Young women who use oral contraceptives (OC) may not get
as much out of their weight-lifting routine as women who are
not on the pill, according to a study released today, which
suggests that OC use impairs muscle gains from resistance
exercise training in women.
"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 stated.
"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
In the study, 73 generally healthy women between 18 and 31
years old participated in whole-body resistance exercises
three times per week for 10 weeks. Thirty-four of the women
used oral contraceptives and 39 did not. The women were encouraged
to eat enough protein to promote muscle growth.
According to the researchers, there were marked differences
in lean muscle mass gains between the two groups. Lean muscle
increased by just 2.1 percent in OC users compared with 3.5
percent in non-OC users.
Lee and colleagues presented their findings Friday at the
American Physiological Society meeting, part of the Experimental
Biology 2009 scientific conference underway in New Orleans.
In a prepared statement from the meeting, the researchers
acknowledge being "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
Other muscle responses, such as strength gains and arm/leg
circumferences, were similar between the OC and non-OC users.
Tests on the women also showed that blood levels of three
muscle-building hormones were significantly lower and one
muscle-breaking hormone was significantly higher in OC users
than non-OC users, Lee said. These findings "could help
explain" why OC users showed diminished muscle gains
from resistance exercise training.
Summing up, Lee said: "Numerous health and performance
benefits including improved exercise/athletic performance,
body composition, esthetic beauty, and self-image can be attained
from the increased muscle mass and strength associated with
resistance exercise training. OC users may not be able to
fully enjoy those benefits while experiencing impaired exercise
performance and difficulties achieving athletic goals due
to diminished muscle responses they get from resistance exercise