If I want to get fitter, should I wear a fitness watch?

My every movement is being quantified, and I am obsessed.

We have a tendency to sleepwalk into adopting new technologies, and my new fitness-tracking watch is no exception. Ever the late adopter, I bought an entry-level model with a single aim: helping me pace myself on my Saturday morning Parkrun. But oh, the bells and the whistles!

A heart-rate monitor. A step counter. Sleep monitoring. Tracking my “streaks” of exercise. A VO2 max tracker. An “intensity minutes” tracker. A calories-burnt counter. Access to training plans. A link to Strava, so my friends can comment on my exercise and I can comment on theirs. Unkindest of all, the Fitness Age indicator. I didn’t sign up for any of this, yet the watch’s app displays them all for my consideration. And now I am obsessed.

Ever the empiricist, I started to wonder what the likely impact of all this quantification was. Would the fitness tracking actually improve my fitness? Would it backfire in some gruesome way? Or, perhaps, both at once?

Early studies of this question were not wholly encouraging. One randomised controlled trial, with results published in 2016, found that adding fitness trackers to a weight-loss programme made the programme less effective. While participants tended to lose some weight with or without the trackers, those with the trackers lost less weight than those without. For those who love counterintuitive findings, this discovery is fun. Yet it is unclear quite how to interpret the finding, or even how seriously to take it. (The study, incidentally, found no significant difference in diet or physical activity between the two groups. Was the effect real and robust, or a fluke?)

If we think fitness trackers might backfire, it’s worth pondering how exactly that could happen. One possibility is that people become so obsessed with hitting their targets that they cheat, perhaps shaking the watch or phone vigorously in the hope of racking up extra steps.

But it’s one thing to occasionally cheat the algorithm and hit a meaningless target, then feel a bit silly about it. It’s quite another to suggest that people are so busy trying to con the fitness tracker that they actually do less exercise than if there was no tracker at all.

Another risk is that the trackers might demotivate people by turning a pleasurable activity into a chore. There is some evidence of that in another 2016 research paper titled “The Hidden Cost of Personal Quantification”. In one of the studies described in that paper, participants went for a walk wearing pedometers, some with the step count visible and some with the step count covered. People with a visible step count walked more but enjoyed themselves less. That is intriguing and certainly suggests a backfire mechanism. On the other hand, that was just one walk. Over the course of weeks and months, are we to picture someone who used to love walking, but then walks less because their smartwatch starts telling them how many steps they’ve completed?

A third risk — and this seems more plausible to me — is that people are driven by their fitness trackers to over-exercise, or to favour one narrow form of exercise, with the result that they become injured and then discouraged.

There is a final possibility: perhaps fitness trackers work perfectly well.

Thankfully, we do not need to rely on these early studies: the intervening years have brought us vastly more data. In 2022, Lancet Digital Health published a systematic review that tried to bring together all the credible research done to that date, covering 164,000 people. The study came to exactly the conclusion you might expect, if you weren’t tying yourself in knots of counterintuition: fitness trackers do help people to be fitter.

More specifically, wearable activity trackers lead people to walk more — 1,800 steps or 40 minutes of extra walking per day — and to lose some weight (1kg) on average. There is also evidence, albeit weaker evidence, that fitness trackers lead people to burn more calories, improve blood sugar and cholesterol, improve wellbeing, reduce disability, and lower levels of pain, anxiety and depression. Emotional wellbeing improves and resting heart rate falls.

Some of these apparent benefits are small or uncertain but, broadly speaking, the picture is what you’d hope: people who were given fitness trackers in a randomised trial were more active than those who, at random, were not. That extra physical activity led to all the benefits we might expect.

None of these studies was designed to answer the question, “If I want to get fitter, should I buy a fitness watch?” Instead, they answer the stranger question, “If I was given a fitness watch as part of an academic study, would I get fitter?”

Consider the parallel pair of questions: “If I want to take up running, should I buy some running shoes?” and, “If I was given some running shoes as part of an academic study, would I run more?” For most purposes, the answer to the first question is obvious and the answer to the second is irrelevant.

Perhaps that’s how I should view my fitness watch. It’s like a gym membership or an exercise bike: great if you use it, pointless if you don’t. And for now, I’m using it. Although it feels rather more like it is using me.