muscle strength more slowly than men
may affect how women are treated for bone fractures
muscles may require longer, more intensive rehabilitation
after bed rest and cast immobilization, as reported today by the
Institute for Neuromusculoskeletal Research at the Ohio University
College of Osteopathic Medicine (OU-COM).
Brian C. Clark, Ph.D., assistant professor of neuro-muscular
biology, the discrepancy may relate to how sex-specific hormones
regulate the growth of muscle mass. The study is the first to report
sex differences in muscle strength restoration following
immobilization of a limb.
may have important implications for how women are
treated for fractures, including more and/or different
rehabilitation methods,” Clark said.
on the study with Ohio University researchers Richard L. Hoffman and
David W. Russ, Ph.D., as well as Todd M. Manini, Ph.D.,
of the University of Florida. The team discussed their findings this
week at the Integrative Biology of Exercise meeting, hosted by the
American Physiology Society (APS) in Hilton Head, S.C. A report of
their preliminary data will appear in an upcoming issue of
Archives of Physical Medicine and Rehabilitation.
researchers set casts to the non-dominant wrists and hands of 10
healthy volunteers – five men and five women – for three weeks.
Wrist muscle strength was measured prior to placement of the casts,
weekly during immobilization and one week after cast removal.
Researchers also used electrical stimulation to induce muscle
contractions, which showed how well the participants’ nervous
systems were able to activate their wrist muscles.
that men and women lost muscle strength at similar rates during
immobilization. But within one week of cast removal, the men’s
strength returned almost to pre-cast levels, while the women’s
strength levels remained 30 percent lower than normal.
did reduce the ability of the nervous system to activate wrist
muscles, and the response was similar in men and women, suggesting
that the slower restoration of strength among women is more likely
due to different rates of muscular strength-building, as opposed to
differences in the nervous system.
According to a
2003 World Health Organization report, women are four times more
likely than men to experience forearm fractures requiring cast
immobilization, and almost 50 percent of women will experience a
bone fracture at some point in their life.
cautioned against over-interpretation of the study results because
of the relatively small sample size. “Our findings indicate that
more work needs to be done to confirm and understand the reasons for
these sex differences, the extent to which they occur, and the
underlying mechanism,” Clark said.
Clark and his
colleagues have begun the next phase of this research, which they
hope will provide more comprehensive answers.