Women who do resistance exercises and take oral contraceptives appear to gain less lean muscle than women who do the same but do not take oral contraceptives, say researchers from Texas A&M University in College Station.

Chang-Woock Lee, one of the researchers, said in an interview with Reuters that the factors that explain the differences in the magnitude of the responses to resistance exercise training between people are generally unknown. “The present study is meaningful in that we have identified a potential new factor that may be independently associated with the characteristics and variability of muscle responses to a controlled resistance exercise training program,” he added.

The study involved 73 women aged 18 to 31 – they were all healthy. They all took part in a whole-body resistance exercise program that lasted ten weeks and involved three sessions per week. 34 of them took oral contraceptives while the rest (39) did not. They were asked to make sure they consumed the right amount of protein to encourage muscle growth.

The scientists found significant differences between the two groups with regard to lean muscle mass growth. Lean muscle mass grew by 3.5% among the women who did not take oral contraceptives, compared to 2.1% among the women who did.

The researchers said they were surprised at how significant the differences were – averaging about 60%. Their findings were presented at the American Physiological Society Meeting, New Orleans.

The scientists stressed that the difference was only found in lean muscle mass gain, while strength gains and arm/leg circumferences changes were fairly similar among the groups.

The women who took oral contraceptives also had lower levels of three anabolic hormones in their blood, compared to the other women. Blood levels of cortisol were significantly higher among the women taking oral contraceptives, the researchers added. Anabolic hormones are muscle building hormones, while cortisol has the opposite effect on muscles.

Three takers of oral contraceptives had lower levels of DHEA hormone at the end of the training period, compared to their levels at the beginning. Among all the women who did not take oral contraceptives, DHEA levels did not change.

It is possible that the varying levels of muscle-building and muscle-breaking hormones factored highly in the different lean muscle gain results, the scientists say.

Although the study observed negative effects of oral contraceptive use on muscle gain in the context of resistance exercise training, the researchers said “future studies are needed to help explain the reasons behind the results”.

Source – American Physiological Society

Written by – Christian Nordqvist