The above, from one of the trainers at Testosterone Plaza (the gym I go to, for you newcomers). She's a gifted trainer -- I've worked out with her a couple of times -- a former ballet dancer and former competitive bodybuilder. But now she's forty. She was in tears in the locker room: she'd fractured her foot that morning, just by stepping the wrong way. She'd made it in to the gym anyway, and had trained the client with whom she'd had an appointment. But she was furious and frustrated, as any sidelined athlete would be: she'd intended to work out after the training session. Back and shoulders, today. The idea of letting your muscles melt back to sludge is one that frightens me, too; I worked out through two successive broken fingers, and played basketball through the healing period of one of them.

But in my trainer's case, something else was working, as well. This is her life. This is what she does: work out, work on her body, exercise, sweat. And behind the anger, I think, was the fear. Sooner or later she'll be too old for this, and each injury brings that moment sooner. Then what?

Sooner or later, I'll be too old for basketball, too, and for running. I'll be sad about it, and I'll probably turn into a ridiculous-looking racewalker, like all my other former-athlete friends still reaching for that endorphin fix. But it's only part of who I am. What do you do when you lose the thing that defines you? Your identity, your own idea of who you are? Athletes are pretty much alone in this danger. Most of the rest of us can ease into successive versions of ourselves, morphing as we get older, but not having to stop.

On the intellectual side, this is one of the reasons I'm perenially interested in the psychology of sports. And on the emotional side, I feel very bad for my trainer.