The Karvonen formula: heart rate reserve explained
The Karvonen method sets training zones using your heart rate reserve — the gap between your resting and maximum heart rate. Because it uses your resting heart rate, it adapts to your fitness level.
The formula
The approach is named after Finnish physiologist Martti Karvonen, whose 1957 study found training improvements appeared above about 60% of heart rate reserve.
Worked example
A 45-year-old with a resting heart rate of 58 bpm, using the Tanaka maximum (176 bpm):
| Step | Calculation | Result |
|---|---|---|
| Maximum HR | 208 − 0.7 × 45 | 176 bpm |
| Heart rate reserve | 176 − 58 | 118 bpm |
| Zone 2 lower | 58 + 118 × 0.60 | 129 bpm |
| Zone 2 upper | 58 + 118 × 0.70 | 141 bpm |
Using percentage of maximum alone (60–70% of 176), the same person would get 106–124 bpm — noticeably lower.
Why resting heart rate matters
| Resting HR | Zone 2 (Karvonen), age 45 |
|---|---|
| 50 bpm | 126–139 bpm |
| 60 bpm | 130–142 bpm |
| 70 bpm | 134–145 bpm |
| 80 bpm | 138–148 bpm |
As fitness improves and resting heart rate falls, the Karvonen range shifts slightly. The method also lines up with how exercise scientists classify intensity: the American College of Sports Medicine defines moderate intensity as 40–59% of heart rate reserve.
Limitations
- It still needs a maximum heart rate. If that comes from an age formula, the error carries through. A measured maximum is better.
- Resting heart rate varies day to day. Use an average of several mornings. See how to measure resting heart rate.
- Medications such as beta-blockers lower both resting and maximum heart rate, so formulas may not apply.
Frequently asked questions
Is Karvonen better than percentage of maximum heart rate?
It is more personal because it accounts for resting heart rate, which reflects fitness. It still depends on an accurate maximum heart rate, so it is only as good as that input.
What percentage of heart rate reserve is Zone 2?
Most five-zone systems use 60–70% of heart rate reserve for Zone 2. The American College of Sports Medicine classifies 40–59% of heart rate reserve as moderate intensity.
How often should I update my resting heart rate?
Every two to three months, or after a significant change in training. Use an average of several morning readings.
Medical note: This is general information, not medical advice. Heart rate formulas are estimates. If you have a heart condition, high blood pressure, diabetes, take medication that affects heart rate (such as beta-blockers), are pregnant, or are new to exercise, ask a doctor before changing your training. Stop and seek help if you feel chest pain, severe breathlessness, dizziness or palpitations. Full disclaimer.
Calculate your Zone 2 heart rate
Sources
- British Columbia Medical Journal, "The science of exercise prescription: Martti Karvonen and his contributions"
- Pollock ML et al. "ACSM Position Stand: The recommended quantity and quality of exercise…" Medicine & Science in Sports & Exercise 1998;30(6):975–991
- Tanaka H, Monahan KD, Seals DR. "Age-predicted maximal heart rate revisited." Journal of the American College of Cardiology 2001;37(1):153–156