If you scroll through the data collected by the typical smart wearable — from smartwatches and smart rings to fitness trackers and more — you‘ll see much more than your number of steps, calories burned or distance. Many devices also will estimate your heart rate variability, VO2 max, time spent in deep sleep and other data.
However, not all this data is accurate. Nor is it helpful, says Thom Rieck, an exercise specialist at Mayo Clinic who has collaborated on several studies about smart wearable technology.
According to Rieck, the most useful and trustworthy smart features tend to be the easiest ones to understand and use.
How accurate are step counters?
Nearly all smart wearables, regardless of price, do a decent job tracking your number of daily steps, says Rieck. This includes smartphones as well as the average $15 pedometer.
These trackers also can motivate you to move, at least in the short term, says Rieck.
“Over the long term, however, people tend to lose interest after around 6 weeks to 3 months,” says Rieck. “Once the novelty wears off, the device often ends up in a drawer.”
To stay motivated, Rieck recommends:
Move your goalposts.
Once you know how many steps you take on an average day, set some short-term activity goals. If you take 2,000 steps a day, for example, consider setting a short-term goal of adding 1,000 steps daily for two weeks. Once you meet that goal, add a new one.
Share your milestones.
You might tell friends or family about your daily steps. Together, you might encourage one another’s progress. Or you could sign up for a step challenge offered in-person or virtually.
Respond to movement reminders and standing goals.
When your wearable gives you one of those “it’s time to stand” messages, heed the call. Get up and move around for a minute or two. Though these short breaks may not seem like they amount to many steps individually, they add up over time. “These short movement breaks can be just as important for your health as a formal exercise session,” says Rieck.
Read more: How many steps to take to improve health.
Smart wearables and heart rate measurement
Higher-end smart devices estimate your heart rate to within 3 to 5 beats per minute of your actual heart rate.
To get an accurate reading, make sure your watch fits snugly. Smartwatches and bands shine light into your skin to measure your pulse. If there’s a big gap between the watch or band and your skin, the surrounding light can interfere with the reading, making it less accurate, says Rieck.
If you want to measure your heart rate during a workout, make sure to tell your device that you’re exercising. That way, the device will know to take more-frequent readings.
When you’re not exercising, you may want to pay attention to changes in your resting heart rate, which refers to the number of times your heart beats per minute when you’re not moving. First, you’ll need to determine a baseline or average resting heart rate over several days. Then, once you know your typical resting heart rate, pay attention to see if it changes.
If your resting heart rate rises
If your resting heart rate is 3 to 5 beats per minute higher than usual, consider whether your body is struggling to recover from or compensate for any of the following factors:
- Lack of sleep.
- Excessive alcohol consumption.
- An infection such as a cold or flu.
- Unrelenting stress.
- Doing too many intense workouts too closely together.
If your resting heart rate drops
As you progress on a new fitness program, your resting heart rate will likely drop a beat or two per month as your heart becomes more efficient at pumping blood. On the other hand, if you take a long break from exercise, you might notice your resting heart rate trending upward.
Read more: Does Zone 2 cardio actually work?
Vo2 max
The term “VO2 max” sounds complicated, but the definition is fairly straightforward. It refers to your oxygen uptake. The “V” stands for volume, the “O2” for oxygen and the “max” for maximum.
“To understand VO2 max, think of a car engine. A race car’s engine easily travels at 55 miles per hour because it’s capable of traveling more than 200 miles per hour,” says Rieck. “Similarly, a high VO2 max makes movement feel easier because it gives you more capacity.”
For example, it takes about 16 to 18 milliliters per kilogram per minute (ml/kg/min) of oxygen to climb a flight of steps. If your VO2 max is 30 to 35, you’ll likely get to the top of the steps without feeling too winded, because you’ve got plenty of oxygen to spare. However, if your VO2 max is between 15 and 20 ml/kg/min, you may need a break or two before getting to the top.
In addition to making movement feel easier, higher VO2 maxes are associated with improved health and greater longevity.
In a lab, scientists measure VO2 max with a face mask that collects the air you breathe out as you exercise. Smart wearables, on the other hand, can use your exercise pace and heart rate to estimate your VO2 max. This estimate is pretty accurate, within 2 to 5 ml/kg/min of your actual VO2 max.
Your target VO2 max will depend on your age, weight and sex, so make sure to input those variables into your smart device.
Your VO2 max will change over time. As you become more fit, you can expect your VO2 max to trend upward within about 3 to 6 months. Heat affects VO2 max, so don’t worry if it temporarily drops during the summer months.
Read more: 5 ways to boost your recovery after a workout
Other health data from smart wearables
Your smart wearable likely tracks much more than your steps, heart rate and VO2 max. However, a lot of this information is either less helpful or less accurate than the three metrics outlined above.
For example, calorie counting features can be off by as much as 93%. Similarly, while most smart wearables can reliably tell your total sleep time, they do a poor job of estimating your sleep stages and number of awakenings.
In addition, some smart wearables advertise technology that will tell you when to work out — and when not to — based on your heart rate variability (HRV), the variation between each heartbeat. It’s thought that HRV may reflect stress and recovery levels. However, the hype over HRV is ahead of the actual science, says Rieck. You’re likely better off listening to your body. You might go easy or even skip an exercise session if you’re feeling run down or haven’t been sleeping well. On the other hand, if you’re focused and energized, it might be a good day for a vigorous session.
Relevant reading
Mayo Clinic A to Z Health Guide, 2nd Edition
A browsable, illustrated one-stop shop for reliable, updated information on the signs, symptoms, tests, treatment and prevention of many common health conditions, from hiccups to cancer.
