By GINA KOLATA


A colleague of mine at The Times who is a triathlete had a question: Everyone tells you to listen to your body, but what are you supposed to listen to?

Turns out it��s not so obvious. Deena Kastor, the American record holder for the marathon, interprets the advice selectively.

��Running isn��t always comfortable,�� she said. ��I remember running through a lot of discomfort and pain.��

And, Ms.Kastor added, she also runs when she does not feel like it.

��So many times the alarm goes off in the morning and you tell yourself you are too tired,�� she said.

But if you ignore those messages from your body and just go out and run or do your sport, she said, ��those are the days when we have the most pride.��

��The trick in listening to your body is to know what you can run through,�� she said. ��If you have a sharp pain you should take care of it.��

So does listening to your body mean learning to understand the difference between a pain that signals a serious injury and one that can be ignored? And if it does, why do athletes like Ms.Kastor become seriously injured, anyway?

Last year she broke her foot about five kilometers into the marathon at the Beijing Olympics. In that same race, Paula Radcliffe, who holds the world record in the women��s marathon, ran less than her best because her training was interrupted by a stress fracture.

Maybe the problem is that it is hard to understand what your body is saying.

����Listen to your body�� is always a tough one,�� said Keith Hanson, a coach who directs the Hansons-Brooks Distance Project, which recruits talented distance runners and supports them while they train full time.

One of his runners, Brian Sell, was in the Beijing Olympics, and others are internationally competitive.

��There are several aches and pains that you can run through,�� Mr.Hanson said, ��and others that need some down time. I always try to follow one key rule: If you are gimping - altering your gait - after 10 minutes of running, then it is an injury and not just an ache or pain. You should never run through injuries. If you do, they almost always turn into compensation injuries. What started as an ankle pain becomes knee and hip problems.��

On the other hand, there is also a different interpretation of ��listen to your body.�� It��s one favored by Asker Jeukendrup, the director of the Human Performance Laboratory at the University of Birmingham, in England, and an ironman triathlete.

Listening, he said, means that you are supposed to listen for ��valuable information�� and learn to disregard ��other negative information that may come into your thoughts that is actually irrelevant.��

Dismiss, for example, ��some feelings of fatigue,�� he said.

The goal is to push your body to its limits, but not beyond. Easier said than done, he admitted. And, he added, not everyone can do it.

Actually, said Tom Fleming, my coach, it is unlikely that anyone can do it. Mr.Fleming won the New York City Marathon twice and has coached athletes ranging from adolescents to nationally ranked runners. ��I never listened to my body,�� he said. ��Maybe I should have. So let��s get that clear right off: I think it��s an impossible task.��

When he was training, Mr.Fleming said, he couldn��t train less or make himself go more slowly. And, he added, if you really listen to your body, you will not achieve what you are capable of.

Athletes need someone else, a coach if possible, he said, to tell them when to rest, when to take an easy day and when to work hard.

Another of my colleagues at The Times, Charlie Competello, said he tries to figure out his body��s signals for himself. But he struggles, arguing with himself about what his body is telling him. He thinks of his internal arguments as a debate between ��Charlie�� and ��Charles.�� They argue in the mornings, when he plans to go out for runs.

����Charlie�� says, ��I��m tired and I��m not going to go out,���� he said. ����Charles�� says: ��No, no, no, you can make it. Go out and do it.����

Usually, he said, Charles wins. He runs and is glad he did.