- Which is better — 220 − age or 208 − 0.7·age?
- Tanaka (208 − 0.7·age) is generally more accurate. The 220 − age formula comes from Sam Fox and William Haskell in 1971 — they noted at the time it was a crude approximation, not a fitted curve. Hirofumi Tanaka and colleagues published a meta-study in 2001 (Journal of the American College of Cardiology) using data from 18,712 subjects across 351 studies; 208 − 0.7·age was their best fit. The two formulas agree near age 40, diverge in both directions outside that. For most adult athletes, especially over 40, Tanaka is closer to truth. That said, the standard error of either formula is around ±10-12 bpm for any individual — for precise zones you need a lab VO2 max test or a careful field test (a hard time-trial of 5-20 minutes, with max HR captured by a chest-strap monitor).
- What is the Karvonen formula?
- Karvonen (Martti Karvonen, Finnish physiologist, 1957) is: Target HR = (Max − Resting) × intensity% + Resting. The (Max − Resting) term is called Heart Rate Reserve (HRR). The Karvonen formula accounts for individual fitness: a trained athlete might have a max HR of 185 and a resting HR of 45 (HRR = 140), while a sedentary person of the same age might have the same max but a resting HR of 75 (HRR = 110). At the same Karvonen intensity percentage, the trained athlete's heart works harder in absolute terms. The %MaxHR method ignores this — both people would get the same Z2 bpm range. For most casual exercise, the difference is small. For structured training, Karvonen is more accurate.
- What are the five zones for, in plain English?
- Z1 (Recovery, 50-60%): so easy you barely feel exerted. Use for active recovery days and warm-ups. Z2 (Endurance, 60-70%): conversational. Most weekly endurance volume should be here — long runs, long rides, base-building. Z3 (Tempo, 70-80%): 'comfortably hard.' Sustained efforts at lactate threshold minus one. Many runners spend too much time here; it's known as the 'gray zone' because it's hard enough to need recovery, but not hard enough to drive the adaptations that Z4 does. Z4 (Threshold, 80-90%): at or just under lactate threshold. Sustainable for ~30-60 minutes. Builds the ability to clear lactate while producing it. Z5 (VO2 Max, 90-100%): intervals only. 30 seconds to 5 minutes at a time, with recovery. Builds peak aerobic capacity.
- How do I measure my resting heart rate?
- First thing in the morning, before getting out of bed. Lie still, find your pulse at your wrist or neck, count beats for 60 seconds. Do this three days in a row and take the average — single-day numbers fluctuate with sleep quality, hydration, and stress. A fitness watch with continuous HR monitoring will report your overnight low, which is usually close to resting. Typical adult resting HR is 60-100 bpm; trained endurance athletes are often 40-55 bpm. A consistently elevated resting HR (5+ bpm above your baseline for several days) is one of the earliest signs of overtraining or oncoming illness — track it.
- What's the '80/20 rule' for endurance training?
- Often called polarized training: roughly 80% of weekly training time in Z1-Z2 (easy, aerobic), 20% in Z4-Z5 (hard, threshold and above), and very little in Z3. The empirical case for it comes from Stephen Seiler's research on elite endurance athletes — rowers, cross-country skiers, runners, cyclists. The studies kept finding the same distribution at the top of the sport. The mechanism is: Z1-Z2 work builds aerobic base (mitochondrial density, capillarization, fat-oxidation) without accumulating fatigue. Z4-Z5 work drives threshold and VO2 max adaptations. Z3 is hard enough to need recovery, but not hard enough to produce either result efficiently. Most recreational athletes spend too much time in Z3 (it feels productive) and not enough in Z2 (it feels too easy).
- Why is my watch giving me different zones?
- Watches differ in which formula they use, which method (% Max vs HRR vs lactate threshold percentage), and whether they auto-adjust based on observed data. Garmin defaults to %HRR (Karvonen) if you've entered a resting HR, %Max otherwise. Apple Watch uses %Max with Fox/Haskell. Polar uses Karvonen by default. Some platforms (TrainingPeaks, WKO) work off lactate-threshold heart rate (LTHR), which only matches age-based zones loosely. If your watch zones differ from this calculator: check which formula and which method it's using; check whether it's using an LTHR rather than Max HR. None is 'wrong' — they're different reference systems.
- I'm on beta-blockers. Are these zones useful?
- Not directly. Beta-blockers reduce your max HR by 15-30% depending on dose, and they blunt the HR response to exercise generally. The %MaxHR-vs-RPE relationship is broken — what feels like Z4 effort might only be 60-65% of your medicated max HR. If you train on beta-blockers, the more useful reference is Rating of Perceived Exertion (RPE on a 1-10 scale), or a measured LTHR done while on your medication. Talk to your doctor or a cardiac rehab specialist before training above moderate intensity. This calculator is built for healthy adults; medicated values need professional interpretation.
- Can I use this for HIIT or strength training?
- Yes for HIIT — the Z4-Z5 zones are exactly what HIIT protocols target during work intervals, with Z1-Z2 between intervals for active recovery. The Tabata-style 20-on/10-off and the Norwegian 4×4 are explicit Z4-Z5 protocols. Strength training is different: HR during a heavy lifting set spikes to anaerobic levels (often 80%+ of max), but that's not the same physiological zone — you're working an anaerobic-glycolytic system, not aerobic. HR-based zones aren't the right tool for prescribing strength work; use sets/reps/% 1RM instead. The calculator is most useful for sustained aerobic and threshold work — running, cycling, rowing, swimming, cross-country skiing.
