When I work with any athlete, one of the first questions I ask is, "what is your sweat rate?" Ninety-five percent of the time, I get a blank stare. When creating a performance nutrition plan, knowing your sweat rate is critical to make sure fluid replacement during exercise is adequate (but not too high). Here is why.

Water plays major roles in the body at any given time, but especially during exercise. During exercise, water inside your body cools your core and muscles, keeping you from overheating too quickly. This helps you perform stronger and longer. In addition, water transports nutrients to your muscle for use in exercise metabolism and then cleans up by transporting metabolites away from your muscle to be filtered and excreted. Water plays a key role in preventing dehydration, which also keeps the athlete mentally “on” throughout the workout. Finally, water acts as a cushion to your organs to protect them in case of impact during sports.

What I refer to as a sweat rate is defined as exactly how much water an athlete loses per hour of exercise. It is important to know your number because sweat rates vary widely from athlete to athlete. Females generally range from 2-5 cups per hour and males range from 4-7 cups per hour.  However, variables such as air temperature, humidity and amount/type of clothing can change sweat rate day to day. Once I know an athlete's sweat rate that tells me how much fluid per hour we need to replace during exercise.

To figure out your sweat rate, pick a workout that is at least one hour long. Weigh yourself before and after that workout. Do not pee during the workout (unless you want to measure it), and keep track of how much fluid you take in during that workout. After the workout ends, take a look at how much weight you lost compared to how much fluid you drank. If your weights are about the same before and after, the amount of fluid you drank matched how much fluid you lost in sweat. If, however, your weight dropped during the workout, you did not drink enough fluid and need to increase your intake next time. By using this simple method, you can easily estimate your sweat rate. When doing this test, it is a good idea to note temperature and humidity during the test for future reference. Be sure to do separate biking and running tests, as most athletes have a different rate for each.

So, get to work! Figure out that sweat rate so you can replace fluids adequately to fit your individual needs this season.

Kate is the owner of RDKate Sports Nutrition Consulting, based out of Naperville, Illinois, where she offers expertise in sports nutrition, eating disorders/disordered eating, intuitive eating and weight management for sport. Katie holds a master’s degree in nutrition with an emphasis in exercise physiology. She is both a registered dietitian and one of only 550 RDs in the United States to be board-certified as a specialist in sports dietetics. As a runner, triathlete, snowboarder and rock climber, Katie understands the physical and mental challenges of being a top athlete. Katie has previously consulted with NCAA Division I and Division III, NFL and NBA athletes; she truly brings both her knowledge and experience to the table as sports dietitian. Katie is available for individual consulting, team talks and group seminars. Visit her website at RDKate.com; from there you can navigate to her weekly blog, Eat to Compete, and connect with her on Twitter or Facebook. Contact her directly at YourRDKate@gmail.com.

The views expressed in this article are the opinion of the author and not necessarily the practices of USA Triathlon. Before starting any new diet or exercise program, you should check with your physician and/or coach.