What Is the 80/20 Rule in Running?

Runners often swear by the 80/20 rule for organizing their training—but there’s no relation to the Pareto principle of the same name. Let’s talk about where the 80/20 idea comes from, how to implement it, and when it is and isn’t a good idea to train this way. 

What is the 80/20 rule for running? 

Briefly, it’s the idea that 80% of your running should be low intensity, and only 20% at medium or high intensity. Recreational runners (like you and me) often run closer to a 50/50 split. The 80/20 rule suggests that we should take some of those faster runs and slow them the heck down to reach a better training balance. 

The 80/20 rule was popularized in a 2014 book, 80/20 Running, by Matt Fitzgerald. Fitzgerald, in turn, based his recommendations off research by Stephen Seiler, who found that elite athletes in a variety of endurance sports, including running, cycling, and cross-country skiing, did about 80% of their training sessions at intensities much lower than they would ever use in racing. In other words: To train your body to go fast, you have to log a lot of miles going slow. This is similar to the idea of “polarized training,” which means that you stick to the extremes—either working very easy, or very hard, rather than spending much time in the in-between.

Note that 80/20 here only refers to how you split up your training: 80% easy versus 20% hard. This is not the Pareto principle, which states that 80% of your results come from 20% of your…whatever. (80% of sales coming from 20% of customers, 80% of your needs met by 20% of the stuff you own, etc.) In running, there is only really one result—your race time—so the question is just how to split up your training time. 80% easy and 20% hard is the balance that, Fitzgerald and Seidler would argue, will get you the best race times.

What counts as low-intensity running?

If you’ve been paying attention to the “zone 2” trend, you’re probably thinking you should be in zone 2 (arguably 60-70% of your max heart rate) for 80% of your training. And you know what? That will get you close enough. Go with it. 

But the definitions more often used in the scientific research aren’t based on heart rate alone. Some of them use metrics we can’t easily measure on our own—go ahead, try to keep your blood lactate below 2 millimoles per liter. 

What’s more useful—and still borne out by research—is to use VT1, the “first ventilatory threshold.” That’s a fancy word for what old heads will know as the “talk test.” If you can carry on a conversation without taking extra breaths mid-sentence, you’re below VT1. That’s what 80% of your training should feel like. 

I know that’s not enough information for the more data-minded among you, so I’ll note that Fitzgerald reported in his book that this level is often found around 77% to 79% of elites’ max heart rate. The exact number might vary from person to person, and heart rate numbers are never totally objective, since they can be affected by heat and stress among other things. But as a gut check, 77% of my own known, tested max puts me around 153, which matches shockingly well to what I consider my easy pace—I try to stay in the low 150s for my easy runs. 

Taking this information together, it turns out we can go a bit higher than “zone 2” and still be at the right intensity for the 80% part of our 80/20 running—as long as it truly feels easy. If you’d like, you could customize your zones on your running watch so that you have a zone that tops out at 77% or so. (It might even make more sense for that to be zone 3 rather than zone 2.) Or if you want to round this number to get an easy-to-remember rule of thumb, you can keep 80% of your running below 80% of your (true) max heart rate and you’ll be right on track.

How to train with the 80/20 rule

Before we can divvy up our training, we need to decide how we’re measuring our training. Are we aiming for easy runs to be 80% of our training sessions? 80% of our miles? 80% of our total training time? 

Fitzgerald, in his book, counted up minutes in easy, moderate, and hard intensity levels. But if you’re doing an interval run, he counted the intervals and the recovery between them as part of your harder intensity work. (A cooldown after those intervals would count as low intensity, though.) 

So you can do the same. It would also get you in the right ballpark to think in terms of miles or sessions. If you do one hard run for every four easy runs, you’re still doing 80/20 (as long as those runs are roughly similar in mileage). 

How important is it to stick to the 80/20 rule? 

Even though it’s called a “rule,” this isn’t a thing you have to follow. It’s just one way of training that matches what a lot of elite athletes do. There has also been research showing that recreational runners can benefit—but that doesn’t mean it’s the only way to train. 

Seidler, the researcher, even told Fitzgerald, the author, that if he could only train twice a week, he’d do a mix of harder and easier work in both sessions. Research on competitive recreational runners found that a 77/23 split and a 46/54 split both resulted in small improvements to 10K time, and the difference between groups was not statistically significant. That said, these folks had 10K times (that’s a 6.2-mile race) under 40 minutes to start, so they were pretty fast to start with, compared to a lot of beginner runners. 

Meanwhile, there’s plenty of other research showing that casual runners can improve with almost any type of training, and that increasing your total mileage (measured in miles per week) is helpful for improving your fitness and your race times. 

The bottom line

If you’re a runner with lots of room for improvement—which covers many of us beginner, intermediate, and casual runners—you don’t necessarily have to slow down 80% of your runs to a crawl. You can use any conversational pace that works for you, even if your watch says that’s zone 3. And since increasing mileage is usually part of improving as a runner, it may make more sense to think about adding easy miles, rather than turning your hard miles into easy ones.