THE GUT-BUSTING CIRCUITS seemed to have served their purpose: By Monday I was so sore I could barely move, and it forced me to contemplate some deep questions: What the hell was this, and why was I doing it anyway?

To be fair, the Gym Jones seminar wasn't simply an opportunity to bathe in the geyser of testosterone that erupts when brawny men gather in a room full of heavy weights. In fact, if anything, I came away from the weekend impressed by Twight's holistic approach, his invocation of restraint, his belief that less really can be more. He encouraged honest self-assessment and rigorous attention to the bigger picture: nutrition, recovery, goal-setting. Of our 20-plus hours in the gym, at least two-thirds had been spent in front of the whiteboard. "I don't want to give a man a fish," Twight told me afterwards. "I want to teach him to fish."

There was a lot to learn, not much of it comforting. For starters, my diet was a mess. Beginning my day with a softball-size blueberry muffin and a triple cappuccino, as I'd done for, oh, the past 15 years, apparently didn't cut it. Training was important, but nutrition was the true foundation, because it was the engine of transformation at the molecular level. Twight pushed a Zone-like strategy of roughly equal parts carbs, protein, and fat. The rules were vaguely familiar: more protein, more fiber, more healthy fats like fish oil, and so on; way fewer processed carbohydrates, a daunting challenge when you realize just how much of the American food supply is created from corn and sugar.

"Want to lose weight fast?" Twight said. "Try not drinking alcohol for a month." These were the facts, he insisted; whether we chose to accept them was up to us.

As fascinating (if discouraging) as I found the dietary discussion, I was even more caught up in the Gym Jones weight-lifting philosophy. Since I was sticking around for a few days, Twight took me to meet Dan John, a strength-training czar who lives in Murray, a suburb of Salt Lake. "Dan is the master of simplification," Twight said on the drive out. "I've probably learned more from him than nearly any other individual."

John, 51, runs the Murray Institute for Lifelong Fitness, or, as he likes to call it, MILF. The way Twight talked about it, I expected MILF to occupy some gleaming hilltop campus, but in fact it's shoehorned into John's two-car garage, between his Mazda 6 and a refrigerator full of soda, beer, and bottled water. A rusty squat rack is pushed up against one wall, and two deep furrows have been worn into the concrete floor where the barbell plates repeatedly land. MILF also has an annex, a weedy alley that parallels an irrigation canal behind the house. When John and his jocks aren't swinging kettlebells or performing squats in the garage, they can often be found out back, dragging a weighted sled up and down the dirt lane.

John spent the afternoon sharing his 25 years of accumulated knowledge about strength and performance. Weight lifting, properly deployed, will serve any athlete at any level because it develops power, he told us, and power is the one thing central to almost every sport. Most of what I knew about weight training I'd learned in high school, where I mimicked routines that had originated in competitive bodybuilding. The strategy entailed isolating muscles and working them until they failed—curls, bench presses, triceps extensions, etc.—and then moving on to the next muscle group. After a while, your muscles got bigger, and, naturally, everyone assumed that a bigger muscle was a stronger muscle.

But that isn't always the case. In fact, exercise physiologists discovered that muscle isolation is often counterproductive when it comes to executing more complex natural movements, where muscles are required to work in concert. Hence the value of Olympic lifting, with its expanded range of motion. Physiologists also discovered that only certain types of lifting make muscles grow larger—specifically, doing eight to 15 reps in sets that end in complete exhaustion. In contrast, slightly modified approaches, like fewer reps with heavier weights, build stronger muscles without making them bigger—particularly appealing to endurance athletes, for whom increased size is considered a liability.

There's legitimate science behind the high-intensity work, too, and both John and Twight believe that, done right, it produces rapid and profound results. The most convincing studies have been done by a Japanese physiologist named Izumi Tabata. In 1996, Dr. Tabata discovered that short-duration, high-intensity training enhances anaerobic capacity while simultaneously increasing aerobic endurance. This allows you to shed more fat than with moderate-intensity aerobic exercise, and it also produces a metabolic afterburn as the body works to repair itself. Circuits like those we did at Gym Jones are sometimes referred to in the weight-lifting community simply as "Tabatas."

"Strength is the glass," John called out as Twight and I walked down the driveway at MILF late that day. "All your other training is the liquid."