Ahead of the Apple Watch's availability of 24 April, Apple has published a new support page detailing the device’s heart rate monitor. As we know, the Apple Watch includes a heart rate reader to measure a person’s intensity during workouts. With knowledge of this intensity data, the Watch is able to more accurately measure the amount of calories a person burns per day. Additionally, a user can check their heart rate at any time using a feature known as the Heart Rate Glance. But beyond these two user functions, this new support document details the technologies behind the hardware as well as some little known software features.
According to the document, the Apple Watch will silently measure your heart rate every 10 minutes. This data will be stored in the iOS 8 Health application for later viewing and integration with third-party health tracking applications and hardware.
According to the document, the Apple Watch will silently measure your heart rate every 10 minutes. This data will be stored in the iOS 8 Health application for later viewing and integration with third-party health tracking applications and hardware.
Your heart rate. What it means, and where on Apple Watch you’ll find it.
Learn how Apple Watch measures your heart rate, and get tips for a more accurate reading.
The average heart rate is 72 beats per minute (bpm). As you exercise, your muscles need more oxygen, and your heart beats faster to deliver it. During workouts, the heart rate sensor in Apple Watch measures your heart rate and displays it right on your wrist. You can also check your heart rate at any time using the Heart Rate Glance. And throughout the day, Apple Watch measures your heart rate every 10 minutes and stores it in the Health app. All this information, as well as other data it collects, helps Apple Watch estimate how many calories you’ve burned. And by checking your heart rate during workouts, you can see how both your intensity level and your heart rate change over time.
How Apple Watch measures your heart rate.
The heart rate sensor in Apple Watch uses what is known as photoplethysmography. This technology, while difficult to pronounce, is based on a very simple fact: Blood is red because it reflects red light and absorbs green light. Apple Watch uses green LED lights paired with light‑sensitive photodiodes to detect the amount of blood flowing through your wrist at any given moment. When your heart beats, the blood flow in your wrist — and the green light absorption — is greater. Between beats, it’s less. By flashing its LED lights hundreds of times per second, Apple Watch can calculate the number of times the heart beats each minute — your heart rate.
The heart rate sensor can also use infrared light. This mode is what Apple Watch uses when it measures your heart rate every 10 minutes. However, if the infrared system isn’t providing an adequate reading, Apple Watch switches to the green LEDs. In addition, the heart rate sensor is designed to compensate for low signal levels by increasing both LED brightness and sampling rate.
For best results, start with a good fit.
Even under ideal conditions, Apple Watch may not be able to get a reliable heart rate reading every time for everybody. And for a small percentage of users, various factors may make it impossible to get any heart rate reading at all. But there are things you can do to help Apple Watch get the most consistent and best heart rate readings possible.
Too loose.
If your Apple Watch doesn’t stay in place, or the sensors aren’t reading your heart rate, tighten the band a bit.
Just right.
Your Apple Watch should be snug but comfortable.
What else affects your reading?
Many factors can affect the performance of the Apple Watch heart rate sensor. Skin perfusion is one. A fancy way of describing how much blood flows through your skin, skin perfusion varies significantly from person to person and can also be impacted by the environment. If you’re exercising in the cold, for example, the skin perfusion in your wrist may be too low for the heart rate sensor to get a reading. Motion is another factor. Rhythmic movements, such as running or cycling, give better results compared to irregular movements, like tennis or boxing.
If you’re not able to get a consistent reading because of any of these factors, you can connect your Apple Watch wirelessly to external heart rate monitors such as Bluetooth chest straps.
Heart rate is just one of many factors that Apple Watch uses to measure your activity and exercise. Depending on your workout, it selects the most appropriate inputs for that activity. For example, when you’re running indoors, it also uses the accelerometer. When you’re cycling outdoors, it uses the GPS in your iPhone. And even when you’re not in a dedicated workout, it tracks how much you move each day. So Apple Watch can give you the information — and the motivation — to improve your fitness and your health.
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