NEW YORK (Reuters Health) - Postmenopausal women at risk of diabetes can safely do a form of resistance training that allows the muscles to produce very high forces with relatively little effort, researchers have found.

Concerns have been raised that such workouts, known as "eccentric resistance exercise," might be harmful to people who are having difficulty processing glucose (sugar) -- an early warning sign of diabetes.

That's because a single bout of eccentric training has been shown to impair the body's ability to respond to insulin. However, these single bouts likely worsened "insulin sensitivity" because they damaged muscle, Dr. Robin L. Marcus of the University of Utah in Salt Lake City told Reuters Health.

To avoid muscle damage, in the current study, the researchers had 10 women complete a 12-week program of knee extension exercise in which force was increased gradually.

After the program, the women had stronger quadriceps, more lean tissue mass in their legs, and could walk further in six minutes, while their insulin sensitivity was not impaired. No changes were seen in a control group of six women who didn't exercise.

Basically, eccentric exercise involves putting tension on a muscle as it opposes a stronger force, which causes the muscle to lengthen as it contracts. "Muscles can generate more force eccentrically than they can in any other way (and) people tend to like it because they don't feel like they're working that hard," Marcus said.

In the current study, women used a machine called an eccentric ergometer, but the researchers are now conducting studies of eccentric exercise using exercises that don't require special machinery. One example: lifting a weight with both legs, and then lowering it with just one leg, or standing up from a chair, lifting one leg, and then sitting down supported by just one leg.

"One of our goals is to...get people in retirement centers or community activity programs to do these higher force exercises in a safe manner, because we think they're beneficial," Marcus said.

SOURCE: Journal of Women's Health, February 2009.