The Apple Watch May Have a Calorie Problem


Updated at 9:40 p.m. ET on February 1, 2024

A little monster lives on my wrist, and every day, I wake up prepared to do battle with it. Most days, I lose.

That gremlin is an Apple Watch, which, like all fitness trackers, is designed to nudge users toward healthy behaviors. Apple uses three digital rings to measure a person’s daily activity in different ways. Each one has a bright color and a simple name. The blue “Stand” ring prompts you to, well, stand more. (Reasonable!) The green “Exercise” ring prompts you to spend more minutes exercising. (Fair enough!) Then there’s the red ring, the “Move” ring. It is the biggest and most prominent in Apple’s design, and it tracks calories burned through movement. It is my nemesis.

When you place an Apple Watch—or any fitness tracker—on your wrist, you are opting in to a reorientation of your daily life. Your goal now is to fill these rings, “closing” them by completing the given task, or to hit a certain number of steps. When I got the Apple Watch for Christmas, I input my personal stats (height, weight, and age) and assumed that its suggested goals for a “moderate” level of physical activity would be achievable, because I consider myself fairly active. Or at least I did. It took three weeks before I finally filled a single day with enough activity to close that red ring.

None of my regular exercise habits would please the thing. I went on three-mile walks. I did a 20-minute pilates session and a high-intensity-interval-training class on the same day. I spent 40 minutes indoor rock climbing. Only when I subjected myself to a 45-minute turbo-cardio-kickboxing class on YouTube (half annoyed, half bemused) did I finally satisfy the machine. I watched with muted delight as the Watch’s little animation seared my finally completed red ring into fitness history.

The experience briefly warped my perception of my own physical fitness. I started to worry I wasn’t doing enough, and I felt pressure to do more intense workouts. My preferred forms of exercise tend to be gentler and more strength-focused. But they are, after all, exercise. I do also meet recommendations from the World Health Organization and the American Heart Association to get 150 minutes of moderate-intensity aerobic exercise a week, at least most of the time. How could it be that this device was making me feel like a weak layabout?

On a basic level, a wearable health device uses sensors to take measurements about a person and their movement. It reports some of these measurements, such as heart rate, back to users directly. Other data points are fed into an algorithm, which then spits out a relevant judgment about some category of a user’s health, such as a sleep or stress score. “Active calories,” the metric associated with that bedeviling red ring, is actually an estimation, and the algorithm behind it is kept secret. Apple, which declined to comment on the record when reached for this article, says that all of its health and fitness features are “subject to rigorous scientific validation processes, in collaboration with medical community experts.”

But several studies suggest that calorie measurements on fitness trackers are frequently inaccurate. “If you look at the systematic reviews on every study that’s ever tested the validity of these wearable devices, the definitive conclusion they always make is these things are useless for energy-expenditure estimation,” Keith Diaz, an exercise physiologist and a professor at Columbia University Medical Center, told me. Because these trackers cannot directly measure calories burned, and because calorie-burn rate varies from person to person, their approximations can be substantially off.

Calories, of course, have a loaded cultural history and a particular, if complicated, association with weight loss. The charitable read is that, in emphasizing them, wearable companies are attempting to present users with a more sophisticated way to think about exercise than steps. You can get your heart rate up by doing plenty of things besides walking or running. “Everything counts,” reads the marketing copy on Apple’s website, which flashes examples such as dancing at a concert and gardening. Experts I spoke with aren’t totally against presenting a calorie counter for this reason; the issue is simply that a user shouldn’t trust that the measurements are fully accurate. In my case, I should have been confident in my physical fitness rather than obsessing over why that red ring wasn’t closing.

That obsession puts the larger issue in a nutshell, however. Fitness trackers tend to emphasize certain goals to keep users engaged in the short term, and health is more of a marathon than a sprint. “The device focuses your attention on what it wants to focus your attention on,” Ida Sim, a doctor and a professor of medicine and computational-precision health at UC San Francisco, told me. This can be a good thing, obviously, if it encourages you to adopt healthier habits and feel better about yourself. Apple’s green ring, which tracks overall exercise minutes, seems very useful for a person hoping to meet those WHO and AHA fitness goals.

But these goals can also be pretty random: The 10,000-steps goal that Fitbit so famously uses doesn’t originate from clinical science. Instead, the idea of encouraging people to do 10,000 steps a day comes from a 1965 marketing campaign by a Japanese company that was selling pedometers. Reached for comment, a spokesperson for Fitbit said, in part, that “Fitbit starts everyone off with a 10,000-step goal, as it’s very easy to remember, and for most people it’s a target that is achievable and gets people to move more.” They added that research has shown that getting more than 10,000 steps a day can improve one’s health.

This gamification can lead users to perform for the wearable instead of for themselves, as I did while furiously kickboxing in my living room. One researcher I interviewed for this story admitted to lowering her daily Apple Watch goals when she’s sick so as to not break her “streak” of closing her ring every day. (Plenty of people on Reddit cop to doing the same.) Apple does allow you to customize your goals, and people I spoke with did suggest lowering my red-ring goal—which felt like an uncomfortable concession that I wasn’t in shape, even if I knew better.

Marco Altini, the founder of a personal-training app called HRV4Training, told me that, at this point, he finds that the devices overall are a bit too focused on engagement. “We shouldn’t always be making adjustments,” Altini, who also serves as an adviser to Oura, a wearable company that makes fitness-tracking rings, explained. Rather than constantly tinkering with our behavior, we should have a long-term plan and accept some natural variation in our output. “The reality of things is that it should be a bit more boring,” he said.

Diaz, the exercise physiologist, told me that, back when he wore a Fitbit, he’d find himself pacing his apartment in the evening trying to get his steps in. “I just didn’t like the relationship that I was forming with the device and with my life,” he said. He’s not saying that no one should use them, he clarified, but the problem with these devices is that they use external motivation, whereas “what the science tells us is that for long-term behavior change, internal motivation is far better.” Rather than being poked to move by a computer on their wrist, a person should find a way to get in exercise that they enjoy, because then they’ll be more likely to keep it up in the future.

To prove his point, Diaz asked me how I felt after finishing rock climbing or surfing. I gushed about the high. Closing Apple’s rings, or reaching 10,000 steps, might feel good. But it’s nothing like the joy that comes from moving your body simply because you want to.


This article has been updated to include a comment from Fitbit.



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