After being on the run in 18 marathons, and finishing 17, I'm finding myself at the health crossroad.

Is it possible to be a chronic runner without chronic injuries? Where does cardiovascular excellence end and orthopedic wretchedness begin? Is it all downhill from here?

Marathons are rich with answers, except we keep asking, as I just did, the wrong questions. The physical ones.

Bones, hearts, aches and aging should be short-run worries. The long-run questions are mental. The 11,000 athletes who ran last Sunday's Marine Corps marathon and the 18,000 of us who did New York the week before had a chance to inch forward to the long distance truth: Running is more mental than physical. Or as Yogi Berra would say, running is 90 percent in the mind and 30 percent in the body.

The mental hazards -- ranging from pulled brainstrings to snapped egos -- are as varied as the physical ones, but much less discussed. From what I've seen, as well as heard and been afflicted with myself, the roads are contagious with several mental ailments:

Speeditis. I once thought it mattered that the clock showed a fast time when I crossed the finish line. Success was a marathon under 3:30, humiliation over 3:30. In the mid-1970s, 3:30 was the qualifying time for the Boston marathon. I made it one year with a 3:29:58, two seconds more and I might have died from speeditis. After a few Bostons, which were sedatives because running there was inevitably a springtime pleasantness, I began to understand that running is natural but speed is not.

Post-marathon depression. This is going around right now. The letdown of finishing the marathon is the pain of having nothing else to live for. The joy of getting out of bed at 6 a.m. to put in 10 miles of training for the marathon is gone. Why get out of bed merely to dress, eat, go to work? Since when is making a living living?

The authority on PMD is Marlene Cimons, 39, a Los Angeles Times reporter in the Washington bureau. She has written about it as well as experienced it. "Everyone tells you how to train for a marathon," she says, "but no one tells you what to expect after it's over. I didn't expect I'd be so totally depressed."

How did Cimons get on her feet again? After her second marathon, she closed a deal on a house and moved into it. "The thing I learned is that, after the race, you should plan something big in your life."

Dabbling in real estate is one therapeutic bigness. Another is to run a marathon the next weekend. It's been done. Tarzan Brown, who twice won at Boston, ran two marathons in two days. Although he died young, he was never known to suffer PMD.

Dropoutphobia. Egos, like cups, can runneth over. The mental abnormality of fearing to drop out of a race means that everything else can zero out but not pride: I will finish NO MATTER WHAT -- including running through pain.

When I got dropoutphobia a few years ago, I entered the D.C. Marathon purposely to see if I could stop at 16 miles. I had finished about 10 marathons by then and was beginning to think something was addictively wrong with me.

On the day when quitting was the hardest goal I could seek, I was not certain that I would have the courage to stop. At 16 miles, I surged and the adrenalin came. I was able to slow down, pull over and stop. This was somewhere near Maryland Avenue and Benning Road. I overheard some spectators on the corner: Look at that guy, he's quitting. Can't take it. He's not tough.

For a moment, I wanted to go over and explain. But what for? Explaining things can be as much a compulsion as finishing things. I had just conquered one. Why not try for another?

Heavy Running.The heavy runner has the delusion that his sport is something more than the frivolity everyone with a half-sane mind knows it is. Healthy running is whimsy. It is a way of staying one pace ahead of the daily dreariness that can press in.

If running runs you, it's no longer play. If it's not playful, why do it?