Before I had my first session with a personal trainer three years ago, I believed the people who used trainers had too much money and not enough independent willpower to just walk over to the damn weights and lift them until it hurts. But after a year at my new gym, picking up said weights about once a week, I thought, I'm bored, I'm hating this, and it's not working. And so I sidled over to the trainer's desk, hoping nobody was watching, and asked for an appointment with a trainer. They introduced me to Tess.

Tess was precisely what I needed: a cheerful, enthusiastic young woman in excellent shape with extensive training in exercise physiology and technique. During that first session she quizzed me on my training to that point, sized me up, and created a workout regimen that helps me toward my goals, loosely defined as "running faster."

Since that day I've stumbled into the gym at 9 a.m. most Fridays to have her briskly hustle me off to the basketball court or the workout studios to perform dozens of unfamiliar exercises, mountain climbers and striders and burpees, all carefully chosen from her extensive repertoire. She works my legs, hips, and midsection, emphasizing flexibility, range of motion, and quick movement, and she'll throw in just a little upper body work so I can go home with that pleasant soreness in my muscles that makes me imagine they're bulging like Schwarzenegger's. And in those three years, I've set a PR in the half-marathon, finished two others in sub-1:30, and qualified for the Boston Marathon twice, while keeping injuries and strains to a minimum. So, clearly, working with my personal trainer has done wonders for me, and I shall never mock those who do it again.

It's wonderful, except that I've retained almost none of the instruction she's provided me on training techniques. On those occasions I've found myself in a gym on the road or at home, without her, I stare at the straps and Bosu balance trainers as if I've never seen them before, unable to remember how to raise my arms without Tess to demonstrate the exercise I'm supposed to do. When using a trainer's brain to guide your workout, it turns out, your own atrophies from disuse.

And for all my success at running during those years, and in fighting off the depredations of the years themselves, it's hard to scientifically separate the benefits of training with Tess from the 20 to 50 miles a week I run, bike, and swim. And the same is true of those injuries I have suffered. Did I strain my hip last year doing too many miles on pavement, or because Tess put me on a weight machine I wasn't ready for? Both hurt, but which caused the injury, and which made it worse?
But even if some heartless physiologist were to prove to me that my sessions with Tess weren't doing me any good at or at least no more good than my old, unguided hours of wrestling with weights, I would still look forward to Friday mornings, and being dragged through the stations of the cross-fit. The benefits of working with a personal trainer, at least for me, are more psychological than physical.

First, I get to enjoy the sympathetic magic of hanging out with someone much fitter, more attractive, and more cheerful than I am. You know, like we're two fellow athletes, hanging at the gym, talking reps and sets, and feeling the burn. Even more important is something even harder to come by in this distracted world, and that is another person's full and complete attention.

While working with me, Tess focuses specifically and intently on what I'm doing, how I'm doing it, how often I've done it, how many more times I should do it, and when I need a break from doing it to go get a drink of water. In her prior job as a social worker—as she tells me, the skills are transferable—she could diagnose people's problems, figure out what they need, and then give them the right instructions. She is particularly adept at modulating her praise: too little, and I'd feel defeated; too much, and I'd feel patronized. Her "Looking goods!" and "Really greats!" are like expertly applied puffs of breath to the coals of my ego, keeping it at a nice ruby glow, which warms the rest of my day.

We amateur athletes are peculiarly devoted to our fitness, and our obsessions can sometimes be a burden to our loved ones and a mystery to everyone else. It is a blessing to have, not all the time but for about an hour a week, someone who will say, "Yes, I understand. You devote hours and hours to competing in races you'll never win, you want to build up muscles that your office job will never require, you want to throw yourself against walls just to see how far you can bounce. I get it, and I'll help you."

Attention must be paid, so sometimes we end up paying for it. And it's worth every penny.

Peter Sagal is a 3:27 marathoner and the host of NPR's Wait, Wait...Don't Tell Me! For more, go to runnersworld.com/scholar.