How Does A Fitness Tracker Work?

Written by: Chris

Updated on:

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Have you ever wondered how a fitness tracker works? It somehow manages to provide you with all these stats on your body and physical activity – but how does it do it? And are they actually helpful, or just another gadget to cost you money?

Today’s fitness trackers work by using a what’s called a three-axis accelerometer to track your various movements in all directions. Without going too in-depth (this would require a whole new article…), this is basically a device that is electro-mechanical, and tracks your movement along three-dimensional axes – named X, Y and Z.

When the accelerometer collects data (such as steps detected), it combines it with your personal data (such as your age, height, etc.) to calculate the stats.

Various other sensors in the device constantly monitor the acceleration, duration, intensity, frequency, and patterns of your movement. Some advanced trackers also have optical sensors that measure pulse and heart rate through your skin.

A fitness tracker will monitor activity or any form of exercise – from walking to running, swimming, cycling, dancing. Trackers are indeed become increasingly more advanced. The more sensors your tracker has, the more data it can collect, and the more accurate the data will be.

The device then stores the data so you can keep track of your progress. Whether you are aiming for a healthier lifestyle or you’re just aiming to lose weight, wearing a fitness tracker can help you.

The Accuracy of Fitness Trackers

For your fitness tracker to be able to present you with accurate information for fitness tracking, you need to program it with your physiological information. For most fitness tracker models, information such as your height, weight, and gender will suffice.

The tracker’s algorithm will use this information to make sense of the initial data its sensors collect from your body and store on the device. You can view the data by linking the tracker to a smartphone or computer that carries the app associated with it.

The app will process the data and present it to you as easy-to-understand stats. The app’s personalized algorithm will process the body movement data and interpret the implication of each recorded movement.

Each movement will then be categorized into different activities, expanded on, and stored under relevant headings on the fitness tracker app.

Now that the fitness tracker app has processed the data from the wearable tracker, you can view a report on the app. Using all the acquired information, the app will show you how many steps you took and how fast you moved.

It can even show you last night’s sleep quality and the number of calories burned in your last workout session. Most modern fitness trackers can also show your heart rate, deep sleep, respiratory rate, sleep stages, basal metabolic rate, and more.

How much information you can view and how you can interact with the information will depend on the fitness tracker and app. For instance, certain apps let you set fitness goals, such as how many calories to burn or how many steps to take in a day.

What Can A Fitness Tracker Measure?

A fitness tracker measures and records a variety of health and fitness metrics. This sets up the definition of what a fitness tracker is and what it’s used for.

These devices typically include sensors and algorithms that can track movement, count calories, measure altitude, and more. This explains how a fitness tracker works and the data it can measure.

Most fitness trackers also include a heart rate monitor that can track the number of times your heart beats in real time during exercise and rest, providing insight into the intensity of your workouts. This expands on the heart rate tracking feature and its usefulness.

Some modern fitness trackers can even measure blood pressure and blood oxygen saturation levels, which can be useful for monitoring respiratory and cardiovascular health. This highlights some of the newer and more advanced features available in fitness trackers.

Additionally, some fitness trackers can track sleep patterns, active minutes, and estimate stress levels based on heart rate variability. This covers other metrics that fitness trackers can measure and the insights they can provide.

What’s the Benefit of Using a Wearable Fitness Tracker?

Multiple people doing push ups while wearing fitness trackers

The largest benefit of using wearable fitness trackers, particularly modern fitness trackers, is that you can monitor and measure your daily physical activity and rest time.

As mentioned earlier, most fitness trackers can give you a general idea of the number of calories your body burns in a day. They can also help you in counting steps and tracking the time you spend on the different stages of sleep at night by measuring your wrist movements.

If you’re looking to improve your fitness levels, such information can be useful for setting and achieving fitness goals.

For this to work, though, a wearable fitness tracker and its accompanying app must provide you with the features needed to achieve your goals. The raw data collected by your tracker must also be presented in a way that’s easy to understand. It also helps if you can check the data using different devices.

Some commercial fitness trackers have apps with features that motivate users. This is done by showing the user their progress and what they need to do to achieve their set goals.

For example, the app may show the number of calories burned in a certain exercise routine, how many more need to be burned to reach the day’s goal, and how many steps need to be taken to reach that goal.

If you reach the goal, the app rewards you with a celebratory message or something more. With this, the tracker is able to help you stay motivated.

Other apps let you share your stats on social media, allowing you to brag to your family members or friends about your fitness progress. The positive feedback from your friends can be a very powerful motivator.

Are Fitness Trackers Worth it?

A woman in the gym checking her fitness tracker

Fitness trackers are worth it for people who want to set and achieve fitness goals. How many calories each person burns doing the same activity usually varies from person to person. The factors that cause this difference are something fitness trackers can’t yet compute.

For example, a person with higher muscle mass or higher testosterone levels will burn calories faster than someone with less of either. This is something that most fitness trackers can’t factor into their calculations, but this doesn’t mean that a fitness tracker is useless.

If your goal is to monitor your physical stats and daily calorie output, a quality fitness tracker can be of tremendous benefit. On the other hand, if your goal is to achieve a specific weight, you’ll need to combine fitness strategies with your use of the fitness tracker.

For some, a fitness tracker’s calorie calculations are sufficient for serving their needs. It helps one be more aware of various aspects of their health, allowing them to improve certain areas of their life. It can guide them towards getting more rest or being more physically active.

The Limitations of Fitness Trackers

Fitness trackers have come a long way in recent years and can measure a variety of metrics related to physical activity and health. However, there are still some things that fitness trackers cannot accurately measure or track:

Strength training: While some fitness trackers have modes for weightlifting or resistance training, they may not accurately track repetitions, sets, or the amount of weight lifted.

Swimming: While some fitness trackers are waterproof, they may not be able to accurately track swimming strokes, laps, or distance swam.

Breathing rate: Although some fitness trackers can monitor heart rate, they may not be able to accurately track breathing rate or respiratory rate.

Body composition: Fitness trackers may provide estimates of body fat percentage, but they may not be as accurate as other methods such as skinfold measurements or bioelectrical impedance analysis.

Emotional well-being: Fitness trackers cannot measure emotional well-being or mental health. While physical activity can improve mental health, it is not a direct measurement of emotional well-being.

Nutrition: While some fitness trackers have features for logging food intake or calorie consumption, they cannot accurately measure the nutritional content of food or provide personalized recommendations based on individual needs.

Medical conditions: Fitness trackers should not be used to diagnose or treat medical conditions. They may provide information about physical activity levels, heart rate, or sleep patterns, but a medical professional should be consulted for a proper diagnosis and treatment plan.

Just understand that your body does far more than a fitness tracker can measure, which means that the information the device can provide you is limited. Plus, there are several factors that can affect the accuracy of the device.

For the best results in improving your overall health, use a fitness tracker to manage your calories but don’t solely rely on it to get what you want. You will also need to improve your diet and find ways to boost your body’s metabolism. This will nudge you in the right direction if you really want to lose weight and achieve your fitness goals.


  1. Systematic Review of the Validity and Reliability of Consumer-Wearable Activity Trackers – NCBI – NIH

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