Training zones help you give every session a clear purpose. They turn instructions such as “easy endurance”, “threshold” and “short sprints” into effort levels you can recognise and repeat.
The Endurance Lab Method uses seven zones across running, cycling and swimming. Whether you are preparing for your first race, a triathlon or an obstacle course event, the aim is to deliver the right effort for today’s workout and recover well enough for the next one.
This guide explains the zone names in your Endurance Lab training plan, the percentage boundaries for each sport and how to set your own targets.
By Tiago Dias, sports physiologist and coach, Endurance Lab, Dún Laoghaire, Dublin.
Why train in zones?
Fitness improves through a combination of training stimulus and recovery. Different intensities place different demands on your muscles, circulation and energy supply. Zones help organise those demands rather than leaving every session to chance.
Without clear targets, easy sessions often become moderately hard, while demanding sessions lose their quality. You accumulate fatigue without consistently achieving the purpose of either workout.
Why most endurance training should feel easy
Lower-intensity work lets you build aerobic fitness and practise efficient movement while keeping fatigue manageable. That supports consistency across weeks and months, which matters far more than winning a single training session.
Most endurance training should therefore be comfortable, with harder work introduced deliberately. The balance depends on your experience, available time, event and training phase. Follow your programme rather than adding intensity because an easy session feels achievable.
For triathletes, remember that fatigue accumulates across swimming, cycling and running. OCR athletes should also account for strength work, carries and obstacle practice.
The seven Endurance Lab zones
RPE means Rate of Perceived Exertion: your overall effort from 0 to 10. Use our complete RPE guide to connect these targets with breathing, talking ability and practical session examples.
| Zone | Endurance Lab name | RPE |
|---|---|---|
| Z1 | Regeneration Aerobic (AI) | Below 2 |
| Z2 | Extensive Aerobic (AII) | 2–3 |
| Z3 | Intensive Aerobic (AIII) | 3–4 |
| Z4 | Aerobic Capacity (LAN) / Anaerobic Lactate Threshold | 5–6 |
| Z5 | Aerobic Power (VO2max) | 7–8 |
| Z6 | Anaerobic Capacity (LAC) / Lactate Tolerance | 8–maximal |
| Z7 | Anaerobic Power (ALAC) / Neuromuscular Stimulation | Maximal |
Z1: regeneration and recovery
Very gentle movement supports warm-ups, cool-downs and recovery between efforts. Breathing stays relaxed. The purpose is preparation or recovery, so avoid turning a Z1 section into extra training load.
Z2: building your aerobic base
This is comfortable endurance work. It develops your ability to keep moving efficiently over longer sessions and supports the use of fat as fuel. You should be able to converse comfortably when running or cycling. Long sessions still require appropriate fuelling and hydration.
Z3: purposeful aerobic endurance
Z3 is a more demanding aerobic effort below threshold, used to build economy and event-specific endurance. Our guide describes efforts lasting up to three hours in appropriately prepared athletes. This is useful work when prescribed, but it should not quietly replace your easy sessions.
Z4: sustained threshold work
Threshold work develops your ability to sustain a strong aerobic effort and manage lactate production and use. Lactate is also a fuel, not simply waste. Breathing is strong and controlled. The guide describes approximately 40–60 minutes of sustained effort, depending on fitness; training repetitions are often shorter.
Z5: aerobic power and VO2max
These very hard efforts challenge your capacity to use oxygen at a high rate. The guide gives approximately 3–8 minutes as the effort-duration reference. Expect substantial breathing demand, with recovery allowing you to repeat good-quality work.
Z6: anaerobic capacity and lactate tolerance
Short, very demanding work develops your ability to produce and sustain high output, with a greater anaerobic contribution. The guide describes approximately 30 seconds–1 minute. Follow the prescribed recovery carefully; extending or shortening it changes the workout.
Z7: sprint power and neuromuscular stimulation
Z7 involves maximal bursts under 10 seconds. The emphasis is rapid force production, muscle recruitment and movement quality. Breathing and heart rate may not peak during such a short effort. Recover properly and stop the sprint work if technique deteriorates.
Training-zone tables by sport
These percentages use a sport-specific threshold, not your maximum heart rate or best-ever sprint. Each boundary belongs to the lower zone in the tables below, avoiding overlapping numerical ranges. Treat boundaries as practical guides: physiology does not change abruptly at a single watt or beat.
Bike zones: percentage of FTP
Functional threshold power (FTP) is a practical reference for sustained cycling power. Multiply FTP by the relevant percentage to obtain watts.
| Zone | % FTP |
|---|---|
| Z1 | Up to 70% |
| Z2 | Above 70% to 83% |
| Z3 | Above 83% to 91% |
| Z4 | Above 91% to 100% |
| Z5 | Above 100% to 102% |
| Z6 | Above 102% to 110% |
| Z7 | Above 110% |
These are the Endurance Lab percentage bands. An actual Z7 sprint requires maximal intent and the prescribed short duration; merely crossing its lower percentage boundary does not make an effort a maximal sprint.
Run zones: percentage of threshold pace
Running pace is usually displayed as minutes per kilometre or mile. In the percentage table, higher percentages mean faster running relative to threshold speed. To convert to time per distance, divide threshold pace in seconds by the percentage expressed as a decimal. Multiplying the displayed minutes-per-kilometre value directly would reverse the intended relationship.
| Zone | % of threshold speed |
|---|---|
| Z1 | Up to 76% |
| Z2 | Above 76% to 87% |
| Z3 | Above 87% to 93% |
| Z4 | Above 93% to 100% |
| Z5 | Above 100% to 102% |
| Z6 | Above 102% to 115% |
| Z7 | Above 115% |
Use effort to adapt on hills, trails or windy routes. A flat-road pace target cannot account for every change in terrain.
Swim zones: percentage of threshold pace (CSS)
Critical Swim Speed (CSS) provides a practical swimming threshold reference. The same conversion principle applies: a higher speed percentage produces a shorter time per 100 metres.
| Zone | % of CSS speed |
|---|---|
| Z1 | Up to 84% |
| Z2 | Above 84% to 91% |
| Z3 | Above 91% to 95% |
| Z4 | Above 95% to 100% |
| Z5 | Above 100% to 102% |
| Z6 | Above 102% to 105% |
| Z7 | Above 105% |
Maintain technique and follow the specified rest. In open water, conditions make RPE and breathing control especially valuable.
Heart-rate zones: percentage of lactate-threshold HR
Use lactate-threshold heart rate (LTHR), with separate running and cycling values where available. These are not percentages of maximum heart rate.
| Zone | % LTHR |
|---|---|
| Z1 | Up to 81% |
| Z2 | Above 81% to 90% |
| Z3 | Above 90% to 94% |
| Z4 | Above 94% to 100% |
| Z5 | Above 100% to 102% |
| Z6 | Above 102% to 106% |
| Z7 | Above 106% |
Heart rate responds slowly during short efforts and changes with conditions. Do not accelerate to chase a sprint heart-rate target. Use the workout’s intended effort, duration and primary measurement together.
How to find your threshold numbers
Field testing
Follow the specific test protocol in your plan. For cycling, a structured power test provides an FTP estimate; the calculation depends on the protocol. Do not assume every test’s average power equals FTP.
For running, a suitably paced time trial can estimate threshold pace and help assess threshold heart rate. Choose a repeatable course and follow the prescribed duration and analysis. A short sprint cannot establish your endurance threshold.
For swimming, our calculator accepts 400 m and 200 m test times, completed in the same session with full recovery between efforts. Their time difference is used to estimate CSS. Record accurate times and use the same pool setup for comparisons.
Lab testing in Dún Laoghaire, Dublin
For a more individual assessment, explore INSCYD and lactate testing at Endurance Lab. Testing helps assess your physiological profile and interpret training targets beyond a generic percentage calculation.
A well-conducted lab assessment provides a stronger individual basis for setting zones, although every test depends on preparation, protocol and interpretation. Bring recent training information and arrive rested, following your appointment instructions.
Put your zones into practice
- Choose a current threshold result for the correct sport.
- Enter it in the calculator and save your targets.
- Check the zone settings in your plan and training device.
- Read each workout’s duration, intensity and recovery together.
- Use RPE to check that the numbers produce the intended effort.
When should you retest and update zones?
Review thresholds every 6–8 weeks, or after a completed training block. Retest when recovered, under comparable conditions. Postpone a maximal test if ill or unusually fatigued.
After a meaningful change, update the correct sport’s threshold and zone settings in TrainingPeaks and your devices. Check a sample workout afterwards. Avoid changing zones because of one unusually good or difficult day.
Calculate your zones now with our free zone calculator. Then apply them through an Endurance Lab training plan, keeping RPE alongside the numbers.
Frequently asked questions
1. Are running and cycling heart-rate zones identical?
Not necessarily. Establish thresholds separately for each sport instead of copying one value into every activity profile.
2. Should I always aim for the top of a zone?
No. A zone is a range, not a challenge to reach its ceiling. Follow the workout’s target and purpose, particularly on easy days.
3. Why do my watch’s default zones look different?
Devices can use different reference values and boundaries. Enter your Endurance Lab settings and confirm whether heart-rate targets use threshold or maximum heart rate.
4. Can I use these zones for OCR?
Use the running zones for relevant running sections. Carries, climbs and grip work create additional muscular demands; follow their specific instructions and use RPE alongside pace.
5. What if a prescribed zone feels wrong?
Check conditions, recovery, sensor accuracy and your threshold date. Reduce effort when needed and investigate a persistent mismatch rather than repeatedly forcing the numbers.
This is general training guidance, not medical advice. Consult a doctor before starting a new training programme.
Want sessions built around your own lab-tested zones? Explore Endurance Lab coaching.
Contact: info@endurancelab.ie
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