Discover how the Apple Watch measures your heart rate and get tips for a more accurate reading.
How To Check Your Heart Rate
With watchOS 3, you can check your heart rate at any time with the Heart rate app. Open the app and wait for the Apple Watch to measure your heart rate.
You can also add the heart rate complication to the clock face or add the Heart Rate app to the Dock so you can easily open the app.
When The Apple Watch Measures The Heart Rate
If you use the Training app, the Apple Watch will constantly measure your heart rate throughout the training session.
With this information and other data collected, Apple Watch calculates how many calories you have burned. Also, Apple Watch measures your heart rate throughout the day when you’re standing still. You can see these heart rate measurements in the background in the Health app on your iPhone. Since Apple Watch only takes this measurement in the background when stopped, the time between these measurements will vary. You can control which third-party apps can access Health data from the Health app in Fonts .
How The Apple Watch Measures Your Heart Rate
The heart rate sensor of Apple Watch uses a technology called “photoplethysmography”.Although difficult to pronounce, this technology is based on something very simple: the blood is red because it reflects red light and absorbs green light. The Apple Watch uses green LED lights combined with light-sensitive photodiodes to detect the amount of blood flowing through the wrist at any given time. When the heart beats, the blood flow to the wrist (and absorption of green light) is greater. Between one beat and another, the blood flow is less. To calculate the number of heart beats per minute (or heart rate), the Apple Watch LED lights flash hundreds of times per minute. Also, the heart rate sensor is designed to compensate for low levels of signal strength by increasing the brightness of the LED lights and sampling frequency.
The heart rate sensor also uses infrared light. This is the method used by the Apple Watch to measure your heart rate in the background.
For Best Results, Start With A Good Fit
Although the conditions are perfect, Apple Watch may not be able to obtain a reliable heart rate reading at all times for everyone. What’s more, for a small percentage of users, there are several factors that can prevent obtaining any heart rate reading. However, there are several steps you can take to help Apple Watch get optimal and systematic readings.
If the Apple Watch is not in place or the sensors do not read your heart rate, adjust the strap a little.
The Apple Watch should not be tight, but comfortable.
What Other Factors Can Affect Reading
There are many factors that can affect the performance of the heart rate sensor of Apple Watch. The perfusion of the skin is one of them. It is a sophisticated way of describing how much blood flows through the skin. The perfusion of the skin varies considerably from one person to another and can also be affected by the environment. If you train in a very cold environment, for example, the perfusion of the skin of the wrist may be too low for the heart rate sensor to get a reading.
Movement is another factor that can affect the heart rate sensor. Rhythmic movements, such as running or cycling, may offer better results than irregular movements, such as playing tennis or practicing boxing.
Permanent or temporary changes in the skin, such as some tattoos, can also affect the performance of the heart rate sensor. The ink, drawing and saturation of some tattoos can block the light from the sensor, making it difficult to obtain reliable readings.
If you can not get a systematic reading as a result of any of these factors, you can connect the Apple Watch wirelessly to an external heart rate monitor, such as a chest strap with Bluetooth connection.
By recording an open water swimming session* in the Entreno app, water can prevent heart rate from being measured, but Apple Watch will continue to count the calories using the built-in accelerometer. By recording a swimming session* in the Entreno app, water can prevent heart rate from being measured, but Apple Watch will continue to count calories, laps, and distance through the built-in accelerometer.
Heart rate is just one of the many factors Apple Watch uses to measure your activity and exercise. Depending on the training, select the most suitable input sensors for that activity. For example, when running indoors, you also use the accelerometer. When cycling outdoors, use the Apple Watch Series 2 or iPhone GPS for your Apple Watch (1st generation). And even if you do not do a proper training, keep track of how much you move each day. Because of this, Apple Watch can offer you the information (and motivation) you need to improve your health and fitness.
* Available only on Apple Watch Series 2. Apple Watch Series 1 and Apple Watch (1st generation) are not suitable for swimming. Learn about the water resistance of your Apple Watch.