Shannon Ware does dead lifts while behind him are Rishi Beri, left, and trainer Dave Werner.

MINNEAPOLIS — Black ink on a dry-erase board outlined the workout of the day. Sally Rodgers, 48, a mother of four, stood still with eyes glazed. She breathed hard, waiting for the pain to begin again.

“Ready, and go!” shouted Damian Hirtz, owner of CrossFit Minnesota, a gym based in an industrial park.

Wind tore through an open garage door. Rock music pumped from a radio. Rodgers was jumping on and off a 2-foot-tall wooden box, her face red, laboring to blast through eight rounds of prescribed pain.

It was a Wednesday evening in late May. I’d come to try a workout with Rodgers and a dozen other exercisers, each one a committed follower of CrossFit’s frantic regimen of getting strong and staying in shape.

As fitness fads go, CrossFit is something of a wonder. Developed in the 1980s, the discipline’s intense and oddball regimens remained underground for years. Participants did hundreds of pull-ups a week and ran sprints followed by power lifting. They heaved tractor tires to develop explosive strength.

Experimentation, intensity and a disregard for conventional exercise wisdom were touted hallmarks of the CrossFit crowd, which grew inside police forces and military squads. Since 2005, the discipline has caught fire with everyday exercisers, and CrossFit Inc., based in Washington, D.C., now touts more than 1,000 affiliated gyms across the country. (Providence has its own CrossFit gym at 175 Broad St. For information, e-mail info@crossfitprovidence.com)

“There is a proven method behind the madness,” said Hirtz, who opened CrossFit Minnesota in 2007.

A Brazilian jujitsu black belt, Hirtz creates a custom workout of the day — “WOD” in CrossFit parlance — six times a week. The workouts range from 15-minute barbell frenzies to endurance days where participants go for 45 minutes in search of their physiological limits.

Each workout gets a name — “Fran” or “Murph,” for example. They mix strength and aerobic regimens in sets that might involve pull-ups, box jumps, running, medicine ball throws, situps and squats. Some days feature laps around a parking lot with a PVC pipe held overhead.

“You can’t do this stuff at a regular health club without getting weird looks,” said Rodgers, who quit a large franchise gym to join CrossFit.

During the day, Rodgers, who lives in Plymouth, Minn., is an office manager. But up to five times a week, she heads to Eden Prairie for a regimen that has helped her lose 30 pounds in a year.

“Fifteen or 20 minutes doing CrossFit is more effective than an hour of regular exercise,” she said.

Like thousands of CrossFitters nationwide, Rodgers, who has two grown sons involved in the activity, can go to the CrossFit Web site ( www.crossfit.com) for a free daily WOD. These boot camp-style workouts can be done at home or in a gym.

A common WOD is easy to follow. “Kelly,” one workout, is five rounds of each of these activities: running 400 meters, 30 box jumps (on and off a 2-foot-tall box) and 30 medicine ball shots with a 20-pound ball.

Rodgers and her sons — one in Pittsburgh, one in Seattle — compare times and splits.

“It’s fun to try and beat them,” she said.