Save Your Knees and Land
on Your Toes
Anterior cruciate ligament injuries are a common and
debilitating problem, especially for female athletes.
A new study from UC Davis shows that changes in training
can reduce shear forces on knee joints and could help
cut the risk of developing ACL tears. The research
was published online Aug. 3 in the Journal of Biomechanics.
"We focused on an easy intervention, and we were
amazed that we could reduce shear load in 100 percent
of the volunteers," said David Hawkins, professor
of neurobiology, physiology and behavior at UC Davis.
Hawkins conducted the study at the UC Davis Human
Performance Laboratory with graduate student Casey
The anterior cruciate ligament lies in the middle
of the knee and provides stability to the joint.
Most ACL injuries do not involve a collision between
players or a noticeably bad landing, said Sandy
Simpson, UC Davis women's basketball coach.
"It almost always happens coming down from
a rebound, catching a pass or on a jump-stop lay-up,"
Simpson said. "It doesn't have to be a big
Hawkins and Myers worked with 14 female basketball
players from UC Davis and local high schools. They
fitted them with instruments and used digital cameras
to measure their movements and muscle activity,
and calculated the forces acting on their knee joints
as they practiced a jump-stop movement, similar
to a basketball drill.
First, they recorded the athletes making their
normal movement. Then they instructed them in a
modified technique: Jumping higher to land more
steeply; landing on their toes; and bending their
knees more deeply before taking off again.
After learning the new technique, all 14 volunteers
were able to reduce the force passed up to the knee
joint through the leg bone (the tibial shear force)
by an average of 56 percent. At the same time, the
athletes in the study actually jumped an inch higher
than before, without losing speed.
Hawkins recommends warm-ups that exercise the knee
and focusing on landing on the toes and balls of
the feet. The study does not definitively prove
that these techniques will reduce ACL injuries,
Hawkins said: that would require a full clinical
trial and follow-up. But the anecdotal evidence
suggests that high tibial shear forces are associated
with blown knees.
Hawkins and Myers shared their findings with Simpson
and other UC Davis women's basketball and soccer
coaches, as well as with local youth soccer coaches.
Simpson said that the team had tried implementing
some changes during last year's preseason, but had
found it difficult to continue the focus once the
full regular season began. In live play, athletes
quickly slip back to learned habits and "muscle
memory" takes over, he noted. More intensive
off-court training and practice would be needed
to change those habits, he said.
"We will be talking about this again this
season," Simpson said. Implementing the techniques
in youth leagues, while children are still learning
how to move, might have the most impact, he said.