A New Fitness Tracker That Actually Uses Science

The days of counting steps are over. The Mio Slice looks at your heart rate to give you an overall health score based in science.

The Mio Slice. (Brent Rose)

Most fitness trackers are nothing but glorified step counters. They set an arbitrary goal, and when you’ve taken enough steps to meet it, you are proclaimed healthy. This is dumb. Different steps require different amounts of energy, depending on incline and altitude, as well as the height, weight, and age of the person stepping, and many other factors. Heart data is a far better indicator of your health and exercise levels, and there’s finally a wearable—and a metric—that puts it first.

The Mio Slice is the first wearable to use the proprietary Personal Activity Intelligence (PAI) score. Strap the Slice onto your wrist, where it monitors your heart rate during rest and activity, and then applies a proprietary algorithm to generate your PAI score. I’m normally against a company using confusing metrics to evaluate fitness (remember the seemingly pointless NikeFuel?), but PAI is built around some serious science.

When developing the PAI system, Mio used data from the HUNT Study, an exhaustive project by the Norwegian University of Science and Technology that collected physical activity and health outcomes data from more than 45,000 participants over 25 years. Based on a retroactive analysis of that data using the PAI algorithm, Mio found that men with a PAI score of 100 or more had a 17 percent reduced risk of cardiovascular disease mortality. Women had a 23 percent reduced risk. Those are big numbers, and the study found that it held true across all age groups and in participants known to be at risk.

So, you want to hit a PAI score of 100, and you can do that any way you want: running, biking, working out at the gym, doing yoga, or dancing. It doesn’t matter, because the Slice cares how hard your heart is working, not whether you’re taking steps. If your exercise routine isn’t getting you to 100, then you know you need to push harder or add something new.

The band is also well designed. It looks like a Fitbit Charge but with a smoother, more polished appeal. It doesn’t get caught on sleeves and has an easy-to-read display. It’s also waterproof to 100 feet (though the company says you can’t read your heart rate while swimming) and tracks your sleep automatically. You can use the button to scroll through the time, PAI score, current heart rate, steps taken, calories, distance, and sleep data. The Slice is on sale now for $130 and works with iOS and Android. Mio will also launch a PAI app for the Apple Watch in the months to come.

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