How heart-rate zone training works
Heart-rate zone training uses your heart rate to control how hard you run, instead of guessing by feel. By keeping most runs easy and a small amount hard, you train each energy system on purpose. The result is more aerobic fitness with less fatigue and lower injury risk.
What heart-rate zones are
Heart-rate zones divide your effort into ranges, usually five, based on a percentage of your maximum heart rate. Each zone trains a different part of your fitness, from gentle aerobic base building at the low end to maximum power at the top. Running in the right zone for each workout is what makes a training plan effective.
How to find your maximum heart rate
Your maximum heart rate (max HR) is the highest your heart can beat during all out effort. The simplest estimate is 220 minus your age, but this can be off by 10 to 20 beats for any individual. More accurate options are a supervised field test, such as several hard hill repeats after a thorough warm up, or a lab test. Your resting heart rate, measured first thing in the morning, is also useful and improves zone accuracy when used with the heart-rate reserve method.
The 5 heart-rate zones
The table below shows a common 5 zone model based on percentage of max HR, with the purpose of each zone.
| Zone | % of max HR | Effort | Purpose |
|---|---|---|---|
| 1 | 50 to 60% | Very easy | Recovery, warm up, cool down |
| 2 | 60 to 70% | Easy, conversational | Aerobic base, fat burning, endurance |
| 3 | 70 to 80% | Moderate | Aerobic fitness, steady efforts |
| 4 | 80 to 90% | Hard | Lactate threshold, race pace |
| 5 | 90 to 100% | Maximal | Speed, VO2max, short intervals |
The 80/20 rule
Decades of research on endurance athletes point to a simple split: about 80 percent of your running should be easy (zones 1 and 2) and about 20 percent should be hard (zones 4 and 5). This is called polarized training. Most amateur runners do the opposite, running their easy days too hard and their hard days not hard enough, which leaves them tired without getting faster.
Why most runs should be easy
Easy zone 2 running builds the aerobic base that everything else rests on. It grows capillaries and mitochondria, strengthens the heart, and improves fat use, all with low injury risk. Running easy also leaves you fresh enough to hit your hard sessions with real quality, which is where the top end fitness gains come from.
Wrist sensor or chest strap?
Wrist based heart rate from a watch is convenient and accurate enough for easy and steady runs and for tracking trends. For intervals, where heart rate changes quickly, a chest strap is more accurate because it measures the heart's electrical signal directly. If your easy runs always feel too hard for the zone the watch shows, double check your max HR setting before blaming the sensor.
Common mistakes
- Running easy days in zone 3, the gray zone, too hard to recover but too easy to drive big gains.
- Using an inaccurate max HR, which shifts every zone up or down.
- Chasing heart-rate numbers on hot days or when tired, when heart rate rises for the same effort.
- Ignoring that heart rate lags effort, so it takes a few minutes to settle into a zone.
RunAI pulls heart rate from Apple Watch on every run and breaks each workout down by heart-rate zone, so you can see whether your easy days were actually easy. Your coach uses this to keep your training balanced toward the 80/20 split.
Frequently asked questions
What are the 5 heart-rate zones?
Zone 1 (50 to 60% max HR) is recovery, zone 2 (60 to 70%) is easy aerobic, zone 3 (70 to 80%) is moderate, zone 4 (80 to 90%) is threshold and race pace, and zone 5 (90 to 100%) is maximal speed and VO2max work.
How do I find my maximum heart rate?
A quick estimate is 220 minus your age, but it can be off by 10 to 20 beats. For better accuracy, do a supervised field test such as hard hill repeats after warming up, or a lab test.
What heart-rate zone should easy runs be in?
Easy runs should be in zone 2, about 60 to 70 percent of your max heart rate, where you can hold a conversation. Most runners go too hard on easy days.
What is 80/20 running?
It is the principle that about 80 percent of your running should be easy and about 20 percent hard. This polarized approach builds aerobic fitness while keeping you fresh for quality hard sessions.
Is a wrist heart-rate monitor accurate enough?
For easy and steady runs and for tracking trends, yes. For intervals with rapid heart-rate changes, a chest strap is more accurate.
Put it into practice
RunAI turns this into a personalized plan that adapts to your fitness, goals, and schedule, with a coach in your pocket every step of the way.
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