How accurate are activity trackers?

Recent research suggests that some activity tracker measurements may be unreliable.

Last year, I received a Fitbit for my birthday. Since I tend to be somewhat technologically challenged, my husband and 21-year-old daughter enthusiastically helped me set up an account and synced my device so I could track everything from my heart beat to the number of steps I took each day. To be honest, now that the novelty has worn off, I use my Fitbit more as a watch than for tracking my activity, but many of my family, friends and colleagues use these devices to keep their exercise on course and also to help them meet their health and fitness goals.

According to a sponsored research study done by the American Council on Exercise (ACE), an estimated 19 million activity trackers were used in 2014 – this number is expected to triple by 2018.  Depending on the model, these fitness wearables not only feature clocks, caller ID and/or music control, they are also designed to track some, if not all, of the following:

  • Number of steps
  • Distance for walking, biking and swimming
  • Stairs/floors climbed
  • Active minutes
  • Heart rate
  • Sleep patterns
  • Calories burned

While this new type of technology is certainly interesting, not to mention trendy, how accurate are the readings? A May 2017 report by Stanford Medical News Center revealed a study conducted by Euan Ashley and his research team which looked at seven different types of fitness trackers and their accuracy in measuring heart rate and energy expenditure. While most of the devices did a pretty good job of measuring heart rate (with an error of less than 5 percent), their measurements of energy expenditure (calories burned) were significantly off, by an average of 27 percent.

The ACE study showed that the activity tracker devices were pretty accurate with tracking the number of steps taken during treadmill walking and running, as well as elliptical exercise. But as with the Stanford study, the devices either over or under predicted number of calories burned making them an unreliable source to track caloric expenditure.     

So what does this mean for the average consumer? There are many benefits to using an activity tracker, with perhaps the most useful reason being that it can help increase physical activity. The ACE reports there are studies that show people are 30 to 40 percent more active when they wear one of these devices. However, the data provided by fitness wearables should never be used when making important health decisions. Michigan State University Extension recommends that you always work with a health care provider when making any decisions in regards to your health. 

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