Do Female Athletes get ACL injuries because of their ANATOMY?
By Emily R Pappas, M.S.
ACL tears are all too common of a trend in female athletes, especially the adolescent population. But are females more “susceptible” because of their anatomy?
Or is there much more to the story we need to consider….
This article helps explain the current science explaining the relationship between the “female” anatomy, knee valgus, training modalities, and ACL injuries.
Sure, ACL tears can happen to any athlete. There’s no denying that the more you play sports, the more frequently you’ll see it happen. But then why do you see female athletes getting ACL injuries so often?
The research is still fresh, but today we’re going to shed some light on why female athletes are really “at risk” and, more importantly, what she needs to do to reduce this risk.
First, let’s look at some of the information we do know.
Fact #1: Female athletes experience ACL tears at a higher rate compared to male athletes.
In fact, some studies have shown that females are at a 2-5x higher risk of experiencing ACL tears compared to their male counterparts. 
Fact #2: ACL Injuries Cost Athletes Big Money.
An estimated 38,000 ACL injuries occur in girls’ and women’s athletics in the US annually at an estimated cost of $17,000. At the national level, surgery and rehabilitation costs associated with female ACL injuries total approximately $646 million per year. 
Fact #3: 80% of ACL injuries are non-contact, “ typically [occurring] during deceleration, lateral pivoting, or landing tasks”. 
What does this mean?
This article aims to break down the theory that female ANATOMY is the reason behind WHY ACL injury rates are so high in female athletes vs. men.
And, because we’re here to help females win on the field, we’ll give you our take on the science that helps explain what female athletes need to be doing to stay in the game throughout their sports career.
Let’s dive in.
Are You REALLY That Different Than A Male Athlete?
As we have stated, female athletes experience ACL injuries more often than men.
You’d think the reason “why” would be pretty straight forward. Men and women have different bodies. Done. Right?
Not so fast.
High knee loading tasks in sports occur at similar levels in both genders...but the reason why females are at a greater risk of ACL injuries remains unclear.
Maybe you’ve heard about the “Q” angle.
It has been 'theorized' that females are at a higher risk of knee injuries because their "wider" hips create a larger Q angle. As the theory goes, this larger angle leads to "unfavorable" biomechanics such as ‘knee valgus’, in movements like jumping, landing and decelerating.
That’s one theory.
Another theory puts the blame on hormones. It bas been "theorized" that hormones lead to ligament laxity, predisposing females to a higher risk knee injuries.... In our previous article, we dove into the research surrounding female hormones and ACL tears.
Big Hint: It’s NOT the hormones.
But what does this mean? Are females innately at a higher risk for injury?
Since we’ve already talked about hormones, let’s dig deeper and really sort out the tangled relationship between knee valgus, the female anatomy, and ACL tears.
So first...what’s the big deal about this valgus?
WHAT’S THE BIG DEAL ABOUT VALGUS?
Valgus. What a terrible name. It just sounds BAD. But...maybe it isn’t as bad as you think.
Before we jump ahead, three questions you might be asking:
#1. What is a knee valgus?
#2. What does a knee valgus have to do with female anatomy?
#3. Is there anything you should do to stop knee valgus in the female athlete?
Great questions! Let’s take it step by step.
Valgus, by definition, refers to movement or displacement away from the midline.
When we talk about ACL injuries, the valgus that causes so much fear is dynamic valgus or the relative internal rotation of the lower extremity (such as your shin) against a relatively fixed foot & pelvis 
WHY does the valgus occur?
Valgus happens just like any movement. It’s a result of the load you put on your body, and how your body reacts to that load.
In movements like a jump landing or a quick stop, load is placed upon the athlete (her body weight x gravity x velocity) . As the force is applied on the body, the body will move in an attempt to absorb the load (through its tissues like muscles, tendons, ligaments, and bone).
In a “biomechanically efficient” landing pattern, there is greater stability at the joint due to co-contraction of the surrounding muscles. Basically this just breaks down to: more force absorbed by muscle, (which is equipped to handle it), and less force absorbed by tendons and ligaments (not as well equipped).
For the knee, good stability in landing, cutting, or deceleration results from a co-contraction of the hammies, quads, glutes, (and maybe some calves). In a perfect world, they all work together, perfectly balanced, in sync, every-time.
But human bodies? They aren’t ever perfect nor balanced. And neither are playing conditions! Even the best athletes do not move with the best technique and efficiency when they are fatigued.
When this co-contraction isn’t perfect, the joint may have more freedom of movement, resulting in decreased stability. This means less efficient movements….like valgus….can occur.
This is where it can be hard to separate the bad reputation of ‘valgus’ from its place in the real world.
Although valgus is not the most biomechanically efficient movement for absorbing load...it is a movement that is NOT inherently bad!!!
Athletes are meant to MOVE. In multiple directions and at multiple velocities.
The efficiency of these movements depends on many other factors. An athlete’s strength, neuromuscular coordination, body awareness, and years of motor skill development ALL play a role in how efficiently a body responds to force.
Rather than villainizing the movement, lets try to understand WHY the body exhibits these movement patterns in the first place.
Think of it this way:
When you are sitting at your desk, you try really hard to sit up with great posture. But an hour goes by and you realize you are hunched over your computer.
Is this position inherently “BAD”. Heck no! Could it be optimized? Depends on what you are trying to optimize
You see, it all depends on your goals. If you want to sit upright, you can improve core musculature & optimize your position at your desk.
If your goal is to get paper written ASAP before it’s due at midnight...it really doesn’t matter how you sit. Great posture or hunched over, your position isn’t going to help you get that paper out!
Ok, so how does this apply to you and valgus?
Let’s look at jumping.
If you’re landing from a jump, is valgus “bad”?
Well if we measure efficiency by the ability to reduce the amount of impact placed on your head, valgus is efficient!!
If we measure efficiency by the ability of the muscles to dissipate forces and reduce the amount of load imposed upon other tissues such as the ACL ligament, valgus...well...is not the best.
When it comes to things like landing from a jump or decelerating from a cut, any increased movement at the joint increases the chance of injury.
Why? Because of a larger freedom of movement. .
Think: More space between the bones = More strain on the connecting ligament.
Check out this diagram and you’ll see what we mean:
To sum it up- for an athlete athlete, valgus is just a movement. Yes it does increase stress on the ACL. But it’s nothing to villainize in and of itself.
The valgus is just an increase in the movement of the knee joint. Yes, it puts more stress on the ligaments connecting the bones of the joint...but it also is a position your body is capable of getting into.
Why that position is chosen by the body is more important than the valgus position itself
Now here’s the BIG question: Why do female athletes demonstrate valgus more frequently than male athletes?. Does this movement relate to their anatomy and play a role in the higher frequency of ACL injuries in female athletes?
ACL Myth #1: The Messy Theories Behind Q Angles, Valgus, & Females
Yes, the female athlete’s body is different that a male athlete.
Research has consistently reported larger knee valgus motions in women compared to men performing side-step cutting movements as well as in jump landing tasks 
Is anatomy the reason woman experiences more valgus than a man?
Could this higher rate of knee valgus occurrences in the female population be related to their Q angles?
What’s a Q Angle?
The Q Angle was first described in 1964 as the angle formed by the intersection of two lines that cross the patella: one going from the hip to the center of the patella, and the other from the shin to the center of the patella. Previously, the Q angle was widely used for evaluating patients with knee problems (especially patellofemoral pain syndrome).
Theoretically, it was believed that an excessive q-angle may favor excessive dynamic knee valgus. 
In fact, most clinicians believed us ladies experienced more ACL tears than male athletes because of this Q angle hypothesis.
But here is the thing: this was just a THEORY.
Remember that science is always changing. And research about the female athlete and the way her body responds to the demands of sports? We’ve only just begun to understand it.
Theories can be refuted over time- and this one is no different. While Q Angles are important, research shows  that not all females have a wider Q angle compared to males.
In fact, researchers have shown an average difference in Q angles between males and females as a meager 2 to 3 degree difference . Even more, men and women of equal height demonstrated similar Q angles! [1,4]
GUESS WHAT: even if females did have significantly larger Q angles, there isn’t much evidence that supports the relationship between Q-angle and knee valgus (medial orientation of the knee in the frontal plane) 
Interestingly enough, a study in 2005  demonstrated “individuals classified has having a larger q-angle (≥17◦) did not present a greater knee valgus angle, in comparison with those with smaller q-angles (≤8◦)
Here is the kicker, once they dug in, researchers actually found the opposite of what we once hypothesized. That is... greater q angles were associated with smaller dynamic valgus !
“Ok, so then what about notch width and ACL size?”
Let’s talk about the notch.
The ‘notch’ (or femoral intercondylar notch) is the area at the base of the thigh bone where the ACL inserts.
It’s been hypothesized that a smaller femoral intercondylar notch may imply a smaller ACL...or at least an increased impingement to the ACL...meaning the ACL can’t handle as much load.
Some supporting research has demonstrated[3,4] a smaller femoral notch width can be a significant predictor of ACL injury.
However, BIG NEWS...this relationship was found to be INDEPENDENT of gender.
Meaning, regardless of gender, if an athlete has a decreased femoral notch, they have a higher risk of an ACL injury.
So yes. SOME females may have smaller ACLs relative to SOME males, and so they might have a smaller capacity to handle load. But “some” doesn’t mean all!
SOME males may have smaller ACLs relative to some females, and thereby also exhibiting a smaller capacity to handle load. It goes both ways!
It’s really important to understand there is NO conclusive evidence that this ACL and notch size relationship has anything to do with gender [3,4].
On the contrary, some research  has indicated this difference in notch size may be more related to height differences rather than gender!
So if anatomy is not the cause, nor hormones (read more here), how can we explain why women have more ACL injuries than men?
What Muscle Mass & Neuromuscular Coordination have to do with ACL Tears.
Let’s look at the stats.
It is currently estimated that 50% of all patients with an ACL tear are between the ages of 15 and 25 years old. For women, the peak age is between 15 and 19 
Previously, scientists postulated that that puberty played a big factor in women’s ACL injury rates. And it kind of does! But not in the way we once thought.
Previously it was hypothesized that during puberty a female’s hips widen, increasing her Q angle, and thus her chances of experiencing knee valgus.
But we’ve already talked about how current research shows there isn’t much of a difference between the Q angles of males and females... and those angles don’t have a big impact on knee valgus.
So researchers have developed another theory. Enter: muscle mass & neuromuscular coordination
Now, scientists believe the increase in ACL tears during adolescence may be related to the growth spurt females experience. Or, more how females grow differently than males.
….“unlike boys, whose pubertal increase in testosterone aids in accumulating muscle mass, pubertal girls have difficulty building muscle, making joint control even more difficult”
—From the text, The Young Female Athlete. Effects of Puberty on Sports Training and Performance, pg 10.
During puberty, males experience both a growth and “neuromuscular” spurt , where the acute rise in testosterone allows males to increase muscle mass relative to their anatomical growth.
For females, without the acute rise in testosterone (an anabolic hormone), there is no automatic increase in muscle mass relative to their increase in peak height. This means a larger skeleton with less muscle and coordination to move that skeleton with “efficiency”
But that doesn’t mean females will always be at a high risk for ACL injuries as a woman in sports.
Rather, because of this lack of neuromuscular spurt, it is recommended that “young women in particular need to train in order to strengthen their leg muscles, improve the control over their knees, and protect their ACLs. Until that muscle strength comes in, young women are at an increased risk of injury” 
Girls could be experiencing these injuries because the majority of female athletes are not provided the training tools they REQUIRE to help meet their unique based on their development.
Valgus is a PREDICTOR for ACL injuries in Female Athletes (and not the cause).
Let’s go back to valgus for a moment.
Instead of fearing the valgus movement itself, let’s ask another question…
“WHY does the knee in so many female athletes revert to that position as the ‘safe’ place to decelerate?”
We mentioned at the start that 80% of ACL injuries in female athletes are non-contact.
Research has indicated that non-contact ACL tears are OVERUSE INJURIES .
It boils down to this: more stress has been exposed to the ligament overtime than it had the capacity to handle.
And that valgus movement your knee made when you cut in that soccer game?
Yeah, that was the straw that broke the camel’s back!
But don’t blame the ‘pop’ on the straw.
When a straw breaks the camel's back, don’t blame the final straw!!
We can’t blame one movement pattern for all ACL injuries.
Instead, we need to identify that pattern as a signal. A signal that the athlete does not have the awareness, coordination, or strength needed to help dissipate forces from landing (jumping or decelerating) most efficiently.
And- most importantly- we need to reconsider how (and IF) the female athlete is training once we see that signal
Reducing YOUR Risk with “Neuromuscular Training”
If you want to give the female athlete her BEST chance of avoiding an ACL injury, you need her to train in a way that best reduces this risk.
Research has demonstrated neuromuscular training modalities can reduce the risk of ACL injuries by about 50% in female athletes. 
Historically, this training includes:
Unfortunately, that is a LOT of variability in these training tools. So which is most effective?
In a review of the NMT training modalities the most effective programs included the following three things:
Lower body strength training
Landing stabilization exercises
The program was provided by a coach or instructor
Meanwhile, the programs including balance, core strengthening, stretching or agility had no added benefit compared to programs without these modalities.
(THIS MEANS improving your athlete’s balance on a bosu ball IS NOT an efficient use of her training time)
Rather, from these results, we can conceive:
Strength training is ESSENTIAL for improved physiology, biomechanics, and long-term performance.
Strength training helps females develop lean tissue and strength.
Larger amounts of lean tissue help female athletes in two ways: these tissues produce AND absorb higher forces, meaning a better dissipation of load when she lands.
Strength training has also been shown to help increase the ligament strength itself, i.e. improving its ability to absorb higher loads .
From a physiological standpoint, a larger proportion of lean tissue (both muscle and ligamentous) leads to a higher failure point of the ligament.
This means stronger athletes with a body composition that favors lean tissue is physiologically capable of withstanding higher loads on her body.
There it is. We’ve found it! A strong, lean-tissue focused athlete has a LOWER chance of injuring her ACL compared to an athlete with a less muscular body composition.
But the benefits go beyond physiology. Stronger muscles also mean more efficient movements and joint stability.
When your muscles are stronger, your body is more adept at recruiting them for movements such as landing from a jump or decelerating from a cut.
Strength training? It works.
Studies  suggest females who strengthen their hamstrings in relation to their quadriceps have improved knee tracking in landing and deceleration movements, leading to a decreased amount of force imposed on their ACL.
How Do You Learn To Land? You’ve Got Two Options...
You’ve got two options when it comes to learning motor skills such as landing. Implicit and explicit learning.
What’s the difference?
Think of an athlete doing a jump landing drill in her soccer warm up.
Her coach is externally cueing her to bend her knees or drive her knees out. She knows this is an important thing to focus on. She knows she should not let her knees cave it. . Now, every time she performs this drill, she internally thinks about not letting her knees cave in. This is an example of explicitly learning how to land.
Now, what’s implicit learning?
Let’s imagine an athlete during a strength training session. She’s lowering a bar situated overhead. As she lowers the bar to her shoulder, her coach cues her to “absorb the bar with her body”. With this movement (a movement that mimics a jump landing), the athlete’s body must find a way to absorb the load.
Could her knees fail to bend or demonstrate valgus while she lowers the bar? Absolutely! But as this drill is practiced, the athlete’s body awareness improves, her muscles are strengthened, and her body eventually finds a better or biomechanically “safer” position such as bending her knees as she absorbs the bar on her shoulders from overhead .
Because she is performing this drill with the goal of absorbing the load overhead rather than avoiding valgus, the acquisition of the motor skill is intrinsic!
Basically, implicit motor learning is the acquisition of a particular motor skill (such as landing with bent knees) without explicit knowledge of the skill itself she is trying to learn.
So why does it matter how you learn?
Research shows that motor skills that are acquired explicit tend to be less resilient under psychological and physiological fatigue .
Basically, if you’re only doing an action because your coach told you to focus on it...it goes out the window once you’re feeling fatigued or under pressure.
But if you implicitly train your body to move in a certain way, you’re much more likely to repeat that movement unconsciously.
Plyometric or jump mechanic trainings can show early successes in reducing ACL injury rates...but fail to sustain those results long term. Researchers have theorized  these results could be linked to the type of explicit motor learning strategies.
Keeping with Your Program Is KEY
The final and MOST IMPORTANT thing to remember: You HAVE to keep with it.
In all of these programs that implement various neuromuscular training modalities, those athletes who did not sustain a 90-100% adherence to the program did NOT show a statistically significantly decrease in ACL injury risk.  This was REGARDLESS if strength training, balance, core strength, or landing mechanics was performed.
Basically DOING NOTHING is not an option if you want to play injury free.
Now eve have the research showing how to reduce ACL injury rates through training. But injuries remain high.
The big problem here is that most female athletes are not engaging in any prevention training habitually.
In fact, the use of ACL injury prevention programs by female high school teams is low nationally (13-20%) and VERY low in rural areas (4%). 
Maybe it’s due to lack of requirements to strength train.
Maybe it’s the lack of understanding of its necessity by sport coaches or parents.
Whatever the reason, if female athletes aren’t habitually training to prevent injury, they aren’t going to reduce their already higher risk of injury.
It’s great to know you’re the type of female athlete that cares about her performance in the long-term. ACL injuries are a big deal- and we want to help you stay in the game.
Here are the key takeaways from all of this research…
#1. Valgus is not the enemy here: Rather, it is a sign that you need to become aware of your body and improve strength in ALL movement patterns (particularly lower body movements)
#2. We Can’t Reduce Injuries Unless We Know WHY They Happen: Instead of fearing a movement pattern or blaming anatomical differences, it is essential that you understand WHY ACL INJURIES occur in female athletes. Only then can we use WHAT WE KNOW to reduce the risk!
#3. How We Learn Matters: Rather than training and athlete OUT of the position or scaring her away from performing it, we should be using strength training as a tool for females to learn how to MOVE. Strength training is a effective neuromuscular training tool that helps females build lean muscle and coordinate their body in such a way that increases the body’s ability to dissipate forces by appropriate tissues when load is placed upon it. Better Training = More Time ON the Field.
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About the author
Emily holds a M.S. in Exercise Physiology from Temple University and a B.S. in Biological Sciences from Drexel University. Through this education, Emily values her ability to coach athletes with a perspective that is grounded in biomechanics and human physiology. Outside of the classroom, Emily has experience coaching and programming at the Division I Collegiate Level working as an assistant strength coach for an internship with Temple University’s Women’s Rugby team.
In addition, Emily holds her USAW Sport Performance certification and values her ability to coach athletes using “Olympic” Weightlifting. Emily is extremely passionate about the sport of Weightlifting, not only for the competitive nature of the sport, but also for the application of the lifts as a tool in the strength field. Through these lifts, Emily has been able to develop athletes that range from grade school athletes to nationally ranked athletes in sports such as lacrosse, field hockey, and weightlifting.
Emily is also an adjunct at Temple University, instructing a course on the development of female athletes.