ATLANTA (AP) – Women are pumping more iron, with nearly one in every five doing twice-a-week workouts, a new federal study shows.

The desire for a more attractive body, along with worries about bone loss, probably contribute to the trend, experts said.

The U.S. Centers for Disease Control and Prevention did the research, which is called the first to look at the national prevalence of weightlifting and other forms of strength-training. It is being published this week in the CDC’s Morbidity and Mortality Weekly Report.

The study found an overall increase in weightlifting and other forms of strength-training. In 2004, about 20 percent of U.S. adults were doing strength-training at least twice a week, up slightly from the late 1990s, when about 18 percent of adults were.

Women improved the most: About 17.5 percent did twice-a-week workouts in 2004, up from about 14.5 percent in 1998. Men, in contrast, held steady at around 21.5 percent.

Body-celebrating women’s magazines like Oxygen and Shape are part of a cultural shift that has led more women to embrace weightlifting, some fitness experts said.

“Women see this as an ideal they’d like to achieve, and it makes weight-training more approachable to women,” said Teresa Moore, an associate professor of exercise science at the University of South Carolina.

Long-term concerns about bone loss, and a recognition that strength-training can help, may also be factors.

“Women are starting to become more interested in strength-training because of the increased prevalence of osteoporosis,” said Judy Kruger, a CDC epidemiologist who was the study’s lead author.

The study’s data come from an annual national survey that involves face-to-face interviews with tens of thousands of U.S. adults. Starting in the year 1998, this question was added; “How often do you do physical activities designed to strengthen your muscles, such as lifting weights or doing calisthenics?”

Researchers saw increases in strength-training from 1998 until around 2002, when the trend line went flat.

“I can’t speak to why it leveled off,” said Kruger, who works in the CDC’s Division of Nutrition and Physical Activity.

Older adults do less strength-training than younger people, but there was a marked increase in the percentage of people 65 and older who did two or more workouts each week. For older men, the statistic rose to 14 percent in 2004, up from 11 percent in 1998. For older women, it rose to almost 11 percent of women in 2004, up from about 7 percent in 1998.

The U.S. government has set a public health goal that, by 2010, at least 30 percent of American adults should be doing strength-training at least twice a week.

The new report indicates that goal may be difficult to attain.

“A lot of people are still electing to stay home and play computer games and video games rather than get out and exercise,” said Moore, who has been powerlifting and bodybuilding since 1982.