ACL Injuries in Young Female Athletes

Brian Grasso is the CEO of the International Youth Conditioning Association and is considered one of the premier authorities on youth athletic development in the world. Access Brian's free database of articles and exercises at www.DevelopingAthletics.com

There has been an epidemic of sorts in the past few years regarding ACL injuries and young female athletes.  In fact, 50,000 ACL surgeries were performed in the United States in 1982, with the majority of ACL injuries being the non-contact variety – essentially, no direct contact led to the injury itself.  That statistic goes right to the heart of my concerns with young athletes.  If the majority of ACL injuries are non-contact based, then either biological or mechanical issues are to blame.  That is, either the injuries are due to unfortunate, yet genetic structural dysfunctions or the result of improper loading and mechanical faults – which is a matter of poor coaching.

Here is the fact – women have higher incidences of non-contact ACL injuries within the context of sporting events than do men.  In fact, according to a 2000 study on this topic ‘recent reports from the National Collegiate Athletic Association institute that female collegiate soccer and basketball players were three to four times more likely to have non-contact injuries than their male counterparts.’  There simply has to be an answer accounting for why this is.

In separate studies, several factual elements of ACL injuries were shown:

1. Non-contact ACL injuries often occur with the knee at modest flexion along with a valgus motion.

2. Quadriceps contraction applies an anterior shear force on the tibia.

3. The above mentioned quadriceps contraction can cause an ACL injury if the knee flexion angle is less than 30 degrees and the hamstring musculature does not supply necessary posterior shear force (when functioning well, the hamstrings provide a counter force which pulls the tibia back from any translation forward). 

Given these points and knowing that female athletes are more prone to non-contact ACL injuries, several assumptions can be made –

1. Young female athletes likely do not show as great a degree of knee flexion and yet more valgus motion than do young male athletes during athletic events and/or training.

2. Young female athletes likely have stronger anterior thigh dominance than posterior (i.e. more quadriceps involvement than hamstring involvement) during athletic events or training.  This factor, of course, has influence over the anterior versus posterior shearing forces. 

If these assumptions are true, and in fact basic biological factors (such as Q-angle) are not entirely to blame for this ACL epidemic, then does poor coaching play a role, at least to some degree, in the female ACL injury syndrome?  For instance, referring to point #1, non-contact ACL injuries occur when the knee experiences too modest a degree of flexion and too much valgus during activities such as running, jumping and cutting – are those not mechanical issues that a qualified coach should notice and correct?

Here is what one study found when attempting to decipher these concerns (the findings were based on a observations of running, side-cutting and cross-cutting) –

1. Knee flexion angle for female athletes was lower than that for male athletes.

2. Female athletes’ knees were steadily in a valgus direction (in fact, 11 degrees more valgus than male subjects).  This is a definitive problem.  According to one study, the load on the ACL due to even a 5 degree motion towards valgus can increase to as much as 6 times of that when the knee is lined up properly in the frontal plane. 

3. Especially during running and side cutting, female athletes experienced more dominance of the quadriceps than did male athletes.

4. Especially during running and side cutting, female athletes experienced less dominance of the hamstrings than did male athletes.

The combination of points #3 & 4 indicate a strong concern.  While the increased quadriceps activation does not necessarily infer an anterior shear, the combination of an increased quadriceps force coupled with decreased hamstring activation will most certainly increase the likelihood of anterior shearing on the tibia through the patella tendon. 

The point is that female athletes tend to incur knee motions during activity that are typical for experiencing non-contact ACL injuries. 

Here is where the debate and argument gets heated for me.  I have been an outspoken critic for years on the ‘quick fix’, ‘short term’ training approach that many trainers and facilities implement with younger athletes.  When you are young and athletic, getting is shape for the upcoming season, improving your vertical jump in 6-weeks, adding 25 pounds to your bench and being able to run at 20 MPH on those high speed treadmills should be distant concerns in contrast to developing fundamental, multi-joint and systemic strength, learning movement economy (or the most efficient means of running, changing direction etc) and perfecting safe and biomechanically sound movement patterns.  A study on the ‘jumping & landing techniques in elite women’s volleyball’ concluded brilliantly that ‘concerning technique, athletes who regularly perform landings and are exposed to the concurrent large impact forces should concentrate on performing landings using a toe-heel contact pattern with greater knee flexion.’    

What a novel concept!  Actually TEACH young athletes the technique of how to run, jump, land and move BEFORE you program endless numbers of drills and exercises. 

Therein lies the crux of my concern – far too many trainers and facilities make the erroneous error of trying to maximize the ability of a young athlete as it relates to performance markers (such as vertical jump) rather than advocating for a developmental approach to improvement that is founded on fundamentals and basics.  In doing so, these trainers are dampening the potential success a young athlete may achieve down the road, and compounding the problem of injury potential rather than easing it.

Here is an example of how you would teach a squat, for example, to a young female athlete –

Four Step Process –

1. Foot Position – I typically start with feet shoulder width apart and toes pointing straight ahead.  Once the athlete is comfortable with the exercise, we can explore other comfortable positions.

2. Lift In-Step – I don’t want this to sound as though I have young athletes ‘remove’ their in-steps completely off the ground, but we instill the notion that they need to be performing the squat exercise by ‘pushing’ through the outside portion of their heels.  This accomplishes a couple of things: a) the issue of knee valgus is removed b) hip, knee and ankle alignment is guaranteed.

3. Set Eyes & Head – When the eyes are down, the head and upper torso will follow.  This causes a forward motion during the eccentric phase and causes both an anterior force through the knee as well as misalignment of the cervical, thoracic and lumber spine.

4. Push Hips Back – first time squatters and young athletes who were poorly guided will often automatically descend into the squat with an anterior motion (i.e. weight on the toes).  By actively pushing the hips back, we are promoting more hip extension during the concentric phase of the squat and therefore higher activation of the hamstrings and glutes with proportionately less quadriceps involvement, consequently reducing anterior shearing forces at the knee joint.

Some, and in many cases all, of the steps in the preceding sequence can be used to teach several lower body exercises including single leg squats, step-ups, lunges and side steps. 

One of the most important factors to understand is that squatting, long considered by many to be an ‘unsafe’ exercise, is actually a critically important progressive action that aids in teaching the fundamental movement patterns associated with preventing ACL injuries. 

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