If you are relying on a fitness tracker to track your activity levels, monitor your heart rate, and record your sleep patterns, it needs to be accurate. Inaccurate data can create a misleading picture of your health and activity, and can also make it difficult or impossible to chart progress and achieve meaningful goals.
However, accuracy in a fitness tracker is a surprisingly complicated subject. Here are the things to look for, and the most accurate trackers available.
The Perception of Accuracy
Many people assume that their first fitness tracker is accurate, and then complain when they get a second one that gives different data than the first. If they are comfortable with the data they get from one device, they don’t like getting different data from a second device.
Unfortunately (for reasons we will explore below) it is very likely that you’ll get different data from two different devices. Don’t assume that the data that “feels right” or that you are accustomed to is necessarily the most accurate.
What Kind of Sensors are in a Fitness Tracker?
Fitness trackers can contain a huge range of sensors, each one of which may be more or less accurate. Here are just a few:
Pedometers have simple pendulums inside that react to the swaying motion of your body as you walk, working much the same way an analog watch does. Every time you take a step, your body swings side to side, and the pedometer clicks forward once.
Most fitness trackers use accelerometers, just like the one in your mobile phone, that tracks the motion of your body on three axes. The accelerometer senses whether you are moving, and in which direction.
Many mobile phones and fitness trackers also have a digital gyroscope, which measures orientation and direction. These can be used to monitor activities that aren’t steps, like curls and pushups.
Optical Heart Rate Sensor
Many fitness trackers monitor your heart rate using light. They shine a beam of light into the blood vessels of your wrist, and count the changes in blood volume that occur with every heartbeat. Advanced sensors can also detect blood oxygen and blood volume.
Most fitness trackers that also have smart watch capabilities (or most smart watches with fitness tracking capabilities) have GPS capability. With GPS, the device can measure your location over time, which allows it to calculate both time and distance for distance-based workouts.
Many advanced trackers also have altimeters, which use air pressure to track your altitude. For outdoor workouts, this can be important, because five miles up hill is very different from five miles on level ground.
Some fitness trackers also have temperature sensors, bio-impedance sensors, and more are being added all the time.
As you can see, the more sensors you have, the more accurate the device is: An altimeter helps outdoor workout data be more accurate, while a gyroscope helps indoor workout data to be more accurate. However, the more sensors there are, the greater the likelihood that some will be more accurate than others.
Each sensor has to be reliable and high quality in order for the most accurate complete picture to emerge.
What is the Most Accurate Fitness Tracker?
According to multiple studies and teams of experts who have done exhaustive testing, the most accurate fitness tracker is the Fitbit Charge, followed by the Garmin Vivoactive.
The Fitbit has an extremely accurate accelerometer and optical heart rate sensor, with an altimeter and accurate sleep tracking.
The Garmin Vivoactive uses precise GPS for accurate workout and sports tracking, along with a gyroscope, and advanced optical heart rate sensors that also detect blood volume and blood oxygen levels.
How You Can Improve the Accuracy of Your Fitness Tracker
Remember that the accuracy of these devices is also affected by your behavior. For example, almost everyone knows that vigorous arm movement can be inaccurately registered as steps or exercise.
Likewise, hiking in an area with poor satellite coverage reduces the accuracy of GPS readings. For the most accurate heart rate information, the wrist band must be worn snugly against the wrist without a lot of excess movement, which can be a challenge during vigorous workouts.
Fitness trackers get more accurate all the time, as the number of sensors increase, and the underlying technologies improve.
For the best accuracy, follow the manufacturer’s instructions on how to wear or use your fitness tracker, and regularly download and review your data so you get the whole picture.