Cardio heart zones are, essentially, levels of exertion as measured based on a percentage of your maximum heart rate. Many wearable fitness devices and apps can easily measure this for you, such as the Zones app for the Apple Watch.
Knowing which cardio zone to target when you engage in cardiovascular activity will ensure your workout is effective and safe. It can also help you judge the intensity of your workout and keep you on track toward your goals. In this article, we outline the five cardio zones so you can choose the one that makes sense for you.