% ) in an environmental chamber set to 30°C and 55% relative humidity while wearing a standard lab-based absorbent sweat patch and an at-home microfluidic sweat patch (Gatorade, Barrington, IL) on the ipsilateral forearm. The lab-based absorbent patch was assessed using standard calculations, and at-home microfluidic patch data were obtained through the associated smartphone application. Spearman ρ correlations were used for reliability between trials. Paired-samples t tests compared the lab-based patch versus the microfluidic patch sweat rate and Na + losses. Results: There were no significant differences in wet bulb globe temperature ( P = 0.41), power output ( P = 0.97), rectal temperature ( P = 0.86), or heart rate ( P = 0.61) between trials. The microfluidic patch failed to provide a sweat rate for 9 of 44 trials (20%). Trial 1 sweat rate was not significantly correlated with Trial 2 for the microfluidic patch (ρ = −0.060; P = 0.84) but was for lab-based sweat rate (ρ = 0.698; P < 0.01). Sweat rate assessed by the microfluidic patch (0.53 ± 0.28 L·h −1 ) was significantly less than lab-based measures (0.96 ± 0.37 L·h −1 ; P < 0.01). The microfluidic patch failure rate for Na + losses was 43%. Na + losses were significantly greater for the lab (1053 ± 203 mg) compared with the microfluidic patch (729 ± 143 mg; P < 0.01). Sweat rate data for the microfluidic patch were within 0.5 L·h −1 for 16/34 trials (47%), and Na + losses were within 200 mg for 36% of trials compared with the lab-based patch. Conclusions: Athletes and sports scientists should take caution when assessing sweat rate and Na + losses using at-home microfluidic patches.