Pain and the ‘Killer Body’ : Your trainer tells you your body fat measures a whopping 27%, meaning your work is cut out for you.

You’re not exactly a couch potato, but you’d rather scour urinals in the men’s room at Dodger Stadium than lift anything heavier than a few bags of groceries. And you hate lugging even those around.

The last time you tried to do something about your baggy arms, you had to call in sick the next day.

Yet when the man in your life starts making eyes at what used to be called “co-eds,” you give in and sign up for three sessions with a personal trainer at a gym called Forever Young. (You figure as long as you’re being narcissistic, you might as well go for it.)

The Spanish inquisitors could have saved a lot of wood. Instead of burning people at the stake, they could have forced them to do biceps curls and drive the next day.

Nonetheless, you saunter into the private gym in Northridge with visions of “Lifestyles of the Rich and Famous” dancing in your head, ready to schmooze with your very own private coach. He turns out to be sixtysomething, with a chest of steel and an attitude to match.

“You really are weak,” he tells you by way of encouragement, raking his eyes over your flaccid limbs. “There’s nowhere to go but up.” (Spoken by a man who, judging by photographs of him in various stages of overdevelopment displayed on the gym walls, never had trouble hefting a grocery bag.)

To nail down just how feeble you are, he hooks you up to an electromagnetic device that measures your body fat. Yours is a whopping 27%, far more than the svelte ideal of 19% or less. All those years of shunning coffee Haagen-Dazs have nothing over your gene pool, it seems.

But you’re determined to join Linda Hamilton in having what a well-known women’s magazine calls “this year’s most necessary accessory--a killer body.” It isn’t enough that you’re a size 6; without muscles, you’re nothing.

So you dutifully pick up the 15-pound barbells and pump iron under the eagle eye of your trainer, who corrects every tilt of your trembling limbs. Each hourlong session consists of 120 sit-ups, 240 bench presses, triceps extensions and other modern tortures.

By the third session, you feel like a convert to the Church of Curves, now that yours are more prominent. A co-worker tells you that you’re among the best-dressed people in the office, and you know it’s not your wardrobe that’s changed. There’s a spring in your formerly plodding step.

But it’s short-lived. Tough as your personal trainer was, he’s nothing compared to the guy who subs for him one wretched night. This twentysomething behemoth inhales 10 dozen egg whites a week, a good protein source if you can stomach it, you suppose.

His style is as overbearing as his appetite. He makes it clear that with weightlifting, there is no such thing as basking in your limited success. Capable of bench pressing 15-pound barbells? Then heave 20-pounders the next time, he insists. And so on into infinity, it seems. A woman you share the gym with one evening leg-presses 500 pounds, her female trainer brags to everyone within earshot. You barely manage 45.

After your session with Mr. Muscle-Bound Geek, as you fondly dub him, you have a charley horse in your right leg that puts you out of commission for a week. And as the week wears on, you miss weightlifting the way you’d miss the afterglow from climbing Mt. Everest--it was fun, but you’d never do it again.

Besides, you decide, it’s high time to focus on the greatest workout of all: maintaining your self-esteem regardless of your body size.