Why Karvonen beats “220 − age”
The classic “220 − age” max-HR formula has a standard error of ±10–12 bpm, which is huge when prescribing intensity. Tanaka et al. (2001) showed 208 − 0.7×age is better for men, and Gulati et al. (2010) showed 206 − 0.88×age is more accurate for women. Karvonen (1957) then adjusts target zones using your heart rate reserve — the gap between rest and max — instead of a simple percentage of max-HR. This personalizes the prescription for fit and unfit people alike.
How to find your resting heart rate
Measure first thing in the morning before getting out of bed. Place two fingers on your wrist or neck and count beats for 60 seconds. Do this 3 mornings and average. A normal adult resting HR is 60–100 bpm; trained endurance athletes are often 40–60 bpm. A smartwatch with sleep tracking usually gives a clean lowest-resting figure each night.
The 80/20 rule of cardio training
Elite endurance athletes spend ~80% of training time in Zones 1–2 and only ~20% in Zones 4–5. Recreational athletes typically do the opposite — too much “moderate” Zone 3 work, which limits both aerobic base and top-end fitness. Build the base in Zone 2, then sharpen with intervals in Zones 4–5. Zone 3 is the dead zone — too hard to recover from, too easy to drive adaptation.
What each zone is actually for
- Zone 1: Active recovery, warm-up, cool-down.
- Zone 2: Aerobic base. The pace you can hold for hours. Builds mitochondria and fat oxidation.
- Zone 3: Tempo / sweet-spot. Comfortably hard. Use sparingly.
- Zone 4: Lactate threshold. The hardest pace you can sustain ~30–60 min. Time-trial pace.
- Zone 5: VO₂ max intervals. 1–6 minute efforts only. Critical for top-end fitness.
References
- Karvonen MJ et al. The effects of training on heart rate. Ann Med Exp Biol Fenn. 1957;35:307-15.
- Tanaka H et al. Age-predicted maximal heart rate revisited. J Am Coll Cardiol. 2001;37(1):153-156.
- Gulati M et al. Heart rate response to exercise stress testing in asymptomatic women. Circulation. 2010;122(2):130-137.