80/20 Running: The Science Behind the Training Approach

Have you heard of the term “run slow to run fast”? It might sound counterintuitive, but this training philosophy actually works. It’s been scientifically validated through what’s known as 80/20 running. And when elite runners like former marathon world record holder Eliud Kipchoge spend 80% of their training time running at a conversational pace, you know there’s something in it. 

While Kipchoge’s easy pace may still be faster than many people’s all-out race pace, it’s all relative – and the “Go slower to go faster” approach is something we can all learn from. Let’s dive into the science behind this approach and how you can apply it to your own training.

What is the 80/20 Rule in Running?

The 80/20 rule is simple. It states that you should spend 80% of your training time running at an easy, conversational pace, and the other 20% at a moderate to hard intensity. Easy running builds your aerobic engine, improving oxygen delivery to your muscles, while preserving energy for hard sessions to develop your speed and power.

Many runners instinctively run the majority of their runs at a moderate to hard pace. That leads to fatigue, meaning many of us are too tired to train truly hard when we need to – which can lead to limited aerobic development and stagnation in performance.

What Easy Versus Hard Actually Means

When we talk about easy running, it should be just that. Many runners find it hard to resist running their easy runs harder than they should, pushing the pace or pressing into higher heart rate zones. 

You should be able to hold a conversation – if you can speak in full sentences, then it’s probably around the right pace for you. But it might be harder than you think to run that slowly. For many runners, this pace might be 1-2 minutes per mile slower than what they’d consider to be “easy”.

The other 20% of your training, then, encompasses all of your quality work. That means interval sessions, tempo runs, hill repeats and race pace efforts make up the medium to hard intensity portion of your training. These sessions should feel like genuinely hard work, but you shouldn’t feel completely destroyed afterwards.

Where Has the Rule Come From?

The “run slow to run fast” philosophy has been around for a while, and it goes by several different names: polarized training, the Maffetone Method, low heart rate training, low intensity training. It’s not the name that’s important, but the concept behind it: that the vast majority of our runs should be done at a low intensity.

The approach was pioneered by Dr Stephen Seiler, an exercise physiologist at the University of Agder in Norway. In the early 2000s, he researched how elite endurance athletes train, analyzing training data from world-class runners, cyclists, rowers and cross-country skiers across different countries. He found that all of these athletes from different disciplines and different places had a very similar approach: they spent around 80% of their time training at low intensity, and just 20% of their time was spent on hard training.

This was backed up by later research also conducted by Dr Seiler and colleagues, which found that the coaches of world-leading athletes in Olympic endurance sports had their athletes doing low intensity training for 75-80% of all of their training.

Seiler's research isolates the cut-off between easy and hard training as the ventilatory threshold, which falls between 77 and 79% of maximum heart rate in well-trained runners, and is similar to the lactate threshold. This is the crucial point where your body switches from primarily aerobic to anaerobic metabolism – that is, the boundary that separates truly easy running from everything else.

What About Recreational Runners?

So the 80/20 approach clearly works for elite runners like Eliud Kipchoge and Paula Radcliffe, both of whom did this type of training at the peak of their record-setting careers. But is it also beneficial for non-elites?

The answer is an emphatic yes. A 2013 study took 30 recreational runners and split them into two groups for ten weeks. The first week followed the 80/20 approach, while the second group did 50% easy running and 50% moderate/hard running. At the end of the ten weeks, the researchers measured the improvement in their 10k times. While both groups improved, the 80/20 group improved more, by 5% compared to 3.6%

What Are the Benefits of This Type of Training?

The clue is in the name of the concept: Run slow to run fast. Ensuring that most of your runs are at an easy pace can help you run faster, as the 2013 study showed – and this seems to be the case whatever level you are.

If you always run slow and never add in any faster runs, then you’re unlikely to improve your times. That’s why the split between easier and harder running is so important. The real benefit of 80/20 training is the fact that it improves the quality of your hard sessions. By running the majority of your runs at an easy pace, you’ll be better rested and less fatigued when it comes to doing your speed work, meaning that you can hit your target paces. Then, you’ll be able to properly recover before the next hard session. Many runners who try to go hard every day find themselves too fatigued to train truly hard when it matters.

And beyond improving your times, 80/20 running can also help to reduce your risk of injury. Easy running places less stress on your bones, joints and soft tissues and allows your body more time to repair and recover. The chronic moderate stress that comes from running harder most of the time is more likely to lead to overuse injuries than taking a polarized approach of running very easy most of the time, and strategically hard sessions occasionally.

How Can I Incorporate 80/20 Running Into My Training?

If you follow a training plan or have a coach, chances are that you’re already following the 80/20 approach. After all, it’s a training technique used by elite athletes for a reason: it works.

But if you’re not already using this technique, it’s easy to adopt. The first step is to understand what “easy” really means for you. Truly easy running should feel almost embarrassingly slow. You should be able to hold a full conversation – so that means if you’re breathing heavily or can only manage a few words at a time, you’re going too hard. It might take you a while to get used to running this slow – but stick with it. And remember, “easy” looks different for everyone. Don’t get caught up in comparing the pace of your easy runs to others on Strava.

Then, you just need to structure your training so it follows the 80/20 principle. And one of the great things about this approach is that it’s scalable, so whether you run three or seven times a week, the principle remains the same.

If you run three-four times a week, you’re looking at two-three easy runs and one quality session, which might look like:

• Easy run: Monday

• Tempo run: Tuesday

• Rest day: Wednesday

• Easy run: Thursday

• Rest day or cross training: Friday

• Easy run: Saturday

• Rest day or cross training: Sunday

If you run 5-6 times a week, then you should be doing 4-5 easy runs and 1-2 quality sessions. You should be sure to space hard sessions out with easy day in between, which might look something like:

• Easy run: Monday

• Intervals: Tuesday

• Easy run: Wednesday

• Tempo run: Thursday

• Rest day: Friday

• Long easy run: Saturday

• Easy recovery run: Sunday

Your hard sessions can change each week, but they could be intervals, tempo runs, hill repeats or runs with segments at race pace. Remember that external factors like heat, hills or fatigue can affect your pace, so you may want to focus on Rate of Perceived Exertion (RPE) rather than pace. RPE is a subjective scale that you can use to measure how hard you’re working during your sessions.

The 80/20 approach requires patience, but the science is clear: this is how the world's best endurance athletes train, and it works for recreational runners too. Trust the process, embrace the easy runs, and watch your performance improve over time.