Wisconsin researcher says fitness trackers offer valuable, accurate health data

Today’s wearable fitness trackers do far more than count steps. The top models monitor heart rates, oxygen saturation, quality of sleep and even menstrual cycles.

Several companies have spent decades making and improving these devices. One University of Wisconsin-Madison researcher says they are remarkably accurate as a result.

Lisa Cadmus-Bertram, director of the Wisconsin Physical Activity Epidemiology Lab and an associate professor of kinesiology at the UW-Madison School of Medicine and Public Health, has studied the accuracy of fitness trackers since 2011.

“I think I bought a first-generation Fitbit near the end of 2010 and have been using them ever since,” she said. “It’s been fun to watch this group of technologies change and evolve over the years.”

Cadmus-Bertram said her research is focused on improving our understanding of how physical activity is related to chronic disease risks.  And the technology in fitness trackers has the potential to help people who have undergone cancer treatment adopt and maintain healthy lifestyles, she said.

But that requires work in the lab, determining the accuracy of the various features of different fitness tracker models.

“How good are they at accurately measuring steps? How good are they at measuring your heart rate when you’re resting? How good are they at measuring your heart rate during exercise? How well can they correctly classify what type of activity you’re doing?” Cadmus-Bertram said while describing her research recently on WPR’s “The Larry Meiller Show.”

This interview has been edited for brevity and clarity.

Larry Meiller: I wear my Apple Watch when I’m golfing. And if I take a particularly strong swing, it’ll ask, “Oh, did you fall down? Should we call emergency services?”

Lisa Cadmus-Bertram: That’s funny. Sometime in class when I’m teaching, I’ll talk about how [fitness trackers can] fall short. When they first came out, they were not very good at counting steps when your hands were stationary, like when I was pushing a grocery cart or a stroller.

The companies are always hard at work trying to improve their pattern recognition algorithms to be able to better understand the difference between, for example, jogging and being on an elliptical machine. Cycling is an activity that’s difficult for trackers, because the tracker is on your wrist, which is not the part of your body that’s primarily involved in the motion of cycling.

There are inherent challenges when you’re trying to measure the activity of a human body which could be moving in different directions at different speeds and in different patterns [at the same time], yet you only have one sensor in one place.

LM: How active does a person need to be before buying one of these devices?

LCB: Zero activity. Regardless of what your goals are, it’s important to know where you’re starting from.

One one of the most valuable aspects of fitness trackers for anybody is to know their resting heart rate and how many steps they take on a typical day. You can start to set some goals around that data.

LM: There are a bunch of trackers out there. What should we look for in a fitness tracker?

LCB: Most fitness trackers are going to have the key features that are most important for most people.

I would recommend the brands that have been around longer and have been better studied by researchers, like any of the Fitbit models. Also Garmin, known for making watches for triathletes and other endurance athletes. Garmin now has a product line for everyday people.

The Apple Watch is another good one. All of these really do have decent accuracy with the core, important metrics: heart rates — especially resting heart rate, minutes of physical activity, intensity of physical activity and steps.

LM: Are there better devices for, say, a runner or a swimmer or weight lifter?

LCB: For more serious runners, especially those running longer distances, Garmin makes some really nice devices. Often they’re accompanied by a chest strap, which is really the most accurate way to measure heart rate during exercise.

Weight lifting and yoga — those are really challenging, because the movements are often not repetitive and regular enough for the tracker to identify.

There are a lot of great apps out there that you can use to program and log weight lifting routines.

LM: Are there fitness trackers that have good security and aren’t too complex?

LCB: Most Fitbits are very easy to use, although they do have a lot of features and they keep adding more.

Fitbit used to be its own company. It’s now a subsidiary of Google, [so users are subject to the company’s] terms of service. That’s something to consider if you’re concerned about sharing your location data.

You may want to choose a fitness tracker that doesn’t include GPS. Although, if you’re carrying a cell phone around with you, your location is available through that anyway.

LM: What are the best devices for tracking sleep?

LCB: The Oura Ring, Apple Watch or Fitbit are solid choices for measuring sleep. I use the Fitbit myself for measuring sleep, and I do find it somewhat helpful.

A lot of the devices now have a new metric called “readiness” or something similar. It combines your heart rate data, resting heart rate and your sleep to give you a picture of how rested and recovered your body is, and how ready it is for the day or for workouts. So that’s another thing to consider if that’s the type of metric that you’re interested in.

LM: What can you do with heart rate and resting heart rate data?

LCB: I go through phases where I’m exercising quite a bit and quite regularly, and then life happens. I have a job and I have three children, so there can be weeks at a time when I’m not exercising. My resting heart rate when I’ve been exercising regularly is probably three or four beats lower per minute than when I’ve fallen off the exercise wagon.

Everybody’s resting heart rate is different. Typically, it’s around 60, 70, 80 beats per minute. But you can really learn a lot by paying attention to your resting heart rate and whether it’s increasing or decreasing as the months and years go by.

LM: Oura Rings. How well do they work compared to a watch?

LCB: They do a lot of the same things as a [fitness tracker worn as a] watch, as they have the same technology.

An Oura Ring looks like a thick wedding band that you wear on your index finger. Depending on how you use your hands throughout the day, you might find that to be a convenient place to wear a tracker.

It also depends on how you like to see the data from your tracker. If you’re OK using an app exclusively, you might not mind the ring [which doesn’t have a display screen].

For me, I like to look at the data on the tracker itself. I would kind of miss having something that I can look at without having to then separately open my phone.