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Heart Rate Reserve (HRR / Karvonen)
Rating
Heart rate reserve is the difference between maximum heart rate and resting heart rate. The Karvonen method uses it to calculate zones more precisely than just a % of the maximum.
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Heart rate zones
In detail
The Karvonen formula: target heart rate = (HRmax − HRrest) × %intensity + HRrest. It accounts for the individual "width" of the heart's working range, not just the ceiling — for two people with the same HRmax but different resting heart rates, the Karvonen zones will differ noticeably, and this reflects the real physiological load more accurately.
How to use it
If you have a low resting heart rate (a sign of good fitness), be sure to use the Karvonen method instead of a simple % of maximum — otherwise your zones will be underestimated relative to the actual effort.