Sweat test exposed hydration mistakes during my workouts

A 45-minute sweat test at the Gatorade Sports Science Institute in Valhalla, New York, found that while I thought I was doing fine, I was under-hydrating and under-fueling. The lab’s chamber matched hot, humid game conditions, and the wearable plus sweat analy

When the doors sealed shut and the chamber dialed in heat and humidity. I felt the usual comfort of experience slipping away. I’d trained for years in roller derby—New York summers, hours of effort, sweat that comes like clockwork. But the environment at the Gatorade Sports Science Institute wasn’t just uncomfortable. It was engineered.

The Institute’s environmental chamber can reach up to 104 degrees and 80% humidity to mimic hot-weather competition conditions. including those faced by the NFL and the US women’s national soccer team. During my test, it ran at 85 degrees and about 50% humidity. I was still pouring sweat. I just didn’t realize. until the measurements came back. how much I was falling short in the basics—water. electrolytes. and carbs.

The Gatorade lab sits about an hour by train from New York City. on the PepsiCo campus in Valhalla. New York. I wasn’t there to buy advice; the Institute works only with Gatorade’s partner athletes. including Caitlin Clark. Lionel Messi. and Venus Williams. Researchers analyze everything from metabolic rate to muscle power and mental function. using results to help athletes perform at their best.

My first shock wasn’t that I sweat. It was how the numbers lined up against my habits.

I started with a hydration assessment—the Institute’s “otherwise known as peeing in a cup” test—where my hydration level was determined by a simple color check. That part confirmed I was well hydrated at the start of the visit.

Then the tests got more precise and a little more personal. Behind a closed door, I stripped down for a precise body weight measurement. After that. I donned a sports bra and compression shorts and climbed into the Bod Pod. a capsule that measures body composition. including the ratio of fat mass to lean mass and muscle tissue. The goal was to understand how my body performs during exercise so the research team could tailor hydration advice based on how much I sweat.

The main event was a grand finale: a 45-minute cardio session in the environmental chamber. Before entering. I was fitted with a heart rate monitor. a strip of gauze to capture my sweat for later testing. and a Gatorade sweat patch—a high-tech. single-use wearable that analyzes how much sweat I’m producing and what’s in it.

I opted for a moderate jog during the required 45 minutes of continuous cardio. Researchers checked my heart rate and my subjective sense of how hard I was working, with bottles of Gatorade ready if I asked for a drink.

By the end, I was covered in sweat—about 34 ounces, according to the analysis. But I had only drank about 6 ounces during the test. The gap mattered.

As a result, I lost 1.8 pounds, about 1.3% of my body weight, while sweating on the treadmill. I felt classic symptoms of dehydration, including a dry mouth and chapped lips.

Tom Coughlin. a sports nutritionist not affiliated with Gatorade who works with pro teams and elite athletes. put it plainly: ideally. if you replace the fluid you lose through sweat. you shouldn’t lose much weight. Instead, I was in the early stages of dehydration, a common issue for athletes. Coughlin said. “Above 2% loss of body weight. you’re starting to get physiological impairments. and your body has to work harder to shuttle oxygen around the body. ” and he explained what that can look like on the ground. For me. it meant it felt harder to keep up the same pace. and if I were competing I’d start to slow down physically and mentally. with a tougher time making snap decisions or reacting quickly during gameplay.

The chamber didn’t just confirm I sweat—it confirmed how fast and how much I do.

Testing revealed I’m a heavy sweater. My high sweat rate means I’ll lose about 1.4 liters of fluid per hour of exercise. putting me at risk of dehydration for efforts longer than an hour. That’s especially relevant because my typical workouts, including roller derby practice, are often two hours long.

There was another detail waiting in the sweat: I’m “salty”—literally. I learned I have particularly salty sweat, losing a moderate level of sodium when I’m working out. Saltiness can vary widely from person to person, ranging from a loss of between 500 mg and 1,500 mg per hour. My rate landed at about 900 mg.

If you can’t test sweat in a lab or with a wearable, Coughlin said, one visible clue is salt marks on your clothes after sweating—an indicator you should up your sodium intake.

Sodium is one of seven key electrolytes, alongside potassium and magnesium, essential for maintaining fluid balance so muscles and nerves can function properly.

The reason this matters isn’t just comfort—it’s safety and performance. Drinking too much plain water without replacing electrolytes can lead to a rare but serious health issue called hyponatremia, which can cause headaches, nausea, cramps, dizziness, or, in extreme cases, death.

While I wasn’t in danger. the lab results showed I was still losing more electrolytes than I replaced with the few sips of Gatorade I took during my run. Coughlin said replacing lost sodium could help prevent a dip in performance that could compromise the bursts of speed and laser focus needed at practices and on game day. “Ideally, you want to maintain that balance you started out with,” he said.

Before this visit, I’d already built a habit around salt. Adding a pinch of sea salt to a tall glass of water had been part of my morning routine. I previously consulted sports dietitian Angie Ashe. and she approved. telling me that a little salt in my water or a homemade electrolyte drink could help improve my hydration as an athlete.

Now, the DIY plan is bigger. For an electrolyte recipe, Ashe recommends a mix of sea salt, coconut water, orange juice, and lemon juice to top up sodium, potassium, and magnesium.

Water and sodium weren’t the only gaps the lab found. My carb intake during the test was also far too low.

For the final missing piece in my personal recipe for workout success: sugar. Coughlin’s view matches a familiar athlete logic—refined carbs can provide quick fuel for athletes who need energy without giving digestion too much to handle. During my sweat test, I had a measly 3 grams of carbs. For my moderate pace, the researchers said I should have been consuming between 10 and 30 grams of carbs per hour.

Coughlin’s guidance runs in the same direction. During a higher intensity activity like roller derby. athletes burn through fuel faster. making carbs even more important to have on deck. Endurance athletes. he said. can use between 60 grams of carbs per hour and up to 120 grams or more for athletes like elite marathoners.

That’s why the takeaway wasn’t just “drink more.” It was that my hydration and fueling strategy didn’t match the reality of my sweat and my workout length.

Weather, humidity, and the type of workout all influence how much you sweat, so having a personalized “sweat profile” helps fine-tune hydration. My plan for the next practice is concrete: packing gummy bears.

I didn’t walk away from the test feeling like I’d totally failed. If I’m grading myself, I’d give it a C—because I wasn’t starting from zero. But the Institute made it clear there was plenty of room to change.

I learned I should:

Drink more water overall during exercise.
Don’t drink plain water alone—mix in some electrolytes.
Add more carbs around a workout, especially for long, high-intensity sessions.
Start drinking (and fueling) before I feel tired and thirsty.

If you often feel run-down during and after workouts, that can be a sign you’re under-hydrated or under-fueled. Coughlin said it’s a common issue during exercise and that the best approach is to be proactive before symptoms start. “The majority of athletes are underfueling. I see that in my own practice,” he said. “Anything over an hour, that’s when you burn through, and energy starts to drop. But elite marathon runners don’t wait for an hour; they’re fueling every 20 minutes.”.

A sweat patch, a chamber, and a few numbers ended up rewriting my routine. Not because I’m new to sweating—I’m not. Because the lab showed I’d been treating it like a background constant, when for performance it’s a cue that something has to be replaced, measured, and rebuilt in time.

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