Most people who are trying to get in shape complain that it just takes too much time. But if you have eight minutes, you have all the time you need to work out with a ROM machine.

The "range of motion" cross-training apparatus, which resembles a combination stair climber and rowing machine, offers the benefits of weight training, cardio and stretching in a shortened workout period. It was invented by Honolulu artist John Pitre and earned Popular Science magazine’s "The Best of What’s New" award in recreation in 1991.

To give it a tryout, I went to RomGym Honolulu on Ward Avenue. I spent the first four minutes of the eight-minute workout performing a continuous back-and-forward rowing motion from a seated position. I felt an upper-body burn in my arms, abs, shoulders and chest.

The second half of the routine — a lower-body workout — involved standing on pedals at the rear of the machine and pumping my legs up and down. It’s not as easy as it looks.

After the eight minutes are up, most folks head to a separate vibration machine for an additional 10 minutes. The platform you stand on vibrates, causing a rocking motion that triggers muscle contractions. Pushups, squats and lunges are a few of the exercises that can be done on the machine for added effect.

The vibration apparatus "uses muscles that you wouldn’t normally use," said personal trainer Trista Barker, who helps clients properly use the ROM machines to get the best results. "The muscles are contracted 45 times per second compared with contracting one time when you do a situp or squat. Standing on the machine also improves circulation."

Other benefits of the ROM system in addition to shorter workout periods are little or no impact on joints and that users don’t need to change machines during the session.

Typically, it takes about three months to see big results, Barker said.

RomGym owner Bob Kawa­mura said the workout is suitable for young and old, and everyone in between. (The youngest gym member is 12, the oldest is 77.)

Diana Jeon, a new media art instructor at Kapiolani Community College, said she went from a size 16 jeans to a size 6 in eight weeks while using the ROM apparatus.

"The first session kicked my butt. I could still feel it a couple days later. After the first week, my thighs were rock hard," she said.

Before starting her routine of two eight-minute sets a day at the RomGym, Jeon said she was working out with weights a couple times a week. Although she tries to control her food intake, she doesn’t follow a strict diet.

The short workout periods are a big part of Jeon’s success at the gym.

"I can talk myself into going for eight or 16 minutes," she said.