80/20 Running: Does It Work for Ultra Runners?

When building an ultra running training plan, 80/20 running is one of the most widely discussed approaches. The principle sounds simple: complete most of your training at an easy intensity and a smaller proportion at a higher intensity. But does that same formula work for every ultra runner?

Should 80% of your running always be easy and 20% hard? Do you need a long run every weekend? And should ultra runners complete back-to-back long runs to learn how to perform on tired legs?

According to ultra running coach and running rehab specialist Paul Tierney, the answer is rarely as simple as following a fixed formula.

Speaking to Mel Berry on the VOOM Performance Podcast, Paul discussed 80/20 running, polarised training and the role of back-to-back long runs when preparing for ultras and multi-day mountain races. His central message was clear: your training should reflect the individual athlete, the demands of the event and, importantly, the amount of time you actually have available.

What is 80/20 running?

The basic principle behind 80/20 running is that the majority of endurance training is completed at a low intensity, with a much smaller proportion performed at a high intensity.

The concept has roots in research examining how successful endurance athletes actually train. Exercise physiologist Stephen Seiler reviewed training characteristics of competitive endurance athletes and found a pattern in which approximately 80% of sessions were performed at relatively low intensity, with around 20% incorporating higher-intensity work [1].

Importantly, though, this doesn’t mean every athlete needs to hit an exact 80/20 split.

Research into endurance training intensity distribution has found that athletes can successfully use different approaches, including polarised and pyramidal models, rather than there being one universally optimal distribution [2,4].

That fits closely with Paul’s approach.

“No one way of doing things fits every situation.”

Rather than focusing too heavily on hitting an exact percentage, Paul suggests first looking at how much training an individual can realistically complete.

“You need to look at the amount of time you have as an individual in a given week.”

From there, the aim is to complete plenty of training at an intensity that allows you to recover and train consistently.

“You need to do a fair bit of relaxed, comfortable, easy, whatever you want to call it, training where you feel like you come back again and are able to do the same thing again the following day without any major problem.”

That ability to repeatedly train could be more useful than obsessing over whether your training distribution comes out at exactly 80/20.

What does the science say about polarised training?

There’s good evidence that polarised training can be effective for endurance athletes, but the research doesn’t show that it is universally superior in every situation.

A 2024 systematic review and meta-analysis published in Sports Medicine examined 17 studies involving 437 participants. Researchers found that polarised training produced a small advantage for improving VO₂peak compared with other training-intensity distributions [3].

Interestingly, the benefit was particularly apparent in highly trained athletes and interventions lasting less than 12 weeks [3].

However, there was no clear advantage for polarised training when researchers looked at time-trial performance, time to exhaustion or performance around the second ventilatory or lactate threshold [3].

Earlier systematic review and meta-analysis evidence has also compared polarised training with threshold-focused approaches, finding potential endurance benefits while highlighting differences between studies and athlete populations [2].

A 2025 scoping review similarly examined polarised training against other training-intensity distribution models across athletes of different performance levels [4].

So while polarised training has a solid scientific basis, the evidence doesn’t support treating 80/20 as a universal formula that every runner must follow.

Does 80/20 training work for ultra runners?

The principles behind polarised training can certainly form part of trail running training, but Paul argues that the percentages shouldn’t automatically be applied to every athlete.

One important consideration is overall training volume.

An athlete training for many hours each week can accumulate a substantial amount of easy aerobic work while keeping higher-intensity training relatively limited.

But what about someone who only has five or six hours available?

Paul says:

“If you do only have five or six hours in the week, you might want to do slightly more than 20% of your training at some sort of a higher intensity than easy.”

Why?

Because the overall training stimulus is lower when total volume is limited.

“Because the total volume of training is relatively low, and therefore to create enough of a stimulus to actually improve or get better, you probably need to do a slightly higher percentage, slightly higher intensity.”

This distinction is important when interpreting research around 80/20 training.

Much of the influential observational work behind the concept looked at competitive endurance athletes completing relatively large amounts of training [1]. Simply copying the percentage distribution of a high-volume athlete doesn’t necessarily mean you’re recreating the same overall training stimulus.

For time-poor runners, therefore, rigidly following an 80/20 split may not always make the best use of the training time available.

Easy running still matters

That doesn’t mean turning every run into a hard workout.

One of the consistent observations within endurance training research is that successful endurance athletes tend to accumulate a substantial proportion of their training at relatively low intensities [1].

Research comparing training-intensity distributions also suggests that combining a high proportion of low-intensity exercise with a smaller amount of harder training can be an effective way of developing endurance performance [2,3].

Paul’s description offers a useful practical way of judging whether an easy session is actually easy enough: could you comfortably train again tomorrow?

Easy sessions should generally leave you capable of returning to training without significant problems.

Higher-intensity sessions can then provide another stimulus for improvement.

What that intensity looks like depends on the runner, their training history, durability, available time and ability to recover.

In other words, an effective ultra running training plan isn’t simply about percentages. It’s about balancing enough training stimulus to improve with enough recovery to keep training consistently.

Do ultra runners need back-to-back long runs?

Another common feature of ultra running training is the back-to-back long run.

The idea is straightforward: complete a long run one day before heading out for another substantial run the following day.

This allows runners to experience moving on tired legs without necessarily having to complete one enormous training run.

But are back-to-back long runs essential?

Paul’s answer is more nuanced.

“There’s times where that might make sense to do some bigger days back to back, especially if your event is something like Dragon’s Back.”

For a multi-day event such as the Dragon’s Back Race, specificity becomes particularly important.

If your race requires you to complete substantial mountain days consecutively, there can be value in experiencing what it feels like to head out again after a long day.

As Paul puts it:

“You should probably have some sort of an experience of having to go out the door the day after having done, you know, whatever it is, five hours or thereabouts.”

What does the science say about back-to-back long runs?

This is an area where it’s important to distinguish coaching practice from established research.

There is considerably less research specifically testing whether back-to-back long runs improve ultramarathon performance compared with alternative ways of distributing the same training volume.

That means we can’t confidently say that every ultra runner needs them.

Instead, Paul’s rationale largely comes back to specificity and training-load management: preparing the body for the demands it will encounter while still leaving enough capacity to recover and continue training.

That’s also why Paul’s approach isn’t simply to prescribe two enormous runs every weekend.

Instead, he suggests asking:

“How could I get a sense of what that’s going to feel like without the risk of not being able to actually train the following week or even not making the start line because I’ve completely overdone it?”

The aim of training isn’t to produce the biggest possible weekend. It’s to create enough stimulus to prepare for the race without compromising the training that follows.

Train for the demands of your race

Someone preparing for a single-day 50km trail race has very different requirements from an athlete preparing for several consecutive days in the mountains.

For multi-day races, learning what it feels like to wake up tired and head back into the hills can provide useful physical and practical experience.

But that doesn’t mean reproducing the full demands of the race in training.

A well-designed training programme needs to balance specificity with recoverability. A huge training weekend might look highly race-specific, but if it requires an extended period of recovery afterwards, the overall benefit may be less clear.

The recovery cost of back-to-back long runs

Big back-to-back days come with a cost.

Paul points out that there have been periods when he could personally tolerate very long consecutive days, but that doesn’t mean the same training would always be appropriate.

Your ability to tolerate back-to-back training can change depending on your fitness, training history and circumstances.

Life outside running matters too.

Work, childcare, sleep, nutrition and other responsibilities can all influence your ability to recover from a demanding training block.

If an athlete deliberately plans a large training weekend, Paul suggests creating enough space around it to recover properly.

A one-off block where you have few other responsibilities and can recover afterwards may be appropriate. Trying to squeeze the same volume into an already exhausting working week could produce a very different result.

Do you need back-to-back long runs for a 100-mile ultra?

Despite how closely back-to-back long runs have become associated with ultra running, Paul doesn’t believe they’re automatically required for someone preparing for a 100-mile trail race.

“In terms of needing to do it, like it’s a thing you need to do to be good at say doing a hundred mile trail race or whatever. No, probably not.”

Instead, consistency throughout the week combined with an appropriate long run can still provide a strong foundation.

Paul explains:

“If you can create a situation where you’re pretty consistent across the week in your training and you do something longer that does stimulate some of these things you get from a long run… you’re probably not gonna be in a bad place doing it that way as well.”

That longer session might be three, three and a half or four hours rather than an enormous weekend consisting of consecutive all-day runs.

For many athletes, consistently completing manageable training may ultimately provide a better return than repeatedly needing several days to recover from huge sessions.

Do you need a long run every weekend?

Another ultra running convention Paul challenges is the assumption that every weekend must contain a long run.

“The idea that you should be doing a long run every weekend is not great.”

Training should change throughout the year.

Research into endurance training supports the broader idea that training-intensity distribution can vary according to factors such as the athlete, training phase and performance level [1,4].

The amount and type of long-distance work you complete can similarly depend on where you are within your training cycle, the event you’re preparing for and how you’re responding to training.

A runner several months away from their target ultra doesn’t necessarily need to reproduce the same long-run structure as someone approaching their most race-specific training block.

Consistency versus the perfect training formula

Taken together, Paul’s thoughts and the wider research point towards the same broader principle:

There isn’t one perfect ultra running training formula.

An athlete with five hours per week available to train shouldn’t necessarily copy the intensity distribution of someone training for 15 hours.

Likewise, someone preparing for a multi-day mountain race may benefit considerably more from back-to-back long days than someone training for a shorter single-day event.

Instead, ask:

• How much time can I realistically train each week?
• Am I doing enough easy training to recover and remain consistent?
• Am I including enough intensity to create an appropriate training stimulus?
• What are the specific demands of my target race?
• Would back-to-back runs prepare me for those demands?
• Can I recover from those sessions without compromising the following week’s training?

The best training plan isn’t necessarily the one that most closely follows a popular formula. It’s the one that provides enough stimulus to improve while allowing you to keep turning up.

Should ultra runners follow 80/20 training?

80/20 running can provide a useful framework, particularly as a reminder that not every training session needs to be hard.

Research supports the broad principle of combining a substantial volume of low-intensity training with a smaller amount of harder work [1,2]. More recent evidence suggests polarised training may offer particular benefits for VO₂peak in highly trained endurance athletes [3].

But current evidence doesn’t show that polarised training is superior to every other approach for every performance measure or every type of athlete [3,4].

That’s why Paul’s advice is particularly relevant to recreational and time-poor ultra runners.

Rather than chasing a perfect percentage, consider the total amount of training you can realistically complete, how well you’re recovering and the demands of the event you’re preparing for.

The same applies to back-to-back long runs.

They can be useful when they’re specific to your event, particularly for multi-day races such as Dragon’s Back. But they aren’t automatically essential for every ultra runner, including those preparing for 100-mile races.

Ultimately, Paul’s approach comes back to the individual.

Train consistently. Include enough easy work to recover. Introduce enough intensity to improve. And use demanding, race-specific training when it genuinely prepares you for what you’ll face on race day, rather than simply because that’s what an ultra running training plan is “supposed” to look like.