Watshoopedia / Training · Intensity
How easy should an easy run be?
You feel rested, your legs feel good and a slightly quicker pace is still comfortable. Do you need to hold back?
A question from an everyday run
“I used to run these routes in lower zone 2. Now I run them in upper zone 2, around 30 seconds per kilometre faster, without noticeably more fatigue afterwards.”
One runner's experience · not a research findingThat is a useful observation. It suggests the quicker pace feels manageable. But it does not by itself show that the training produces greater improvement: recorded intensity is also higher. Improved fitness, different conditions or a change in overall load could also play a part.
The question is: Does that extra speed give you something you want, without the cost appearing in the next session or several weeks later?
First: zone 2 can mean two different things
On many watches, zone 2 is an easy zone within a five-zone model. In much of the research, zone 2 is the range between the first and second thresholds. That is substantially harder. Your watch's heart-rate zones do not necessarily match your physiological thresholds either.[1][2]
The key distinction: If your “lower” and “upper” zone 2 both genuinely lie below the first threshold, we are discussing two versions of easy training. That is different from turning every easy run into a tempo session.
Easy kilometres do more than support recovery
Easy training can improve fitness in its own right. A 2026 meta-analysis found improvements in measures including maximal oxygen uptake and the first ventilatory threshold compared with control groups. These are more than kilometres collected while waiting for the next hard session.[3]
More space between sessions
Fewer runs may allow more room for load within each session. But two short runs and four runs including a long run and intervals are very different weeks. Work, sleep and other training also count.
More demands to balance
At high volume, repeating the training and retaining energy for quality sessions becomes more important. This makes very easy runs practically useful. The mileage is not a magic boundary, though.[4]
Practical interpretation: the number of running days alone does not determine the right pace. Consider total volume, session duration, intensity and what you are used to.
What the research actually says
The sources support some flexibility, but offer no universal answer on lower versus upper zone 2.
Similar measured improvement, less time
Festa and colleagues compared two programmes in 38 recreational runners over eight weeks. The group doing more training between the thresholds improved without a detectable difference from the polarized group, with approximately 17% less training time.
Limitation: Outcomes included 2 km performance. This short study compared whole programmes, not lower versus upper zone 2 below LT1. A lack of statistical difference does not prove equivalent effects.
Read the study and source details →No clear winner for everyone
Rosenblat and colleagues pooled 13 studies involving 348 participants. They found no overall significant difference between polarized and pyramidal training in oxygen uptake or time-trial performance.
Subgroup findings suggested recreational athletes might respond better to pyramidal training, while competitive athletes might benefit more from polarization. Both models contain mostly easy training.
Read the analysis →Easy training works too
Nuuttila and colleagues pooled 50 studies of low-intensity training in adults. Higher intensity within the range studied was associated with larger improvements in oxygen uptake, but there was considerable variation.
Limitation: This was not a direct test of lower versus upper zone 2 in established runners. It cannot be translated into “run 30 seconds faster”.
Read the analysis →Easy does not have to mean the very bottom
A panel of 14 researchers and coaches described zone 2 as training just below the first threshold. They also stressed that the expected adaptations are not necessarily unique to this intensity.
Limitation: This is expert judgment, not a trial showing that every easy run should sit close to the threshold.
Read the expert assessment →What about 80/20 and the “magic of zone 2”?
A 2024 meta-analysis found a small advantage for polarized training in maximal oxygen uptake, particularly in short trials and highly trained athletes, but no clear advantage in time trials. The newer analysis above also found no universal winner. [4] [6]
A critical 2025 review challenges the claim that zone 2 is established as the optimal intensity for mitochondrial adaptations in the general population. However, it addresses different questions from how a recreational runner should distribute all their runs. [7]
Our interpretation: Treat 80/20 as a possible guide, not a requirement for every easy run to be very slow. The proportion of sessions and the proportion of training time are also different calculations.
Benefits and drawbacks of a slightly quicker pace
Practical trade-offs, not proven effects of a specific change in min/km.
When it still feels easy
- More running in the same time. Relevant when your schedule limits you.
- Potentially more stimulus per minute. Greater long-term improvement is not guaranteed.
- Better flow and enjoyment. If very slow running feels unnatural, a freer pace may make training more enjoyable.
When the cost increases
- Less margin below the first threshold. Hills or an off day can make the same pace more demanding.
- Less energy later. Consider the next quality session and the following weeks, not only how you feel immediately afterwards.
- Breathing does not tell the whole story. Muscles and tendons also need to tolerate the load. An easy heart rate does not guarantee that faster running suits you right now.
Keep the comparison clear: the same time at a faster pace means more kilometres. The same distance at a faster pace means a shorter session. Those are two different changes.
Spring in your step—or “flat” legs?
“When I feel more muscle tension, I can run faster at the same perceived effort than when my legs feel ‘flat’.”
One runner's experience · not a research findingThat experience is relevant when choosing pace. But we cannot identify precise muscle tone or measure running economy by feel alone. Springiness, resting muscle tone and mechanical stiffness during running describe different things.
A responsive stride
Your legs feel light, coordinated and elastic. This could fit with effective muscle–tendon interaction, but the feeling cannot tell you exactly which mechanism has changed.
Stiffness and energy cost
Mechanical stiffness describes resistance to deformation under load. A meta-analysis found that some measures of leg stiffness were associated with a lower energy cost. It does not show that deliberately tensing your muscles makes you more efficient.[9]
What does Bakken say?
Bakken describes monitoring muscle tone to manage training load and recovery. He emphasizes allowing high tone to fall between sessions. He also writes that increased tension or “muscle contact” after strength work can be useful before some later sessions. These are experiences and hypotheses from elite practice, not controlled evidence that higher muscle tension improves running economy.[8]
Do tendons take over shock absorption when muscles tire?
That description is too simple. Tendons are themselves connective tissue and work with muscles in every stride. They transmit force, stretch and return elastic energy. Muscle activity helps load the tendons; they are not a backup system that switches on only when muscles work less effectively.[10]
There is also a difference between storing and returning energy and absorbing and dissipating it. Fatigue can change the interaction and movement patterns, but this does not automatically mean that tendons must take a larger share of the impacts.
In a study of 14 trained runners, measured Achilles tendon stiffness fell after 90 minutes of running while running energy cost increased. Estimated tendon energy return was unchanged, whereas estimated calf-muscle energy cost increased. The study did not measure injuries or test whether “flat legs” cause greater impact loading on connective tissue.[11]
What does this mean on an easy run? Use both breathing and how your legs function as information. Feeling springy can make a particular pace more comfortable. Heavy or poorly coordinated legs are a reason to adjust expectations even when your heart rate is low. Feeling light does not establish lower tendon loading, and is no reason to force a faster pace or deliberately tense your muscles.
Practical interpretation: aim for a relaxed stride that works well with today's load. Research does not identify one optimal muscle tension that every runner should try to achieve.
How should you choose the load in your own week?
These practical considerations are our interpretation of the research and coaching experience. Start from the training you already tolerate.
- Choose one familiar, shorter run. Keep roughly the same distance. Leave your long run and hard sessions as they are.
- Let the pace come naturally. Start easy. Only increase if you can still speak comfortably in full sentences and clearly feel in control. The talk test is a guide, not a precise threshold measurement.
- Watch for a delayed cost. Monitor your legs, sleep and next quality session over time. Do not increase pace, volume and the number of hard sessions together.
- Assess the benefit. Better flow and consistent execution are valuable. Assessing fitness development takes a longer trend under comparable conditions—for example, pace at roughly the same heart rate and perceived effort.
Choose the easier option when unusually tired, increasing volume, returning from injury or saving energy for an important session. Pain and increasing stiffness are reasons to adjust the load even if your aerobic fitness feels good.
Example: three runs, three purposes
An illustration for an experienced runner already comfortable with around 30 km per week. These distances are examples, not a recommendation for everyone.
Use easy days or rest between runs as needed. With two weekly runs, you can vary the quality work between weeks. With four, an extra easy run is often practical. These are options, not a rule prescribing a particular number of hard sessions.
What if your easy pace is also your marathon pace?
For some recreational runners, a realistic marathon pace may overlap with upper zone 2 in a five-zone model. But “marathon pace” is not a fixed heart-rate zone: the zone model, training level and race duration matter. A small study found a strong association between speed at the first ventilatory threshold and marathon performance, without making that threshold speed a universal marathon pace.[13]
About 57 minutes
May be a comfortable aerobic run for someone well trained for this pace.
About 4 hours
Feeling comfortable early on does not demonstrate readiness to hold the pace all the way to the finish.
This connects easy-run intensity to “How much do I need to train for a marathon?” In a study of 441 marathon runners, weekly volume and the longest training run were associated with finishing time. These were observational data, not a prescription for how many kilometres everyone must run.[12]
In practice: When marathon pace really is easy for you, a run at that pace can provide both aerobic training and practice at race pace. That does not make every such run a recovery session. Duration and total load still need managing, and running slightly faster is not a proven substitute for an adequate training base.
What counts as adequate depends on current volume, experience, time until the race and whether the goal is to finish or achieve a particular time. That is a natural next question to take into Runplanner.
What to take into your next run
An easy run can have more than one appropriate pace. When rested and still running comfortably, you do not need to slow down simply to stay at the bottom of a watch zone. Choose pace according to the run's purpose and the whole training week. Fewer running days do not automatically make greater intensity the better choice.
Sources and further reading
Selected studies and a first-hand account of coaching practice. This is a targeted literature review, not a systematic review. Publications checked on 25 September 2026.
- Sitko et al. (2025): What Is “Zone 2 Training”?
Expert panel on definitions and expected adaptations. Experience and expert judgment, not an intervention trial.
- Nuuttila et al. (2025): The accuracy of fixed intensity anchors to estimate lactate thresholds in recreational runners.
Study of 165 runners. Supports the limitations of fixed percentage boundaries for individuals.
- Nuuttila et al. (2026): Effects of Low-Intensity Endurance Training on Aerobic Fitness and Risk Factors of Cardiometabolic Health in Working-Age Adults.
Systematic review and meta-analysis. Fifty studies across a broad adult population.
- Oliveira et al. (2024): Comparison of Polarized Versus Other Types of Endurance Training Intensity Distribution.
Meta-analysis of 17 studies. Oxygen uptake and performance tests do not necessarily lead to the same conclusion.
- Festa et al. (2020): Effects of Different Training Intensity Distribution in Recreational Runners.
Open-access original study. Published in January 2020; its DOI and journal volume contain 2019.
- Rosenblat et al. (2025): Which Training Intensity Distribution Intervention will Produce the Greatest Improvements…?
Individual-participant-data network meta-analysis. This article's appraisal is based on the available abstract.
- Storoschuk et al. (2025): Much Ado About Zone 2.
Narrative review of mitochondrial adaptations and fitness in the general population. Appraisal based on the abstract.
- Marius Bakken: The Norwegian model of lactate threshold training.
First-hand account of elite practice, including muscle tone and strength training. Experiences and hypotheses are distinguished from controlled research findings.
- Liu et al. (2022): Running economy and lower extremity stiffness in endurance runners: A systematic review and meta-analysis.
Associations between mechanical stiffness and running economy. Different stiffness measures are not interchangeable.
- Fletcher & MacIntosh (2017): Running Economy from a Muscle Energetics Perspective.
Review of muscle work, tendon stiffness and energy cost. Greater stiffness is not necessarily better in every tissue or situation.
- Fletcher & MacIntosh (2018): Changes in Achilles tendon stiffness and energy cost following a prolonged run in trained distance runners.
Original study of 14 runners. Tendon stiffness and running economy were measured; energy return and local muscle energy cost were estimated.
- Fokkema et al. (2020): Training for a (half-)marathon: Training volume and longest endurance run related to performance and running injuries.
Observational study including 441 marathon runners. Associations do not establish an individual minimum mileage or guarantee a result.
- Esteve-Lanao et al. (2021): Predicting Recreational Runners’ Marathon Performance Time During Their Training Preparation.
Sixteen recreational runners followed through 16 weeks of training. Threshold speeds were associated with marathon performance; this does not establish a universal marathon heart-rate zone. Appraisal based on the abstract.