20 miles is NOT enough (but what is?)

“The long run is what puts the tiger in the cat” — Bill Squires


Everyone agrees that the long run is a crucial part of your marathon training. What people DON’T agree on is how long your longest run needs to be. Look at cookie-cutter programs and you’ll see everything from 16 miles to 30 miles recommended for the longest training run. Obviously with a range that big, it can be tough to figure out what the right answer is. The answer will vary depending on your experience, goals, injury history, and more, but I think there are some key principles that can help guide you.


Our bodies are lazy


I want to start by going over one big concept: your body is lazy.


Don’t worry, everyone’s body is lazy. Most of us know all too well that if you stop running, your body doesn’t stay in great shape just because it feels like it. That’s because your body won’t do any work it doesn’t have to. In a practical sense that means when you’re training for something, you better train in a way that matches what you want to be able to do. Coaches call it “specific adaptation to a specific stimulus.” That’s why you can be in great running shape and still get winded walking up a few flights of stairs.


In the case of marathon training, one of the biggest things that you need to train your body to do is to produce energy at a high level for a long period of time. That’s why the long run is so important!


Since your body isn’t going to get in great shape without the proper training, I like to use the rule of thumb that your longest long run should be at least as long as the TIME that you’ll be running for the marathon. So, if you’re planning to run 3:30 in the marathon, your longest long run should be at least 3:30.


Classic marathon training: 20 miles


Given that, let’s look at what a 20 mile long run (the most common recommendation in cookie-cutter marathon training programs) would equal time-wise if you were running a minute slower than goal pace on your long runs:


Marathon longest run


As you can see, you would be running shorter than your goal time — and if your goal time is over 3 hours, it’s shorter by a pretty significant amount. If you’re training to break 3:40 in the marathon and your longest long run is 20 miles, you’ll only run 3:10 on your longest run. Your body isn’t going to think “I bet we’re going to be out here longer soon — let’s make sure we’re ready for it!” That’s just not how our bodies work. So the last 30 minutes of your marathon will be terra incognita — and that’s a lot of time for something to go wrong.


How long is long enough?


So how long SHOULD your long run be if you want it to be the same amount of time as your marathon? Check out this chart (uses the same goal pace +1 minute assumption):


Marathon longest run chart


Using this chart and doing some rounding leaves you with roughly:


  • 22 miles as your longest run if you’re planning to break 2:30
  • 23 if you’re running between 2:30 and 3:40
  • 24 if you’re running between 3:40 and 5:15


Hitting those numbers for your long run will take some extra effort — and may mean that you need to start your marathon training program a few weeks earlier than normal to safely build up to those levels — but teaching your body how to work for that long will definitely pay off on race day. After all, the marathon will be hard enough without asking your body to do something it hasn’t done before!