Understanding the Karvonen Formula in 2026
The Karvonen Formula, developed by Finnish physiologist Martti Karvonen in 1957, remains the gold standard for personalised heart rate training zone prescription. Unlike the simple "220 − age" approach, it factors in resting heart rate — a proxy for cardiovascular fitness — through a concept called Heart Rate Reserve (HRR).
Athletes and sedentary individuals of the same age can have resting heart rates that differ by 30–40 bpm. The Karvonen method accounts for this difference, producing training zones that accurately reflect individual cardiovascular capacity.
Heart Rate Training Zones Reference Table
| Zone | % HRR | Physiological Goal | Perceived Effort (RPE 1–10) | Typical Duration |
|---|---|---|---|---|
| Zone 1 — Recovery | 50–60% | Active recovery, blood flow | 2–3 (Very Light) | Unlimited |
| Zone 2 — Fat Burn | 60–70% | Aerobic base, fat oxidation | 4–5 (Light–Moderate) | 45–120 min |
| Zone 3 — Aerobic | 70–80% | Cardiovascular efficiency | 5–6 (Moderate) | 30–60 min |
| Zone 4 — Threshold | 80–90% | Lactate threshold, speed | 7–8 (Hard) | 10–30 min |
| Zone 5 — Max Effort | 90–100% | VO₂ max, peak power | 9–10 (Maximal) | < 10 min |
The Karvonen Formula Step by Step
Example — 35-year-old, RHR 60 bpm, Zone 2 (60–70%):
- 1HRmax = 220 − 35 = 185 bpm
- 2HRR = 185 − 60 = 125 bpm
- 3Zone 2 lower = (125 × 0.60) + 60 = 135 bpm
- 4Zone 2 upper = (125 × 0.70) + 60 = 147 bpm
Compare this to the age-only method (Zone 2 = 111–130 bpm) — a 15–17 bpm difference that would have placed this fit individual in the wrong training zone.
Why Resting Heart Rate Matters
A lower resting heart rate indicates greater cardiac stroke volume — the heart pumps more blood per beat. Elite endurance athletes often have RHR below 40 bpm. This affects zone boundaries significantly:
| RHR | Zone 2 Lower (age 35) | Zone 2 Upper (age 35) |
|---|---|---|
| 40 bpm (athlete) | 129 bpm | 140 bpm |
| 65 bpm (average) | 132 bpm | 144 bpm |
| 80 bpm (deconditioned) | 133 bpm | 145 bpm |
The differences are modest at Zone 2 but diverge significantly at Zones 4–5, where accurate intensity control is critical for avoiding overtraining.
How to Measure Resting Heart Rate Accurately
- 1Measure on 3 consecutive mornings immediately upon waking, before rising or checking your phone.
- 2Count beats for 60 seconds (or 30 seconds × 2 for accuracy).
- 3Use the average of the 3 readings.
- 4A chest-strap heart rate monitor or wrist pulse oximeter yields the most reliable result.
Practical Training Application
- 80/20 Rule: Research shows elite endurance athletes spend ~80% of training in Zone 2 and ~20% in Zones 4–5. This polarised distribution maximises aerobic adaptation while managing fatigue.
- Zone 2 for Fat Loss: Sustained Zone 2 work (60–70% HRR) maximises fat oxidation as a fuel source. Sessions of 45–90 minutes 3–4× per week produce measurable body composition changes within 8 weeks.
- Zone 4–5 for Performance: High-intensity intervals (HIIT) in Zones 4–5 increase VO₂ max, running economy, and lactate threshold — key performance limiters.