3 Reasons to Stop Doing a 20 Mile Long Run

In marathon training, there is one main goal: run longer and farther until your body is ready for the full 26.2. Because of this, most standard marathon training plans ask runners to gradually increase the length of their runs until they reach 20 miles. Many plans use the 20 mile run as the peak of training, the Holy Grail, after which the runner is ready for the distance. However, research shows that the 20 mile long run might not be necessary for most marathoners after all.

This is controversial topic. A few weeks ago, I suggested that a good marathon training plan will not have you running longer than 3 hours, and your long run should only be 25 – 35% of your total weekly mileage.

As a result, a handful of people commented or asked a variation of the following question:

…how, then, can you run your 20 mile long run if you are running slower than 9:00 min/mile pace?

My quick answer was, “you don’t.” To be clear, the 20 mile long run can become problematic for those running significantly slower than 9:00 min/mile ( I say this as someone who has run 3 marathons slower than this). I also want to be clear, there is nothing wrong with running a 4, 5 or even 6 hour marathon. We all have different goals and reasons for running.

I realized that I didn’t have a very good answer to the 20 mile long run question, and so I recently spent some time digging into books, reading articles, and talking with coaches to gain some insight. Below is a quick summary from a few of those experts.

Assuming it will take you considerably longer than 3 hours to run a marathon, here are 3 reasons you might want to stop running a 20 mile long run:

1. The 20 Mile Long Run Increases Your Chance of Injury

By running longer than 3 hours during your marathon training, you significantly increase the odds that you will develop an overuse injury. Many beginner marathoners have strong aerobic capacity due to biking, swimming, skiing or other non-running activities, but their muscles, bones, ligaments and other body systems are not used to the pounding on pavement that comes from running for 3+ hours.

In the same way, your recovery time is lengthened the longer and further you run. If you run a 3+ hour long run on Saturday, you may need double the recovery time compared to if you were running for only 2 hours.

Steve Magness, writer of the quintessential running book The Science of Running, writes,

If too little recovery is allowed, then the body never fully recovers or adapts and can enter Selye’s exhaustion phase; this is what is commonly referred to as over training (Magness, p.122)

2. You Won’t Get Faster

Research has shown that the bulk of your aerobic development happens at or around the 90 minute mark. Beyond that, you don’t see a whole lot of improvement. Jeff Gaudette of Runners Connect, a popular online running website, says:

The majority of physiological stimulus of long runs occurs between the 90 minute and 2:30 mark.

Running longer than 3 hours may help you mentally, but physically it could do more harm than good.

My own coach, Antonio Vega, has said that long runs that are much longer than 3 hours could potentially take away from the time of your next run. Additionally, if you cap yourself at 3 hours, you can incorporate other things (speed, marathon pace, etc) to maximize your long run. You may not be going as far, but your running will be of better quality.

Luke Humphrey of the famed Hansons Running, an elite distance program in Michigan, says;

…after 3 hours of running, you have crossed the point of diminishing returns…. the structural damage to your muscles, along with fuel depletion, that you are going to have to take several days to recover from a singular run.

3. You Neglect other More Important Physiological Systems

Shifting your body to burn fat as fuel is key to running a marathon. Being able to run at a given pace for 26.2 miles is the crux of the marathon, and in order to do so you need to teach your body to burn less glycogen at that pace – whether that is 8, 9 or 12+ minute pace.

To support this idea, Gaudette says this;

The total amount of time on your feet during a 3-hour plus run adds considerable fatigue to the legs… In the long-term, this means you can’t complete more marathon specific workouts throughout the following week, which I believe, and research has shown, are a more important component to marathon success.

He suggests beginner runners (anyone running 3:45 or slower), focus on more marathon specific work like building aerobic threshold. He touts the theory of accumulated fatigue which involves a shorter long run and some marathon-ish paced runs (a harder effort) before that run. This helps to simulate the fatigue your body feels in the later miles of the marathon, and thus training your body how to handle the distance.

So… Should YOU Stop Doing a 20 Mile Long Run?

As with most things, you have to combine research with personal preference. I’m not a coach, but if you are going to run slower than a 4 hour marathon, yes, I think you should stop running a 20 mile long run.

Jack Daniels, (legendary running coach, not the distiller) suggests:

…your longest long run be no longer than 30% of your total weekly mileage (for those running 40 or fewer miles per week), and 25% or 150 minutes (whichever comes first) for those over 40 miles a week (Daniels Running Formula, p. 50).

This means someone planning to run a 4 hour marathon would only be able to get in about 16.5 miles, which is even more conservative.

In short, most would say you could run a 10k after only doing a long run of 2 miles. Similarly, an ultra marathoner could complete a 100 miler by only running a 30 mile long run. So why do marathoners need to run 75% of the total distance?

What is your Experience with the 20 Mile Long Run?

I know that there are tons of runners out there running less than 40 miles a week with a 4 hour, 20 mile long run. Thousands finish the marathon all of over the country every year at this pace.

I am curious what would happen if people focused on increasing their overall volume of running, rather than simply that one big long run?

I would love to hear about your experience on this topic. What has worked, and what hasn’t? Share in the comments below or send me an email.