Your heart rate can tell you a lot about your fitness. It can also help determine if you’re exercising at the desired intensity. Instead of stopping to check your pulse in the middle of a workout, you can use a smartwatch or fitness tracker to see your heart rate in real-time.
But have you ever wondered how it measures your heartbeat and how accurate it is? How do smartwatches and fitness trackers “listen” to your heartbeat? The short answer is that they use light and photoplethysmography (PPG) technology. Thankfully, the technology behind it is easier to understand than trying to pronounce it. So, let’s explore a bit deeper into how it actually works.
The Science Behind PPG
Fitness trackers shine an LED light on your skin from their sensor and detect how much of that light is absorbed or reflected. This method helps measure your heart rate because your blood absorbs light differently depending on how much is flowing through your blood vessels. Depending on the brand, it will shine this light dozens or hundreds of times per second. The more samples, the more accurate a reading.
When your heart beats, it pumps more blood throughout your body, increasing blood volume and pressure in your blood vessels. More blood absorbs more light, meaning less is reflected back. When your heart is between beats, less blood flows, so more light is reflected to the sensor. Your fitness tracker uses these changes to calculate how many times your heart beats per minute, also known as BPM.
Your fitness tracker uses an LED light, usually green or infrared, where the tracker touches the top of your wrist. It emits light that penetrates your skin and hits the tiny blood vessels underneath. Your blood absorbs some of the light, reflecting the rest back to the fitness tracker’s sensor. Then, it measures how much light it receives and determines when your heart is beating. After a few moments, it has enough information to calculate your heart rate from its measurements, giving you your current heart rate. Fitness Trackers do a good job estimating your heart rate, but they’re not perfect.
How Accurate Are Fitness Trackers?
Any activity involving fast arm movements can make the readings less reliable. If your fitness tracker is too loose or too tight, the sensor may have difficulty taking measurements. Darker skin and tattoos can absorb more light, making it harder for the fitness tracker to detect changes. Body temperature can affect readings. For example, if you’re cold, your blood vessels shrink, affecting the sensor’s accuracy. Obesity can also make it harder for light to reach the blood vessels.
Even with these challenges, fitness trackers do a good job of measuring your heart rate, especially when you’re at rest, such as sitting, sleeping, and during light activity. They’re also useful for estimating your heart rate during workouts like walking, running, or any cardio when your arms do steady rhythmic movements.
Can You Rely On Your Fitness Tracker?
Your fitness tracker is great for general heart rate monitoring and tracking trends over time. It’s useful for monitoring the intensity of your exercise and resting heart rate and seeing how stress, sleep, and workouts affect your heart rate.
Chest-strap monitors can be more accurate than fitness trackers. Instead of light, they use electrical signals, like hospital ECG machines, to measure your heart rate. They are more precise for high-intensity workouts and endurance training.
A chest-strap monitor may be better if you want more precise heart rate tracking, do high-intensity workouts, or need a more accurate reading for serious training or health monitoring. On the other hand, a fitness tracker is ideal if you want a convenient way to track your heart rate trends, care more about general fitness, sleep tracking, or stress levels, and are okay with general estimates.
However, neither a fitness tracker nor a chest-strap monitor is a replacement for medical tests or devices. If you need precise heart rate readings or blood pressure for any health reasons, you should use a medical-grade device or see your doctor.
The Takeaway
Fitness Trackers use light from an LED sensor to estimate your heart rate by measuring changes in the blood flow of your blood vessels. They aren’t as accurate as medical-grade devices found in healthcare facilities. However, they are an excellent option for estimating your heart rate for everyday health and fitness tracking.
FitTrend’s mission is to help you along your self-improvement journey, promote an active lifestyle, and help you achieve your goals. Our journal can help you track your workouts, weight, mood, calories, and more. Also, FitTrend allows you to connect supported gadgets to your account to make it easier for you to update your journal automatically. Create your account today and start using FitTrend for free!
Disclaimer: No content on this site should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.
