Fitness Trackers Might Help Us Live Longer (if Only We Used Them)

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Activity monitors could improve our health and extend our lives — if only we could be motivated to use them. Those are the conclusions of two new studies about the promise and perils of relying on fitness trackers to measure and guide how we move.

The monitors, which are expected to be a popular holiday gift again this year, can generally track our steps, speed, stance (sitting or not), distance, energy expenditure and heart rate. The absolute accuracy of these numbers, however, is somewhat suspect, with past studies finding errors in many of the monitors’ measurements. But the inaccuracies are usually consistent, the studies show, so the trackers can reliably indicate how our movements change from day to day.

The broader problem with activity monitors has been that we have not known whether the information they generate actually relates directly to our health. We have not had proof that what most trackers tell us is healthy actually is.

Consider, for instance, the recommendation that we should exercise moderately — such as by walking briskly — for 150 minutes per week. Most activity monitors incorporate those guidelines into their calculation about how much exercise people should complete.

But those recommendations were based on studies in which people told scientists how much they remembered moving. The people had not worn monitors.

So for one of the new studies, published last month in the American Journal of Epidemiology, volunteers did. As part of an ongoing, government-funded study of Americans’ health, almost 4,000 middle-aged men and women donned activity trackers for a week. The researchers compared the tracker results with their self-reports, to come up with and confirm an objective measure of how much activity they were getting. (Their movement patterns were broadly similar whether they wore the monitors or not.)

Researchers then followed the participants for up to 10 years, checking their names against those in the National Death Registry, to determine whether objectively meeting the 150-minute-per-week guideline affected how long people lived.

It did. Those men and women who, according to their activity trackers, had exercised moderately for at least 150 minutes per week were about 35 percent less likely to have died prematurely than the men and women who, according to their trackers, had been less active, the researchers found.

Those results, while unstartling, do provide the first, scientifically compelling rationale for owning an activity monitor, says Dr. Timothy Church, a professor of preventive medicine at Pennington Biomedical Research Center in Baton Rouge, La., who wrote a commentary to accompany the new study. When your monitor prompts you to walk for 30 minutes on most days, he points out, it now has objective proof that doing so may extend your life.

He also expects that additional studies will soon begin to pinpoint precisely how much and what types of exercise might lessen our risks for specific diseases, providing findings that could be subsequently incorporated into our activity trackers. The devices could then tell us whether today’s lunchtime walk will have been sufficient to affect our risk for Type 2 diabetes or whether another stroll around the block might be advisable.

But benefits from activity monitors will ultimately depend on whether and how we use the gear, of course. And a telling study published last month in The Lancet Diabetes and Endocrinology indicates that people can be funny about their interactions with their fitness trackers.

In that study, scientists in Singapore recruited 800 office workers and gave most of them an activity monitor, although some went without one to serve as controls. The others were told to use the monitors to achieve basic exercise goals, with one group getting cash if they reached those goals, and another earning money for their favorite charity. The last group was told to meet the targets simply because it was good for their health.

After six months, people getting cash to exercise were exercising the most. There were slight increases in activity among the other people using activity monitors.

Then the monetary incentives ended, although the participants were asked to keep using their monitors and meet their exercise goals anyway. Six months later, the researchers checked in again. By then, the people who once had received cash to exercise were exercising the least, the monitor data showed. Activity also had declined in the charity group. But unexpectedly, those in the group given monitors but no money were exercising more now than at the last check.

The data for everyone was limited, however, because most of the participants had quit wearing their monitors most of the time.

The upshot of these two studies seems to be that activity monitors have the potential and, increasingly, the scientific undergirding needed to influence how long and well we live. But they cannot fulfill that potential until we understand whether they actually motivate us to move and how.

“Obviously, far more research is needed,” Dr. Church says. But one unscientific experiment already underway could turn out to be a useful guidepost.

“Look at Pokémon Go,” he says, the interactive phone app during which users locate and capture cartoon characters seemingly situated in the real world. The game rewards players who walk or run various distances. “That could be the future of activity trackers,” Dr. Church says: science-based health monitoring that also is fun.