Sweat Rate Formula: How much should you drink on the run

Sweat Rate FormulaWith the temperatures rising, this is the perfect time to tighten the screws on your hydration. As you start training for fall marathons, you should start using your Saturday (or Sunday) long runs to figure out how much you sweat, and how many fluids you need to take during your run to negate the effects of dehydration.

Some experts say you should drink as much as you sweat – if you sweat 48 ounces in an hour, you should drink 48 ounces of fluid in an hour.

Other experts, like those over at The Science of Sport,  say you should only drink when you are thirsty, and that your body knows how many fluids you need; our ancestors used to run miles and miles and miles for food and survival and they did it without a sweat rate calculator. They drank when they were thirsty and but for the ocassional lion attack, they were okay.

So what’s the right answer? I’m not sure. What I do know is that running and everything about it is an experiment of one. What you eat the night before a long run or race may not work for me.

For Nerds: Sweat Rate Formula

And so it is with hydrating on the run.

Experts say your performance starts to suffer in a run or race when you lose anywhere between 3 to 5 percent of your body-weight in sweat. For many of us, that’s any run longer than an hour during the late Spring and Summer months.

Wherever your beliefs lie, it’s important to know just how many fluids your body loses during a run. So I’ve provided a neat little sweat rate formula (left and below) to help you nail down your fluid losses. For instance, if you lose 3 pounds during a 60-minute run, (and you don’t consume any liquids), your sweat rate would be 48 ounces.

Now, there is no way you can replace all the fluids you lose on the run. However, knowing your sweat rate, you can try to drink enough fluids so that you don’t lose more than 3 to 5 percent of your body-weight.

Use the sweat rate calculator on this page to figure out how much sweat you lose in an hour and adjust your drinking on the run rate accordingly.