Sweat can be irritating and gross, but we all know it plays a major role in our body’s ability to cool itself down in the heat. Unfortunately, dripping sweat also means you’re losing vital fluids that benefit athletic performance and overall wellness.
This is why you need to know about the concept of sweat rate: the amount of sweat lost during a one-hour period of normal exercise.
To avoid dehydration (or the opposite, overhydration), you should focus on replacing these fluids at the same rate you lose them — and that requires an understanding of your own personal sweat rate.
How to Calculate Your Personal Sweat Rate
Determining the rate at which you lose sweat can be done with just an hour of exercise and a scale, according to Dr. Daniel V. Vigil, associate clinical professor at UCLA’s David Geffen School of Medicine and team physician for UCLA’s women’s soccer and softball programs. Start by weighing yourself in nothing but your birthday suit just prior to your workout. A digital scale works best for this, as it will show more detailed numbers (Think: 155.4 vs. 155). For more accurate results, make sure your bladder and bowels are empty before you step on the scale.
Then, exercise for a one-hour period in normal (nonextreme) conditions. Vigil says it’s important to choose a type and intensity of exercise that mimics an activity you commonly perform or are trying to accomplish.
“If you’re training for a marathon, run at the pace that you’re going to run the marathon,” he says. “You can swim, ride a bike, run or do whatever exercise you’d like.”
Immediately after your workout, dry off as much as possible and weigh yourself again, in the nude and using the same scale. The difference between your weight before and after exercise is how much sweat you lost during that time period. Convert your sweat loss to ounces, which directly correlates to how much fluid you need during a workout.
For example, if you lost 1.5 pounds (24 ounces), your sweat rate is 24 ounces per hour. This tells you that you need to drink that same amount each hour to stay properly hydrated.
Vigil recommends not drinking or eating during this test — but if you must, record the amount of fluid or food you take in, and add that to your weight difference. (Using the above example, if you drank 10 ounces of water during your workout and still lost 1.5 pounds, your sweat rate would be 34 ounces per hour.)
How Much Sweat is Normal?
While everyone sweats at different rates, a number of factors can determine how quickly your shirt will become sopping wet. These factors include fitness level, exercise type and intensity, recent changes in weight, temperature and humidity.
More sweat isn’t necessarily a bad thing. According to Vigil, the typical sweat rate for healthy people of average size is around 17 ounces per hour. Contrary to what you might believe, the fitter you are, the more you will sweat. Fitter people have the ability to work harder and longer, often leading to higher internal body temperatures. Our sweat acts as a mechanism to cool us down when things get hot, so it makes sense someone working harder would see more sweat.
Understanding exactly how much sweat your body produces will allow you to stay properly hydrated and perform at your best — a formula for success at any level.