Almost everyone owns a fitness tracker these days. Learn to use it to your advantage, whether you’re trying to clock more steps, improve your cardio score or sleep better.

As the fitness and wellness movement continues to gain momentum, more people across all ages are working out regularly, eating clean, and taking conscious charge of their health. Many are also turning to fitness trackers and wearable technologies which provide objective and measurable data in order to keep track of their progress.

Fitbit, Garmin, Polar and Apple are just a few of the brands available on the market for fitness trackers and related wearable technologies. The variety of fitness trackers you can find is staggering. From basic step tracking to heart rate monitoring, GPS, calorie tracking and sleep monitoring, no matter how simple or demanding your fitness needs may be, there is a device for everyone.

If you are a fitness buff who uses a fitness tracker regularly, you probably keep track of the steps you take daily, and try to hit a stipulated step count. Perhaps you keep track of your heart rate during workouts and modulate the intensity of your exercises accordingly. Your device tells you how far and fast you have run or swum. Maybe after a hard workout you look at the calories expended and tell yourself you have earned a “cheat meal“. Or when you are feeling exceptionally sluggish at the gym and wonder why, you realise that you slept poorly for the last few days – all from your wearable device.

But exactly how reliable or accurate is the data from your fitness tracker? Should you really be religiously modulating your lifestyle habits based on the feedback it provides? While some data fitness trackers spew out may be useful, some other data may need to be taken with a pinch of salt.

(Also read: 10 Clean Eating Tips For Weight Loss and Better Health)

Get walking

Multiple studies have shown high validity for step tracking across many popular brands. The number of steps you take in a day can be a good reflection of how sedentary you are, which in turn can affect your health. The more steps you take, the higher your non-exercise activity thermogenesis (NEAT), which is the amount of energy you expend through your regular daily activities of living.

A useful way to make use of this might be to monitor the usual number of steps you take in a day and then add an additional but attainable goal of 2,000 to 3,000 more steps to motivate yourself to move more. You may be surprised, but a leisurely window shopping trip to a large mall may easily attain those additional thousands of steps.

Don’t “eat back” the calories you have expended

Research suggests that the energy expenditure data from your fitness tracker is likely to be inaccurate.

A systematic review and meta-analysis by researchers from the University of Leeds, published in the British Journal of Sports Medicine, looked at data from 60 existing studies involving 40 different fitness trackers. They found that energy expenditure measurements vary vastly between devices, with a sizeable margin of error – either over or underestimating calories expended, depending on the device and activity involved. Devices which used a heart rate monitoring function to compute energy expenditure tended to be more accurate than those without.

For those looking to lose weight, using your fitness tracker to religiously calculate calorie intake and expenditure may lead you astray. Instead, it may be more useful to look at your trend in energy expenditure.

(Also read: 7 Easy Ways to Cut Calories Without Feeling Hungry)

The accuracy of heart rate monitoring is device dependent 

Most devices utilise photoplethysmography (PPG) for heart rate measurement. The pulse signal on your wrist can be detected using a light source and a light sensor on your fitness tracker. The amount of light which is reflected back to the light sensor depends on your blood flow rate. Some devices use a green light, while others may incorporate infrared light.

Unfortunately, the accuracy of heart rate monitoring can be affected by motion artefacts which affect the contact between your skin and your fitness watch – for instance, during high-intensity exercise, which ironically means your tracker may be unable to record your heart rate when it matters the most to you.

The accuracy of heart rate monitoring is also highly device-dependent from comparison studies. For example, various studies have shown that an Apple Watch’s heart rate monitoring function appears to be fairly accurate, including across various exercise intensities.

Your fitness tracker’s heart rate monitoring function can be useful as a rough guide to your exercise intensity, but you should not be excessively fixated on the numbers shown.

Don’t fret excessively about your sleep 

Sleep is extremely complex and formal sleep studies take into account multiple physiological parameters including brain wave activity, eye movement, muscle movement, breathing, etc.

Many fitness trackers utilise an accelerometer (which detects arm movement) to measure sleep. With these devices, a lack of movement can often be misinterpreted by the device as time spent asleep. If you are an insomniac who wakes up multiple times at night but lies still trying to fall sleep, your fitness tracker might misinterpret this as a night of restful sleep. Newer and more advanced devices claim to utilise a variety of other parameters to determine one’s stages of sleep, but few studies have been done to compare the accuracy of these devices to formal sleep studies.

(Also read: Sleeping With The Lights On Might Make You Fat)

Your fitness tracker may be useful in giving you a rough gauge about your sleep habits but in individuals who suspect they may suffer from issues with their sleep, a formal sleep study in a clinical setting will be more useful.

Fitness trackers have their utility and limitations – they can be great in providing useful rough data to guide your fitness journey, but don’t let yourself fret excessively about the numbers on your watch. Just get out, get moving, and get healthy.

Dr Grace Huang is a resident physician at DTAP Clinic Robertson, a general practice clinic with a special interest in men and women’s health, and sexual health.