The state of sweat testing

If you wipe away your sweat without a second thought, you could be wasting a powerful tool that can tell you what your body needs to perform at its best, says Rolando Garcia, manager of the Columbus Circle location of E at Equinox in New York City.

Elites and pros have armies of scientists who collect their sweat and send it to sophisticated facilities for analysis. Thanks to consumer tests from companies like Levelen and Precision Hydration, everyday athletes now have the opportunity to harness its power, too.

Here’s what your sweat says about your body and why you should consider shipping it off to a lab.

What can sweat tests tell you?

People perspire at vastly different rates, says Sandra Fowkes Godek, Ph.D., co-founder of Levelen and a professor of sports medicine at West Chester University in West Chester, Pennsylvania. Several factors play a role, like genetics, diet, weather, gender (men generally perspire more than women), and weight (larger typically means sweatier).

These tests reveal exactly how much fluid and sodium you lose when you exercise so you can figure out how you should replenish your body.

Why does this matter?

This information can help you develop a personalized electrolyte and hydration plans, which are both key for having a solid workout. Knowing how much fluid to replace is important for athletes of all kinds, whether you’re spending hours in the heat or going to the gym daily.

It’s also helpful if you’re training in the morning before work, says Kelly Barnes, MS, a senior scientist at the Gatorade Sports Science Institute in Barrington, Illinois. Studies show that losing more than two percent of your body weight in fluids can impact your memory, mood, and reaction times. Failing to replace lost water weight can make you less focused and more prone to errors than if you hydrate properly, she says.

On the flip side, overhydrating can lead to hyponatremia, which occurs when the sodium levels in the body drop too low. As a result, cells retain water, which causes swelling that can interfere with your heart, kidneys, liver, and other organs. (Garcia developed the condition when he drank a gallon of water a day and ate a low-sodium diet as a competitive Brazilian Jiu Jitsu fighter.) In short, sweat tests can help you find your hydration sweet spot.

Who should get their sweat tested?

Pros of all kinds (football players, triathletes, and marathon runners alike) are incorporating sweat testing into their overall nutrition and recovery strategies. They’ll often do them repeatedly in different conditions to see how things like humidity and heat affect their sweat, Godek says.

Even if you’re not an elite athlete, these tests can help you prep for a big race or competition. It’s particularly important for people who train daily (if not more) and who compete for long periods of time, like during a tournament, or with minimal recovery in between sessions.

If you frequently have symptoms of dehydration or electrolyte imbalance like cramps, headaches, or unintended weight loss, a sweat test can help you figure out how to minimize them, Godek adds.

What do these tests entail?

UK-based Precision Hydration does in-person testing at about a dozen locations in the US and a few abroad. You can also fill out their online questionnaire, which uses an algorithm based on past results to give you semi-personalized feedback.

Levelen's at-home kit is complete with tweezers and a sweat patch, which you stick on your forearm while you workout. After 30 to 40 minutes or once it's drenched, you remove it with the tweezers to avoid contamination. Then you send the sample back along with with details about how much water weight you lost during your workout, how long you wore the patch, and what you drank during that period.

Still, contamination is hard to avoid even for experienced scientists, and the process of taking sweat from a square-inch or so of skin and applying the results to the whole body is complicated, Barnes says. For the best results, Garcia recommends doing a sweat test consultation with a Tier X coach at Equinox or another professional. A doctor can use your results to spot other health hazards and make changes to micronutrient levels in your diet, he adds.

Are there other ways athletes can learn more about their sweat?

Yes and no. Try this DIY technique: During an hour-long session, keep track of exactly how much you drink and whether you relieve your bladder at all. Weigh yourself nude (or close to it) before and after the session, Barnes says, then plug the numbers into a hydration calculator, like the GSSI’s, to calculate your sweat rate. Aim to replenish about 65 to 70 percent of what you lost within an hour post-workout.

Sweat comp is tougher to gauge on your own. If you see white streaks on your clothes or salty crystals on your skin, you’re probably a salty sweater, though taking a test is the only way to know for sure.

Even armed with this information, you’ll have to experiment before you find the best hydration routine, Barnes says. If you lose a lot of salt, she recommends adding a packet of Endurance Gatorlytes, with 780 milligrams of sodium and 400 milligrams of potassium, to 20 ounces of Gatorade (you need carbs to absorb the electrolytes) and drinking it during and after your workout. Note how your body feels on this regimen (like if you have fewer cramps) and adjust accordingly.

Levelen and Precision Hydration offer drinks with more electrolytes. If you take their tests, the results will give you specific recommendations.

What’s next?

Scientists are working on wearable sensors to monitor sweat rate and electrolyte levels in real time. They’re also testing other strategies that close the gap between the gym and the lab. (Think of them as the sweat-testing equivalents of farm-to-table eats.) “We’re looking at all avenues to see how we can make it easier for athletes to do this on their own,” Barnes says.

She envisions a future in which athletes can get readouts to their phones telling them exactly what they need to replenish and when, taking all the guesswork out of the hydration equation.