To Track or Not Track? Accuracy of Using Fitness Trackers

Technology has added tremendous benefit to our understanding of exercise adaptation and has become widely available and heavily used to track fitness.  Wearable technology was named the top trend in fitness according to a survey published in the American College of Sports Medicine’s Health and Fitness Journal.  With an increased demand and availability technology will continue to have a place in health and fitness circles. Today we will review some of the good and the bad that come from fitness trackers.

The Pros:

Using biometrics like heart rate, steps per day, calories per day and so forth can be a very useful tool to guide training.  Understanding your baseline activity gives a clear picture of your habits, which helps to shape your program to modify variables like time and intensity.  Fitness trackers can provide empirical data that can be tracked over time, thereby validating progress.  This reinforces individual accountability for exercise habits, which in turn helps to maintain adherence to a program and ideally leading to long term progress.  Many fitness trackers have reminders built in or send notifications on your daily activity.  Even just wearing the tracker can serve as a physical reminder to get up and move more throughout the day.  Most apps offer some sort of platform to compare your activity with friends and other users. This type of social interaction and competition is also effective at keeping people motivated to maintain and improve their activity levels.

The Cons:

When we bring energy expenditure to light, it is very hard to get exact numbers for how many calories we burn from looking at biometrics like heart rate, steps per day, calories per day and so forth.  An absolute measurement of energy expenditure would require measurement of oxygen consumption.  Much of the interpretation build into the fitness trackers and apps available are based on calculations and assumptions.  The difficulty with this is that not everyone is the same, therefore the calculations and assumptions will not always be accurate for everyone. Take steps for example, what does the activity tracker count as one step?  Individual kinematics, height, weight, step height and stride length can absolutely change the amount of work done by an individual.  These variables make it hard to account for each individual case, potentially leading to significant variations from one individual to the next.  Even heart rate tracking has shown variation.  In a study published in the Annals of Internal medicine, several wrist-based heart rate monitors were assessed for accuracy.  Patients wore the trackers while hooked up to an electrocardiogram (ECG) to compare heart rates.  At rest, the activity trackers varied plus or minus 5 beats per minute.  During exercise, there was a substantial difference, noting a range from 41 bpm underestimation to 36 bpm overestimation of heart rate compared to the ECG!  Even though the study sample size was small, this challenges the accuracy of wrist based heart rate monitors especially if the purpose is to increase fitness and performance.

The Bottom Line:

Individual results may vary.  For most of us, using a fitness tracker will be accurate enough to provide helpful insights and aid accountability.  High risk patients with serious cardiovascular, pulmonary or other conditions that require more strict monitoring would do well to invest in wearable technology that has higher accuracy.  Chest strap heart rate monitors will typically provide higher accuracy over wrist based trackers because the measurement is taken close to the heart thus reducing lag time.

At the end of the day track your biometrics with a grain of salt.  Understand that the underlying calculations used to derive steps and calories may not be as accurate as you hope.  The easiest way to make sense of the numbers is to find your baseline, and strive to make gradual improvements week in and week out to improve your average.  Don’t be afraid to seek expert opinion if you feel like you are in a slump or plateauing in your training.  Having more in depth metabolic testing can provide you with better interpretation, especially for energy expenditure both resting and exercise.  At SSMI we believe metabolic testing to be vital statistics that every patient should have tracked over time because they are equally important for clinical conditions as well as sports performance


Alex Edwards, CEP

Exercise Physiologist


Disclaimer:  Articles are based on real cases seen at Scottsdale Sports Medicine. The information on this site is not intended or implied to be a substitute for professional medical advice, diagnosis or treatment. All content, including text, graphics, images and information, contained on or available through this web site is for general information purposes only. Please consult your medical professional for individualized healthcare.



Thompson WR. WORLDWIDE SURVEY OF FITNESS TRENDS FOR 2016: 10th Anniversary Edition. ACSM'S Health & Fitness Journal. 2015; 19(6): 9-18.

Rapaport L. Fitness Trackers Not Always Great for Monitoring Exercise Heart Rate. Medscape. Apr 10, 2017.