For almost all of us, exercise was once synonymous with pure merriment. Time was, we made our way across the monkey bars and skipped rope without any thought of burning calories or building muscle — without knowing or caring what phrases such as “body mass index” or “blood cholesterol level” meant.

It wasn’t a workout; it was recess.

The founder of Gravity Defying Fitness, Lorelei Ashe MacDonald, aims to help grown-ups recapture their lost playfulness. She developed an exercise regimen that makes use of playground props (a jungle gym, a hopscotch course) as well as equipment that might seem more appropriate under a circus tent (a trapeze, a pair of suspended rings).

Ms. MacDonald, 42, recently retired as a trapeze artist after a decades-long career. She performed with the Bay Area troupes Circus Finelli and Velocity Circus, and went on to teach at the San Francisco Circus Center, home to a professional aerial program and a clown conservatory.

Last year, after moving back to her native New York City and earning a personal-training certification, Ms. MacDonald began teaching clients the fundamentals of aerial movement. “The pursuit of something more than just being able to lift a heavier weight is very satisfying,” she said. “Here, you learn how to lift yourself up, to hold yourself in the air, to move in a more dynamic and controlled way.”

To date, Gravity Defying Fitness has been available exclusively to private clients, who range in age from mid-20s to over 55. But this weekend, Ms. MacDonald will begin teaching a weekly 90-minute group class at Hype Gym in Murray Hill.

In preparation for the course, open to members and nonmembers, the gym is being outfitted with a trapeze and a floor-to-ceiling climbing rope. Based on the aerial conditioning courses Ms. MacDonald taught at the circus school, the Hype class will include cardiovascular intervals, core and leg exercises, and balance drills, all done with the goal of teaching students elementary trapeze moves.

As a former gymnast (and playground daredevil), I was eager to try Gravity Defying Fitness. Ms. MacDonald, who works with clients at a number of non-chain gyms throughout the city, agreed to teach me the basics at Hype.

My Saturday afternoon session began not on a trapeze, but on a treadmill. After a few minutes of fast-paced walking on an incline, I was instructed to turn to my right for 20 seconds of sideways skips, or shuffles. This drill was repeated twice on either side. Then it was time to stretch, and to practice holding a position called “little boat,” which, according to Ms. MacDonald, is the basis for all aerial movement: The back is pressed firmly against the mat, legs are straightened and lifted about 30 degrees, arms are extended forward, stomach is rounded and flexed, and head and neck are several inches off the ground.

After a few more mat-based abdominal and core exercises, Ms. MacDonald led me outside to a playground with a metal jungle gym. In elementary school, I remember gliding back and forth across the monkey bars. Now, just hanging from the bars for more than a few seconds was a challenge; moving between them was not an option.

Ms. MacDonald talked me through a series of hanging shoulder shrugs, leg lifts, and assisted pull-ups. In between exercises, Ms. MacDonald had me skipping on a hopscotch course for two minutes at a time. To mix things up, sometimes she’ll have her clients jumping rope or bouncing on a miniature trampoline during these cardiovascular intervals.

Back inside, I practiced holding myself up on a pair of suspended rings, trying all the while to keep my arms straight and the rings steady. Each attempt left me breathless.

The session ended with some mat-based stretches, during which I reflected on the jungle-gym portion of the workout. What as a child came so naturally to me was now not only a physical challenge but also a source of fear: I worried about losing my grip and falling to the ground, even though it was only a few feet below.

Ms. MacDonald told me not to be discouraged, explaining that after a two-decade recess hiatus, my monkey-bar skills simply needed to be relearned. As for the fear part, she told me: “If you face your fears here, it will make you bolder in the rest of your life.”

Hour-long private session, $115 and up; 90-minute group class, $50, beginning June 8 at Hype, 480 Second Ave. at 27th Street, 646-201-9387. Membership not required to participate, space is limited. For more information on Gravity Defying Fitness, visit gravitydefyingfitness.com.