What is a marathon?

It is everything and nothing.

A cakewalk for some, a death march for others. It is a chance to prove to yourself that your body is functioning as perfectly as possible. It can be a moment, too, to realize that such proof means nothing. So you're physically fit. What's that do for anyone, either for a neighbor across the street in pain or for millions of poor people across the ocean in torment from starvation? Tell the hungry about your premarathon carbo-loading. They'll be impressed.

I have never met a marathoner whose exhilarations about going the distance weren't expressed in much the same joyful words and tones used by novelists who have just sent in a finished manuscript or carpenters who have built a beautiful cabinet or gardeners whose strawberries come in large and red.

Late last Sunday afternoon, I had a phone call from a friend who had finished the New York City Marathon a few hours before. She had prepared for the event for nearly two years, about 2,000 miles of preparation for one race of slightly more than 26 miles. This was a high point in her life.

The next day, I spoke with another woman whose voice had all the same joy in it. But she wasn't a runner. She taught illiterates how to read. She was a volunteer tutor. Yet everything expressed in her feeling of accomplishment and pride in the teaching of reading was an echo of the runner calling from New York.

So the marathon, in context, is only one of thousands of tests that can challenge the spirit. "Human beings are animals with a zest for going beyond the immediate," Lionel Tiger and Robin Fox wrote in "The Imperial Animal."

For most runners, marathons differ from shorter races because of the coma factor. Somewhere around the middle of the second half -- between 18 and 22 miles -- the will disengages itself from the body. Until now, the body screaming, "No!" has been under the control of the will shouting back, "Yes!" But slowly this coercive relationship fades, and the argument has been won by the body. The will agrees with it. At 22 miles, you are moving, but it's not running.

You are in a coma, with the life support system turning off. All that's pulling you to the finish line is a subconscious urge to satisfy your curiosity. Can anything worse be ahead? What's ahead?

Willpower recovers from marathons much better than body power. Runners who say they felt fine a few days after the race are deluded. Physically, a marathon means no more than being 26 miles closer to an injury. To run marathons is to be a cardiopulmonary wonder but an orthopedic wreck.

"A singular fact about distance runners," Dr. Richard Shuster writes in the current issue of The Runner, "is that almost all of them develop injuries at some time. Authorities are calling this a new kind of epidemic. Surveys indicate that some 60 percent of those who run 30 miles a week, and 80 percent of those who run 60 miles a week develop injuries."

Many runners who took up the sport five years ago when the boom began are acknowledging that they overdid it. They are nursing their injuries while making podiatrists and orthopedists wealthy. As the born-again athletes are tapering off their weekly mileage, so are the greats of the sport. Frank Shorter says, "Instead of 120 miles a week, I'm doing 90, but all things considered, it seems enough."

No doubt nonmarathoners will be making much of how the distance runners were suckered into the sport by the prospects of the cardiopulmonary benefits, and never dreamed that as the heart was strengthening the knees were weakening. But joints that work at 80 percent capacity for athletes are not half as disastrous as hearts and lungs that work at 40 percent capacity for loungers.

In my fantasies, I sometimes think that marathoners are better people than nonmarathoners.

But I don't fantasize about runners for long. You can run 26 miles, but you are still finite. All that can be said about marathoners is that at some point in their lives they decided to carry things a bit further than their conservative selves and the conservative world said was good for them.

Of course 26 miles is going too far. But, "Man is a maximizer," says George Sheehan, who ran his best marathon (3:01) in the 1979 Marine Corps at age 60. "He is ripe for excesses and exuberances. When life becomes a celebration, we are likely to overcelebrate."