Hydration status during exercise is often determined by measuring body mass change, fluid intake and urine output. However, obtaining these measurements can be an invasive, time-consuming process. Hydration status may be detectable by analyzing blood flow patterns of the superficial (just under the skin) blood vessels. Wearable devices are now abundant among the general population, and despite attempts from several groups, a hydration status metric based on noninvasive wearable device metrics has not been developed. With wearables, a light source connected to an optical sensor transmits and reflects light through the body. The light sensor detects absorption of the light based on wavelength measurements of the detected light. Absorption of specific wavelengths of light energy is dependent upon the amount of oxygenated blood in the vessels. When the vessels expand and relax, the amount of blood volume in the observed tissue increases and decreases potentially causing a shift in the photoplethysmography (PPG) wave detected by the wearable. The shift in the shape of the PPG wave may be detected in a way that indicates the relative change in tissue hydration levels. However, to our knowledge, no wrist worn device that utilizes PPG has been successfully able to predict hydration status. Therefore, this study aims to utilize photoplethysmography (PPG) technology in a wearable device to accomplish this approach to hydration monitoring.

Inclusion Criteria:

• Study subject is 18-45 years of age, inclusive
• Subject is male or female
• If female, subject is not pregnant, planning to get pregnant, or currently breast feeding
• Subject is willing to avoid alcohol consumption 24 hours prior to visit(s)
• Able to speak, write, and read English
• Provision of written consent to participate
• Subject is not taking medication that may interfere with the study, as indicated on the general health questionnaire (GHQ)
• Subject has no health conditions that would prevent completion of the trial, as indicated on the GHQ
• Subject is willing to fast overnight (no food or beverage, only water, ~8- 10 hours)
• Subject is willing to refrain from vigorous exercise for 24 hours
• Subject is willing to eat the exact same food the day prior to each visit to the testing site
• Subject is willing to undergo fluid restriction to induce dehydration
• Subject is willing to wear a wrist worn wearable device for the duration of the study

Exclusion Criteria:

• Subject has participated or currently enrolled in a clinical trial within the past 30 days
• Subject has participated in any PepsiCo trial within the past 3 months
• Subject has a condition or is taking medication that the investigator believes would interfere with his/her ability to provide informed consent, comply with the study protocol, which might confound the interpretation of the study results, or put the person at undue risk, as indicated on the GHQ
• Subject is employed by, or has a parent, guardian, or other immediate family member employed by a company that manufactures any products that compete with any Gatorade product. If subject is unsure if a company would be considered a competitor to Gatorade, they will be asked to please let the study investigator know the name of the other company and the nature of their relationship to that company before they sign the informed consent.
• Subject has a health condition or is taking medication that can be worsened by fluid restriction, as indicated on the GHQ