As a self-proclaimed unladylike runner, it probably comes as no surprise to you that I’m a profuse sweater. As in, I’m pretty certain I sweat more than the average human being while exercising. If you’re lucky unlucky enough to see me running in the hot summer months of July and August, you’ll surely believe I’ve been swimming laps in my running clothes as opposed to logging miles on the pavement. I can wring my tank tops out like wet wash cloths after nearly every long summer run. But the moral of this story is not that I’m a gross, sweaty, stinky runner (although true); it’s that fluid intake in hot weather is critical.

Did you know that runners can easily lose 2 to 3 liters of fluids per hour due to sweat?

Imagine how consecutive days of sweating through hot weather running and hard workouts can affect us. It can lead to significant losses of electrolytes, which help us regulate our fluid levels, contract our muscles (cramping may be caused by the loss of certain electrolytes) and transmit impulses to our nerves.

We all sweat at different rates, so it’s important to know how to calculate your sweat rate to ensure you’re getting the right amount of fluids during workouts that last more than an hour.

How to Calculate Your Sweat Rate

To calculate your sweat rate, follow these steps:

• Immediately before your run, weigh yourself (while naked) on a scale.
• Go for a 60-minute run in hot weather. (Don’t do this run naked. Be sure to put on clothes.)
• After your run, weigh yourself again (while naked).
• Your sweat rate is the amount of weight you lost during the 60-minute run.

So what does your sweat rate mean?
For every pound you lose while running, you need to consume about 32 ounces of water/fluid per hour. For example, if you lost one pound during your run, you need to drink 32 ounces per hour while exercising. If you lost 1.5 pounds, you need to consume 48 ounces of water per hour.

Average sweat rate is commonly 32 to 48 ounces with a loss of about 1,000 to 1,500 milligrams of sodium per hour, making the consumption and replenishment of electrolytes from a sports drink or electrolyte replacement tab/powder important. I love this article by Jesse Kropelnicki on the Brooks Blog that talks in depth about electrolytes and their importance during running.

A water loss of 2 percent body weight will begin to impact your performance, your mood and may increase your risk of heat-related injuries. You’ll probably lose your appetite too (which is a common feeling after running a marathon or hard race). If you lose 5 percent of your body weight from water, you can expect a 30 percent decrease in your performance, which can also be a threat to your health.

So the next time you’re on your run and you look like you’ve spent the past hour in a pool instead of out on the road, remember that all the sweat you’re losing must be replaced with fluids to help you maintain hydration and a healthy electrolyte balance.

Note: The advice in this post is from learnings about fluid intake from the North American Academy of Sport Fitness Professionals, the organization I have received my marathon coaching certification from.

Are you a heavy sweater? What is your favorite fluid of choice to keep you hydrated and your electrolytes balanced while running?