WASHINGTON (AP) _ In addition to the steps you learn, aerobic dancing can include a step to walk on. Step training promises a high-intensity workout and a low risk of injury by having participants simply move onto and off of a low bench.

Sound easy? Well, consider how much you weigh. And consider that you lift your body each time you step up, said Connie Williams, owner of BenchAerobix Inc., Atlanta.

''You're using very large muscle groups and pumping more blood through the heart,'' Williams said. ''Heart rate does definitely rise very quickly.''

She and a fellow Atlanta fitness instructor, Gin Miller, developed the concept about three years ago. It's like climbing stairs, but with only one stair - a wooden or plastic platform 4 to 12 inches high.

Step training is simple up-and-down movements that are hard to cheat on, making it easier to keep working out at your target level, Williams said. And men who don't like the complexities of standard dance-style aerobics are comfortable with simply moving on and off the bench, she said.

Step training by well-conditioned athletes at an aerobic cadence of 120 beats per minute can use more energy than running at 7 miles an hour on a treadmill, said researchers Peter and Lorna Francis of San Diego State University in California.

The husband and wife team are consultants for Reebok International. The footwear company based in Stoughton, Mass., began marketing its Step Reebok program with Miller after the Williams-Miller partnership dissolved.

The Francises also compared the impact on the legs from running, walking and step training by having the athletes perform the activities on special plates that measured the force they exerted.

Step aerobics is gentler on the legs than running, and similar to walking, they said.

The impact of running peaked at three times body weight, while step training peaked at 1.75 and walking at 1.25 times body weight, the study said.

Also, it said, the impact of running was sharper - much of it occurring so fast that reflexes were not able to adjust muscles to cushion the shock, the study said. Walking and step aerobics showed similar patterns - both allowing enough time for reflexes to kick in, the report said.

A step trainer almost always has one foot either on the ground or the bench, absorbing part of the stress, Peter Francis said. A runner, on the other hand, strikes the ground hard and with only one foot.

The Francises' study involved only 10 people ages 19 to 35 - and its findings, strictly speaking, can only be applied to healthy young athletes, Francis said.

There have been no scientific studies on injuries, but a lot of people are taking part in step training and relatively few injuries have been reported, which argues for the safety of the activity, he said.

Men and women seem to have different injury patterns, Williams said.

Because women have wider hips and closer-together knees, stepping to and from the bench sideways tended to give some of them knee injuries, she said. Changing the angle seemed to solve the problem, she said.

Injuries tended to affect the lower back in men, who had more weight in their upper body, because they slumped forward as they stepped up, Williams said. Keeping the chest up and shoulders back helps to prevent that, she said.

In addition, participants must keep their areas clear of other objects such as purses and towels, and must watch their feet as they mount the bench, to prevent tripping, she said.

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