Your heart rate tells you something no GPS watch can measure: how hard your body is working at this moment. Not how fast you are going, not how many kilometres you have already covered, but what the actual effort is for your heart and lungs.
Training by heart rate is for most runners the most accessible and insightful way to bring structure to training sessions. You do not need expensive extra equipment for it, the basic principles are quickly understood, and the effects (if you apply them consistently) are noticeable within a few weeks.
Why your heart rate controls your training
While walking, your heart pumps oxygen-rich blood to your working muscles. The faster you run, the more oxygen your muscles require. And the faster your heart has to beat to keep up with that. Your heart rate is therefore a direct reflection of your exertion level.
That makes heart rate different from speed: speed says something about the result, heart rate says something about the effort. Do you walk the same route on a hot day, tired after a bad night, or uphill? Then your heart rate will be noticeably higher at the same pace. So speed deceives you. Heartbeat not.
The disadvantage of heart rate is the delay: your heart does not immediately adapt to acceleration. After a sprint, it takes 30 to 90 seconds for your heart rate to reflect the new effort. This is a limitation for interval training. It is perfect for endurance running, which is the most valuable application of heart rate training.
Step 1: Determine your maximum heart rate
Everything in heart rate training is based on 2 numbers: your maximum heart rate (HR-max = the highest heart rate that your heart can reach with maximum effort) and your resting heart rate (see step 2).
The well-known formula to calculate your maximum heart rate
The most commonly quoted formula is simple: 220 minus your age. A 40-year-old would then have a HR max of 180.
The problem: this formula is based on a statistical average and has a large individual variation. Someone of 40 can have an actual HR max of 165 or 195: both completely normal. If you base your zones on the wrong HR max, you will structurally train at the wrong intensity.
A more accurate formula from Sally Edwards also takes body weight into account:
- Men: 214 – (0.5 × age) – (0.11 × weight in kg)
- Women: 210 – (0.5 × age) – (0.11 × weight in kg)
But this also remains an estimate. The only reliable way to know your HR max is to measure it.
Measure your HR max yourself
Method 1: after endurance training
At the end of an endurance run, accelerate for a maximum of 1 minute. Stop sprinting, wait 10 to 15 seconds and record your heart rate. This is a reliable approach.
Method 2: interval test
Warm up for 10 minutes. Then run 8 blocks of 2 minutes with a 1 minute walking break in between, going a little faster with each block. You complete the last block completely. The peak value that your watch registers is your measured HR max.
Method 3: exercise test by a sports doctor
The most accurate method. A sports doctor determines your HR max and your turning point via a controlled treadmill test and immediately gives you your personal zones. Recommended if you want to train seriously or if you have or suspect a heart condition.
⚠️ Note: Never do a maximum test without warming up, and do not use it if you have recently been ill, have not slept well, or as a beginner without any running base.
Step 2: Measure your resting heart rate
Your resting heart rate is the second value you need. And it is at least as important as your HR max. Measure it in the morning before you get up, preferably after a normal night's sleep. Lie still, breathe calmly, and read the value on your watch or count manually on your wrist for 60 seconds.
An average resting heart rate is between 50 and 70 beats per minute. Well-trained endurance athletes are regularly below 50, sometimes even around 40. A structurally higher resting heart rate than you are used to is an early signal of fatigue, illness or overtraining.
Preferably measure your resting heart rate several mornings in a row and take the average. One measurement is too sensitive to coincidental variation.
Step 3: Calculate your heart rate zones with the Karvonen method
Determining zones based on your HR max alone is outdated. Two people with the same HR max of 180 but a resting heart rate of 45 and 70 respectively have a completely different heart-lung profile, and therefore different zones. The method that takes this into account is the Karvonen method, also known as the heart rate reserve method.
The formula works with your heart rate reserve (HRR): the difference between your maximum heart rate and your resting heart rate.
HRR = HR-max − resting heart rate
You then calculate your target heart rate for a specific zone as:
Target heart rate = resting heart rate + (HRR × % intensity)
Each zone has a lower and upper limit. You calculate this by applying the formula twice: once with the lowest percentage of the zone, once with the highest.
| Zone | % HRR | Name | Feeling | Training effect |
|---|---|---|---|---|
| Zone 1 | 50–60% | Recovery | Walking pace, completely comfortable | Active recovery, blood flow |
| Zone 2 | 60–70% | Endurance run | Quiet, it's easy to have a conversation | Aerobic base, fat burning, mitochondria |
| Zone 3 | 70–80% | Tempo duration | Conscious effort, conversation becomes more difficult | Increase aerobic threshold |
| Zone 4 | 80–90% | Threshold | Heavy breathing, no conversation | Anaerobic threshold, lactate tolerance |
| Zone 5 | 90–100% | Maximum | Exhausting, unsustainable | VO₂max, maximum speed |
Example: HR max 180, resting heart rate 55 → HRR = 125
| Zone | Calculation | Heart rate range |
|---|---|---|
| Zone 1 | 55 + (125 × 0.50) to 55 + (125 × 0.60) | 118–130 |
| Zone 2 | 55 + (125 × 0.60) to 55 + (125 × 0.70) | 130–143 |
| Zone 3 | 55 + (125 × 0.70) to 55 + (125 × 0.80) | 143–155 |
| Zone 4 | 55 + (125 × 0.80) to 55 + (125 × 0.90) | 155–168 |
| Zone 5 | 55 + (125 × 0.90) to 55 + (125 × 1.00) | 168–180 |
Compare this with the outdated method that only works on HR max of 180: zone 2 would then amount to 108–126 (60-70%). That's a difference of more than 15 strokes! Enough to train in the wrong zone for weeks without realizing it.
Zone 2: the most underestimated zone
If there is one zone that makes a difference in the long term, it is zone 2. And it is also the zone that most runners avoid the most. Not because they don't know, but because it feels too calm.
Zone 2 is the zone where you can still comfortably have a conversation. On a scale of 1 to 10 you feel around a 4: clearly active, but far from heavy. For many runners, this means people passing them in the park. That ego feeling is exactly the reason why they unconsciously go too fast and structurally end up in zone 3: the so-called "gray zone" which is too heavy to recover from quickly, but too light to really make you faster.
What zone 2 does physiologically:
- It stimulates the production and growth of mitochondria = the power plants of your muscle cells
- It increases capillary density: more small blood vessels deliver oxygen to your muscles faster
- It increases your stroke volume: your heart pumps more blood per beat, so it can work more quietly with the same effort
- It improves your fat burning: in zone 2 you use fat as a primary energy source, which saves your glycogen stores for higher intensities
The result? After weeks or months of consistent zone 2 training, you will notice that you run faster with the same low heart rate. Same route, same effort, but more kilometers. That's aerobic progression.
"Zone 2 training may seem slow, but it is the key to getting faster. You build a strong aerobic foundation, improve your fat burning and reduce your risk of injury."
The Athletic Trainer
The 80/20 Rule: Experts and research agree that the most effective training build looks like: 80% of your training volume in zones 1 and 2, and 20% in zones 3 to 5. Most recreational runners do the opposite, and then wonder why they get stuck in their progress.
Factors that influence your heart rate
Heart rate is an accurate measure of effort, but not a constant. Several factors can make your heart rate higher or lower at the same pace:
- Temperature and humidity: Your heart rate increases noticeably in the heat. Adjust your pace, not your heart rate target.
- Fatigue and sleep: Had a bad night? Your heart rate responds slower and your zones shift.
- Illness or recovery: An increased resting heart rate is an early signal that your body is still recovering. Don't continue training.
- Cafeïne: Temporarily increases heart rate, making zones at the beginning of a workout unreliable.
- Stress: Mental stress increases your heart rate through the nervous system, even when you are physically resting.
- Altitude: less oxygen in the air = higher heart rate for the same effort.
- Medication: Beta blockers artificially lower the heart rate, making heart rate zones unusable. Discuss this with a doctor.
Do you see a higher resting heart rate than normal? That's your body saying: take it easy today.
Heart rate drift: the phenomenon that deceives your zones
During a long run at a constant pace you see something strange: your speed remains the same, but your heart rate slowly increases. After 60 minutes you run at the same wattage as after 20 minutes, but your heart rate is 5 to 15 beats higher.
This is called heart rate drift (cardiac drift) and has several causes: dehydration, heat, and increasing muscular fatigue. The body gradually switches to less efficient energy processes, causing the heart to work harder.
What it means for you: During long runs, it's normal to need to slow your pace halfway through to stay in zone 2. Anyone who starts at a fixed speed will inevitably end up higher in the zones than planned. Steer by heart rate, not by speed.
Chest strap or pulse measurement? The honest answer
Most sports watches measure heart rate via green LED lights on the wrist (= optical heart rate measurement). Handy, because no extra accessory is required. But for serious heart rate training it has a serious limitation.
Pulse measurement:
- Sufficiently accurate at low intensity and constant speed
- Delayed and inaccurate with rapid intensity changes (intervals, hills)
- Sensitive to motion artifacts (arm swinging, jerking while running)
Chest strap:
- Electrocardiographic: measures each heartbeat directly
- Accurate at any intensity and with rapid changes
- Slight discomfort when wearing, but almost all serious runners swear by it
For endurance running you can get away with a pulse measurement. A chest strap is strongly recommended for interval training. The delay and inaccuracy of pulse measurement then makes zones largely meaningless.
How do you start? A practical entry-level guide
Step 1: Measure your HR-max and your resting heart rate
Use the interval test from the first part, or start with the Sally Edwards formula as an estimate. Measure your resting heart rate several mornings in a row before getting up and take the average.
Step 2: Calculate your zones via Karvonen and set them on your watch
Calculate your heart rate reserve (HR-max − resting heart rate) and apply the Karvonen formula for each zone. Enter the limits manually on your sports watch. Most watches (Garmin, Polar, Coros, Suunto) let you set this and notify you if you walk outside your target zone. Do not use the automatic zone calculator of your watch, because it usually only works based on HR max.
Step 3: Do two à three weeks exclusively zone 2
Ignore speed completely. Only run as fast as zone 2 allows. For many runners this means almost walking in the beginning: that is normal and quickly disappears.
Step 4: Gradually add intensity
Once zone 2 feels stable, add one interval training or tempo run per week (zone 4). The 80/20 split as a guideline.
Step 5: Recalculate your zones after 3 à 6 months
Your fitness improves, your HR max may shift slightly, and your zone 2 is at a different pace than at the start. Recalculating your zones is essential to continue training at the right level.
Heart rate vs power: when do you choose what?
Heart rate and power are not competitors: they measure different things. Heart rate measures how your body responds to exercise. Power measures how much energy you deliver.
For most runners, heart rate is the best entry point: accessible, no additional investment (a sports watch is sufficient), and more than accurate enough for endurance training. Do you want more control over interval training, pacing during races under varying conditions, or insight into your running efficiency? Then a power meter like Stryd adds significantly.
You can read more about power and the comparison with heart rate in our guide on running on power.
Frequently asked questions
My heart rate does not increase in zone 2. Am I walking too slowly?
Is the 220-min-age formula useful?
Can I measure heart rate with my Apple Watch or regular sports watch?
My heart rate is always lower in the morning than in the evening. What value do I use for my zones?
Do you want to take the next step and refine your pacing during competitions? Read our guide on running on power. Or see how to integrate heart rate into a complete training approach via our running technique page.
Bart Vandenbussche is passionate about sport and never shies away from a sporting challenge. He has run several marathons (including sub-3h), is an Iron+Ultra Viking, and currently has the Hyrox bug.
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