What heart-rate reserve adds
Heart-rate reserve (HRR) is the range your heart can work across: maximum heart rate minus resting heart rate. The Karvonen method, published by Finnish physiologist Martti Karvonen, scales each zone within that reserve rather than against the raw maximum.
The practical effect: a fit athlete with a low resting heart rate gets lower, more appropriate targets than plain %HRmax would give. The formula is target HR = intensity% × (HRmax − RHR) + RHR, applied across the same five-zone band percentages.
Measuring resting heart rate correctly
Accuracy depends on a good resting heart rate. Measure it first thing in the morning, before you sit up, before caffeine, ideally averaged over several days. A chest strap or the resting figure from a wearable both work.
A 5-bpm error in resting heart rate shifts every Karvonen zone, so it's worth getting right. Resting heart rate also responds to fitness, sleep and stress, a creeping morning resting rate can be an early sign of fatigue or illness.
Karvonen vs %HRmax
For the same athlete, Karvonen zones sit higher in bpm than the equivalent %HRmax zones because resting heart rate raises the floor of every band. Neither is 'wrong'; they use different anchors. Karvonen is more individual; %HRmax is simpler. For the most accurate zones of all, use a lactate-threshold heart-rate test.
Worked example
Max 185 bpm, resting 50 bpm → heart-rate reserve = 135 bpm:
| Zone 2, Endurance (60–70%) | 131–145 bpm |
| Zone 3, Tempo (70–80%) | 145–158 bpm |
| Zone 4, Threshold (80–90%) | 158–172 bpm |
Notice the floors sit higher than plain %HRmax; that's the resting heart rate at work.
Frequently asked questions
Is the Karvonen formula better than percentage of max?
For most people, yes. By including resting heart rate, Karvonen personalises zones to your fitness, so a well-trained athlete with a low resting heart rate gets more appropriate targets. It's still an estimate, though, a lactate-threshold heart-rate test gives the most individual zones of all.
What is heart-rate reserve?
Heart-rate reserve is the difference between your maximum and resting heart rates, the full range your heart can work across. If your maximum is 185 and resting is 50, your reserve is 135 bpm. The Karvonen method scales each training zone within this reserve rather than against the raw maximum.
When should I measure resting heart rate?
Measure it immediately on waking, lying still, before sitting up, caffeine or stress raise it. Averaging several mornings gives the most reliable figure. A consistently rising morning resting heart rate often signals accumulated fatigue, poor sleep or an oncoming illness.
Sources
- Karvonen, Kentala & Mustala (1957). “The effects of training on heart rate.” Annales Medicinae Experimentalis et Biologiae Fenniae 35:307–315.
- Joe Friel, The Cyclist's / Triathlete's Training Bible. LTHR field-test protocol and %LTHR zone definitions.