Measuring Cation Concentrations in Sweat Using a Wearable Fabric Sensor

Many endurance athletes face challenges in recovering effectively after high-intensity workouts. To optimize recovery, athletes should understand the physiological changes taking place within their bodies. Understanding what athletes are losing in their sweat during exercise can help them determine how best to rehydrate. Personalized hydration strategies can improve an athlete’s performance by up to 40%. The work presented here will focus on the development and testing of a novel wearable fabric sensor (WFS) to help athletes monitor biomarkers in sweat, specifically sodium.

The WFS allows for the non-invasive collection of sweat sodium concentration during exercise. While various sweat sensors are available, most rely on conductivity measurements to estimate a value for sweat sodium concentration value. While accurate to total electrolyte concentration, this approach falls short in providing athletes with comprehensive insights into sweat sodium composition and more personalized hydration improvement strategies. The wearable fabric sensor presented here selectively monitors for sodium concentration in sweat, giving athletes the personalized information they require.

This study recruited 10 healthy adults (20-68 yrs) through fliers and Internet notices at Cleveland State University from June 2023 to October 2023. Upon arrival to the laboratory, consent was obtained, and exercise participation clearance was established using a PAR-Q+ form. The subjects then wore the WFS, and sterile gauze adhered to the body using tegaderm and cycled continuously for 60 minutes. The sterile gauze was removed and centrifuged at the end of the testing for analysis using a laboratory-quality sweat sodium analyzer (Precision Hydration, conductivity-based measurement) and a flame photometer (Jenway)

Cations within sweat mainly consist of sodium and potassium, rendering concentrations of other cations negligible. Using flame photometry, we were able to quantify the exact concentrations of sodium and potassium in the sweat samples. The average percent of sodium found in sweat was 83%, assuming that sodium and potassium make-up 100% of the cations in sweat. A WFS provides a non-invasive way to verify that sodium levels in the sweat are normal and can give the athlete valuable information. The accuracy of the flame photometer to the SSA was 3.35 mM, or 6%. The accuracy of both the flame and sweat sodium analyzer (SSA) to the WFS was variable to each batch of experimental WFSs, which ranged from 1-22 mM.

These findings contribute to a better understanding of post-exercise hydration needs and inform athletes about their sweat, leading to better recovery and performance.