Not All the Data You Get From Your Fitness Tracker Is Accurate—These Are the Most and Least Reliable Metrics

Photo: Getty Images/mixetto
Whether it’s the Apple Watch, FitBit, Oura Ring, or (and!?) the Garmin Forerunner—to name just a few—wearables have become as integrated into our daily use and lives as a smartphone or any other part of clothing. As the market cap and development of wearables has progressed—from semi-cumbersome gadgets that could only track a few data points to sleek items that track the distances of our steps, how well we sleep, what our heart rate variability is like, and so on—the reliance on wearables has also naturally increased.

However, with that expansion comes a potential double edged sword: “paralysis by analysis.” Having so much data can easily overwhelm us. What do all these stats actually tell us, and what can we actually do with that info? Knowing the most accurate fitness tracker metrics can be helpful here.

Experts In This Article

“Having more data and the awareness of all the factors that influence your health and fitness is great,” says Andy Barr, DPT, fitness coach and owner of Quantum Performance. “But I’ve found that an increasing number of clients are deluged with abundance of data from their wearable devices and unable to make heads or tails of it without spending considerable time doing their own research and educating themselves…time they don’t have and time they thought would be saved by getting a wearable in the first place!”

To maximize the value of the data you’re getting, focus on the most accurate fitness tracker metrics. According to high-level research looking at the validity and reliability of wearables, the most widely accepted and backed use for wearables is to track heart rate. Second to heart rate is step count. The next tier down—essentially the “very mixed evidence tier”—is using a wearable to track overall energy expenditure and heart rate variability. In the lowest, “not generally accepted” tier is VO2max, training load, and sleep and stress. The lowest tier is not all that surprising when you consider the relative complexity of these metrics and how many variables that need to be accounted for.

Opinions from leading experts align with the research in that wearables can be effective for simpler trackable actions like counting steps and heart rate but the more complex the action, the less accurate it is.

Measuring complex variables like training load or stress is difficult to do accurately without advanced equipment and expert knowledge, so it’s no surprise that wearable technology—which is still relatively in its infancy—is unable to do it reliably.

This isn’t a knock on wearables—the majority of health and fitness tech can’t measure higher complexity variables. Yet they’re still excellent tools for major health indicators like heart rate and step count.

To make your wearable data more reliable and accurate for step count and heart rate, Dr. Barr says “use your watch for seven to 10 days and get a feel for the average because each wearable tracks things differently with different levels of error. Additionally, most wearables tend to overestimate things at lower and higher intensities so you want to give it a larger sample size to get more accurate measurements.”

To put it simply, don’t take your wearable at face value immediately. Give it a week or so and look at the fluctuations for every day and you should have a pretty good idea of your averages.

To put a bow on it all is some excellent general advice from Tim DiFrancesco, DPT, owner of TD Athletes Edge: “Wearables are one piece, and along with them, we all need to be better at listening to our own bodies rather than taking any one metric or technology as gospel,” he says. “Health is just too complex and there’s just too much room for error when doing that; however, combining tools like wearables with rate of perceived exertion [RPE] and wellness scale information can give us a much clearer picture and awareness of health and fitness.”

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