One of the drawbacks of the fad for wearable health trackers is that the numbers they record to show what physical activity you did today mean very little to the vast majority of people.
For example, how does knowing that you walked 6,283 steps help you achieve your long-term health or fitness goals? Obviously, walking those steps in a hike up a mountain produces a different health result than many trips to the pub. Similarly, knowing that your heart averaged 143 beats per minute during a 20-minute workout doesn’t really tell you that much.
Ulrik Wisloff, a professor of physiology at the Norwegian University of Science and Technology in Trondheim, is at the forefront of research into exercise and cardiovascular health and has thought about this problem for a decade.
“What I have been wondering is how we can put heart rate data into a meaningful variable,” he says.
“Just knowing how many steps you walked or what your heart rate was doesn’t tell you anything. We needed a universal metric that would tell you how much you have done, whether you are cycling, swimming or running.”
As a result of years of research, Prof Wisloff and his team have come up with a metric they call Personal Activity Intelligence or PAI, which they pronounce “pi”. It’s quite simple: your workouts are converted by an algorithm in a smartphone app or wearable device into a single number. They chose 100 as the goal, meaning you just have to keep track of one measure to see if you are exercising sufficiently.
They tested the algorithm of 5,000 Norwegians and then went back to check its usefulness with a much larger health study in the 1980s of 40,000 people.
“Those who had a PAI below 100 didn’t have a very good health profile,” Prof Wisloff says. “Those whose PAI was above 100 were much healthier.”
In fact, they found that people who managed to stay above 100 PAI lived, on average, five years longer than those who did not. Of course, there was more benefit for those who started exercise younger. But even people who exercised sufficiently at 70 lived for an extra two years.
Many readers may be familiar with the Norwegian University’s online fitness calculator, which now has more than 1m users. Prof Wisloff says that the PAI measurement is more useful because the calculator is a snapshot of your health, while PAI tells you whether you are exercising enough to achieve optimum health.
While Prof Wisloff hopes the PAI measurement will be widely used in the fitness industry, the first implementation has been by a Canadian maker of heart rate monitors, Mio Global, based in Vancouver.
I have been using the company’s Mio Fuse wristband, which is temperamental to set up but gives a pretty accurate heart rate whether you are swimming, cycling, on a treadmill or just walking. The device doesn’t calculate your PAI — one that does is due out in June — so you need to connect it with a Mio PAI app for your Apple device or Android phone.
The beauty of the PAI measurement is that it is cumulative, incorporating the last few days’ exercise, whether low or high in intensity: cycling in city traffic is measured alongside jogging and interval running. As long as you remain above 100 PAI, you have achieved your health goal for the week.
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