Two Distinct Types of Sweat Profile in Healthy Subjects While Exercising at Constant Power Output Measured by a Wearable Sweat Sensor

Wearable sweat sensors have enabled real-time monitoring of sweat profiles (sweat concentration versus time) and could enable monitoring of electrolyte loss during exercise or for individuals working in extreme environments. To assess the feasibility of using a wearable sweat chloride sensor for real-time monitoring of individuals during exercise, we recorded and analyzed the sweat profiles of 50 healthy subjects while spinning at 75 Watts for 1 hour. The measured sweat chloride concentrations were in the range from 2.9–34 mM. The sweat profiles showed two distinct sweat responses: Type 1 (single plateau) and Type 2 (multiple plateaus). Subjects with Type 2 profiles had higher sweat chloride concentration and weight loss, higher maximum heart rate, and larger changes in heart rate and rating of perceived exertion during the trial compared to subjects with Type 1 profiles. To assess the influence of level of effort, we recorded sweat profiles for five subjects at 75 W, 100 W, and 125 W. While all five subjects showed Type 1 sweat profiles at 75 W, four of the subjects had Type 2 profiles at 125 W, showing an increase in sweat chloride with exercise intensity. Finally, we show that sweat profiles along with other physiological parameters can be used to predict fluid loss.