The Accuracy of Fitness Trackers

Fitness trackers are quickly becoming a big part of our lives. Thanks to the advent of the smart watch, one in five Americans owns some sort of fitness tracking device. In this article, we’ll share the benefits and downside of owning a fitness tracker, what fitness trackers track and how, and how accurate they are. Then, we’ll share our reviews of the most popular fitness trackers on the market.

Benefits of Wearable Technology

There are a lot of wonderful benefits to fitness trackers. First, they give objective feedback, which means that you have objective information on where there’s room for improvement versus just “feeling” like you need to improve something. Another benefit to wearing these trackers is that it helps with consistency. Usually, these wearables have some sort of metric or way to tell you that you didn’t get whatever activity or health goal in for the day. Wearables can almost function like a coach in that regard, so you can stay on track to achieving whatever health goal you’re looking to achieve. Trackers are also great tools to measure trends over time over time, helping you to understand your habits, and to see when you’re improving or changing your habits.

How do Fitness Trackers Work?

Fitness trackers are designed to give “estimates” and not exact measurements. This is based on your weight, height, gender, age, and other information you enter when you first set up your device. The information you give your device allows it to first estimate your BMR (basal metabolic rate), which is the rate at which you burn calories at rest in order to maintain basic functions like breathing and living. Again, it estimates your BMR based on the personal data you give it. If your device tracks heart rate, your heart-rate data is also included in this estimate, which most devices are tracking.

Your heart rate is typically derived through something called photoplethysmography, or a pulse oximeter waveform, which measures blood oxygen levels using light. However, there are some variables that can make this reading less accurate, including a mislocation of the sensor, certain rapid hand movements, skin tone, body hair, and tattoos. The BMR is the basic measurement that a fitness tracker uses to give metrics like calories burned throughout the day.

For steps walked per day, fitness trackers use an accelerometer, which detects arm swinging in a walking motion. Because of this, your step count can certainly be inaccurate. For example, a lot of arm swinging motions can add more steps a tracker records. It’s suggested to wear a tracker on your non-dominant arm to compensate for this inaccuracy. Additionally, most trackers estimate stride by plugging your height and weight into an equation with accelerometer measurements to calculate your step count. All of these measurements are wonderful and mostly accurate, but not exact.

What is heart rate variability?

Heart rate variability (HRV) is measured by some fitness trackers like WHOOP, and is the variation in time between successive heartbeats. HRV is believed to be influenced by your sympathetic and parasympathetic nervous systems. The sympathetic nervous system is responsible for the “fight or flight” response, while the parasympathetic nervous system is responsible for the “rest and digest” response.

Keep in mind there are currently no set standards for HRV. Medications can impact heartbeat variation, and the accuracy of HRV tracking methods is still under scrutiny, but the technology is improving. In the future, HRV may offer a noninvasive way to signal imbalances in the autonomic nervous system that can be useful in understanding our overall health.

Calorie Measurements

Most trackers are currently far from accurate in measuring calories burned. In fact, there is at least a 27% margin of error in calculating calories burned with a fitness tracker. A couple of studies even found a 93% error, so that gives you an idea of how variable this stat can be.

One of the reasons for this inaccuracy is the more you do consistent activity, the more your body adapts to that activity and the less calories it actually burns over time doing that activity. This evolutionary trait has allowed for our survival as a species for melinia, but it’s incredibly hard for a fitness tracker to track. In fact, it doesn’t! Instead, fitness trackers give you an estimate of calories burned from BMR and accelerometer measurements, which are not entirely accurate to begin with. However, a fitness tracker should know if you’ve been a couch potato for a day vs. going for a run. Taking all of this into consideration, a healthy way to engage with calorie tracking is to look at trends over time.

Drawbacks of Fitness Trackers

There are definitely drawbacks to fitness trackers; the human element! Fitness trackers give objective (but not 100% accurate) information about calorie burning etc., and people tend to get hung up on these metrics. If you tend to get wrapped up in living by the calories burned or steps per day metrics, then you might want to consider how much you are losing emotionally and mentally vs. gaining with numbers that are not totally accurate to begin with.

Another drawback is that fitness trackers are uncomfortable to wear. There’s lots of adjusting throughout the day, which may in turn throw off the accuracy of the metrics a tracker is measuring.  Some companies, like WHOOP, are designing sports bras, swimsuits, and underwear to slip the tracking device into, so that might be worth trying.

Are Fitness Trackers Worth It?

The biggest takeaway is that these devices are useful for monitoring trends and keeping you accountable. They can gamify fitness and make you stay on track. But, keep in mind the algorithms they use are not super accurate.

Our Favorite Wearable Fitness Trackers

Whoop Fitness Tracker Review

The WHOOP strap is super popular because it measures Heart Rate Variability, which is an indicator of how recovered you are. WHOOP creates a recovery score each day as a percentage and a color: either green, yellow, or red. WHOOP also gives you a target strain score to achieve for the day to optimally perform. However, if you get a low recovery score, that doesn’t mean you shouldn’t train. You can actually build to an overreaching stage of your training, which can be beneficial for whatever adaptation you’re trying to achieve. However, you should prioritize your recovery after you’re doing this.

The WHOOP strap also tracks respiratory rate during your workout and throughout the day, and it keeps tabs and metrics on your resting heart rate over time. During the height of the COVID pandemic, scientists used the metrics (willingly) gathered from WHOOP wearers to write peer reviewed articles on COVID-19. The articles they wrote were based on how heart rate can help monitor infection and predict the risk of COVID infection.

WHOOP also gives metrics on sleep, calories burned in the day and provides a thorough monthly report on what it tracks. You can also fill out a journal everyday, which improves its accuracy. WHOOP also has an alarm that can vibrate. One drawback to WHOOP is it doesn’t track your steps.

Oura Ring Review

The Oura ring is pretty similar to the WHOOP as far as metrics it tracks. It tracks HRV, sleep, steps, calories burned, and more. It is a ring that you wear on your finger, so some people find that to be much better than wearing a watch or something around their wrist.

The up front cost is a bit more for the ring and you do need to use an app in order to look at the metrics (just like the whoop). The Oura Ring also focuses on recovery metrics versus just fitness tracking. And bonus, it does track steps.

Apple Watch Review

The apple watch is probably the most common fitness tracker, most likely for its ability to be much more than a fitness tracker. In terms of fitness tracking, however, the Apple Watch tracks your steps, blood oxygen levels, heart rate, can perform an electrocardiogram (which can detect an irregular heart rate), sleep tracking, mindfulness and stress monitoring, and women’s health tracking.

The aging population is starting to buy the Apple Watch for its electrocardiogram capabilities and ability to detect a fall and make an emergency call with your exact coordinates if you are unresponsive. If you’re an outdoor enthusiast, one of the best features it has is an SOS system that can call for help with your exact coordinates if you get lost on a hike or backcountry trip., which is definitely lifesaving.

FitBit Review

Fit Bit is probably the next most popular tracking device after the Apple Watch. It depends on which model you have, but it generally tracks steps, heart rate, gives a calorie burned estimate, tracks sleep, estimates distance traveled, and floors climbed.

There are a TON of different models out there so you can find something sleek and stylish or something that looks like a fitness watch.

Both Apple Watch and Fitbit have displays on the watch (versus the Whoop and Oura Ring) so you don’t need to have your app open while you’re training to see your workout results in live action.

Want to learn more about fitness trackers and which one we like the most? Listen to Episode #63Fitness Trend: Wearable Technology for Workouts – Is it Worth It? on the Stronger Than Your Boyfriend Podcast.

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