Understanding Heart Rate Zones for Training
Heart rate zones divide your effort range into bands, each training something different. The Heart Rate Zone Calculator works them out from your age.
The formula, and how rough it is
Zones are usually derived from maximum heart rate, and max is usually estimated as 220 minus your age. That formula appeared without a published derivation and has stuck because it is easy.
Its standard deviation is around 10 to 12 beats per minute. So a 40-year-old's estimated max of 180 honestly means most 40-year-olds fall between about 168 and 192, and some sit outside that. Zones built on the estimate inherit the error, which is why a prescribed zone can feel far too easy or genuinely unpleasant.
Better formulas exist - Tanaka's 208 minus 0.7 times age is more accurate across age groups - and all of them are population estimates. The only way to know your own max is a supervised maximal test, and that is not something to attempt alone if you have any cardiac risk factors or have not trained in a while.
What each zone is for
Zone 1, 50 to 60 per cent, is recovery - walking pace. Zone 2, 60 to 70, is the easy aerobic base where you can hold a conversation. Zone 3, 70 to 80, is steady work where talking gets clipped. Zone 4, 80 to 90, is hard, sustainable for a while but not comfortably. Zone 5, 90 to 100, is sprinting.
The useful insight is that most endurance training should be easier than people make it. The widely cited pattern among trained endurance athletes is roughly eighty per cent of time at low intensity and twenty per cent hard. The common amateur mistake is spending everything in zone 3 - too hard to recover from, too easy to drive adaptation.
Talking is a better gauge than a number
Given how wide the formula's error is, perceived effort is often the more reliable instrument. If you can speak in full sentences you are in zone 2. Short phrases is zone 3. A word at a time is zone 4. Nothing is zone 5.
That test needs no device and does not care whether your max is 168 or 192, which is a real advantage over an estimated number.
Resting heart rate is worth more attention than most people give it. A gradual fall over months is a good sign of improving fitness, and a sudden rise of five to ten beats above your own normal often means you are ill, under-recovered or short of sleep.
Common questions
Should I train in the fat burning zone?
The proportion of fat burned is higher at low intensity, but total energy is higher when working hard. For body composition, total expenditure matters more than the fuel mix.
Why is my heart rate higher in hot weather?
Because your body is also cooling itself. The same pace can cost ten to twenty extra beats on a hot day, which is normal rather than a sign of lost fitness.
Are chest straps better than watches?
Yes, noticeably. Wrist optical sensors lag during intervals and misread when cold or loose.
How does this relate to VO2 max?
Both describe aerobic fitness from different angles - the VO2 Max Estimator estimates capacity rather than zones.
Want your own zone estimates?