Garmin patent hints at hydration & hematocrit tracking

A new Garmin patent details an optical sensing system that can go beyond heart rate and SpO₂. It outlines how watches might one day measure hydration, hematocrit and even tissue oxygen saturation.

Pulse spectroscopy could bring new health data to Garmin watches

We’re used to seeing Garmin watches measure heart rate and oxygen levels. That’s been standard for a while now. But a recent US patent shows the company is thinking bigger. This one talks about something called “pulse spectroscopy” and how it could unlock several new metrics you don’t see on wearables today.

As first reported here, the patent (US 12,343,124 B2) was published by the US Patent Office a few days ago. What caught our attention can be found a number of pages in, and it’s the list of biomarkers the tech aims to measure. Hydration levels, hematocrit, and tissue oxygen saturation are all mentioned. None of these are available on current Garmin devices. But if this system becomes reality, that could soon change.

What the tech actually does

Pulse spectroscopy works by shining light at different wavelengths into your skin and analyzing how that light scatters or gets absorbed. It’s a more advanced version of the optical tech used in current smartwatches. The trick here is that the system adjusts both the wavelength and intensity of the light dynamically. It also adapts to the person’s skin tone, wrist thickness and movement.

That extra flexibility makes it easier to pull out specific signals from deeper layers of tissue. So instead of just getting a heart rate, the system can estimate concentrations of different molecules in the blood. That’s where metrics like hematocrit or hydration start to become possible.

The patent also describes how the device can alternate between different “illumination cycles” during rest or activity. It’s constantly filtering noise from motion and other sources, which is crucial if you’re trying to measure something subtle like tissue oxygenation or fluid shifts.

Why this would be useful

Hydration tracking is the one that has me most excited. A handful of watches dishes out hydration figures based on sweat loss guesstimates or activity logs. But those are rough estimates – pretty useless stuff. Then there are patches that you attach to your forearm. These are more precise as they measure actual sweat loss. But the patches are messy and typically single-use.

The Garmin tech would offer a direct measurement from a watch sitting on your wrist. Something based on actual light absorption patterns in your skin. That would be useful in heat, during long workouts, or for anyone who tends to under-drink without realising it. The tech would work around the clock.

Hematocrit is a bit more niche, but potentially useful for endurance athletes. It tells you the proportion of red blood cells in your blood. Low levels might suggest you’re iron deficient or not recovering well. High levels can indicate dehydration or even overtraining. You don’t need that data every day, but knowing your baseline and seeing trends could be useful for planning training blocks or flagging recovery issues early.

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Tissue oxygen saturation is a local measurement. Unlike SpO₂ which reflects general oxygen levels in arterial blood, this tells you how much oxygen your muscles are actually using. It’s something that can shift fast during exercise. You see similar data in lab testing setups with muscle oxygen sensors strapped on the thigh or arm. Having that baked into a wrist-based device would be a big deal for anyone who wants to track real-time strain, recovery, or HIIT workouts.

A long way from retail, but the direction is clear

To remind, this isn’t the only Garmin patent that mentions pulse spectroscopy. Just over a month ago we dug up another one which mentions glucose measurements from the wrist. What is actually outlined is a method to estimate HbA1c. The tech would calculate a user’s average blood glucose levels over a period of months, not minutes. So something that follows trends.

All of this points to an exciting future as far as health tech. Of course, patents don’t always lead to features. But Garmin has been laying the groundwork for deeper physiological sensing for a while now.

I wouldn’t expect any of this to show up overnight. But it does tell us where things might be heading. Hydration and tissue oxygenation tracking make sense in a future Forerunner or Fenix. Especially if they can pull it off with optical tech and without the need for disposable sensors or extra gear.

For now, these are patents. But they are worth watching.

*This article first appeared on Gadgets & Wearables, where the story was originally reported.

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