What are training zones? Heart rate, power and pace zones
6 min readUpdated:
Training zones are a way of dividing intensity into personal ranges. Each zone targets a different adaptation and is derived from a value you have measured — FTP, threshold pace, critical swim speed or threshold heart rate. That turns "easy" and "hard" into targets defined by your own physiology rather than one number for everyone.
In this guide
Why train by zones at all?
Endurance does not come from a single intensity. Long, comfortable sessions build the aerobic base, the capillary network and your ability to burn fat. Work around threshold lets you hold a high pace for longer. Short, hard repeats push your maximal oxygen uptake. Zones make clear which of these adaptations each session is serving, so every workout has a purpose.
The second reason is control. "Run at tempo today" means something different to everyone; for one runner it is a conversational pace, for another it leaves them gasping. A zone target is measurable: a wattage, a pace, a heart rate range. That way the easy day is genuinely easy, the hard day is genuinely hard, and the two never blur together.
Heart rate, power, pace and RPE: what does each measure?
These four measures look at the same thing from different angles. Power and pace show how much work you produce — your output. Heart rate and perceived effort (RPE) show what that work costs your body — the internal response. Good training reads both together: the same wattage can feel easy one day and hard the next.
- Power (watts): The most direct measure on the bike. It responds instantly and tells you what you are producing regardless of wind, gradient or fatigue.
- Pace (min/km, min/100 m): Practical for running and swimming. Reliable on the flat and in the pool; misleading on hills, in heat and into wind.
- Heart rate: Shows the body's response, but it lags behind effort and drifts upwards with heat, poor sleep, caffeine and long sessions.
- RPE (1–10): Needs no equipment and takes everything into account; using it well takes a little practice.
Zones are built from a measured anchor value
Every zone system rests on a reference point — an anchor. That anchor is usually threshold: the highest effort you can sustain for a long time, roughly around an hour. On the bike it is functional threshold power (FTP), on the run threshold pace, in the pool critical swim speed (CSS), and for heart rate your threshold heart rate. Zones are then defined as ranges below and above that value.
Different sources use five-, six- or seven-zone models, and the boundaries vary slightly. That detail matters far less than getting the anchor right. Zones built on a guessed value shift the entire week: if threshold is set too high, easy days become tiring; if it is set too low, hard sessions fail to give enough stimulus. Age-based maximum heart rate formulas also vary widely between individuals.
The anchor does not stay put. As you improve, threshold rises and targets written from the old value become too easy; after a break, it falls. So values need refreshing from time to time with a test done on a rested day. The new result recalculates your zones and brings the plan back in line with where you are today. If targets have felt effortless for weeks, or your heart rate at the same pace has dropped noticeably, your values are usually out of date.
No power meter or heart rate strap? Use perceived effort
You can train by zones with no device at all: perceived effort (RPE) is one of the oldest and most robust methods. On a 1–10 scale, 1 is barely moving and 10 is an all-out effort you cannot sustain. Easy sessions sit at the low end, threshold work feels "uncomfortable but controlled", and the hardest repeats can only be held for a few minutes. RPE reflects not just the effort but your sleep, the heat and your fatigue, which is exactly its strength.
The talk test makes RPE concrete. If you can chat in full sentences, you are in the easy zone. If you can only manage short phrases, you are at moderate-to-high intensity. If you cannot get more than a word out, the effort is hard. For a runner with five hours a week and no watch, every easy run should happen at full-sentence pace and the one hard session at short-phrase pace.
The most common mistake: the grey zone and drifting easy days
The most common problem among amateur athletes is not training too hard; it is doing easy days too fast and hard days not hard enough. Every session ends up somewhere moderate and "a bit of a push". This grey zone is too tiring to allow recovery and not hard enough to give a real stimulus. The result is constant fatigue and stalled performance.
- Matching someone else's pace in a group run or ride pushes the easy day into moderate.
- Holding pace on climbs: keep power or effort steady uphill, not speed.
- Not backing off when heart rate climbs in the heat or late in a long session.
- Training from an outdated threshold value, so the zones no longer reflect reality.
- Trying to finish every session faster than the last: progress is measured in weeks, not sessions.
Frequently asked questions
There is no single correct number; common models use five, six or seven zones. They all follow the same logic: intensity from very easy to maximal is split into ranges based on a measured value such as threshold. Which model you use matters far less than keeping the anchor value current and keeping easy and hard sessions clearly apart.
If you can, use both. Power is better for holding a target within a session because it shows your output instantly and directly; in short intervals heart rate lags behind. Heart rate tells you how your body is responding to that power. If it is higher than usual at the same wattage, that can signal fatigue, heat or illness.
It gives a rough starting point, but individual differences are large; two people of the same age can have very different maximum heart rates. Basing zones on a threshold heart rate measured in a test is more reliable than an age formula. Without a measurement, perceived effort (RPE) is often a better guide than a formula that may be wrong for you.
If you train consistently, testing every few months on a rested day is a common approach. Test sooner if targets start to feel noticeably easy, or if you are coming back from a long break. Avoid maximal tests close to a race: they add fatigue and the result can be misleading anyway.
This guide is general information, not medical advice. If you have a health condition, an injury or pain that does not go away, see a health professional before you train.
