How Long Should Your Longest Run Be Before An Ultramarathon?

By Jason Koop,
Head Coach of CTS Ultrarunning,
Author of “Training Essentials for Ultrarunning”

When I give training talks, I can inevitably count on being asked, “How long should my longest run be?” When I get this question, I usually retort with, “Why do you need a long run?” Silence ensues. The silence stems from the fact runners rarely think about why they need a long run. And even more specifically, why their long run needs super-long in preparation for an ultramarathon.

“How long should my longest long run be?” is an inherently flawed question and assumes the following:

1. The longest long run is somehow a singular prerequisite for the event. This is similar to how the 16- or 18-mile-long run has become ubiquitous in marathon training.
2. The longest long run builds some magic fitness not otherwise attained in training.
3. It is universal for everyone.

Here’s the truth: there is no magic long run distance that will automatically qualify you to be ready for an ultramarathon. I’ve coached successful ultramarathon runners whose long runs are as little as 20% and as much as 80% of the distance they are racing.

Yes, long runs are important. They build aerobic capacity, reinforce your musculoskeletal framework, increase fat oxidation. On top of that, they offer a dry run for a whole host of other aspects important to ultrarunning. These include your race day nutrition and perhaps putting you in a spot of adversity.

But you know what? All these areas improve through all your training, not just the long runs. In fact, you shouldn’t do a long run for a few narrow and very specific physiological adaptations. Physiology does not work that way. You accomplish those adaptations during the entirety of training. They do not result from one (or even a few) run(s), no matter the length. So how do you find out how far you need to go during a long run? Here’s how to get to the answer.

Take a quick look at the numbers

In my experience, ultrarunners put far too much emphasis on their singular longest long run. They feel they ‘must’ do a 50-miler in advance of a 100-miler or ‘have to’ do 20 miles in advance of a 50k. From a physical standpoint, the singular longest long run matters very little. This is because of the limited amount of training you can do on one single day. Even if it’s a really big day, it’s only a tiny fraction of time compared to your weeks and months of cumulative training.

Hypothetically, let’s say you are training for a 100k event. So, you come up with some arbitrary (yes, that word is intentional) logic that tells you that you need a 7-hour long run in training. Let’s say you have been training for 4 months, at an average of 10 hours per week. That means you have 160 hours of training in the bank. In this case, your 7-hour long run constitutes 7/160ths of your total training load, or about 4.3% of your total training volume.

That might look like a lot on paper. But, consider that you would probably run about 3 hours on that day anyway. As a result, the difference between your arbitrarily-long 7-hour run and a normal long run is only 4 hours. That’s 2.5% of your total training volume. Now, consider you will likely have to recover more during the week following the longer long run. This reduces the overall training volume for the entire period, further reducing the impact of the extra time and effort you put into that really long, long run.

Why longest long run doesn’t matter

My point with the arithmetic exercise is this: from a physiological standpoint, it matters very little if your longest long run varies by a few hours. If you are doing things right, you will have hundreds of hours of training to build up to your key event. Completing one single run that is a couple of hours longer is a small drop in the bucket.

Don’t pick your long run volume arbitrarily based on your race distance (as in the case of the 16-mile marathon long run). Similarly, you should not pick your long run volume based on some narrow physiological rationale. Instead, look at your current training and then examine what you’re trying to accomplish – beyond the physical – during your longest runs.

Build your bridge from both sides

Now that I’ve made the case for how not to think about your long run, let’s take a good look at good reasons to do long runs. Then we’ll whittle down to ways to determine what your longest long run should be.

Training is like building a bridge. On one side, you have your current fitness, capacity for work and musculoskeletal resilience to handle long runs. On the other side is the event you are training for, with all the physical and mental challenges it will throw at you.

Your job during training is to bridge the gap between where you are now and where you need to be on race day. The amount you can reasonably handle puts you on the near side of the bridge. Good rationales for doing a long run puts you on the other side, scheming for what you should prepare for as the event approaches.

By looking at both, you can come up with the answer to this mystifying question. You must consider both sides of this equation to determine the length of your longest long run. However, the near side (where you are currently) is far more important and will drive the majority of the process.

Step one: The long run reasonability test

I dislike overgeneralized formulas that point to magic solutions to training problems. The overused “you should only increase your weekly volume/long run by 10%” rule is one of them. Early in the annual training cycle, any moderately experienced runner (which nearly all ultrarunners are) should be able to increase their volume more quickly. As training goes along, a 10% increase is much riskier.

When I have a new athlete who has a reasonable amount of training experience, I use the chart below as a starting point to determine how long of a long run they can reasonably handle for any given week of training. I call this, the long run reasonability test (creative, I know). I customize this chart for each athlete based on their experience. With more experienced athletes I can be more aggressive. I also look at injury history – I’m less aggressive with athletes who have a history of injuries – and a host of other factors. Irrespective of the athlete, the gist remains the same.

Before you dive in to the minutiae, focus on the ‘Increase in long run %’ column. It goes from 20% for a couple weeks, to 10% to 5% to 2.5% to 1.25%. For the math geniuses out there, yes, I’m cutting the increase down by half every few weeks. Quite perceptive of you! You also might notice that every few weeks the percentage increase is zero. This is to accommodate for recovery weeks, race weeks, or any other reason to back off of the progression. What have I determined with this test? Only what is reasonable for any moderately experienced runner to handle for a long run on any given (but not every given) week.

FAQs on Reasonability Test

Here are some questions you likely have at this point: 

Question- Is this the perfect answer?

Answer: Nope.

Question: Is this the exact same formula for every athlete?Unsubscribe anytime.

Answer: Of course not.

Question: Should I really do a 6 hour and 59 min long run on week 6?

Answer: No again. That’s a silly amount of precision. Be practical, round up or down as necessary.

Question: Should I follow this long run progression every single week?

Answer: Absolutely not.

The only thing you should use this type of chart for is as a guidepost to estimate what is reasonable for a long run during any particular week of training. In my example, if I had a runner that had a current long run of 4 hours per week, in 16 weeks they could reasonably handle about an 8-hour long run. In Week 8-12, the runner could reasonably handle anywhere between a 7- or 8-hour run. Is that what their long run ends up being? Sometimes yes, sometimes no, depending on the actual progression and the ‘good rationales’ exercise in the next section.

For this example (after going through the exercise in the next section), I would have the athlete target 1-2 long runs per month to be near these ‘reasonable’ targets. This means in Week 4, they could run a long run that is a little over 6 hours, and in Week 6 they could run a long run for 7 hours, etc. The other long runs are ~50-75% of these ‘reasonable maximums’.

To build from the other side of the bridge, and take the entirety of training into context, I ask the athlete a series of questions rooted in what goals they would like to accomplish during the long run.

Good rationales for your longest long run

Let me reiterate: there is little physiological rationale to support the idea that a singularly long, long run will be particularly beneficial. If that message from earlier didn’t resonate with you, please reread the first section!

Yes, long runs improve you physically, but so does the rest of training! The entirety of training is more important than an individual long run. Your long run(s) represent a small fraction of your overall training; it is important to treat them as such.

So why even do long runs if the physical side does not matter too much? Good question. Long runs need to serve a purpose beyond physiology. In my opinion, there are three good rationales for doing any particularly long run:

1. Work on your nutrition plan
2. Build confidence
3. Work through troublesome logistical scenarios, such as running through the night or in big temperature swings.

Step 2: Long Run Questionnaire

Therefore, to further home in on what that longest of runs should actually look like, ask yourself these questions:

1. How long does my run need to be to practice my nutrition plan? (The minimum for this is 4 hours for just about any ultramarathon runner.)
2. How long does my long run need to be to give me confidence?
3. How long does my long run need to be to work on any logistical consideration (running through the night, big temperature swings, etc.)?

After you have finished the mental exercise, you can line up all 3 reasons, complete with their timeframes. This way, you can see what makes sense in relation to the ‘long run reasonability test’. Using my previous example, the athlete might answer the three questions as follows:

How long does my run need to be to practice my nutrition plan?

I feel I need 4-5 hours for this because after 3 hours, I don’t like sweet foods any longer.

How long does my long run need to be to give me confidence?

I feel I need 6-7 hours for this because the longest I have ever run is 6 hours.

How long does my long run need to be to work on any logistical consideration (running through the night, big temperature swings, etc.)?

I feel I need 5-6 hours for this because the race I am training for will start at 8 AM in the 40s and warm up to the 80s by 2 PM.

In this case, all these timeframes meet the ‘long run reasonability test’, but at different points.

Reasonability supersedes any particular reason

From time to time when I go through this exercise, the timeframes to practice nutrition, build confidence, or work on logistical issues are mismatched. There simply isn’t enough time to meet the reasonability test and complete a run long enough to accomplish one of the good rationales.

In this case, bend on the time needed to work on nutrition, confidence or logistics. If you have been diligent on the reasonability test, that should supersede all. Find a way to increase your confidence by doing a shorter run, or may be back-to-back runs. Cobble together the logistics by starting a run in the middle of the night. The point is, don’t compromise reasonable progression for one or a few of the of the other good rationales you have for a long run.

Are long runs over 4 hours beneficial?

Recently in ultrarunning training lore, a notion has been perpetuated that long runs over 4 hours are no longer beneficial. I can’t claim to know exactly where this fable originated, but I have received enough questions on it (including one in the comments section below) that it’s worth addressing.

If you scour several decades of coaching and training practices across all endurance disciplines (Ironman triathlon is a particularly good example of this), you will find countless examples of athletes training for longer than four hours. It’s so common that when I posed this concept to my fellow cycling and triathlon coaching colleagues, they looked at me as if I had grown a third head.

Being a curious bunch, we scoured the scientific literature. Let me be clear, little compelling scientific literature exists to suggest that long runs over four hours reach a point of significant diminishing returns. You can come up with some mechanistic argument. For instance, if you train one day per week for four hours it’s not a beneficial as training for four days per week for one hour each. However, that’s a far-fetched example to draw conclusions from.

Strain increases with time

If anything, hour for hour, the longer you run the more strain each additional minute of time contains. Sixty minutes at the end of a 4-hour run is far more stressful than 60 minutes when you are fresh. That extra physiological stress, provided it is balanced by adequate recovery and nutrition, should result in a bigger adaptation.

Most literature on block training (concentrating the training stress is shorter timeframes- back to back interval days for example) points to a similar conclusion. The extra time spent during your long runs is more beneficial than if that time were evenly redistributed during the week. For example, if you had a 10 hour per week training budget, you could spread that budget out evenly during the week (2 hours a day for 5 days, for example). Or, you could choose to undulate the volume so it’s greater on some days (3 X 1-hour runs, a four hour run and a 3 hour run). I would argue (and most coaching practice points to this as well) that the latter is more effective in most circumstances.

The take home

The duration of your long runs and longest long run should be established with intent. That intent should not be driven by some arbitrary and predetermined number that acts as a prerequisite for success. Similarly, the intent should not be driven from the physical rationale that you need a long run to improve your aerobic capacity, mitochondrial density, musculoskeletal integrity, fax oxidizing enzymes or any other physiological phenomenon.

Your long run intent should come from your current training status, how long you have, and what reasonable progression looks like. Then, you should consider specifically what you want to accomplish during the long run, aside from the physical. Ultrarunners should be giving their long runs purpose that extends far beyond the physical gains they could get.

There’s no need to fear that runs greater than four hours diminish in benefit. In fact, hour for hour the long run packs more of an adaptative punch (to a certain point) compared to spreading that time out evenly during the week. I hope these exercises can put you on a path to realize not only how long your long runs and longest long run should be, but why you should be doing them in the first place!