Reliability of a wearable sweat rate monitor and routine sweat analysis techniques under heat stress in females

Introduction: The aim of the study was to evaluate the reliability of five different sweat analysis techniques which measure; whole body sweat rate [WBSR], local sweat rate [LSR] (via technical absorbent [TA] method and KuduSmart® monitor), sweat conductivity [SC] and sweat gland activation [SGA] in a female population when exercising moderately 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 exercise intensity) and two main trials, separated by 2 days. Main trials consisted of 30-min seated rest in the environmental chamber (35 °C, 50% relative humidity) in an upper body sauna-suit, before its removal, and walking at a moderate intensity (4 metabolic equivalents) for 30-min (speeds ranged from 4.8 to 6.5 km h−1). WBSR was measured via nude mass pre and post exercise. The TA and Tegaderm patches (for sweat sodium chloride) were placed on the back, forearm and chest for the entire 60-min, replicated for all participants for both trials. SGA was assessed following the 60-min trial and the KuduSmart® monitor was placed on the left arm for the 30-min of exercise. Results: WBSR, LSR methods 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] (< 0.04 L min−1, 0.13 mg min−1 cm−2 and 8 mmol L−1, respectively). SGA method showed moderate intra-class correlation (r = 0.80), with high TEM (5 glands) 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.