How accurate are fitness trackers?


How accurate are fitness trackers?

A helping hand would be very welcome when you’re managing your weight or better yet, monitoring various parameters of your body. Fitness trackers provide a much-needed solution for people striving for a healthier lifestyle and athletes of all levels. You’re probably used to sacredly glancing at your wrist and checking how many steps you’ve taken. But the question that poses itself is that are we basing our exercise output and lifestyle choices on false data? Let’s dissect this issue in its entirety.

What are fitness trackers?

Fitness trackers are extremely popular portable smart gadgets that are wearable around the wrist. Designed to keep track of your activity, fitness trackers utilize different types of sensors. Let’s go over some of the most pervasive sensors throughout today’s fitness trackers:

  • 3 Axis Accelerometer: tracks and senses movement in every direction (inclination, orientation, and tilt of the body) by taking inertial measurements of velocity and position.
  • Gyroscope: measures angular velocity in order to detect radial (rotating) motion.
  • Optical Sensor: uses light on the skin to measure the pulse. By measuring the rate at which blood is pumped through the capillaries, this sensor can be used to track the heart rate.
  • GPS: for the most part, fitness trackers come with built-in GPS (global positioning system), which is able to read radio signals sent from a series of satellites to calculate your exact position (in a process called triangulation) anywhere on the planet in less than a tenth of a second.
  • Altimeter: measures the altitude of an object above a fixed level by tracking pressure and height. It is most commonly used for mountain climbing.

Similar to pedometers, fitness trackers measure the steps you’ve taken. In addition, they take into account the distance travelled, speed, energy expenditure, sleep patterns, and more. Fitness trackers are marketed to provide you with a wide array of insights and metrics into how your body functions during sedentary and physical activities.

According to, the global fitness tracker market size is projected to be 114.36 billion USD by 2028. This surely means that more funds will be allocated by companies that are leading the global fitness trackers market towards technological innovations and ingenuity. However, what is the state of today’s top of the line fitness trackers?

Before you can fully gain access to the fitness tracker’s features on the app of your choice, you’ll most likely have to input basic information about your body type, such as age, weight, height, and gender. The internal mechanism of all fitness trackers is generally the same, in that they are running the raw data through their own proprietary algorithm that each company has designed separately.

What can fitness trackers help you with?

Counting steps: the likes of Fitbit recommend taking 10 thousand steps per day (goal emphasized by public health officials), whilst Garmin recommend a more realistic, yet subpar goal of taking 6 thousand steps per day. Each company has taken a stern stance regarding the minimum goals a person should set. Regardless, you can rest assured that the steps you’re taking are generally accurate.

Minutes of physical activity: Australia’s Physical Activity and Sedentary Behaviour Guidelines for Adults (18–64 years) (Department of Health 2017b) claims: “adults should be active on most, preferably all, days every week; accumulate 150 to 300 minutes (2½ to 5 hours) of moderate intensity physical activity or 75 to 150 minutes (1 ¼ to 2 ½ hours) of vigorous intensity physical activity….” Your fitness tracking app can easily record the duration of your physical activity so that you can meet the national physical activity guidelines.

Motivation and accountability: Imagine working with a life coach who you’ve fully entrusted with supervising the motivation and accountability aspects of your life. It’s often hard for a life coach to commit to you every single day of the week, which leaves a lot of room for you to go back to your old ways. On the other hand, fitness trackers are distinguished for getting people moving. In fact, many have reported that they feel bad if they’re notified through their app that they still have a number of steps to take and they haven’t taken action yet. According to a study conducted by the Association for Talent Development: “by having scheduled accountability with someone, you only have a 5% chance of not achieving your goal.” Motivation and accountability are two of the major factors as to why fitness trackers have become the latest craze.

What can’t fitness trackers help you with?

Heart rate: by relying on the undisputed science behind the use of metabolic devices, or respirometers, researchers have been able to put the efficacy of fitness trackers to the test. Surprisingly, the numbers are widely off. In a summary, once you’re doing aerobic activity, your fitness tracker picks up a lot of noise, thus underestimating or overestimating your heart rate. Unless you have an electrode on your chest, measuring the heart rate through a light against your wrist will not give you accurate data. Lastly, how tired you are, whether you’ve had coffee, or whether you’ve previously worked out are not taken into account, making the metrics of the app more prone to being volatile.

Calories burned: although most people are not interested in their heart rate during sedentary behaviour (reading, watching tv, working on your laptop) and resistance training, we still expend a significant amount of energy throughout the course of these activities. Fitness trackers underestimate the number of calories we burn because the heart rate is somehow stable compared to aerobic activity. Also, the fitness tracker is not aware whether you’re a person who tends to have more fat tissue, or whether you’re extremely muscular (a person who burns a lot of fat). Therefore, it is relying on broad estimations and generalizations. The results seem to vary with specific activity, where the number of calories burned is underestimated or overestimated.

Conclusion: it turns out that fitness trackers are relying on a lot of guess-work. Their overall rate of error is said to be up to 30%. Who would’ve known! Nonetheless, don’t be too disheartened about the money that you’ve invested in your fitness tracker because nothing has not gone to waste. As misleading as it is when it comes to key metrics, you can definitely still use it as a benchmark so you can have an idea about where your body lies. Fun fact: The future wearable will not be on your wrist but in your clothes.

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