Easy endurance is a useful part of training. A five-zone percentage range does not measure your first threshold or establish one optimal intensity for every adaptation.
How it feels
Easy and conversational
Why use it
Build a repeatable endurance routine
An example
A conversational run or ride paced so that the intended easy effort remains sustainable.
These names describe this guide’s five-zone convention. Thresholds, effort and useful session duration vary with your zone system, sport and individual testing.
Training intensity changes continuously. A zone system divides that continuum into bands so you can communicate a workout, summarize a session or compare patterns over time. The bands make a training log easier to use; they do not create sharp biological changes at every color boundary.
Always identify the model, metric and anchor. Five percentage-based heart-rate bands, three zones based on physiological thresholds and cycling power bands can all be useful, but the same number may mean something different in each. A zone number without its definition is incomplete information.
Our five-zone explorer follows the app's percentage convention: Recovery, Endurance, Tempo, Threshold and High intensity. With a maximum-heart-rate anchor, the bands use 50–60%, 60–70%, 70–80%, 80–90% and 90–100%. With heart-rate reserve, those same percentages are applied to maximum minus resting heart rate, then resting heart rate is added back.
These names communicate common training uses, not laboratory findings. Zone 4 does not certify a lactate threshold; Zone 5 does not certify VO2max; Zone 1 does not certify recovery. The methods explorer shows why a different anchor can produce different bands while the underlying person has not changed.
Recovery: the easiest band, often used for light movement and easier workout phases.
Endurance: an easy band commonly used to build a repeatable aerobic routine.
Tempo: the middle band, useful for describing purposeful steady work.
Threshold: a hard band whose name must be distinguished from a measured threshold.
High intensity: the highest band, interpreted alongside duration and workout structure.
Physiological landmarks provide another kind of map
Lactate and gas-exchange tests can identify changes in the response to increasing exercise. Research often uses two landmarks to organize a three-zone model: below the first threshold, between thresholds and above the second. Read the specific test definition rather than assuming every paper located the same boundaries.
Exercise-intensity domains such as moderate, heavy and severe describe physiological behavior. They are not interchangeable with public-health intensity labels or every threshold-derived zone chart. Different proposed upper landmarks do not automatically agree; a fixed lactate value or a percentage estimate cannot simply stand in for critical power.
Muscles use interacting pathways to supply energy. Their relative contributions change with the activity and duration, rather than switching on one after another. The aerobic system remains involved during demanding efforts, and the label anaerobic does not describe everything happening above a colored boundary.
Fuel choice is another question. Fat and carbohydrate use cannot be read as exact personal percentages from five heart-rate bands. A fuel-use measurement describes a particular test condition, whereas body-fat change requires follow-up measurements over time. Keep those questions separate when evaluating a fat-burning claim.
Intensity, duration, frequency and initial fitness all matter when studying training. An easy session repeated across a substantial program is different from a brief isolated session; a harder protocol may look more efficient when its result is divided by training time. The denominator changes the question.
A large systematic synthesis found mitochondrial changes across continuous endurance, high-intensity and sprint-training categories. This supports describing several routes to adaptation rather than promising one exclusive zone. Muscle structure, oxygen uptake, performance and day-to-day repeatability remain distinct outcomes.
Make the zone number part of a useful training record
A strong log can answer what you did, what you intended and how it felt. Record the activity, total duration, zone method, work structure and perceived effort. Add short context when weather, terrain or an unusual reading changes the interpretation.
Use that record to compare similar sessions and to see how the week fits together. A colorful chart is a summary, not a standalone assessment of readiness, recovery or health. The next chapters turn this foundation into a method choice, a distribution view and a complete workout review.
Sources and further reading
The examples in this guide illustrate training concepts. Percentage bands and planning heuristics are identified as conventions; they do not measure your individual thresholds. The research library describes study populations, methods, outcomes, and limitations.
Mølmen, Almquist and Skattebo · 2025 · Systematic review and meta-regression; published online in 2024 and in the 2025 journal volume, with searches through February 2022.
Practical interpretation: Compare intensity, duration and the outcome together. Gains per hour and gains over a complete program answer different questions.
Limits: Broad training categories, different measurement methods and statistical adjustments. Meta-regression associations are not randomized comparisons of every possible program.
Jamnick, Pettitt, Granata, Pyne and Bishop · 2020 · Critical review of measurement methods and their relationship to exercise-intensity domains.
Practical interpretation: Name the method and measurement. Do not treat LT2, a fixed lactate value, FTP and critical power as automatically equivalent.
Limits: Method validity for acute responses does not itself establish which prescription produces the best long-term training adaptation.
Schoenfeld, Aragon, Wilborn, Krieger and Sonmez · 2014 · Randomized four-week comparison of volume-matched fasted and fed aerobic training.
Practical interpretation: A claim about fuel use during a session needs separate evidence before it becomes a claim about long-term body-fat change.
Limits: Small, short study with dietary restriction. It compared feeding conditions, not five heart-rate zones, and cannot establish equivalence in every population.
Achten and Jeukendrup · 2003 · Graded cycling tests with indirect calorimetry, including repeated tests under standardized fasted conditions.
Practical interpretation: Avoid treating a fixed zone percentage as everyone's Fatmax or claiming that maximizing session fat oxidation guarantees greater body-fat loss.
Limits: Acute, fasted laboratory measurements in trained men. It measured fuel oxidation, not weight loss or long-term training superiority.
