If you agree to be in this study, you will be asked to report to our exercise science research center for two total visits (2 separate trials separated by at least 4 days) and the total time commitment for this study will be approximately 5 hours. Prior to each trial, you will be provided with urine jugs and food/fluid logs to record food and drink intake for 24hr. You will be asked to log food/fluid intake 24hr leading into trials. We ask that you match your diet for both trials, as much as possible. Also, we ask that you match caffeine consumption prior to trials. Lastly, we ask that you refrain from strenuous exercise and alcohol consumption for at least 12hrs leading into trials. Either of these exclude your participation in the study for safety reasons. You will be asked to provide a small urine sample upon arrival to the lab before trials. The purpose of this is to verify hydration prior to exercise in the heat. If you are not hydrated upon arrival, you will be provided and asked to drink 16oz (a bottle) of water prior to the trial. Next, you will be seated, have 2 electrodes placed on your inner forearm and researchers will apply electrical stimulation for about 5min. Typically, people feel slight tingling or nothing at all during this procedure. This is a passive way of making you sweat on your forearm. Sweat will then be collected via a small disc applied to your forearm. Immediately following this, you will have your nude body mass measured and you will be instrumented with a lab-based sweat collection patch (large band-aid on the forearm), a Gatorade sweat collection patch on the opposite forearm, and the Hdrop sweat detection device on your left upper arm. the hDrop device is non-FDA approved device because it does not provide a medical diagnosis, but serves as an education and recovery tool. These devices will all be synced with electronic applications (phone apps) to assure data collection. You will then self-insert a rectal thermistor ~15cm past the anal sphincter to monitor core temperature throughout exercise (for safety purposes). You will also be fitted with a heart rate strap that goes around your chest. You will then be asked to enter the environmental chamber and exercise for 60min. The environmental chamber will maintain a consistent temperature (80 degrees F) and humidity (~45% relative humidity). You will be monitored for safety throughout exercise and you will be allowed to cycle (stationary bike) or run or walk (treadmill) at your own pace/intensity. Pace and intensity will be recorded during the first trial and matched for the second trial. Because fluid consumption may impair accuracy of sweat collection devices, participants will not be allowed to consume fluids during exercise.

Prior to each trial, participants will be provided with urine jugs and food/fluid logs to record food and drink intake for 24hr. They will be asked to log food/fluid intake. They will provide a small urine sample to verify hydration prior to exercise in the heat. If participants arrive dehydrated, they will be provided and asked to consume 16oz (a bottle) of water. Next, Participants will be seated, have 2 electrodes placed on their inner forearm and then get iontophoresis (direct current electrical stimulation) applied for about 5min. This is a passive way of eliciting a local sweat response. Sweat will then be collected via a small disc applied to their forearm. Immediately following this, participants will have their nude body mass measured and they will be instrumented with a lab-based sweat collection patch (large band-aid on the forearm), a Gatorade sweat collection patch on the opposite forearm, and the Hdrop sweat detection device on their left upper arm. These devices will all be synced with electronic applications (phone apps) to assure data collection. Participants will then self-insert a rectal thermistor ~15cm past the anal sphincter to monitor core temperature throughout exercise. They will also be fitted with a heart rate strap across their chest. They will then enter the chamber and exercise for 60min. The environmental chamber will maintain a consistent temperature (80 degrees F) and humidity (~45% relative humidity). Participants will be monitored for safety throughout exercise and they will be allowed to cycle (stationary bike) or run or walk (treadmill) at their own pace/intensity. Pace and intensity will be recorded during the first trial and matched for the second trial. Because fluid consumption may impair accuracy of sweat collection devices, participants will not be allowed to consume fluids during exercise. Exercise will be arrested if participants experience signs/symptoms of heat illness, get exhausted, or no longer want to continue. Following exercise, sweat collection devices will be collected and analyzed for sweat electrolyte concentration and/or sweat rate detection. Upon completion of exercise, participants will towel dry and have nude body mass measured again. They will be provided fluids and snacks following exercise while monitored for 15min post-exercise. Following this, they will be allowed to leave once they have been scheduled for their second trial. Following their second trial, they will be compensated for their participation.

Inclusion Criteria:

• Healthy exercisers
• No orthopedic injury
• No chronic conditions
• Able to exercise for 60min in the heat

Exclusion Criteria:

• Chronic conditions
• Not 18y or over 39y
• Taking medications that alter fluid balance or thermoregulation
• Current orthopedic injury

Deidentified data will be shared according to reasonable requests made to the corresponding contact here, or within peer-reviewed publications.