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Ray Fagenbaum, MS
Warren G. Darling, PhD ABSTRACT It has been estimated that there
are 2200 ACL ruptures each year alone in female college athletes, who are
four times more likely to injure this ligament than their male
counterparts. The total cost
for these female athletes to undergo surgery and have rehabilitation is
$37 million per year. Current
research has focused on trying to find the reasons why females suffer
higher rates of injury, and if there is a method to prevent the high
incidence. Many articles have
focused on what has been defined as an altered landing strategy in
females. It has been reported
that women land with a more forceful quadriceps contraction than males,
which could overpower the hamstrings and tear the ACL.
However, another study by Rozzi et al found that the lateral
hamstring muscles in college level female athletes had greater peak EMG
amplitude after a jump. This
is the muscle one would expect to protect the ACL The knee flexion angle has also
been observed in athletes. It
is known that the hamstrings can serve to protect the ACL when landing
with a knee flexion angle of 30 degrees or more.
However, landing with less than 30 degrees, and in some instances
near extension, may place the hamstring at such a disadvantaged position
that it cannot protect anterior tibial translation. These authors wanted to test the
hypothesis that female athletes would exhibit lower hamstring muscle
activation during landing from a jump, and have less knee flexion than
men, especially under fatigued conditions. 6 male and 8 female varsity
basketball players with no history of knee problems participated in this
study. Each performed a jump
from both feet and landing on the dominant leg, approximately 25 cm away,
and also a jump down from 25.4cm and 50.8 cm platforms, again landing only
on the dominant leg. A Cybex
isokinetic machine was used to fatigue the athletes prior to jumping, and
EMG pads were placed on all major muscle groups while a surface goniometer
measured the knee flexion angle at the time of impact, as determined by a
switch platform. Results show that both men and
women had similar activation patterns during the different jumps.
The only difference, even with fatigue, was that women tended to
land with higher normalized quadriceps muscle EMG activity, and lower
normalized gastrocnemius activity. The
gastrocnemius, in both groups, showed strong activation just prior to
contact, and the quadriceps were usually activated prior to foot contact,
but reached their peak after contact.
Hamstring activation had high variability between jumps for the
same person. In other words,
one jump the person would show activation prior to landing, and the next
jump would not show activation until after they had landed. One surprising find was that women
tended to land with higher knee flexion angles than men, which was the
opposite of what was hypothesized. A
greater knee flexion angle would actually serve to protect the ACL.
Also, the women tended to move more rapidly into flexion, which
would be of benefit as long as the hamstrings are contracting to protect
the ACL. The authors suggest that factors
other than knee muscle activity and knee angle just be major contributors
to the high rates of ACL injury in female athletes. COMMENTS The authors acknowledge that the
small sample size, the fact that the jumps and lands were in a controlled
environment, and that 3 of the females were not able to reach adequate
fatigue on the Cybex are all limiting factors.
Also, because all came from the same team at the same school, there
may have been a training tactic that biased the results. The authors did not say if they trained using a program
similar to that of the Cincinnati College of Sports Medicine. The study does pose interesting
questions, especially “why do female athletes have a higher rate of
injury?” Other factors,
such as high Q-angle, menses, and weakness have all been proposed. The landing strategy theory makes the most sense, especially
since programs have been developed to train this landing pattern, and have
shown significant reductions in injury.
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