Firstbeat Gets Calorie Counts Right

People want to know how many calories they burn throughout the day. In fact, research shows tracking calories is one of the primary reasons people buy and use fitness trackers.

Accurate calorie counts provide insight for better personal health decisions and reveal the effectiveness of weight management efforts. They can also guide nutritional choices, helping you to ensure you have the necessary energy to perform daily tasks, meet challenges, and to support recovery.

Unfortunately, despite the high demand for this vital information, many of the widely used methods to provide it are simply unreliable. Inaccurate calorie counts are particularly troublesome for those who adopt a healthy approach to weight management, where long-term goals are achieved from changes of a few hundred calories per day.

Today, millions of people around the world benefit from reliable calorie counts provided by Firstbeat. This includes tens of thousands of elite athletes using the Firstbeat Sports professional team platform, as well users of the many wearable devices that rely on the Firstbeat analytics engine to provide personalized insight based on their daily activities.

Understanding the challenge

The amount of energy your body uses is measured in calories and is changes based on the intensity of your physical activities. Lying in bed or performing sedentary work at your desk requires very little energy. Activities like walking, climbing stairs, or going for a jog cost more energy. The greater the intensity of your activity, the more energy is required. Turn that light jog into an all-out sprint and the amount of energy your body uses jumps up dramatically.

The challenge of providing accurate calorie counts is, then, largely a problem of measuring the intensity of physical activity. Place that information into the right context and you’re well on your way to solving the challenge of providing reliable calorie counts.

In recent years, there has been an explosion in the number and types of wearables devices capable of tracking heart rate. This data is sometimes used to estimate the intensity of physical activity with the goal of improving the accuracy of calorie counts, but not every method that incorporates this information is equal.

While heart rate information can provide some guidance, the relationship between heart rate and activity intensity is not particularly stable. In addition to normal variations in individual physiology, your heart rate is influenced by many factors that are not directly related to physical activity. A stressful situation will send your pulse racing, but no one would confuse public speaking with exercise. The energy costs of these activities are very different.

A lack of correlation between heart rate and activity intensity produces high error rates for calorie counts that rely on heart rate alone. These error rates are typically in the range of 25-30%, rendering feedback unreliable for informed decision making.

Complicating this issue even further is the fact that not all wearable devices capable of monitoring heart rate utilize this data to improve the calorie counts provided. A few devices rely entirely on feedback from on-board accelerometers to estimate changes in physical activity levels. An inability to reliably link movement to activity intensity in the body greatly increases the opportunity for error, making this approach even more unreliable.

A better way is the best way:

Firstbeat’s ability to automatically detect personal fitness (VO2max) levels is already step towards better calorie counts. Bringing fitness into the picture boosts ensures personalization well beyond just your age, sex, height, and weight. However, the most remarkable advantage of the Firstbeat method stems from the ability to accurately assess activity intensity in terms of oxygen consumption.

The American College of Sports Medicine correctly identifies oxygen consumption (VO2) as the key to unlocking the challenge of measuring activity intensity. Taking this understanding into account, the calculation Firstbeat uses to provide calorie counts relies on a combination of heart rate, respiration rate derived from heart rate variability, and a third variable provided by the Firstbeat analytic engine that allows the model to measure oxygen consumption (VO2) as it changes.

You might be surprised to learn that each breath you take is coded into your heartbeat data. This phenomenon is known as respiratory sinus arrhythmia (RSA). As you inhale, your heart rate increases slightly, and when you exhale your heart rate decreases slightly. Analyzing beat-to-beat changes in your heart allows Firstbeat monitor your respiration and use it to enhance the accuracy of your calorie counts across the full range of activity intensities.

While the combination of heart rate and respiration rate is a powerful step toward improving calorie count estimates, there is still room for improvement. This comes in the form of understanding what happens to the air that enters your body via respiratory system. This means identifying much oxygen is actually being used to produce energy. To do this, Firstbeat relies on neural network based modeling techniques borrowed from the world of artificial intelligence.

Once Firstbeat has established activity intensity in terms of oxygen consumption (VO2), this information is interpreted based on how various levels of oxygen usage relate to energy production pathways in the muscles. This provides the foundation for understanding the degree to which fats, carbohydrates and proteins are being metabolized and transformed into energy.

The ability to measure activity intensity in terms of oxygen consumption allows Firstbeat to avoid the pitfalls of calorie counts that rely on heart rate alone. This means accounting for changes in activity intensity, even when the relationship between intensity and heart rate becomes unreliable.This solves real-world problems like overestimation of calories during recovery breaks and unexpected training interruptions, like when you’re out for a run and need to stop for a traffic light. Your heart rate remains elevated despite a dramatic decrease in the intensity of your activity. It also reduces error related to cardiac drift, a normal increase heart rate that can occur during prolonged activity without an increase in activity intensity.


Multiple studies have investigated the reliability of the Firstbeat energy expenditure calculation method. These tests have been performed using both traditional ECG type chest belt monitors and heartbeat data obtained from optical sensors, like the type typically used in wrist based devices.

An early validation study conducted at the University of Bayreuth, in Germany, revealed the Firstbeat method to be within 7% of laboratory energy expenditure calculations. A more recent test conducted, in 2016, by members of the IEEE Engineering in Medical and Biology Society confirmed the Firstbeat method to be accurate within 6.7% during activities of medium- to hard- intensity measured using wrist worn optical sensor.

Additional studies describe accuracy of the Firstbeat method to be a 22-60% improvement over conventional heart rate based energy expenditure calculations.

Getting it right for you.

As powerful as it is, the Firstbeat method needs help to make sure that the feedback it provides is accurate for you. Here are a few things you can do to improve the calorie data you get from your device.

  1. Enter your background data. Make sure the height, weight, sex, and age information stored on your device is correct and kept up to date.
  2. Wear the device properly. The quality of your heartbeat data impacts the reliability of your calorie usage feedback, so make sure to follow the best practices for your device.
  3. Use your device regularly. This helps ensure that fitness data used to personalize your calorie counts is stable and accurate.
  4. Identify your maximum heart rate. Your device provides an initial estimate of your maximum heart rate based on your age, but updating this value to your real maximum heart rate will improve the accuracy of your calculations.

For an even deeper look at Firstbeat’s Energy Expenditure calculations, check out our white paper on the subject, here.