Accurate calorie tracking all day, particularly during workouts, is a blessing and can be made easily available for anyone having a fitness tracker or planning to buy one.
Apple is said by many to be the ideal in sleep and activity tracking. Being an Apple Watch owner since the Series 3, I have some insights to share. But before I convince you to buy it as your next activity tracker, let’s break down some facts. Is it really accurate for calorie tracking?
The Findings:
- The Journal of Personalized Medicine published a study that stated that although all devices used in the test exceeded the allowed threshold for EE (energy expenditure), the Apple Watch was the best out of all. It is noteworthy that the “best” out of all still means a high error range.
- Another study, Accuracy of Heart Rate Watches: Implications for Weight Management, states that the Apple Watch slightly underestimated the step count with a small error margin.
- While the Heart Rate in this study published in JMIR MHealth and UHealth was found to be excellent in reliability as compared to ECG measurements. The Mean Absolute Error (MAE) for HR ranged from 6.34 bpm to 7.55 bpm, with an Intraclass Correlation Coefficient (ICC) as high as 0.958.
- Another study explored the accuracy of Apple Watch Series 6, Polar Vantage V, and Fitbit Sense, published in the European Journal of Sport Science. The Apple Watch determined the highest accuracy in measuring heart rate across five activities. While none of these devices stood out for calculating energy expenditure, heart rate is also a very important factor.
- The researchers at Stanford University School of Medicine report that across seven devices, including the Apple Watch, the most accurate device was also off by around 27%, while the least accuracy recorded was as bad as 93%.
Although the energy expenditure in all these studies was found not to be reliable, the Heart Rate was measured to excellence. And since the Heart Rate is one of the major factors in calorie counting, the Apple Watch is definitely at the top, at least as compared to other wearable devices.
How Does Apple Watch Track Calories?
The Apple Watch depends on various sensors, such as the high‑g accelerometer and high dynamic range gyroscope. These sensors help it differentiate between rest and active periods to track everyday movement, steps, and activity.
These, along with personal data added to the Health app, such as age, gender, height, weight, and heart rate readings from the heart rate sensor, help with calculating total calories.
The watch uses its algorithm when you put in a certain type of workout to calculate active calories.
My Experience with the Apple Watch
No wearable device can accurately measure calories burned; however, one that can track other biometrics, such as sleep, temperature, oxygen, etc., tends to be more precise. Being an Apple Watch user for ages and having used it on my own fitness journey (shamelessly starting every 1st Jan), I think I have a fair bit of experience to judge its accuracy.
So, the pattern I have observed over the years leads me to believe that the calories counted by my Apple Watch are correct and off by around 20-30%. So, personally, when I’m counting calories, I never factor in those calories in my total calorie intake budget. This is because if my watch calculates around 600 calories burned, I would take it as 300-400.
On the days of a heavy weightlifting session, I listen to what my body needs, and if it is an additional snack, it is absolutely justified. For the most part, I try and stick to the number I have set for myself. This is what has kept me laser-focused on my weight loss goal.
What has made me come to this conclusion is not just my personal opinion but also a test conducted by Shervin Shaikh on YouTube, depicting how the Apple Watch was overestimating calories burned by 6.5% to 70.3%. Although reasonably close in the second running test he conducted, it was less reliable in the first running test and off by 22.5% during cycling.
Another observation by The Wearable Guy states that the Apple Watch overestimated his calorie expenditure by 10-25%. A 12-week experiment concluded that the results were pretty accurate, with a weight difference of only 0.4 pounds.
Factors That Affect the Accuracy:
Personal data
The first time we use the Health app on the iPhone, it asks us various questions about things like gender, age, height, and weight. The Apple Watch uses this information to personalize burning calories while resting, also known as basal metabolic rate (BMR). Hence, changing it timely whenever something changes is crucial for an accurate count of calories burnt.
Heart Rate Monitoring
Heart rate is one of the most essential metrics in tracking calorie expenditure. Especially during workouts, tracking exertion levels gives insights into calories burned. The heart rate sensors on the Apple Watch are very accurate, almost at par with medical-grade devices, as revealed in the studies mentioned above.
Sensors
The sensors on the Apple Watch, such as a high‑g accelerometer and high dynamic range gyroscope, track everyday movement, steps, and activity, which helps it differentiate between rest and active period. This helps with calculating active calories as well as total calories.
Workout types
The type of workout you choose sets the algorithm for calculating calories according to specific workouts, their intensity, and their duration. It is very important to choose the correct workout out of the list for the closest match to your actual calories burned. This should be fairly easy since the Apple Watch supports a wide range of workouts.
Fitting of the watch on your wrist
A pretty basic factor for an accurate measurement is the snug fit of the watch. A loose-fitting watch during a workout would be influenced by the free movement and the light from surrounding areas.
Tips to Improve Apple Watch’s Accuracy for Calorie Tracking:
- Updating your health data on the Health app regularly, helps the algorithm to calculate calories very closely to your body composition.
- Choosing the right workout from the list of workouts provided is also very important. If the exact workout you’re doing isn’t on the list, choose one that is the closest.
- Having a snug fit of the watch on your wrist will eliminate outside noise and help in providing the best possible results.
- Calibrating your Apple Watch by walking or running at a normal pace on a flat surface with a good GPS signal helps the watch to get acquainted with your fitness levels and physical conditions, resulting in an accurate measurement.
Wrap Up
While no device can be 100% accurate in measuring your calorie expenditure, the Apple Watch comes pretty close.
No fitness tracker is perfect, and others may not always give you values even close to the real thing. I heard someone describe the Apple Watch’s calorie accuracy as “precise, but not accurate,”. Honestly, I couldn’t have put it any better.
