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The Long Run: Why It’s the Foundation of Distance Training

Training Basics

There is something different about a long run.

An easy 5K can fit into a busy morning. A 30-minute tempo run can be squeezed between meetings. Intervals can be finished before you have time to think about how hard they were.

A long run asks for something else.

Time.

You have to stay on your feet for an extended period, manage your effort, fuel yourself, deal with accumulating fatigue, and keep running when the first few kilometres start to feel very different from the last few.

That is exactly why long runs are so valuable.

For distance runners, the long run provides a training stimulus that shorter sessions cannot completely reproduce. It develops the ability to sustain exercise for a prolonged period and gives you an opportunity to practise the pacing, fueling and mental skills that become increasingly important as race distance increases.

But a long run is not simply "the run you do on Sunday."

How long it should be, how fast you should run it, and how often you should do it all depend on the athlete and the race.

What Does the Long Run Actually Develop?

The obvious answer is endurance.

But endurance is not one single physiological quality.

Long-duration running places sustained demands on the cardiovascular system, energy metabolism, muscles and neuromuscular system. Repeated endurance training can improve aerobic capacity, running economy and the ability to sustain a given running speed. Research in recreational marathon runners, for example, has shown improvements in aerobic threshold, anaerobic threshold and running economy over a structured 16-week marathon training period.

The long run also exposes you to something that a 30-minute easy run cannot fully replicate:

fatigue accumulation.

Your body has to continue producing running movements as the session gets longer. You have to maintain technique and pacing while your energy stores are being used and your perception of effort changes.

This is particularly relevant to marathon and half marathon runners.

A large observational study of recreational half marathon and marathon runners found that greater weekly training volume and longer endurance runs were associated with faster race performances. In the marathon group, a longest training run below 25 km was associated with slower finish times. These findings are associations, not proof that simply adding distance will make every runner faster.

The long run is therefore one part of a larger training system.

It is not magic.

It is a way of accumulating a specific type of endurance stress.

How Long Should a Long Run Be?

This is where running advice often becomes overly simplistic.

You will hear rules such as:

"Your long run should be 20% of your weekly mileage."

"Your long run should never exceed 30 km."

"Your long run should be 30% of your weekly volume."

There is no single scientifically established percentage that works for every runner.

The appropriate duration depends on your race distance, training history, weekly volume, experience, current fitness and how much recovery you have available.

A beginner training for a 10K does not need the same long run as an experienced marathon runner.

And a marathon runner doing 80 km per week does not need the same long run as someone doing 35 km.

A better approach is to think about the purpose of the session.

For a 10K runner, a long run might be around 60 to 90 minutes.

For a half marathon runner, it may progress toward roughly 90 minutes to two hours or more.

For a marathon runner, longer sessions may extend beyond two hours and, depending on the training plan and athlete, into the 25 to 35 km range.

These are practical training ranges, not universal prescriptions.

Research in recreational runners supports the general importance of longer endurance runs for half marathon and marathon preparation, but it does not establish one ideal distance for every athlete.

The key is to build the long run gradually and make it fit within your overall training load.

Should Long Runs Be Easy or Fast?

Most long runs should be predominantly easy.

That does not mean every long run needs to be slow from start to finish.

There is a place for faster long runs, particularly as runners become more experienced and race-specific training becomes important.

But it is useful to separate two ideas:

The long run develops endurance.

The quality session develops a specific performance quality.

If every long run becomes a hard workout, you may create more fatigue than your training plan can absorb.

This is consistent with the broader evidence on endurance training. Systematic reviews of middle- and long-distance runners have found that training programs containing a large proportion of low-intensity running, alongside smaller amounts of threshold and high-intensity work, are commonly associated with improved endurance performance.

That does not mean slow running is the only useful running.

It means that hard running needs to have a purpose.

A standard long run might be entirely easy.

A more advanced session might include:

• Easy running followed by a controlled progression
• Marathon-pace segments
• Half-marathon-pace segments
• Alternating easy and moderate sections
• A faster final portion

These workouts can be useful because they combine endurance with race-specific intensity.

But they are harder than a conventional long run and should be treated as such when organizing the rest of the week.

Fueling the Long Run

Fueling becomes increasingly important as the duration of the run increases.

Your body stores carbohydrate primarily as glycogen in muscle and liver. During prolonged exercise, these stores contribute substantially to energy supply.

Carbohydrate intake during longer endurance sessions can help maintain performance and delay fatigue.

For exercise lasting approximately one to 2.5 hours, commonly cited evidence-based guidance recommends around 30 to 60 g of carbohydrate per hour. For longer events, particularly beyond 2.5 hours, trained endurance athletes may be able to use higher intakes, up to approximately 90 g per hour, when multiple transportable carbohydrate sources are used.

That does not mean every 90-minute easy run requires 90 g of carbohydrate per hour.

The appropriate intake depends on duration, intensity, the athlete and the purpose of the session.

A key reason to practise fueling during long runs is also practical.

Your gastrointestinal system needs to become familiar with the strategy you intend to use during racing.

If you plan to take gels during a marathon, your long runs are where you should discover which products, quantities and timing work for you.

Do not wait until race morning to test them.

For a shorter long run, you may not need to consume carbohydrate during the run at all. For longer sessions, particularly those approaching or exceeding two hours, carbohydrate becomes increasingly relevant.

The goal is not simply to survive the long run.

It is to practise the fueling strategy that supports the training you are trying to accomplish.

Hydration Matters Too

The same principle applies to hydration.

Sweat losses vary considerably between runners.

Temperature, humidity, body size, pace, clothing and individual sweat rate can all affect how much fluid you lose.

That means there is no single amount of water that every runner should drink during a long run.

The American College of Sports Medicine recommends an individualized approach to fluid replacement based on factors including exercise duration, environmental conditions and sweat rate.

Long runs are therefore a good opportunity to learn what you actually need.

If you are preparing for a hot-weather race, practise drinking in similar conditions.

If you are racing for several hours, practise carrying and consuming fluids.

And avoid turning hydration into a competition.

Drinking excessively can also be dangerous.

The objective is to replace an appropriate amount of fluid, not to drink as much as possible.

Long Runs Should Progress

The long run should not jump from 10 km to 25 km simply because your training plan says that you eventually need to run 25 km.

Your body needs time to adapt to increasing training stress.

A common approach is to gradually increase long-run duration or distance over several weeks, followed by a lighter week when appropriate.

The exact progression should depend on the runner.

Someone who already runs 40 km per week will tolerate a different long-run progression from someone who has recently started running 20 km per week.

This is also why the long run should be considered alongside total weekly volume.

A 25 km run inside an 80 km training week represents a different training load from a 25 km run inside a 35 km week.

Research examining marathon preparation has found associations between overall weekly volume, longest run and performance. It is therefore difficult to isolate the long run from the rest of the training program.

The long run is one piece of the training puzzle.

Not the entire puzzle.

The Long Run for 10K Runners

You do not need marathon-style long runs to become a better 10K runner.

The 10K is long enough for aerobic endurance to matter, but short enough that speed, threshold ability and running economy also play major roles.

A recreational 10K runner might use a weekly long run of approximately 60 to 90 minutes, depending on experience and total training volume.

The run can remain comfortably easy for much of the training cycle.

As race day approaches, some runners may benefit from incorporating controlled faster sections.

The important thing is that the long run should complement the other sessions.

If Tuesday is a demanding interval workout and Thursday is a threshold session, turning Sunday into another hard session may simply create three demanding days.

The purpose is to arrive at the next quality workout ready to execute it.

The Long Run for Half Marathon Runners

The half marathon sits in an interesting middle ground.

It is long enough that endurance and fueling matter substantially, but short enough that race pace can be relatively high.

The long run therefore becomes particularly useful for developing the ability to maintain good mechanics and controlled effort for an extended period.

Many recreational runners will progress their long run toward roughly 16 to 21 km during a half marathon build.

Again, this is not a universal requirement.

A 21 km training run is not automatically necessary for every half marathon runner.

In an observational study of 556 recreational half marathon runners, those completing longest endurance runs above 21 km were associated with faster finish times and less pace decline during the race. But this was an observational relationship, so it cannot establish that simply adding a run beyond 21 km caused the improvement.

That distinction matters.

Good training recommendations should be based on evidence without pretending that observational associations prove causation.

The Long Run for Marathon Runners

For marathon runners, the long run becomes even more important.

You are preparing to run 42.2 km.

That requires substantial aerobic capacity, but it also requires the ability to keep running after several hours of accumulated fatigue.

Research examining marathon training has consistently identified training volume and long-run characteristics among factors associated with marathon performance. A meta-analysis incorporating 85 studies and 137 cohorts found associations between marathon performance and variables including weekly distance, number of weekly runs, longest run, and the number of runs of at least 32 km.

That does not mean every marathoner should run multiple 32 km training runs.

In fact, the optimal number and length of long runs depends heavily on the athlete and the overall plan.

The purpose is to provide enough marathon-specific endurance without creating so much fatigue that the rest of the training suffers.

This is why marathon plans often include several progressively longer runs rather than repeatedly running the full race distance.

You are training the system without needing to reproduce the race itself every weekend.

Common Long-Run Mistakes

Running too fast

The most common mistake is turning the long run into a race.

If the purpose is aerobic endurance, there is usually no advantage to forcing the pace simply because you feel good during the first few kilometres.

Start controlled.

Let the effort build naturally.

Making every long run a test

Not every long run needs to tell you how fit you are.

Some runs are simply there to accumulate time on your feet.

Trying to set a personal best every weekend can make the training harder than intended.

Increasing distance too aggressively

Long runs create substantial training stress.

Adding several kilometres at once can make the session disproportionately difficult, particularly for less experienced runners.

Progression should reflect your current training background.

Ignoring fueling

If you are running for several hours, hoping that you can simply "push through" without practising nutrition is unnecessary.

Long runs are your laboratory.

Use them to test your race-day strategy.

Forgetting the rest of the week

A 25 km long run does not exist in isolation.

The recovery run on Monday, the intervals on Tuesday and the strength session on Wednesday all matter.

A long run that compromises the next several days may not be productive simply because it was long.

The Long Run Is Not About Distance Alone

The best long run is not necessarily the longest one you can survive.

It is the one that provides the intended training stimulus and allows you to continue progressing afterward.

For a 10K runner, that may mean 60 to 90 minutes of easy running.

For a half marathoner, it may eventually mean 90 minutes to two hours or more.

For a marathoner, it may mean progressively longer sessions that develop the ability to run efficiently deep into a prolonged effort.

The numbers are different.

The principle is the same.

The long run teaches your body and your mind to keep going.

It develops the endurance that supports distance performance, gives you a place to practise fueling and hydration, and teaches you how your pace and effort change as fatigue accumulates.

But it works best when it is part of a balanced training week.

Easy runs provide volume.

Quality sessions develop speed and threshold-related abilities.

Strength training can support running economy and performance.

Rest allows adaptation.

The long run connects much of it together.

You do not need to finish every long run exhausted.

You need to finish enough of them well that, over months of consistent training, the distance that once seemed intimidating starts to feel familiar.

That is what the long run is really building.

Not just the ability to run farther.

The ability to keep running well when farther starts to hurt.

References

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2. Schubert, M. M., et al. (2018). An evaluation of the training determinants of marathon performance: A meta-analysis with meta-regression. Journal of Strength and Conditioning Research.
3. Esteve-Lanao, J., Del Rosso, S., Larumbe-Zabala, E., Cardona, C., Alcocer-Gamboa, A., & Boullosa, D. A. (2021). Predicting Recreational Runners' Marathon Performance Time During Their Training Preparation. Journal of Strength and Conditioning Research.
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