Researchers from the Department of Health and Kinesiology at Texas A&M University in College Station, as well as the Human Energy Research Laboratory at the University of Pittsburgh, have found that OCs actually limit muscle gain from strength training in women under 35. The research involved 73 relatively healthy women aged 18 to 31. Of these, 34 used OCs and 39 did not. Both groups participated in a whole-body resistance exercise program consisting of 13 exercises performed three times per week for 10 weeks. At each session, they completed three sets of six to 10 repetitions of each exercise at 75 percent of maximum strength. The women were encouraged to eat enough protein to promote muscle growth.

Tests on the women showed that OC users had significantly lower levels of three muscle-building hormones—DHEA, DHEAS, and IGF-1—and elevated levels of one muscle-breaking hormone—cortisol. Lee said these findings “could help explain” why OC users showed diminished muscle gains from resistance exercise training, but that “vigorous future studies with more stringent control and clever design will be definitely needed to confirm the results and/or elucidate the underlying mechanism conclusively.”

The study findings were presented at the 122nd annual meeting of the American Physiological Society, which is also participating in the scientific conference “Experimental Biology 2009” being held in New Orleans.