The Kidney's Response to Exercise in Heat, and the Impact of Vitamin B3 on This Response

To answer these questions, researchers will compare the chemical changes in each participant under progressively higher levels of heat stress, and while taking either vitamin B3 or a placebo. This clinical trial will occur in two stages. Participants may choose participate in stage 1 only, stage 2 only, or both parts of this clinical trial. During stage 1, participants will exercise using a stationary rowing ergometer in a hot and humid environmental chamber for three sessions, each session separated by about a week. * Each session, they will be asked to work out at a progressively higher intensity with climate conditions kept the same in the chamber. * More intense exercise produces greater heat stress, resulting in lower, moderate, and higher levels of heat stress exposure across the three sessions. * Researchers will see how chemicals in the blood and urine, along with physical measurements like heart rate and body temperature, change across these different levels of heat stress. During stage 2, participants will exercise using the same rowing ergometer in the same environmental chamber. They will do this for two sessions, each separated by about a week. * One of the sessions each participant will take vitamin B3, and the other session each participant will take placebo. * Heat stress exposure will be the same each session. * Researchers will again see how chemicals in the blood and urine, along with physical measurements like heart rate and body temperature, differ between sessions with vitamin B3 and sessions with placebo