Heart rate training gives runners something pace alone cannot: a real-time measure of physiological effort. On a hot day, a hilly course, or when accumulated fatigue makes your legs heavy, pace becomes unreliable. Heart rate reflects what your body is actually doing, regardless of external conditions.
But heart rate training is only useful if you understand the zones, know how to set them correctly, and apply them to the right workouts. Most runners get at least one of these wrong -- and the most common error is running their easy days too fast, which undermines the entire purpose of zone-based training.
The 5-Zone Model
Multiple zone systems exist (3-zone, 5-zone, 7-zone), but the 5-zone model is the most widely used in running and the most supported by research. Each zone corresponds to a distinct physiological intensity and training purpose.
| Zone | Name | % of Max HR | RPE (1-10) | Primary Purpose | How It Feels |
|---|---|---|---|---|---|
| Zone 1 | Recovery | Below 60% | 2-3 | Active recovery, warm-up | Very easy, could do it all day |
| Zone 2 | Easy/Aerobic | 60-70% | 3-5 | Aerobic base, fat oxidation | Comfortable, full conversation |
| Zone 3 | Tempo/Moderate | 70-80% | 5-7 | Muscular endurance | Comfortably hard, short sentences |
| Zone 4 | Threshold | 80-90% | 7-8 | Lactate threshold | Hard, a few words at a time |
| Zone 5 | VO2max/Anaerobic | 90-100% | 9-10 | Maximal aerobic power | Very hard, cannot speak |
Key Takeaway
The 5-zone model maps heart rate ranges to distinct physiological training targets. The critical distinction is between Zone 2 (easy aerobic running that builds your base) and Zone 3 (moderate effort that is too hard to recover from easily but too easy to produce significant speed adaptation). Most recreational runners spend too much time in Zone 3.
Zone 2: The Most Important Zone for Distance Runners
Zone 2 -- easy aerobic running at 60 to 70 percent of maximum heart rate -- is where the majority of your training should occur. This is not motivational advice. It is a consistent finding across decades of research on elite and recreational endurance athletes.
At Zone 2 intensity, your body preferentially burns fat for fuel, stimulates mitochondrial biogenesis, builds capillary density, and strengthens aerobic enzymes. These adaptations form the foundation upon which all faster training is built.
The problem: Zone 2 feels slow. For many runners, it requires a pace 60 to 90 seconds per kilometre slower than they instinctively want to run. Accepting this slowness is the single hardest mental adjustment in heart rate training -- and the most important.
How to Determine Your Maximum Heart Rate
Your heart rate zones are only as accurate as your maximum heart rate estimate. The most commonly used formula -- 220 minus age -- is also the least accurate.
The Problem With 220 Minus Age
The 220-minus-age formula was never based on original research. It originated from a rough observation by Fox et al. (1971) and was popularised through repetition, not validation. Studies have shown that it has a standard deviation of plus or minus 10 to 12 beats per minute, meaning it can be off by 20+ BPM for any given individual.
| Method | Accuracy | Practicality |
|---|---|---|
| 220 minus age | Poor (SD: +/- 10-12 BPM) | Very easy |
| Tanaka formula (208 - 0.7 x age) | Slightly better (SD: +/- 7-10 BPM) | Very easy |
| Field test (see below) | Good (within +/- 3-5 BPM) | Moderate effort required |
| Lab test (graded exercise test) | Excellent (gold standard) | Expensive, requires lab access |
Do not base your training zones on 220 minus age. A 40-year-old runner with a true max HR of 192 would get an estimate of 180, leading to zones that are approximately 6% too low. This means "easy" runs would actually be moderate, and "threshold" runs would be sub-threshold -- undermining both adaptations. Use a field test instead.
The Field Test Protocol
The most practical method for finding your true maximum heart rate is a field test. Here is a reliable protocol:
- Warm up for 15 minutes with progressive effort
- Run a sustained hard effort of 3 to 4 minutes (approximately 1 kilometre)
- Jog for 2 minutes
- Run an all-out effort of 2 to 3 minutes (approximately 800 metres)
- The highest heart rate recorded during the final effort is approximately your maximum heart rate
Perform this test when rested (not after a hard training day), on flat terrain, and ideally repeat it 2 to 3 times over several weeks to confirm the result.
Heart Rate Zones by Max HR
Once you know your maximum heart rate, calculate your zones:
| Max HR | Zone 1 (below 60%) | Zone 2 (60-70%) | Zone 3 (70-80%) | Zone 4 (80-90%) | Zone 5 (90-100%) |
|---|---|---|---|---|---|
| 170 | Below 102 | 102-119 | 119-136 | 136-153 | 153-170 |
| 175 | Below 105 | 105-123 | 123-140 | 140-158 | 158-175 |
| 180 | Below 108 | 108-126 | 126-144 | 144-162 | 162-180 |
| 185 | Below 111 | 111-130 | 130-148 | 148-167 | 167-185 |
| 190 | Below 114 | 114-133 | 133-152 | 152-171 | 171-190 |
| 195 | Below 117 | 117-137 | 137-156 | 156-176 | 176-195 |
| 200 | Below 120 | 120-140 | 140-160 | 160-180 | 180-200 |
Some coaches and platforms use heart rate reserve (HRR) instead of percentage of max HR. HRR accounts for resting heart rate: Zone % = ((Max HR - Resting HR) x target %) + Resting HR. This method produces slightly different zones and is considered more accurate for fit individuals with low resting heart rates. Both methods are valid.
The 80/20 Principle: Polarised Training
Research by Stephen Seiler, studying the training patterns of world-class endurance athletes across multiple sports, consistently found the same intensity distribution: approximately 80 percent of training volume at low intensity (Zone 1-2) and 20 percent at high intensity (Zone 4-5), with very little time in Zone 3.
This is the polarised training model, and it outperforms every alternative distribution tested in controlled studies.
| Training Model | Zone 1-2 | Zone 3 | Zone 4-5 | Research Outcome |
|---|---|---|---|---|
| Polarised (80/20) | 77-83% | 0-5% | 15-20% | Best performance improvement |
| Threshold (moderate) | 50-60% | 25-35% | 10-15% | Moderate improvement, higher fatigue |
| High-volume, low-intensity | 90-95% | 3-7% | 0-3% | Good base, limited speed gains |
| High-intensity focused | 40-50% | 15-25% | 25-35% | Short-term gains, high burnout/injury risk |
Key Takeaway
The polarised training model -- 80% of volume in Zone 1-2 and 20% in Zone 4-5, with minimal time in Zone 3 -- consistently produces the best performance outcomes in research. This means 4 out of 5 runs should be genuinely easy. For most recreational runners, this requires deliberately slowing down on easy days.
For detailed guidance on what to do during that 20 percent of hard training, see our interval training guide.
Using HR Zones for Different Workouts
| Workout Type | Target Zone | HR Guideline | Duration |
|---|---|---|---|
| Recovery run | Zone 1 | Below 65% max HR | 20-40 min |
| Easy run | Zone 2 | 60-70% max HR | 30-60 min |
| Long run | Zone 1-2 | 60-75% max HR | 60-180 min |
| Tempo run | Zone 3-4 | 75-85% max HR | 20-40 min |
| Threshold intervals | Zone 4 | 82-88% max HR | 8-20 min work periods |
| VO2max intervals | Zone 5 | 90-100% max HR | 2-5 min work periods |
For interval sessions shorter than 3 minutes, heart rate is a poor real-time guide because of cardiac lag -- your heart rate takes 1-2 minutes to reach the target zone. For short intervals, pace and perceived effort are more reliable. Use heart rate for post-workout analysis (did I reach the intended zone?) rather than real-time pacing during the interval.
Common Heart Rate Training Pitfalls
Running Easy Runs Too Fast
GPS data analysis from platforms like Strava consistently shows that recreational runners average 70 to 80 percent of max HR on their "easy" days -- firmly in Zone 3, not Zone 2. This is the most common and most damaging error in heart rate training.
The fix is simple but psychologically difficult: slow down until your heart rate stays in Zone 2, even if the pace feels ridiculously slow. Over 4 to 8 weeks, you will notice your pace at the same heart rate gradually increasing -- a direct measure of improving aerobic fitness.
Ignoring Cardiac Drift
Heart rate naturally rises during a run even at constant pace. This phenomenon, called cardiac drift, is caused by rising core temperature, progressive dehydration, and shifting blood volume. During a 90-minute easy run, heart rate can drift upward by 10 to 15 beats per minute without any change in effort.
Practical implication: if your easy run starts in Zone 2 and drifts into Zone 3 after 45 minutes, you do not need to slow down dramatically. Judge the run by the average heart rate for the session, not the final kilometres. However, if you start in Zone 3, drift will push you into Zone 4 -- and that is no longer an easy run.
Obsessing Over Daily Variations
Heart rate varies day to day based on sleep quality, stress, hydration, caffeine intake, and illness. A heart rate that is 5 to 8 beats per minute higher than usual on an easy run is normal. It becomes a concern if elevated heart rate persists for 3 or more consecutive days, which may indicate overtraining, illness, or insufficient recovery.
For context on how training volume interacts with intensity distribution, see our analysis of marathon training volume and what the data shows.
Frequently Asked Questions
Should I use a chest strap or wrist-based HR monitor?
Chest straps are significantly more accurate, particularly during high-intensity efforts. Wrist-based optical sensors can lag by 5 to 15 beats during intervals and are unreliable during workouts with rapid HR changes. For Zone 2 easy running, wrist sensors are adequate. For interval training analysis, a chest strap is recommended.
My easy pace feels too slow in Zone 2. Is that normal?
Yes. If you have been running your easy days too fast (Zone 3), transitioning to true Zone 2 will feel awkwardly slow for 3 to 6 weeks. This is the adjustment period. Your aerobic system needs time to develop. After 8 to 12 weeks of disciplined Zone 2 training, your pace at the same heart rate will improve noticeably.
Does heart rate training work for every runner?
Heart rate training is not useful for runners on certain medications (beta blockers, some blood pressure medications) that artificially suppress heart rate. For these runners, perceived effort (RPE) is a more reliable intensity guide. Additionally, runners with cardiac arrhythmias may see unreliable HR readings.
Data sources: Seiler and Kjerland (2006), "Quantifying training intensity distribution in elite endurance athletes"; Fox et al. (1971) and Tanaka et al. (2001) on maximum heart rate estimation; Stöggl and Sperlich (2014), "Polarized training has greater impact on key endurance variables"; Esteve-Lanao et al. (2007), "How do endurance runners actually train?"