What are heart rate training zones?

Heart rate zones divide exercise intensity into ranges, each producing different physiological benefits. The 5-zone system: Zone 1 (50-60% max) for recovery, Zone 2 (60-70%) for fat burn and aerobic base, Zone 3 (70-80%) for aerobic endurance, Zone 4 (80-90%) for lactate threshold, Zone 5 (90-100%) for VO2 max and peak performance.

How much time should I spend in each zone?

The 80/20 rule is supported by research: 80% of training volume in Zone 1-2 (low intensity) and 20% in Zone 4-5 (high intensity). This polarized distribution builds aerobic base while maintaining high-intensity adaptations. Most recreational athletes make the mistake of training too much in Zone 3 (moderate) which provides less benefit per hour than either low or high intensity.

What is Zone 2 training?

Zone 2 training (60-70% max HR) is the aerobic base zone where fat is the primary fuel source. It improves mitochondrial density, fat oxidation efficiency, and aerobic capacity. Peter Attia, Andrew Huberman, and many endurance coaches emphasize Zone 2 as the foundation of longevity-focused fitness. Aim for 3-4 hours per week of Zone 2 training.

What is the difference between Karvonen and simple percentage zones?

Simple percentage zones use % of max HR only. Karvonen (Heart Rate Reserve) zones use: Target HR = ((Max HR − Resting HR) × %) + Resting HR. Karvonen zones are higher in BPM than simple percentage zones because they account for your resting HR baseline. For a fitter person with low resting HR, the difference is larger. Karvonen is more accurate for personalized training.

Heart Rate Zones Calculator

Get your personalized 5-zone heart rate training system with exact BPM ranges using the Karvonen formula. Understand when to train in each zone and how to structure your weekly training for maximum results.

Your Heart Rate Training Zones

              Max Heart Rate
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Heart Rate Reserve —

Recommended Zone —

Zone 2 (Fat Burn) —

Your 5-Zone Training Chart

Zone	% HRR	BPM (Karvonen)	BPM (% Max)	Goal	Duration / Session

Weekly Training Distribution (80/20 Rule)

Approach	Zone 1–2	Zone 3	Zone 4–5	Best For

The Science of Heart Rate Zone Training

Training in specific heart rate zones targets different energy systems and produces distinct physiological adaptations. Understanding which zone to train in — and for how long — is the foundation of effective exercise programming.

Zone 2: The Longevity Zone

Zone 2 (60–70% HRR) has gained significant attention from longevity researchers. At this intensity, mitochondria are the primary driver of energy production. Consistent Zone 2 training increases mitochondrial density and fat oxidation capacity — both strongly associated with metabolic health and longevity. Aim for 45–90 minutes per session, 3–4× per week.

The 80/20 Principle

Research on elite endurance athletes (Seiler 2010) shows that ~80% of training volume is done at low intensity (Zone 1–2) and ~20% at high intensity (Zone 4–5). This "polarized" approach outperforms training at moderate intensity (Zone 3) for both performance and health. Most recreational athletes make the mistake of training in Zone 3 too often — too hard to recover from, not hard enough to drive high-intensity adaptations.

Frequently Asked Questions

Related Reading

Zone 1 (50–60% max HR): very light, recovery. Zone 2 (60–70%): light aerobic, fat-burning base. Zone 3 (70–80%): aerobic, tempo effort. Zone 4 (80–90%): threshold, hard sustained effort. Zone 5 (90–100%): maximum effort, sprint intervals. Some systems use 3 zones; the 5-zone model is most common in endurance training.

Zone 2 (60–70% max HR) burns the highest percentage of calories from fat. However, higher-intensity zones burn more total calories per minute, which matters more for overall fat loss. The "fat-burning zone" misconception overstates the difference — total calorie deficit drives fat loss more than which zone you exercise in. Zone 2 training is valuable for building aerobic base and improving cardiovascular efficiency.

The 220-minus-age formula is a population estimate — individual max HR can vary by 10–15 bpm. The most accurate method is a graded exercise test or a field test: after a thorough warm-up, run hard uphill for 2 minutes, jog for 2 minutes, then sprint all-out for 1 minute. The highest HR reached is close to your true max. Only do this if you are healthy and conditioned.

Max HR = 220 − 35 = 185 bpm. Heart rate reserve (HRR) = 185 − 60 = 125 bpm. Using Karvonen: Zone 2 (60–70% HRR) = (125 × 0.60 + 60) to (125 × 0.70 + 60) = 135–148 bpm. Zone 4 threshold zone (80–90% HRR) = 160–173 bpm. For a 45-minute Zone 2 run, maintain 135–148 bpm throughout. This runner should aim for 80% of weekly training volume in Zone 1–2 (below 148 bpm) and reserve Zone 4–5 work for interval sessions twice per week.

Zone 3 (70–80% max HR) is called the grey zone or black hole because it is too intense to allow full aerobic adaptation and too easy to drive meaningful high-intensity gains. It accumulates fatigue without delivering the benefits of either Zone 2 or Zone 4. Polarized training research by Stephen Seiler shows that elite endurance athletes deliberately avoid accumulating too much Zone 3 volume — they get better results by spending more time in Zone 2 and supplementing with Zone 4–5 intervals.