A free, weekly workout session for neighbors has beefed up to become Jam Fitness, a new downtown business offering group aerobics and other physical training.

Owner Jason Derby said he and his wife, Mary Gardinier-Derby, joined friend Jennifer Lindsay to open the fitness center, 5613 Sixth Ave., on Oct. 1.

Derby works full time for a Milwaukee industrial waste firm while his wife and Lindsay, center co-directors, handle most of the classes and activities.

The group focuses on group training, step aerobics, cardio workouts and similar offerings but hopes to add exercise machines and other workout equipment. They have several instructors for classes, too.

The business has a Web site at www.jamwithmary.com. The phone number is 308-5338.

Derby said he’s participated in triathlons and his wife has taught aerobics classes around the city for about 20 years.

Lindsay had taught classes at various gyms for about 10 years and was not working during the summer when the fitness center idea began, he said.

Derby’s wife had been laid off from a Wadsworth, Ill., trucking firm in March, and she decided to provide informal workout gatherings Sunday mornings for people in their neighborhood.

Participation grew to 15-20, and someone urged them to open an athletic center.

“It started out as a fun way to pass the time in summer because of unemployment and led to a start-up business,” he said. “If those 15 to 20 people hadn’t pushed us into this direction, we wouldn’t have done it.”