If your idea of a workout consists, as mine did, of a pleasant run and a few sit-ups, your first CrossFit session isn’t just a shock—it’s like being tased.

For the first 13 miles I’m a machine, chugging up the hills and running with purpose on the flats. Those lung-searing sprints evidently worked: my heart thrums quietly under the hood, a Porsche that has only been asked for second gear.

Lapping the course, I head back out for mile 14. Now you’re in uncharted waters, I think. As if on cue, the hills appear again and my legs go rubbery. I choke down a Gu and some water and am carried for miles on a second wind. How do I feel? To be honest, not great. But no worse than in the other marathons I’ve run.

At mile 19, I pause for a cup of Coke and make the final turn toward the tape. “Let’s see what the wall wants to do to me,” I mutter. But the wall never comes. Weird calf cramps jab me for the last five miles, forcing me to walk for several seconds, but I fall in beside a fellow sufferer, we pick up the pace late, and I finish in 3:39—a personal record by five minutes.

So did CFE deliver? Yes, mostly. It got me to the starting line without injury. I ran strong on a tough course. What’s more, I’m the quickest, most bulletproof all-around athlete I’ve ever been.

Would I use CFE to train for my next race? Yes, mostly. I’ve now incorporated some speed work and weights into my normal routine. Next marathon, though, I’ll toss a few big runs into the mix, in a nod to conventional wisdom.

It’s also a nod to what makes me happy, which is why we exercise to begin with. Several days after the race, while visiting my sister, I went on my first casual run. Down Post Road, past the interstate, the road becomes a country lane, growing quiet and unspooling before me, and I chase it around the next bend, through the stop sign, toward the ocean. It feels good to be released from the tyranny of the track—away from the wind sprints, away from my heart’s desperate pounding. My legs are as well trained and twitchy as a racehorse’s; they want to move fast. But I won’t let them, not today. I switch off my stopwatch, set my mind to wandering, and settle in for a long, slow, delicious ramble.    

Correspondent Christopher Solomon wrote about the Teton Traverse in July 2012. He lives in Seattle, Washington.