Nix Biosensor takes the guesswork out of hydration

Athletes always need to be conscientious of their hydration, and those playing endurance sports like tennis require even more attention to this detail. As little as a 2.5% loss of bodyweight through fluid loss, which may not produce any noticeable symptoms of dehydration, can cause a significant decrease in performance during high-intensity exercise, as well as lead to muscle fatigue. Sweat rates and electrolyte loss can vary greatly depending on the individual and playing conditions, which makes a one-size-fits-all approach to hydration an imperfect solution.

That’s where the Nix Biosensor can help. Dubbed a “portable hydration lab” by the brand, it continuously measures sweat and electrolyte loss in real time as you exercise. It streams this data to the accompanying app on your smartphone while you’re in action. Not only does it analyze and store the information, but the app can be set up to notify you when to consume fluids at certain intervals to stay hydrated.

The sensor is designed to be worn on the outside of the biceps. It's virtually weightless and stays attached with a latex-free patch that sticks on like KT Tape. The pod twists into the patch and sits around the cuff line of a short sleeve shirt. During numerous court sessions I incurred no security issues or any noticeable intrusion when playing. The only time the patch showed any peeling was after getting jostled during a pick-up hoops game. When not in use, the pod sits in a charging case.

Once the app is opened and synced with the sensor, you can set up the workout. It asks whether you’re running or cycling, indoors or outdoors, and your mile pace. As of now, there are no sports settings, so you can select the “other” catch-all category. However, Nix worked with me to find a pace (12 min/mile) that better replicates the stop-and-go nature of tennis. They’re in the process of expanding the app to include a more varied selection of training modalities.

The app uses your location—I actually couldn’t connect the sensor to my phone via Bluetooth until I enabled location—so it can incorporate atmospheric conditions to help with data accuracy. You can also input what drink you’ll be hydrating with, from a list of possibilities, or you can enter your own custom beverage. There’s an option to set notifications to alert when it’s time for a drink by either time or fluid loss. Even if you don’t opt for a reminder, the app still displays recommendations on replenishment.

Once you start your workout, it can take 20-plus minutes of activity for enough sweat to accumulate in the sensor before any readings appear. That’s why it’s recommended to use the sensor only on workouts of at least 45 minutes, which is not an issue for most tennis matches. The changeover on odd-number games serves as the perfect opportunity to check the app to see if it’s time for a swig. It can also sync with Garmin and Apple watches, but I only experimented with my smartphone.

The app seems to work better when it’s front and center. If you background it for another app, the notifications don’t register or lag. Otherwise the prompts work fairly smoothly. I don’t have measurement markings on my beverage bottle, so when I got a message like “Drink 4 oz,” I’d take a couple of gulps. Swipe up and you’re hydrated.

After a session is completed, all the data is transferred from the sensor to the app for a more thorough analysis. This process ranged from straightforward to somewhat sluggish. It always eventually worked, but sometimes I needed to reboot the app to complete the process. Being new technology, there are some growing pains, which is why it’s constantly being updated to address any bugs and connectivity issues.

In addition to its real-time support, the app takes the information from workouts to create an overall sweat profile. This is the catnip for fitness junkies who seek metrics—counting steps, tracking sleep, heart rate variability—to scrutinize their conditioning. The three major markers are sweat and electrolyte loss rates—how much you’re losing of both per hour—and sweat composition. This lets you know on average how much you should be consuming during workouts. According to the Nix website, the sensor’s cumulative fluid loss reading is 82.8% accurate when compared to the gold standard: change in nude body mass.

Another cool feature is the app has a chart of several dozen popular electrolyte drinks, and will recommend one based off the user’s sweat composition. For instance, my sweat composition averaged 44 mg/oz. I typically drink Liquid IV when I play, which has a slightly higher concentration of electrolytes—not by much and I often water it down. The app proposed Gatorade Gatorlyte as my suitable match.

All this information does come with a price. The pod costs $129 with four patches included. The patches are single-use only and a four-pack of refills is $25. It could become expensive if used frequently. However, the sensor is really not meant to be worn with every workout. It’s a way to monitor fluid replenishment under different conditions and over time, or to use as a gameday coach for a daunting race or match.

So if you’re the type of player who really sweats the details—you knew that was coming—the Nix Biosensor can ensure your hydration requirements are as finely tuned as your forehand.