Trackers, Apps and Step Counts

Quick Intro

Fitness trackers are useful for trends, but their numbers vary in accuracy. Step counts are reasonably reliable, usually a little low. Heart rate from the wrist is fair during steady exercise. Calorie figures are rough guesses that can be far off. Use a tracker to see whether you are moving more or less over weeks, not to judge any single number.

This article explains what trackers measure well, what they measure poorly and how to use them sensibly.

Steps

Step counting is one of the things wrist trackers and phones do best. A large review of studies found that several major wrist devices counted steps accurately in laboratory tests, and an overview of the research found typical step errors were small, more often undercounting than overcounting.

That is accurate enough to compare one week with the next. Remember that steps do not capture everything: cycling, swimming, strength training and pushing a pram with a wrist-worn device may barely register.

Heart Rate

Wrist trackers measure heart rate by shining light through the skin. In a well-known study of several wrist devices, most measured heart rate within a few percent of a chest monitor during cycling, but accuracy was lower during walking and varied between people, including with body size and skin tone. Devices have improved since, but it is sensible to treat wrist heart rate as a guide, not an exact reading, especially when effort changes quickly or the wrist is moving a lot.

Chest straps are usually more accurate if you want precise heart-rate data. For most people, though, the talk test is a simpler guide to effort than a heart-rate number.

Calories

Calorie figures are the least reliable number a tracker gives. In the same study, none of the devices estimated calories burned closely, and errors were large. Estimates depend on assumptions about your body that may not fit you.

Treat calorie numbers as a rough indication at best, and avoid using them to decide how much to eat. Exercise and weight loss explains why the energy used in exercise is easy to overestimate.

Sleep and Other Scores

Many trackers also give sleep stages, recovery scores, stress scores and fitness estimates. These are based on combinations of heart rate, movement and assumptions. Some people find them a useful nudge, but how accurate each one is varies between devices, and they are best treated as rough trends. How you feel matters as much as any score.

Using a Tracker Well

Watch trends, not days. Compare weekly averages over months.
Use it to nudge habits. A reminder to move, or seeing your step count rise, can help.
Compare yourself with yourself. Different devices measure differently, so comparing your numbers with a friend’s tells you little.
Do not chase round numbers. A step target of 10,000 has little evidence behind it as a threshold. More steps help up to a point that is lower for older adults. Is walking enough exercise? explains more.
Take breaks if it causes stress. If tracking makes exercise feel like a chore or causes worry, it is fine to stop.

Apps and Programmes

Many apps offer workout plans, follow-along videos and reminders. They can be useful:

A plan removes decisions. Knowing what to do each session makes it easier to start.
Videos show the movement, which helps beginners learn.
Reminders and streaks can help build a habit, as long as a broken streak does not make you give up.

Choose plans that start gently, increase gradually and let you adjust to your level. Be wary of apps that promise fast results or push very hard sessions on beginners.

You Do Not Need One

Trackers are optional. The most useful signs of progress, such as easier stairs, talking more comfortably at the same pace and doing more reps, need no device at all. How to tell you are getting fitter lists them.

Who This Applies To

This applies to anyone using a consumer fitness tracker or phone app. If you need accurate heart-rate monitoring for a medical reason, follow your doctor’s advice on which devices to use. A tracker is not a medical device, and any worrying symptom should be checked by a doctor whatever the device shows.

FAQ

Are step counts accurate?

Reasonably so. Most major devices count steps well enough for tracking trends, usually slightly undercounting.

Can I trust the calories my watch says I burned?

Not closely. Calorie estimates can be far off. Treat them as rough.

Is wrist heart rate accurate?

Fairly accurate during steady exercise and less certain when effort or wrist movement changes quickly. A chest strap is usually more accurate.

Do I need a tracker to get fit?

No. Simple signs such as the talk test and a training log tell you what you need to know.