Check exercise intensity from effort.
Exercise intensity is read from how close your working heart rate sits to your maximum. The age formula 220 minus age gives a rough ceiling, and the working rate as a share of that ceiling maps onto the familiar five zones. The Karvonen method — measuring against the reserve between resting and maximum — is shown too because it adjusts for fitness: a trained person with a low resting rate lands in a different zone than the plain percentage suggests.
Percent of maximum
Percent of max = working heart rate / (220 - age) x 100
Karvonen reserve method
Percent of reserve = (working HR - resting HR) / (max HR - resting HR) x 100
Educational estimate only. Not medical advice — discuss results with a qualified clinician before changing treatment, medication or exercise.
It carries a standard deviation of roughly 10 to 12 beats, so individuals commonly sit well above or below it. A measured maximum from a graded test is far more reliable.
Percent of heart rate reserve tracks metabolic effort better and is preferred once you know your true resting rate. Percent of maximum is easier to use and fine for casual zone checks.
Heat, dehydration, caffeine, illness and poor sleep all raise heart rate at a fixed workload. On those days the same pace genuinely is harder work.