The study involving 73 women aqged 18-31 set participants in a whole-body resistance exercise program for ten weeks. 34 took oral contraceptives and 39 did not. Their diets were monitored for protein intake that would support muscle growth.
There were significant differences in lean muscle mass gains between the two groups.
According to the researchers, "We were surprised at the magnitude of differences in muscle gains between the two groups, with the non-OC women gaining more than 60% greater muscle mass than their OC counterpart." They added that even though the study has observed negative effects of oral contraceptive use on muscle gain in the context of resistance exercise training, "future studies are needed to help explain the reasons behind the results."
Source: American Physiological Society (APS)