Heart Rate Zones and Maximum Heart Rate: How the Estimates Work

When percentage-of-maximum zones mislead

Several circumstances make age-based zones a poor guide, and the American Heart Association notes the most important one: medications that lower heart rate.

• Beta blockers and some other heart rate-limiting medicines reduce the heart rate you can reach, so percentage-of-maximum zones calculated from age will overshoot. People taking them are usually advised to use perceived exertion instead, and to follow their clinician’s guidance.
• Heart conditions, including some arrhythmias, can make heart rate an unreliable guide to effort.
• Pregnancy changes resting and exercise heart rate and has its own exercise guidance.
• Wrist-worn optical sensors are less accurate during high-intensity or irregular movement than a chest strap, which can mean the number on your wrist is not the number your heart produced.
• Heat, altitude, illness, dehydration and lack of sleep all raise heart rate at a given effort.

A refinement: heart rate reserve

The percentage-of-maximum method ignores how fit you are, and a more individual version uses heart rate reserve, the gap between your maximum and your resting heart rate. The target is calculated as resting heart rate plus a chosen percentage of the reserve. This is often called the Karvonen method, after the researcher who described it, and it gives a higher target for anyone whose resting rate is low.

Worked example: a 40-year-old with an estimated maximum of 180 and a resting rate of 60 has a reserve of 120. At 60 percent of reserve the target is 60 plus 72, or 132 beats per minute, while 60 percent of maximum alone would give 108. The two methods answer slightly different questions and neither is a measurement of how hard your body is actually working, which is one more reason to cross-check with the talk test.

For most people this extra step is not worth the complexity. It matters mainly for people who are very fit, whose resting rate may sit in the 40s or 50s, or for anyone who finds that percentage-of-maximum zones feel consistently too easy.

How zones relate to weekly activity targets

Zones describe the intensity of a single session, and public health guidance is expressed over a week. The American Heart Association recommends at least 150 minutes of moderate-intensity activity a week, or 75 minutes of vigorous activity, or an equivalent combination, which is why its target heart rate guidance is organized around those two intensity bands.

In practice, that means most people do not need to spend long in the hardest zones to meet the guidance. Brisk walking, cycling at a conversational pace and similar activities fall in the moderate band for many adults, and a vigorous minute counts for roughly two moderate minutes in the usual accounting. Someone new to exercise can reasonably start at the lower end of the moderate range and build up gradually.

Resting heart rate is a separate question

Training zones concern heart rate during effort. Resting heart rate, usually measured on waking and before getting out of bed, is a different number with its own interpretation. The American Heart Association gives a typical adult resting range of 60 to 100 beats per minute, with athletes often lower, and a resting rate that drifts upward over days can reflect illness, stress or poor recovery.

The two are related in one practical way: some training methods use heart rate reserve, the difference between maximum and resting rate, rather than a simple percentage of maximum. That is a refinement for people who track closely and not something a casual exerciser needs.