The authors of the new research studied two groups of 18- to 31-year-old women: 34 who were on the pill and 39 not on the pill. All were active and healthy and took part in a 10-week resistance-exercising training program (three times a week) as well as analysis of their body composition both before and after the program.
Women not taking oral contraceptives gained more than 60 percent more muscle mass than those on the pill.
There were other changes noted in participants on the pill, including reduced concentrations of the hormone DHEA, which Lee explained, is an anabolic hormone and therefore builds muscle.
But some of these changes would be expected in women taking contraceptives, Weiss-Kelly said.
The U.S. National Women's Health Resource Center has more on birth-control pills.
SOURCES: Chang Woock Lee, doctoral student, Department of Health and Kinesiology, Texas A&M University, College Station; Jennifer Wu, M.D., obstetrician/gynecologist, Lenox Hill Hospital, New York City; Amanda Weiss-Kelly, M.D., director, pediatric sports medicine, Rainbow Babies and Children's Hospital, University Hospitals Case Medical Center, Cincinnati; April 17, 2009, presentation, annual meeting of the American Physiological Society, New Orleans
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