Runners learn — the hard way, naturally — that there is an invisible barrier at the 20-mile mark known as The Wall, the point where you’ve burned off the body’s ready-to-use chemical energy.

You remember the feeling. Your thoughts, once as free and fluid as your running, turn to viscous sludge, like wet concrete. Your legs abruptly submit their resignation. All vital signs, as measured by your sodden brain, point toward system collapse.

The Wall. Bonk.

After you’ve hit the wall once, you wait for it to rear its head on the next 20-miler. If you’re training for a marathon, the whole 26.2-mile marathon, you should run a few 20-milers as part of your training. The Wall… you know it’s out there, lurking — a real, physical, insidious thing out there, stalking you from behind a bush at the 20-mile mark.

If it wasn’t already there waiting for you, chances are you’ve conjured it by worrying about it. Running is more than a physical battle, it is also a psychological battle; running is many psychological battles, and some of them are fought before you even lace your shoes. When you see a 20-mile run coming on your calendar, you grind your teeth and remember what a savage experience that last one was.

But hey, we survived that, and we came back for more.

What I’m enjoying — yes, enjoying — about training for the upcoming Chicago Marathon this year is that I’ve finally whipped The Wall at 20 miles. My last three training runs at that distance have been successes. Compare this to my previous two 20-mile training runs, back in May, were not successes — they were very much a rude reminder that will is only part of the equation in running.

What changed?

Aside from familiarity with the distance — just getting into the ring with the brute — I’d say that the biggest change is adding some nutrition to my body while running. I’ve never eaten much while running — partly from stubbornness (the tough don’t need fuel), partly from curiosity (let’s see what happens when I run the tank completely dry). So even during the Pineland Farms 50 km race in May I ate nothing more than a handful of gummy bears at each aid station. I crashed later in the race, but it was interesting to see what it was like. Then I cranked out the Escarpment Trail Run in July, an evil 30 km race in the Catskill Mountains, with nothing more than a handful of M&Ms at one aid station in the middle, followed by a crash at the end. In training I never ate, never drank -- and never prospered at long runs.

So much for the zero nutrition control for the experiment.

Now when I go out for a 20-mile run, I pack three PowerBars — Cookies and Cream flavor, which seem to be (a) slightly moister, i.e., easier to chew and swallow, and (b) the best tasting Power Bar, which is a tallest midget contest if there ever was one — and 24 ounces of water in my Delaney fit Camelbak. (Indulge me this foray into "gear." I despise talking about "gear." )

("Gear.")

This has worked well for me. On a 20-mile run, I stop and walk at five, ten, and fifteen miles, eat a PowerBar, drink some water, then run again. I feel like this is cheating a little, this walking while running, but what the hell? This routine contributed to a successful 20-mile run, which fed my confidence, which contributed to another successful 20-mile run, fed confidence, contributed to a successful 21-mile run.

Scheduling the calorie breaks at specific distances makes the system work. If I ever stopped on previous long runs, it was due to the feeling that I needed to stop — that my body was pulling the emergency cord on the train, lurching the system to jerking halt. That kind of stop jangles your nerves, and twenty miles offers the runner too much time to consider the causes of the stop over and over and over. Stopping right at five, ten, and fifteen lets the conscious brain think it is in charge. Placate that damned thing and you could probably run forever.

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