(Ivanhoe Newswire) -- Oral contraceptives appear to impair muscle gains in young women and are associated with lower hormone levels, according to a new study.

Researchers set out to examine the effect of oral contraceptives (OC) on healthy women between the ages of 18 and 31. The women participated in a 10-week whole-body resistance exercise-training program. Their results were compared to women enrolled in the same program but who were not taking birth control pills.

All of the women were encouraged to consume high levels of protein each day to make sure they consumed enough calories and protein to promote muscle growth. They exercised three times a week for 10 weeks under the supervision of exercise physiologists.

Blood samples were drawn before and after the training and assessed to measure anabolic (muscle building) and catabolic (muscle breaking) hormone levels in the blood.

The researchers found there were significant differences in lean mass gain between the two groups of women, although other muscle responses, such as strength gains and arm/leg circumferences, were similar. Resting/fasting blood concentrations of the anabolic hormones were significantly lower in the women taking OC compared to those not taking the daily pills.

"We were surprised at the magnitude of differences in muscle gains between the two groups, with the non-OC women gaining more than 60 percent greater muscle mass than their OC counterpart," the researchers were quoted as saying.

SOURCE: Study presented at the 122nd Annual Meeting of the American Physiological Society, April 18-22, 2009 in New Orleans