Women who exercise on a regular basis and take oral contraceptives (OC), have less muscle increases than those who do not take birth control pills, according to researchers from Texas A&M University in College Station.
The study, carried out by Chang Woock Lee, a doctoral candidate in the department of health and kinesiology at Texas A&M University, College Station, and his colleagues, also found that the use of oral contraceptives was linked to lower hormone levels in women.
The investigators based their findings on the analysis of 73 healthy women with the ages between 18 and 31 years. All of them were asked to include enough protein in their diet in order to help them develop their muscles. Out of 73 women, 34 were using birth control pills, whereas the remaining 39 did not take any contraceptives. Both groups took part in a 10-week of whole-body resistance exercise training, consisting of 13 exercises performed three times a week. At each session, participants needed to complete three sets of six to ten repetitions of each exercise at 75 per cent of maximum strength.
According to the scientists, there were noticeable differences in lean muscle mass gains between the two groups. Lean muscle increased by just 2.1 per cent in women who were using oral contraceptives, compared to 3.5 per cent in non-OC users. In a prepared statement from the meeting of the American Physiological Society, the researchers reported how surprised they were to find such significant differences in muscle gains between the women in two groups, with the non-users of OC gaining more than 60 per cent greater muscle mass compared to those who used oral contraceptives.
Tests on the women also revealed that blood levels of the three key muscle building hormones - anabolic hormones - were significantly lower and one muscle-breaking hormone - cortisol - was significantly higher among the women taking birth control pills, compared to the other women, Lee said. These findings could provide an explanation why OC users showed diminished muscle gains from resistance exercise training. The scientists pointed out that the difference was only found in lean muscle mass gain, while strength gains and arm/leg circumferences changes were almost the same among the groups.
Summing up, Chang Woock Lee said that there are numerous health and performance benefits, such as body composition, esthetic beauty, and self-image that can be obtained from the increased muscle mass and strength that are a result of resistance exercise training. In his opinion, users of oral contraceptives, may not be able to enjoy to a full extent all those benefits "while experiencing impaired exercise performance and difficulties achieving athletic goals due to diminished muscle responses they get from resistance exercise training." The experts also said that the results are particularly important because many high-performance athletes take birth control pills to control their menstrual cycles.
However, at this point, Lee and his team do not find any reason for women to stop using birth control pills. They say that in spite of the fact that the study has found some negative effects of oral contraceptive use on muscle gain in the context of resistance exercise training, the future investigation on this matter is needed in order to explain with certainty the reasons behind the results. "It is premature to say anything conclusively at this point," affirmed Lee.
The findings of the study were presented this week at the 122nd annual meeting of the American Physiological Society, which is also participating in the scientific conference Experimental Biology 2009 being held in New Orleans.
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