The Karvonen Method
The simplest approach takes a percentage of maximum heart rate. The Karvonen method is better, because it works from heart rate reserve — the span between resting and maximum — which accounts for fitness:
Target = ((Max − Resting) × intensity) + Resting
Two 32-year-olds with resting rates of 48 and 72 get meaningfully different zones from Karvonen and identical ones from the simple percentage method. The fitter person's zones sit lower, which is correct.
Estimating Maximum Heart Rate
The familiar 220 − age is convenient and inaccurate, with a standard deviation of about 12 beats. The Tanaka equation, 208 − 0.7 × age, fits the research data better, particularly for people over 40. For a 32-year-old the two give 188 and 186; for a 60-year-old, 160 and 166.
A measured maximum from a graded exercise test or a hard, well-paced race effort beats any formula.
Target Heart Rate Chart
For age 32 with a resting rate of 62 bpm, maximum 186:
| Zone | Intensity | Heart rate | What it trains |
|---|---|---|---|
| Zone 1 — very light | 50–60% | 124–136 | Recovery, warm-up |
| Zone 2 — light | 60–70% | 136–149 | Aerobic base, conversational pace |
| Zone 3 — moderate | 70–80% | 149–161 | Aerobic fitness, steady tempo |
| Zone 4 — hard | 80–90% | 161–174 | Threshold, speed endurance |
| Zone 5 — maximum | 90–100% | 174–186 | VO2 max intervals |
The Fat-Burning Zone Myth
At low intensity a higher proportion of calories comes from fat, which is where the label came from. But higher intensity burns more calories in total, including more fat calories in absolute terms. For fat loss, total energy expenditure is what matters, and the "fat-burning zone" is a poor guide to it.
Zone 2 is genuinely valuable — it builds mitochondrial density and aerobic capacity with low recovery cost — but for building endurance, not for preferentially burning fat.
Polarised Training
Research on elite endurance athletes consistently finds a polarised distribution: roughly 80% of training time at low intensity and 20% hard, with very little in the middle. The common amateur pattern is the opposite — most sessions moderately hard, which accumulates fatigue without the adaptation of either end.
Frequently Asked Questions
How do I measure my resting heart rate?
Take your pulse for 60 seconds immediately on waking, before getting up, across several days and average them. A typical adult sits at 60–100 bpm; trained endurance athletes are often in the 40s.
Why is my heart rate higher on some days?
Heat, dehydration, caffeine, illness, poor sleep and accumulated training fatigue all raise it — commonly by 5–10 bpm at the same effort. A persistently elevated resting rate is a reliable early sign of overtraining or illness.
Is a high maximum heart rate better?
No. Maximum heart rate is largely genetic, declines with age, and does not correlate with fitness. What improves with training is the work you can do at any given heart rate.