Are wearable health and fitness data trackers reliable?

When it comes to wearable activity trackers patients are most concerned about their heart rate, according to Lee.

The most common wearables—wrist devices such as activity trackers and smartwatches—measure heart rate in a variety of ways. Many wrist devices use a process called photoplethysmography, which determines heart rate by measuring the light reflecting off the blood flowing in your skin. Some newer-generation wrist devices use single-lead electrocardiograms (ECG), which assess the heart’s electrical activity through the skin and sweat.

While each of these methods can give you an accurate estimate, their readings aren’t exact.  

“The issue with these devices is that they can be easily fooled by hand, arm, and wrist movements,” Lee says. “This can cause numbers to wildly vary when you use them during a workout, so wearing them tightly during exercise is the best way to improve accuracy.”

The larger, and trickier, question is: Should users rely on this data? Unfortunately, there is no single, one-size-fits-all response, just as there isn’t a single “normal” heart rate for every individual

“Heart response to exercise can be highly varied and affected by medical conditions, medications, lifestyle factors, and state of fitness,” Lee says. “Before beginning an exercise program, you should talk to your doctor about your expectations, limitations, and your heart rate range.”  

With this information, you will be better able to judge if your heart rate data from your activity tracker is measuring in your range. Also, you can quickly identify when your numbers are outside of your established range, making it easier to speak to your doctor about your health concerns.

Calculating daily steps is another popular health metric measured by wearable devices, especially for users looking to increase their mobility. However, there are many factors that could change the accuracy of those numbers.

These devices use computer algorithms based mainly on your height to assume the size and speed of your gait, or your walking pattern. Differences in the build of your body could cause the algorithm to make incorrect assumptions about your movement. Variations such as shorter legs relative to your height, a slower natural walking pace, or needing to use an assistive device can all compromise the accuracy of the data.

“I think what matters most when it comes to calculating daily steps is the movement itself,” Lee says. “Don’t get hung up on the exact number of steps. What’s important is making the effort to consistently move your body.”

Workout enthusiasts and people looking to lose weight will often turn to their devices to help them keep track of the number of calories they have burned throughout the day.

However, this is another measurement that relies on computer algorithms to make assumptions about your exercise intensity and individual body metabolism, which could mean a less-than-exact reading of your calories burned during activity.

“Instead of focusing on calories burned, you’re better off setting a goal to exercise 150 minutes a week, which is considered the ideal amount,” Lee says. “If you are exercising, you’re burning calories!”

Some wearable activity trackers and smartwatches also include technology like a pulse oximeter, a device that uses light to measure how much oxygen is in the blood. This technology can yield fairly accurate results. While this may seem like a helpful fitness measurement, it’s not necessary for most people, Lee notes.

“If you do not have significant lung disease, oxygen saturation at rest or with exercise is generally not a necessary measurement,” Lee says. “But, if you have been diagnosed with lung disease and/or low oxygen at times, you should discuss the value of measuring your oxygen with your health care provider.”

While activity trackers and similar devices can provide a pretty good range or estimate of your metrics, they should not be your primary focus when setting health and fitness goals for yourself.

“Focus on doing the exercise,” Lee says. “Worry less about measuring it, because the actual exercise is often more valuable than the numbers on the screen.”

And, whether you’re using these devices for exercise or to monitor health issues, talk to your doctor to determine how you can best use the data to help you reach your goals.