Smartwatches are constantly adding “lifesaving” technologies like fall detection, emergency calls, AFib alerts, and the latest Pixel Watches heart rate loss feature, all to keep you safe. But there’s also a less flashy, more common concern that most watches address as an afterthought: tracking hydration and sweat loss.
I’ve wanted better hydration for watches for a while, but last weekend news broke of 35-year-old runner Bobby Graves dying of cardiac arrest after finishing the Disneyland Half Marathon last weekend — a day after self-diagnosed heat exhaustion in 100-degree heat. — brought it to the forefront of my mind.
This man was my age, had run several half and full marathons before and was not at an age where people would worry about heart health. Perhaps the medical report sheds light on extenuating circumstances, but there’s a reason why an expert quoted by SFGate is warning people to “make sure you’re hydrated” in hot weather.
Smartwatches have tools to estimate sweat loss due to exercise; Samsung even claims it’s clinically accurate. But most other brands (besides Garmin) ignore it, and those who do follow it don’t do enough about it.
I’d say it’s past time for hydration to become a priority for fitness brands. Excessive heat only gets worse over time, and watches need to be prepared for it.
Keeping track of hydration is as simple as possible
Both Wear OS and WatchOS have some water tracking apps like WaterMinder and Waterllama. Samsung’s One UI Watch has a first-party Hydration tile, and Garmin watches let you download hydration tracking at a glance from the Connect IQ store.
They differ in appearance and niche features, but they all work pretty much the same way: you open an app or tile and tap a button to say you drank a cup of water. The screen shows how much fluid you have left to drink that day. You can also schedule regular reminder pop-ups to check if you’ve had a drink.
It is useful enough in everyday life! But this daily water reminder doesn’t take into account context, like how hot it is or whether you’ve exercised; you need to change the target yourself. And the combination of hourly reminders to drink and exercise can be so annoying that most people ignore or turn them off.
Some fitness watch brands like Coros and Polar allow you to set reminders to refuel or rehydrate during workouts, but at pre-set intervals; again, there is no context as to how much water or electrolytes your body actually needs.
Ideally, the watch would detect when the user has sweated (or is sweating) more or less than usual, and dynamically recommend that the person drink more water to avoid problems related to dehydration and heat exhaustion.
Accurate sweat tracking IS possible with smart watches
Earlier this month, Samsung boasted that a University of Michigan clinical trial proved how accurate its Galaxy Watches are compared to medical heart rate (90%), VO2 Max (82%) and sweat loss (95%) sensors. That’s pretty much what I expected from a wrist-based optical HR sensor, but I was surprised by the sweat accuracy.
Samsung doesn’t track your sweat loss directly. It estimates “based on your body size, age, gender, and exercise intensity, including heart rate, ambient temperature, and other conditions.” I had always used my Galaxy Watch Ultra’s post-run sweat loss numbers as a guess, but apparently that’s an educated guess.
The only one direct A consumer anti-sweat tool that I know of is the Nix Biosensor. It sticks to your bicep and sends your sweat down an “inlet” with electrodes at each end, calculating its “velocity” to determine your sweat rate. It then extrapolates how much sweat the rest of the body is losing because different parts of the body have different sweat rates.
The Nix sensors are potentially useful for serious athletes and I plan to test them for a future column. But they are niche and worn only for exercises; we need regular everyday wearable smartwatches to be the authority on sweat.
The Pixel Watch 3’s cEDA sensor can detect “tiny changes in your skin’s sweat levels” for stress data, but I don’t think it’s designed to track overall sweat loss. Apple patented a sweat sensor that “measures the amount of fluid lost over a period of time” and even shows the rate of sweat loss in real time, but the patent doesn’t guarantee the company can make the concept work in real life.
For now, I’m happy to see more brands emulate Samsung and Google by using their standard heart rate and body data to estimate sweat loss after a workout. In the end, however, they have to go even further, in line with Apple’s patent.
Imagine: Let’s say you’re running a half marathon with the Galaxy Watch 7 in warm conditions. During your run, the data screen shows you in real time how much sweat you estimate you’ve lost, perhaps calculating a new total every few minutes or every mile. At certain thresholds, perhaps every 500ml of sweat loss or a customizable number, it can buzz your wrist to indicate you need to refuel soon.
If your body sweat rate slows down during a run, this is a serious sign of dehydration. The Galaxy Watch will alert you to stop and rehydrate or seek medical attention immediately, just as it would alert you if it detects an arrhythmia or low heart rate.
Once you’ve crossed the finish line, the watch will give you an estimate of your total sweat loss, just like it does now. But it also automatically adds the total amount of sweat you lost to your Hydration plate. Samsung advises you to “replace 150% of what you lose in 1-2 hours” so I’d assume that could easily multiply the total sweat loss of your workout by 1.5 and add fluid ounces to that.
Then it can send post-workout notifications one and two hours later, reminding you to log your water totals in the hydration pane to confirm you’re fueling up properly.
This is my vision of how it could work. And ideally, the sweat sensor wouldn’t only activate during exercise, but measure sweat continuously (like the Fitbit cEDA sensor) and start monitoring more frequently when you hit a certain sweat or heart rate threshold, or when your local weather and humidity are particularly important. high.
This would be useful for farm workers, deliverymen in hot vans, construction crews and many other outdoor workers, not just athletes.
Garmin comes closest to my idealized vision of useful sweat loss data, though it buries the Hydration Tracker tool in Connect IQ as if in shame. Once you’ve downloaded it, you can go to the app’s settings and turn on “Goal auto-increment” to add your workout sweat loss to your regular daily goal.
I tested it with my Garmin Forerunner 965 and it added six cups of water to my total for the day after sweating so much during a 10K on a hot day. But Garmin underestimates my sweat compared to Samsung and not following his advice to “replace 150%”. I always need more water than the Garmin suggests, so this is more useful in theory than in practice.
For the sake of runners who are trying to push through and finish races when their bodies are trying to finish them, fitness watches need to be ready to step in at any moment, not just alert you at the finish line that you’ve sweated. river.
Instead of relying on algorithms, they’d be better off starting to directly measure how much your body sweats to get custom data, as reasonably accurate brands like Garmin and Samsung give mixed results with heart rate estimates. For sweat data, warnings about drinking water or electrolytes seem more relevant.
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