The Athlete's Slow Pulse: Heart Rate Reserve
In a hurry? Skip straight to the numbers.
Open the Karvonen Target Heart Rate Calculator →A well-conditioned endurance athlete may have a resting heart rate far below the average person's — sometimes remarkably low. This slow pulse is a badge of fitness, and it is the key to a smarter way of setting training zones: the heart rate reserve, which personalizes effort by accounting for how fit your heart already is.
The Resting Heart Rate
How fast your heart beats at rest is a genuine window into cardiovascular fitness. A fitter heart is a stronger, more efficient pump, moving more blood with each beat, so it needs fewer beats to do its job. As fitness improves, resting heart rate tends to fall — which is why a low resting pulse is a hallmark of endurance conditioning.
The Athlete's Heart
Endurance training reshapes the heart, enlarging and strengthening it so each beat ejects more blood. This is sometimes called the “athlete's heart.” The consequence is a strikingly slow resting rate in trained athletes, whose powerful hearts can sustain circulation with far fewer beats than an untrained person needs. The slow pulse is not weakness but efficiency.
| Resting rate | Suggests |
|---|---|
| Lower | Often better conditioning |
| Higher | Less conditioning (or other factors) |
Heart Rate Reserve
Because resting rate reflects fitness, it belongs in any personalized training calculation — and this is where heart rate reserve comes in. It is the span between your resting and maximum heart rates: the range over which your heart can rev up. Two people with the same maximum but different resting rates have different reserves, and thus different fitness, which a good method should respect.
The Karvonen Method
The Karvonen method uses heart rate reserve to set training zones, taking a percentage of the reserve and adding it back to the resting rate. This personalizes the target to the individual's fitness, unlike a flat percentage of maximum heart rate that ignores resting pulse entirely. A fitter person with a lower resting rate gets appropriately adjusted targets — a more honest gauge of relative effort.
Setting Personalized Zones
To compute a Karvonen target, use the Karvonen Target Heart Rate Calculator. See all five zones with the Heart Rate Zone Calculator, and recovery with the Heart Rate Recovery Calculator.
Ready to Put This Into Practice?
Now that you understand how it works, plug in your own numbers and get an instant, accurate result.
Use the Karvonen Target Heart Rate Calculator Now →