Heart Rate Zones: Which Pulse for Which Workout

Your pulse is the most honest training partner you have: it shows in real time how hard your body is actually working — regardless of pace, wind or daily form. Heart rate zones translate that signal into a control language: five ranges, five stimuli, five adaptations. Once you know your zones and use them consistently, every session has the right intention — and that is exactly what separates structured training from simply collecting miles.

Why zones at all?

Every training adaptation needs the matching stimulus: fat metabolism and muscle capillarization respond to long, easy efforts. Lactate clearance at threshold needs controlled hard work. Maximal oxygen uptake (VO2max) needs very short, very intense bouts. A single "medium pace" activates every system a little — but none of them properly.

Zones solve this problem: they divide the performance range into segments with a clear physiological effect. Instead of "somehow fast today", the plan reads: 60 minutes of zone 2 for base endurance, or 5 × 4 minutes in zones 4–5 for VO2max. Heart rate is the most practical control signal because it measures directly what is happening inside the body — not just what is visible on the road.

The five zones at a glance

The percentages refer to threshold heart rate (LTHR) — the model used by most training platforms. The bracketed values show the rough orientation relative to maximum heart rate.

• Zone 1 — Active recovery (below 81% LTHR / approx. 50–60% HRmax): Very easy, conversation effortless. For recovery sessions, warm-ups and cool-downs.
• Zone 2 — Base (81–89% LTHR / approx. 60–70% HRmax): The most important range of all. "Chat pace", develops fat metabolism, mitochondrial density and capillarization. 70–80% of your total volume belongs here.
• Zone 3 — Tempo (90–93% LTHR / approx. 70–80% HRmax): The "grey zone" — too hard for recovery, too easy for real threshold stimulus. Short portions are fine; as a default state it is inefficient.
• Zone 4 — Threshold (94–99% LTHR / approx. 80–90% HRmax): Just below the anaerobic threshold. Improves lactate clearance and race-pace durability. Typically 2–3 blocks of 10–20 minutes per session.
• Zone 5 — Maximum (100%+ LTHR / 90–100% HRmax): VO2max and sprint work. Intervals from 30 seconds to 5 minutes, with full recovery in between.

Determining your zones: three methods

Age formulas. "220 minus age" is statistics, not measurement: the standard deviation is ±10–12 beats. For a 40-year-old, true maximum heart rate can sit anywhere between 168 and 192. Acceptable as a rough starting point, unsuitable for steering your training.

Field test — the best practical solution. After a 10–15 minute warm-up, run or ride 20 minutes as fast as you can while keeping the effort perfectly even. The average heart rate of those 20 minutes is a very good estimate of your threshold HR. Training platforms — including Peakora — derive all five zones from it. The test takes less than an hour, costs nothing and hits reality within a few beats.

Lab test. A lactate step test or spiroergometry with a sports physician: the most expensive option (€100–250) but the most precise — including a true lactate threshold and metabolic data. Worthwhile for ambitious athletes about once a year.

Karvonen: resting HR sharpens the math

Another common method is the Karvonen formula, which includes resting heart rate alongside maximum HR: target HR = resting HR + intensity × (max HR − resting HR). An example: resting HR 50, max HR 185, desired intensity 70% gives 50 + 0.7 × 135 = 144 beats.

The advantage: heart rate reserve reflects individual fitness better than max HR alone — two 40-year-olds with identical max HR but resting rates of 48 versus 65 will train in meaningfully different ranges with Karvonen. The downside: you need two reliable measurements instead of one. Measure your resting pulse in the morning, lying down, right after waking, on three days, and take the average.

The five most common mistakes

• Running zone 2 too fast. The classic. As soon as the ego joins in, the "easy" endurance run tips into zone 3 — fatigue rises, training effect falls. The fix: cap pace by heart rate, walk briefly uphill if needed. Exactly this discipline is the core of the 80/20 principle that world-class athletes use for the bulk of their volume.
• Never updating the zones. Fitness shifts threshold HR by 5–10 beats per season. Training with two-year-old zones means training past the target. Re-test every 8–12 weeks.
• Overrating optical wrist sensors. During intervals, in cold weather or with a loose watch, optical sensors produce fantasy values. For quality sessions, the chest strap remains the standard.
• Expecting instant HR response. Heart rate takes 30–60 seconds to react to a stimulus. Steering short intervals by pulse is impossible — use pace or power instead and read heart rate only as a retrospective check.
• Treating every spike as a problem. Single jumps from gusts of wind, traffic lights or stress are normal. What matters is the weekly trend, not the individual data point.

Cardiac drift and confounding factors

Even at a perfectly constant pace, heart rate climbs over the duration of a session — cardiac drift. Dehydration and rising core temperature reduce stroke volume, and the heart compensates with a higher rate. Five to ten beats per hour is normal, considerably more in the heat. On top of that come confounding factors: caffeine (plus 3–5 beats), sleep deprivation, an oncoming illness, altitude and mental stress.

The practical consequence: on long sessions, use your heart rate from the first half as the reference, not the overall average. And if your pulse sits 10 beats above expectation for no obvious reason, treat it as an early warning sign of unabsorbed load — the same logic we describe in detail in the article on recovery in endurance sports.

Heart rate, pace or power — which one when?

Heart rate measures internal load; pace and power measure external output. The ideal is the combination: on the bike, power is the most precise control signal — instant response, independent of wind and gradient. For running, pace works well on flat ground and not at all on hills. In both cases, heart rate remains the most honest control instance: it shows what the external output actually costs your body. Track both in parallel and fitness gains become visible in black and white — the same output at a lower pulse means an adapted system.

How Peakora uses heart rate zones

In the Peakora engine, zones are not decoration but control logic: every planned session carries a target zone, and the intensity distribution of your week follows the 80/20 principle — roughly 80% of time in zones 1–2, only 20% in zones 3–5. Completed sessions are converted into load via your threshold HR: the Training Stress Score (TSS) is calculated from duration and intensity relative to threshold — a hard interval session weighs exactly as much heavier as an easy base run weighs lighter.

And because fitness changes, the engine changes the zones with it: regular field tests are a fixed part of the plan, and after every test the entire model recalibrates. You never maintain tables or calculate percentages — you simply train in the zone the plan prescribes for today.

Frequently asked questions about heart rate zones

What is the easiest way to calculate my heart rate zones?

Best done with a field test: warm up for 10 minutes, then run or ride 20 minutes at your maximum sustainable, even effort. Your average heart rate over those 20 minutes is your threshold HR, from which all five zones are calculated. Formulas like 220 minus age can easily be off by 10–15 beats.

Which heart rate zone burns the most fat?

The percentage of fat used for energy is highest in zone 2 — but fat loss depends on your overall calorie balance. Easy zone 2 training also builds exactly the mitochondria that metabolize fat. In short: lots of zone 2, not the mythical fat-burning pulse at faster speeds.

Why does my heart rate rise during a session at the same pace?

That is cardiac drift: fluid loss and rising core temperature reduce stroke volume, and the heart compensates with a higher rate — often 5–10 beats per hour. Heat, caffeine and lack of sleep amplify the effect. On long sessions, steer by your heart rate from the first half.

How often should I re-test my heart rate zones?

Every 8–12 weeks or at the end of each training phase. As your fitness improves, your heart rate at a given pace drops, and the old zones no longer fit. Re-testing also makes sense after illness, longer training breaks or a sensor change (e.g. chest strap instead of wrist).