Activity Tracker
Looking every bit like a watch or bracelet depending on the model, an activity tracker is worn on the wrist by the pulse to measure the heart rate, keep track of movement, and calculate calorie burn with those two data points.1Some even provide GPS navigation so your spouse doesn’t have to keep picking you up a block away from home every time you call to tell them you got lost on your run. Ahhhhhh, modern technology!
When worn while working out, an activity tracker helps to assess intensity level better than the rate of perceived exertion (RPE) scale and more accurately than the monitor on a piece of cardio equipment…
…or maybe not.
Studies have found that activity trackers measure heart rate accurately enough to help you pin down exactly how hard you’re working as opposed to grading yourself on a scale from 1-10, which just gives a general idea.2One on the RPE scale means extremely light effort you can continue all day, such as strolling through the woods. At 4-5, you’re breathing a little heavier but can still carry a conversation. At this level, your intensity is moderate. When your breathing deepens and gets so rapid that you have to pause every few words to breathe, then you’re at 6-8 and the activity you’re doing can be considered vigorous. An activity tracker for heart rate is also much more convenient than doing the calculations to find out your heart rate zone and then manually taking your pulse to see if you’re exercising at your desired intensity level.3To find out your target heart rate zone, you first have to calculate your maximum heart rate (MHR). One formula is: 206.9 – (0.67 × age). Once you know your MHR, multiply it by your chosen percentage to arrive at the desired heart rate zone, with moderate intensity at 60-70 percent of your MHR and vigorous intensity at 70-85 percent. So if you’re 27 years old and want to do a moderate intensity workout, then your MHR is 189 and your target heart rate should be anywhere from 113 to 132 beats per minute. When it comes to calories burned, though, activity trackers aren’t to be trusted as much as they are.
Based on the findings of a study that compared activity trackers to super-precise lab instruments, no activity tracker on the market has an error rate below 20 percent, with some being off by as much as 93 percent!4Shcherbina, A, et al. “Accuracy in Wrist-Worn, Sensor-Based Measurements of Heart Rate and Energy Expenditure in a Diverse Cohort.” Journal of Personalized Medicine, vol. 7, no. 2, May 2017. That’s just one study looking at five models from different brands, but several studies share similar findings with activity trackers and calorie burn.
For someone trying to manage their weight, the gross inaccuracy of activity trackers can be problematic, as them thinking they’re burning more calories than they actually are may lead them to overeat.5As an example, calorie tracking apps like MyFitnessPal encourage users to eat back the calories burned through exercise, with the daily amount of calories changing per day to account for the amount of activity performed rather than daily intake remaining fixed. So what happens? People complain about not losing any weight! That’s what happens!!! Why is because their activity tracker is overestimating the amount of calories they burn on any given day, resulting in the amount of calories the app tells them to eat back being more than they need to maintain a calorie deficit. To avoid this very common problem, don’t pair your activity tracker with a calorie tracking app (nor add exercises to your daily food diary)!!! That’s why if choosing to wear an activity tracker, it should only be used for the heart rate function. If used for energy expenditure purposes, it should only be to provide a picture of calorie burn rather than being something you depend on.
Glossary: caloric deficit, calories, exercise, intensity, work out, workout
