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How do smartwatches measure calorie consumption?

Unlike before, an increasing number of people are now donning smartwatches. Even some enthusiasts of mechanical watches, unable to resist the allure, have switched to relatively "affordable" yet stylish smartwatches.

Most individuals are drawn to the smartwatch's 'health monitoring' and 'exercise assistance' features. Essentially, regardless of whether someone exercises or not, everyone is aware of using a watch to check their heart rate.

Measuring heart rate is fairly straightforward, akin to feeling one's pulse, and can be monitored anytime, anywhere. However, a smartwatch, often costing hundreds to thousands of dollars, offers more than just heart rate monitoring. There are numerous valuable features.

For instance, for those who exercise regularly, there's a practical feature: 'calorie consumption monitoring.' However, since fitness is not as popular in our country, and smartwatches have only gained popularity in recent years, most people are unfamiliar with how to utilize this feature. Today, let's discuss it briefly.

What are Calories?

"Burn my calories" – many people associate calories with this phrase, corresponding to weight loss scenes in advertisements. It's easy for people to think of calories as a unit measuring fat or even directly as fat.

It's somewhat related, but the accurate definition isn't quite like that.

"After this exercise, 209 calories were burned," pay a bit more attention after each training session, and you'll see similar statistics displayed on the smartwatch.

So, calories are essentially a unit of heat, much like meters for length and grams for weight. Its symbol is cal, but measuring calories is not as intuitive. How is it measured? Under atmospheric pressure, 1 calorie of heat can raise 1 gram of water by 1 degree Celsius.

Moreover, calories can be converted like "kilometers" and "kilograms" to "kilocalories," also known as "large calories" or "kcal."

The measurement method seems a bit abstract? Alright, let's not delve into how calories heat the water inside our bodies. All we need to know is that calories measure the energy needed to maintain normal bodily functions.

All bodily functions, from relatively static heartbeats, blood circulation, and brain activity to dynamic activities like standing, walking, running, playing sports, all require energy.

How Does a Smartwatch Measure Calorie Consumption?

Now, this might puzzle people. Measuring heart rate is understandable; those rays on the back of the dial, by measuring the size of blood flow in the wrist, easily determine the rhythm between heartbeats.

But for calorie consumption, something invisible and intangible, how is it measured? Does the smartwatch have a heat sensor?

Indeed, implementing hardware to measure heat is too demanding. In reality, the principle behind measuring calories is similar to how a smartphone predicts traffic congestion for navigation—it doesn't directly measure the target with hardware but utilizes complex algorithms.

Calorie measurement mainly relies on calculating the following types of data:

Each person's height, weight, and gender serve as baseline values. Inertial sensors (accelerometers, orientation gyroscopes) in the smartwatch and motion data from GPS (speed, altitude, distance, etc.). Real-time heart rate. These data are then fed into algorithms for real-time calculations, approximating the user's current calorie consumption.

Therefore, the principles behind measuring calories and heart rate differ fundamentally. It's more accurate to say that the data is "calculated" rather than "measured." It's evident that such data cannot guarantee precision, but it is close to laboratory conclusions and endeavors to account for differences in individual energy expenditure.

Why Understand Our Calories?

Unlike the primary significance of heart rate monitoring, monitoring calories consumed serves the purpose of assessing our exercise effects, even achieving the 'data-driven operation' of our bodily goals.

For most ordinary people who exercise, apart from the basic need to maintain good health, the main goals are generally divided into two categories: losing weight and building muscle.

From the perspective of physiology and other underlying sciences, achieving these two goals essentially involves controlling the data of our caloric intake and expenditure.

For weight loss, the goal is to expend more calories daily than gained calories;

For muscle building, it's the opposite—daily calorie intake should exceed expenditure.

The body primarily obtains calories through eating and drinking, deriving thermal energy elements from food. However, eating is inherently a chaotic affair, and currently, there's no tool to measure how many calories we've consumed. We can only rely on manual counting. (Nowadays, the calorie content of almost every type of food is readily available.)

But knowing how many calories we've burned is relatively easy with a smartwatch. Firstly, there's a basic formula to estimate our approximate daily expenditure in a static state. Then, during each exercise, the smartwatch assists in recording the calories burned. Finally, before the day ends, a simple addition is done.

This way, whether our daily calories are in surplus or deficit becomes a simple arithmetic calculation.

Of course, determining how many calories need to be lost for weight loss or gained for muscle building is not a straightforward algorithm.

At the very least, we need to know, with the help of the calorie parameter, individuals aiming to adjust their body status can more scientifically guide their diets.

Choosing foods with different calorie levels, essentially creating the most suitable food combinations, helps achieve balanced nutrition and a healthy lifestyle.

However, besides calories, balanced nutrition is also a crucial consideration when choosing food.

Understanding the concept of calories, the question on the cover, "Why do we get hungry faster in winter?" is also easily answered: winter is too cold, to maintain body temperature, the body will actively consume more calories. Rapid calorie consumption naturally leads to quicker hunger, one of the reasons why people tend to gain weight more easily in winter.

As technology advances, wearable devices will become more sophisticated. Let's not just use them to check the time and measure heart rate; otherwise, we'd be wasting 80% of the potential of these powerful products. By fully exploring their capabilities, we can experience more joy from using technological products.


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