Reliability of a wearable sweat rate monitor and routine sweat analysis techniques under heat stress in females: Physiology and Pharmacology of Temperature Regulation, Croatia

Introduction: The aim of the study was to evaluate the reliability of sweat analysis techniques which measure; whole body sweat rate [WBSR], local sweat rate [LSR] (via technical absorbent [TA] method and KuduSmart monitor [SMART]), sweat composition [SC] and sweat gland activation [SGA] in females when exercising under heat stress. Methods: Fourteen females (age; 26 ± 7 years, body mass; 66.5 ± 7.6 kg, height; 167.1 ± 6.4 cm) completed a preliminary threshold walking test (to determine intensity) and two main trials, separated by 2 days. Main trials consisted of 30 minutes seated rest in an upper body sauna-suit before its removal and walking at a moderate intensity (4 metabolic equivalents) for 30 minutes (speeds ranged from 4.8-6.5 km.hr-1) in 35°C, 50% relative humidity. WBSR was measured via nude mass pre and post exercise. The TA and Tegaderms patches (for sweat sodium chloride) were placed on the back, forearm and chest for the entire 60 minutes, replicated for all participants for both trials. SGA was assessed following the 60 minute trial and the KuduSmart monitor was placed on the left arm for the 30 minutes of exercise. Results: WBSR, LSR methods (TA and SMART) and SC demonstrated no difference between trials (p>0.05), good agreement (within limits), strong correlations (r=>0.88) and low typical error of measurements [TEM] (<0.04L.min-1, 0.13 mg.min-1.cm-2 and 8 mmol.L-1, respectively). SGA method showed moderate reliability (r=0.8), with high TEM (5 glands, 22%) and large limits of agreement. Conclusion: Sudomotor function is reliable, as demonstrated by good reliability, small TEM and strong correlations. The use of these sweat techniques is appropriate and practical in females who are exercising at moderate intensity under heat stress, and so, may aid future interventions. SGA shows larger variation and should be used with caution.