A new study out today suggests that (in young women at least) the birth control pill may impair muscle gain.

The study followed 74 women between 18 and 31 years old. Of that sample test group 34 used oral contraceptives (OC) and 39 did not.

According to the researchers there were significant differences in gains from resistance exercise training for the two groups of women.

According to Reuters.com:

"Lean muscle increased by just 2.1 percent in OC users compared with 3.5 percent in non-OC users.

"The factors that explain the differences in the magnitude of the responses to resistance exercise training between individuals are largely unknown," Chang-Woock Lee, from Texas A&M University in College Station, told Reuters Health.

"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," the researcher added."

In others, the women using the pill had a much harder time building muscles mass which is a critical component to not only strength training, but also speed in endurance sports such as running, biking, swimming. and triathlon.