The experimental protocol for the dryland and pool studies was approved by the Institutional Review Board of Northwestern University (STU00207078), and all subjects gave written informed consent before participation. The experimental protocol for the Kona IRONMAN Triathlon was approved by the Sterling Institutional Review Board. All subjects consented to their images being taken as detailed in the protocols of the Northwestern and Sterling Institutional Review Boards. Imaging devices used for Northwestern sweat volume trials with a smart phone (LG Nexus 5X) recorded the device status within 5 min of finishing the exercise. Collected sweat volume was determined by counting the number of completed serpentines to the nearest half serpentine (±0.75 μl). Measurements of percentage of body weight loss (total body loss) and mass gain of skin-mounted absorbent foam pads (local loss) provided two methods of comparison to the volume collected in the SIS epifluidic device. A body weight scale with 4-g precision (Adams GFK 330ah) enabled high-precision measurements of percentage of body weight loss before and after exercise while wearing either a swimsuit or underwear. The animal (dynamic) measurement mode was used, which filters variations resulting from movement during the weighing procedure. Body weight measurements for the Kona IRONMAN Triathlon trials were performed in the nude after a 5-min warm up and after swimming using a Tanita scale with 10-g precision. Cleaning the application sites with an IPA wipe removed residual salts/oils and ensured good adhesion of the device. A rosin skin pretreatment (Gordon Labs, Stik-It) enhanced underwater adhesion during the Kona trials. Applying the pretreatment only to the skin underneath the adhesive prevented the inhibition of the sweat glands in the collection area. After applying to the skin, pressure was applied for 10 s to ensure good adhesion. Absorbent foam pads (3M Tegaderm 3582) mounted nearby the SIS devices recorded local sweat loss. Weighing the absorbent pads immediately following the workout using a microbalance (Vibra 224R) produced the wet weight. Placing the pads in a 50°C oven for 24 hours evaporated the water before weighing again (dry weight). Weight due to skin oils, salt content, etc was assumed to be negligible. Subtracting the dry weight from the wet weight and dividing by the area of the absorbent pad (1000 mm2) yielded the local sweat loss. Calibration and reference chloride measurements were performed on a Chloro-Chek Chloridometer with a coefficient of variation of 1.02% at 100 mM. No skin irritation due to the epifluidic device or the absorbent pad was observed during the trials.

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