My daughters want to know why I’ve started working out at the Y. I want bigger muscles, I tell them. I want to be stronger. They think this is hilarious: a forty-six-year-old man acting like he’s sixteen.

But at sixteen, I acted like I was forty-six. I began college that year and was too busy for sports, too serious. A couple of decades later, I took up running, which is terrific for endurance but did nothing for my flabby middle, my shoulders, my arms, my chest.

My daughters still don’t get it. To them, my body is familiar, predictable, a fixed star in the firmament of middle age. It’s a father’s body, sour with the sweats of work and worry, strong enough.

What difference does it make how I look? Instead of straining to do one more overhead press, I could be at the Columbia Street Bakery, drinking coffee and reading the newspaper. I could be nibbling on a bran muffin or — life is short — a raspberry-chocolate croissant, instead of getting right up in gravity’s face, adding ten more pounds to the bar.

The eight Nautilus machines face a wall-to-wall mirror in a windowless room. With their creaking cams and chains, they look like they belong in a medieval dungeon. In this more secular age, we torture ourselves.

My interrogator eyes me coolly. I won’t deny it, I say. I’m goaded by vanity. I tried to love my body. All those years of psychotherapy. It was like trying to love spinach. He lights a cigarette. I figured maybe I’d love myself more if I looked better. He raises an eyebrow. OK, I admit, that’s not real love. He nods. But it feels great: the body called from slumber, a troubled dream of irrelevance, fat replaced by muscle, arms and chest taking on a more defined shape. Very good, he says. Two more sets, he says. And remember, he says, you don’t build strength by repeating easy movements. Once you can overcome the resistance, increase the resistance. When you work at the limit of your strength, you force the muscle to adapt.

This is a metaphor for life, I think. What’s that line from Rilke? The purpose of life is to be defeated by greater and greater things. But I spend enough time thinking. I’m here to work the lower back and the abdominals, not to think. I’m here to do the duo squat, the leg curl, the pullover, the arm cross, the decline press, the lateral raise, the overhead press, the arm extension, the arm curl. I’m here because my ancestors were large, heavily muscled animals, who for millions of years ran down other animals for food, while I sit at a desk all day, running down fleeting thoughts. I’m here because I’m estranged from my body, rarely knowing myself through dint of hard work. I’m here because when I was a kid, I asked for a set of weights and got a lecture instead about how weight lifters are muscle-bound, not to mention stupid and conceited. Was my father threatened that I might become stronger than he was?

Cut the crap, my interrogator warns. You’re here because you’re a privileged white male, who can afford to workout instead of work. You’re here, spending too much time resting between sets, while real men — and real women, too — are getting out of bed, groggily getting dressed, and shuffling off to a day of real work.

The people here are real enough for me. There’s the burly truck driver who boasts, not long after the Gulf War, that his son has joined the Air Force. There’s the house painter who chides me when I change the dial from the rock station to National Public Radio. There’s the Vietnam vet who scolds me for not breathing right: exhale during the pressing part of the lift, he warns, inhale on the return. Momentarily confused, I forget to breathe altogether. He shakes his head. And don’t forget to breathe, he sighs.

But we don’t talk much. I’m here to exercise my body, not my big mouth. I’m here to stop being bullied by the past, to stop making excuses, to stop pretending on hot summer days that it’s not really hot enough to strip off my shirt.

Of course, there are mornings I don’t show up at all, when I’m too busy or too depressed, when I don’t want to look like another middle-aged man trying to stop the inevitable ruin of his body. Time has already taken a couple of bites; it likes the taste. But the next morning I’m back, winking in the mirror at the fool who’s determined to be lean, tough, and chewy before time licks the plate.