Concept
Heart-rate reserve
The difference between maximum heart rate and resting heart rate. It is used to create training ranges that reflect both ends of an individual's heart-rate response.
How it is calculated
Subtract resting heart rate from maximum heart rate. A target intensity is calculated as a percentage of that reserve, then resting heart rate is added back.
Why it can be useful
Two runners with the same maximum but different resting heart rates may receive different working ranges, making the method more individualized than maximum-heart-rate percentage alone.
What limits it
The result is only as good as the maximum and resting values entered. Daily resting heart rate also changes with sleep, stress, illness, and measurement conditions.
Use a multi-day resting-heart-rate trend and a credible maximum estimate, then confirm the range with breathing, effort, and recovery.
Heart-rate-reserve zones are not automatically correct just because the formula uses more inputs.