in a world In a place where unmanned spaceships land on Mars and artificial intelligence can read your mind, one would think someone would come up with an accurate way to gauge how much an athlete should drink while exercising. Rehydration or replacement of fluids lost through sweating, exhaling and passing waste is essential. When dehydration leads to weight loss of 2 percent or more, the body spins out of control, with increased cardiovascular stress, decreased aerobic capacity, and impaired thermoregulation. After losing 12% of body weight due to dehydration, a person dies.
It is rare for an athlete to exercise so dehydrated that he dies. But it’s also odd to consider that, with such an important physiological need, many athletes rely on thirst as the definitive guide to how much fluid they should drink during exercise. The problem with this built-in system is twofold. By the time your brain registers that you need water, your body is usually already dehydrated. Plus, it’s easy to quench your thirst before you’re fully hydrated.
Outside of the lab, the most accurate standard for determining fluid loss in athletes is naked weights before and after activity. (For every pound of body weight lost, you should consume 16 ounces of water.) But this method doesn’t help runners determine how much fluid they’re losing during a 16-mile marathon.
Cyclists can rely on GPS computers with drink alarms that flash every 15 minutes to remind them to take a sip from their water bottle. Runners and fitness enthusiasts can wear smartwatches with hydration sensors, such as the Apple Watch, that use electrodes attached to the skin to measure the conductivity of the wearer’s sweat. This can determine the concentration of electrolytes (or lack thereof) in the sweat, which helps determine the user’s hydration level. There’s also a $25 gadget called the GX Sweat Patch, sold by Gatorade, a single-use biosensor that, when applied to the inner left forearm, measures a user’s sweat rate, fluid loss and Sodium loss. When this data is transferred to the companion iOS app, it serves as a guide for the athlete’s future performance.
However, until recently, biosensing technology capable of analyzing the composition of an athlete’s sweat to provide personalized, real-time hydration recommendations while they were exercising remained out of reach because the sensing technology wasn’t affordable enough to be built into consumer products.
Photo: Nix Biosensors
In December, a Boston startup founded by Harvard Business School grad and marathon runner Meridith Cass unveiled the Nix Hydration Biosensor, the first wearable sensor that promises to give athletes real-time sweat science. Cass, also a former college basketball player, began thinking about using biosensing to measure hydration after she struggled with her body’s responses to heat and humidity while training for a marathon. “I’ve had some long runs where I feel really sluggish,” she says, “and I wonder, ‘Is the hydration sensor okay? Would anyone else find it helpful besides me?'”
Here’s how the Nix works: When attached to the bicep (via a protective membrane on the bottom of the patch, about the size of a round orange slice), the patch measures sweat distribution locally on the body and extrapolates it to The entire area of the body is calculated algorithmically. As sweat drips over the electrodes on the bicep patch, the patch measures the amount of sweat twice along its flow path. By comparing data from these two locations, the sensor can determine how fast fluid is moving through the body. When connected to the iOS companion app via Bluetooth, the sensor relays hydration notifications to the phone at user-defined intervals. The focus is on keeping athletes within 1% of their starting body weight (or 1% dehydrated) while exercising to avoid the serious handicap that dehydration brings.
