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THE 20-MILE LIMIT: How long should your longest run be

By Hal Higdon

A RUNNER RECENTLY POSTED A QUESTION to my Facebook page about the apparent 20-mile limit for long runs in my marathon training programs. “Why the limit?” the runner asked. She recently had completed one of my novice half marathon programs with 10 its peak long run mileage. But for intermediate and advanced half marathoners, the last long run peaks between 12 and 16 miles. Following this logic, should not some of my marathon programs peak anywhere from 24 to 32 miles?

“It’s such a stretch between 20 and 26.2 miles,” worried the runner. “If I want to push my mileage farther, how far should I go?”

“Go no farther,” I warned. I feel strongly that 20 is plenty for all novice and even for most intermediate and advanced marathoners. Yes, runners might achieve a somewhat higher level of fitness by pushing beyond 20. But the twin risk of injury or overtraining rises with each extra mile added. I would rather send those following my programs to the starting line undertrained than overtrained. They are much more likely to have a positive experience.

That didn’t satisfy my questioner. She wanted a better reason. She wanted to understand the science behind the 20-mile limit. Unfortunately, the science is fuzzy. It’s a tough topic to study. Are metric-oriented runners who peak at 30-K (18.5 miles) less prepared than linear runners peaking at 20 or 22 or 24 or even beyond? My scientific friends generally agree that the benefits of long-run training begin around 16 miles and may continue beyond 20 miles, but I am aware of no studies that prove this, and I’m not even sure how one might design such an experiment.

My proof comes from outside the human performance laboratories, specifically my experience from having coached perhaps a million runners to finish marathons. These were runners who made the jump from 20 to 26.2 without a twitch. The three-week taper is the reason, providing the necessary rest to make the jump doable. If experienced runners with 5-10 marathons on their resume want to train harder and longer, they can experiment with that approach, but in the meantime, I advise against going too far too soon.

We are all different. We all come to this marvelous sport of long distance running with different abilities and different talents and different desires. A confession: During my years of peak training, my longest long runs were 23.2 miles; my midweek sorta-long runs 15.6 miles. Those distances were dictated partly by availability of convenient courses.

Keep in mind also: I was young and foolish, training twice daily, averaging more than 100 miles a week. Runners operating at that mileage level can float through long runs of 20 barely breaking a sweat. Others—the majority of recreational runners—stretch to achieve mileage levels one-third of that level. I do not want to push them beyond their abilities. More miles should be added to any program only gradually and perhaps with a coach closely observing.

Should 20 miles continue to be a limit? Yes, if you are following one of my programs. No, if you feel you are ready to go beyond. Every runner should be free to train to the limit of his or her ability. Good luck covering the extra miles if that is your choice.


HAL HIGDON is a Contributing Editor for Runner’s World and author of more than three dozen books including, most recently, Hal Higdon's Half Marathon Training, available autographed through this Web site.