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Posted by Tim Harford

https://timharford.com/2025/10/the-relentless-rule-of-my-fitness-tracker/

https://timharford.com/?p=9617

At a time when we’re all blaming digital devices for ruining our attention spans, our children’s mental health and even the future of democracy itself, let’s give credit where it’s due: my cheap fitness watch has changed my life.

Three and a half years ago I started running at my local Parkrun, taking more than half an hour to limp around the 5k course for the first few weeks. After a few months of consistently showing up I made the kind of progress one might expect. But when I bought an entry-level runner’s watch, things really started to change.

Urged on by the watch, I began training several times a week and lengthening the runs to 10k, 10 miles and beyond. My wife got the bug — and her own watch. Our daughter described us as “running mad”. You be the judge: mad or not, I’m running the London Marathon in April next year. As a stubborn non-runner for the first 49 years of my life, there’s no way I’d have signed up for that sort of insanity without the watch.

These fitness trackers are not without their downsides, and I’ve become fascinated by the way they’re a microcosm of our increasingly quantified lives. The most obvious objection is that they are a privacy nightmare. They track our location and make sharing it easy and tempting. Stanislav Rzhitsky, a Russian submarine commander, was assassinated while going for a run in his local park; he was in the habit of posting his running routine on Strava. In the US, a man was convicted of murdering his wife after her Fitbit data contradicted his account of events.

And it is not just location: Carissa Véliz, the author of Privacy is Power, warns that with the right technology, heartbeat data can be as distinctive as a fingerprint. It’s unclear how much is already up there in the cloud, waiting to be abused by someone or other.

Fitness watch manufacturers would rather focus on these trackers as tools for performance. Even in this respect, there is a mixed picture. Like any good performance metric, my watch provides me with structure and helps me optimise my running. I can feed in a goal — a distance, a time — and it will generate a training program. Once-difficult tasks, such as running at a consistent pace, become straightforward.

Yet like many performance metrics, the watch can also nudge me into counter-productive activity such as overtraining to the point of injury. The sleep-tracking function tempts many people into thinking too much about sleep, which is the sort of thing that can make it hard to drift off. There’s a term of art, “orthosomnia”. It means that you’re losing sleep because you’re worried that your sleep tracker is judging you.

There is another subtle effect at work, something called “quantification fixation”. A study published last year by behavioural scientists Linda Chang, Erika Kirgios, Sendhil Mullainathan and Katherine Milkman invited participants to choose between a series of two options, such as holiday destinations or job applicants. Chang and her colleagues found that people consistently took numbers more seriously than words or symbols. Whether deciding between a cheap, shabby hotel or an expensive swanky one, or between an intern with strong management skills or one with strong calculus skills, experimental subjects systematically favoured whatever feature had a number on it, rather than a description such as “excellent” or “likely”. Numbers can fixate us.

“A key implication of our findings,” write the researchers, “is that when making decisions, people are systematically biased to favour options that dominate on quantified dimensions. And trade-offs that pit quantitative against qualitative information are everywhere.”

They may or may not be everywhere, but they are certainly in my fitness regimen. My watch takes walking, cycling and running seriously — especially outside rather than on a treadmill — but a hard session at the gym barely registers. It will count my steps for me, but I have to count my own pull-ups. The result is an incessant tug away from exercise that may be good for my body or my spirit, but which doesn’t “count” — and towards the kind of aerobic, trackable activity that the watch rewards.

Management theorists have long known about this problem. Steve Kerr’s essay in the Academy of Management Journal, “On the Folly of Rewarding A While Hoping for B”, is 50 years old and the folly seems more common than ever, perhaps because we now have an ever easier selection of automatically generated metrics upon which to fixate.

Quantification fixation may explain an early, infamous study of using fitness trackers for weight loss, published in 2016, which found that the trackers made it harder rather than easier to lose weight. That might be a statistical fluke, but it might also reflect the fact that when you exercise more you may be inclined to eat more. The fitness tracker monitors and therefore encourages extra exercise, but turns a digital blind eye to extra calories — this is quantification fixation in automated form.

A different aspect of the same problem is when I face a choice between the run prescribed by my watch, or an opportunity to run with a friend — possibly over the wrong terrain, for the wrong distance, at the wrong pace. “Wrong”, of course, being defined by the sensors in the watch. It is almost always better to seize the opportunity for a sociable run, but do I always seize it? I do not. It’s a shame to let down a friend, but it’s a disaster to let down the watch.

We live in a quantified world and in many ways our lives are better as a result, whether the metrics have been used to create more effective medicines or more efficient delivery vans. My watch may be a punctilious little wrist-worn box of tricks, but my running, and indeed my overall fitness, is far better than it was before I bought it.

Still, we would do well to keep the quantification revolution in its proper place. I never would have started running in the first place without the friends who encouraged me to show up at Parkrun, a movement that relies on community spirit, deftly seasoned with just the right amount of quantification.

And I’m not running a marathon because my watch told me to do it; I’m running in memory of a young woman who died of cancer at the age of 20. The fitness watch is a means to an end, not the end in itself. All I need to do is to remember that.

Written for and first published in the Financial Times on 11 Sep 2025.

Loyal readers might enjoy the book that started it all, The Undercover Economist.

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https://timharford.com/2025/10/the-relentless-rule-of-my-fitness-tracker/

https://timharford.com/?p=9617