Training by pace feels intuitive. You set a target, you try to hit it, and you judge the workout by whether you succeeded. The problem is that pace does not account for what is actually happening to your body on any given day. Heat, humidity, sleep, stress, and fatigue all affect how hard your body is working to hit a given speed. Heart rate training cuts through all of that and tells you what your body is actually doing, not just how fast your feet are moving.

Your heart rate is a direct measure of how hard your cardiovascular system is working. By training within specific heart rate ranges, you ensure that each workout is achieving its intended physiological purpose, whether that is building your aerobic base, developing threshold fitness, or pushing your top-end capacity.

Most heart rate training systems divide effort into five zones. Zone 1 is very light activity. Zone 2 is comfortable aerobic effort where you can hold a conversation. Zone 3 is a moderate push where talking becomes harder. Zone 4 is a sustained hard effort, and Zone 5 is near-maximum intensity. For most recreational endurance athletes, the majority of training should happen in Zones 2 and 3, with harder efforts used sparingly.

To use heart rate training effectively, you first need an estimate of your maximum heart rate. The common formula of 220 minus your age is a rough starting point, but it varies by individual. A more accurate method involves a field test where you push to maximum effort over a short, all-out run or ride and record the peak number on your monitor.

A chest strap heart rate monitor gives the most accurate readings during exercise, especially at higher intensities where wrist-based optical monitors can lag or lose accuracy. For most training purposes though, a wrist monitor is close enough to be useful.

The biggest adjustment most people need to make when starting heart rate training is slowing down on easy days. Almost everyone runs those days too fast. Once you commit to keeping your heart rate in the right zone, the pace usually takes care of itself, and the fitness follows.