Why Is My Longest Marathon Training Run Only 20 Miles?

Black athlete running in a race
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Many first-time marathoners wonder why so many marathon training schedules max out at 20 miles for long runs. How can you be prepared—both mentally and physically—to run 6.2 miles beyond your longest run?

There is a lot of debate about this issue. But most running experts tell recreational marathoners that it's not a good idea to run more than 20 miles at one time during training. Running that distance takes a toll on your body. You'll need a long recovery period, and you run a high risk of getting injured.

When it is part of an overall training plan, one that includes speed work, cross-training, strength training, and adequate rest, running 18 to 20 miles as your longest training run will prepare you to complete the marathon. The potential negative effects of running farther than that outweigh any possible benefits, such as feeling more mentally ready to run 26.2 miles.

The Effects of Long, Slow Distance Training

It's important to remember that being prepared for your marathon is not about just one long run. It's about the consistent training you've been doing for months. If you've been following your marathon training schedule, you'll be ready, even though you've never run 26 miles before.

A marathon training schedule is built to increase the distance of your longest run steadily and gradually. Most schedules aim at increasing it no more than 10 percent per week. This is a rule of thumb for athletic training to consolidate fitness gains without increasing the risk of injury. You add a little more stress to your muscles, aerobic metabolic system, and mental toughness. But the stress is only enough that you are fully recovered in a week for your next long, slow distance run.

With your long training runs, you are building calluses on your feet so they will be less likely to blister. You learn where you chafe and what to use to prevent it. You learn how to hydrate right and when to take on energy snacks. You also develop the mental toughness and confidence to get through hours of running.

The Three-Hour Rule

Some running coaches recommend that you run for no more than three hours on long-run days. This could mean doing less than 20 miles, depending on your pace. The theory is that after three hours, your muscles just don't benefit from additional work. Instead, they're so tired that your form suffers. Once that happens, your risk of overuse injuries goes way up.

Plus, beyond this point (whether it's three hours or 20 miles, depending on your pace and your training schedule), your body will need more time to recover—as much as several days. One look at any marathon training schedule shows: That much recovery time just doesn't fit.

Tapering Before the Marathon

During the two to three weeks before your marathon, you'll be cutting back your mileage (and adding in some extra sleep, too, if you can). This tapering period will allow your body to recover from all those months of training. Your muscles will store energy to use on the big day. A typical tapering schedule might look like this:

Time Before Marathon
  • 3 weeks

  • 2 weeks

  • 1 week

Weekly Mileage
  • 80 percent of your max

  • 50 to 75 percent of max

  • About 35 percent of max

With a proper taper, you'll feel rested and ready to take on the 26.2-mile distance. And running less means less risk of injury. You do not want to have to drop out of the marathon because you are hurt. By tapering to allow your body to be in top, uninjured condition, you will make it to the finish line on race day.

What About that Final 6.2 Miles?

Yes, it's hard to get from the 20-mile marker to that finish line. Your legs are tired, your energy stores are depleted (this is when you might hit the wall), and your mind might be playing tricks on you. But you do have some extra help from the crowd and the environment on race day. You might even enjoy a runner's high. Try these strategies to finish strong:

  • Fuel up with energy gels or shots throughout the race, so you aren't on empty as you hit the 20-mile mark. Be sure to practice this on your long runs so you know what foods work for you. The same goes for water and sports drinks.
  • Pace yourself from the beginning. If you start out too fast (which is easy to do when your race-day adrenaline gets pumping), you'll run out of steam later.
  • Check your form. It's easy for it to start to slip at this point. Taking the time to scan your body and make adjustments could be a welcome distraction and will help you keep moving.
  • Psych yourself up. Many runners like to look at the first 20 miles as one event (one they've already successfully completed in training) and the final 6.2 as a second one: A 10K with a 20-mile warm-up. You can do this! Focus on one mile at a time.
  • Use the crowd. Spectators can make a big difference. Take in all the people cheering you on. You really are almost there.
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By Christine Luff, ACE-CPT
Christine Many Luff is a personal trainer, fitness nutrition specialist, and Road Runners Club of America Certified Coach.