Women on the pill are more likely to incur an injury than women who are not taking ethinyl estradiol to prevent pregnancy. Sports scientists at the University of Copenhagen discovered that synthetic estradiol prevents the muscle attachments from being strengthened by training.
When men train by running, their tendons get thicker. If young women do the same, their tendons do not grow. Female athletes are also more likely to develop tendon injuries than male athletes. In animal tests the female sex hormone estradiol reduced the growth of tendon tissue. As synthetic estradiol is an ingredient in contraceptive pills, it's valid to pose the question whether 'the pill' increases the chance of injury.
This is the question the researchers set out to answer by doing a trial using two dozen women with an average age of 25. The women did 4-5 hours of physical exercise a week. Half of them had been using contraceptive pills for 7 years, including Cilest [35 microgram ethinyl estradiol and 0.25 mg norgestimate] or Lindynette [30 microgram ethinyl estradiol and 0.0075 mg gestoden]. [HE-OC] The other half had never taken contraceptive pills. [LE-NOC]The women had to exercise their legs in the lab by doing a kind of leg extension and making a kicking movement.
A day later the researchers took samples of tissue from the muscle attachments that the women had exercised. The researchers measured the concentration of the PINP molecule in the tissue sample. The higher the concentration, the more new tissue you manufacture. Taking the pill prevented this from happening.
IGF-1 stimulates growth of muscle attachments. When the researchers measured the concentration of IGF-1 in the blood, they saw that it had decreased. The researchers observed the same – but even more extreme – in the women's muscle attachments.
The reduced concentration of IGF-1 in the pill using women may be the result of an increased production of the binding protein IGFBP-1, the Danes discovered. IGFBP-1 neutralises IGF-1. IGFBP-3, another binding protein, doesn't do this and protects IGF-1 from being broken down. IGFBP-3 enhances the working of IGF-1. Taking the pill increases the concentration of IGFBP-3, but by less than the amount by which it increases the concentration of IGFBP-1.
So you could say that contraceptive pills probably increase the chance of women developing injuries. The researchers are not prepared to stick their neck out at this stage. More research is needed first, they say.
Source:J Physiol. 2008 Jun 15; 586(Pt 12): 3005-16.