Numerous studies have shown that female athletes are
more likely to get knee injuries, especially
anterior cruciate ligament (ACL) tears and chronic
pain, than their male counterparts. While previous
research has focused on biomechanical differences as
the main source of these problems, a 2012 study (Link...)
suggests another distinction that could play a role:
changes across the menstrual cycle in nerves that
control muscle activity..
In studies on rats, scientists at Johns Hopkins have
found new evidence that the predominance of the
hormone testosterone in males may explain why women
are up to 10 times more likely than men to suffer a
specific type of serious knee injury common among
athletes.
Specifically, they found that normal male rats with
natural supplies of testosterone had stronger
anterior cruciate ligaments, or ACLs, than those
that had been castrated and no longer produced the
hormone. Their findings are described online in the
journal The Knee.
"The primary implication of the study is that
testosterone may contribute to the ACL's ability to
withstand tensile loads and may be one of multiple
factors responsible for the disparate ACL injury
rate between men and women," says William Romani, a
physical therapist and sports medicine researcher
who was a visiting faculty member in the Johns
Hopkins University's Department of Biomedical
Engineering from 2009 to 2015.
Senior study author Jennifer Elisseeff, a biomedical
engineer at Johns Hopkins University, says the new
finding could eventually lead to techniques that use
circulating sex hormone levels to identify athletes
at higher risk for ACL injury who may benefit from
training strategies to strengthen the ligament.
More than 200,000 people in the U.S. get ACL
injuries, ranging from partial to full tears, most
often while playing sports. Previous studies have
found that girls and women are anywhere from two to
10 times more likely to tear an ACL than men doing
similar activities. Explanations for the sex
differences include differences in anatomy,
strength, reflex times, and hormones.
Romani, who now works with the AARP Foundation's
Experience Corps, conducted previous research on
rats showing that estrogen—a predominantly female
hormone—reduces ACL strength, but he also found that
knee ligaments in both sexes contain receptors for
testosterone.
"Our thought was that while estrogen may make the
female ACL weaker and more prone to injury, the male
hormone testosterone may act to strengthen the ACL
and protect it from injury," Romani says.
In the new research, Romani and Elisseeff removed
the ACL—still connected to the tibia and femur—from
16 healthy, 12-week-old male rats. Eight of the rats
were normal, with testosterone levels averaging 3.54
nanograms per milliliter, and eight had been
castrated, giving them nearly undetectable levels of
the hormone, at 0.14 nanograms per milliliter. The
researchers measured the cross-sectional area of
each ACL and then connected the bones—with the ACL
stretched between them—to a machine that could pull
the bones apart, tugging on the ACL. Then, they
tested the strength of the ligaments by measuring
how much force it took to tear each ACL.
The researchers found that it took more force—34.5
newtons, compared to 29.2 newtons—to tear the ACLs
from rats with normal levels of testosterone,
indicating that the ligaments were stronger. Since
researchers have generally accepted that a stronger
ACL is less prone to injury, the results support a
link between testosterone and ACL injuries.
More work is needed to explain exactly which
pathways and molecules testosterone and estrogen act
through to influence ligament strength, and whether
the hormones have the same impact on other ligaments
in the body.
See also
Nerve and Muscle Activity Vary Across Menstrual
Cycle (22/10/2012)
Link...
For more information
Johns Hopkins University
Link...
MDN |