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Finish First Insider, Issue #32
November 07, 2008
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Please enjoy another issue packed with evidence-based information about sports performance training and news about current events at Finish First Sports Performance. If you find value in this e-newsletter, please forward this message to your teammates, coaches, or other parents of hard working athletes.

Anatomical Causes of ACL Injuries

By Coach J. Hoy, CSCS, USAW, Jump Stretch, Inc. Certified,
Elite Performance Scientist

It is no surprise to most of us that young female athletes are experiencing ACL injuries at an ever growing, alarming rate. It is one of the most common non-contact related injuries in female athletics. It has the potential to end an athlete’s career--and rehabilitation is long, painful, and not always 100% successful.

Why are so many young girls getting ACL injuries and what do we know about stopping this epidemic?

Unfortunately, there is no easy answer.

Research has narrowed it down to several factors that affect one’s risk of having an ACL injury. By addressing these factors, you can help reduce your risk of injury. As I have said in previous newsletters about injury prevention and risk reduction, it is impossible to prevent 100% of the injuries that occur. Sports are unpredictable, and when the competitive environment is unpredictable, injuries often occur. However, it is possible, through a well-planned and progressive exercise program, to reduce the risk of an athlete getting injured (reducing risk through preparation is key!).

Before I get into the risk factors that have been identified by research, I want to provide a few images of the knee joint and the ACL. The ACL, or anterior cruciate ligament, is a fibrous tissue that connects from the bottom of the femur (posterior-lateral) to the top of the tibia (anterio-medial). The ACL provides stability in the knee and prevents forward translation of the tibia (with its relationship to its femur attachment). (The femur is the top bone in the first diagram, and the tibia is the larger of the bottom bones in the same diagram. In the second diagram, the femur is the top bone, and the tibia is the bottom bone).

In the realm of ACL injuries, there are those that are classified as non-contact and those that are classified as contact related. Contact injuries typically occur when a force is applied to the front (anterior) or inside (medial) of the tibia or knee while the knee is in a flexed position (leg is locked out). ACL injuries are also common with other injuries of the knee, such as an MCL (medial collateral ligament) tear. Non-contact injuries would include an ACL tear from movements such as landing, jumping, pivoting, planting to change direction and knee hyperextension. Physical therapy statistics show that about 70% of ACL injuries are non-contact related. The good news here is that the risk of non-contact injuries can be reduced through various types of preventive training.

According to injury statistics, female athletes are up to 8 times more likely than men to rupture the ACL--Scientists don’t know exactly why--but they have discovered several characteristics that may increase the risk of injury of female athletes. These include: anatomical causes such as quadriceps dominance, ligament dominance, asymmetric imbalances, or weak “core”; environmental causes such as the movements of the sport (jumping, running, landing, etc.), climate, and type of playing surface; and hormonal causes.

To keep this article from being too long, I am just going to address the anatomical causes. I will address the environmental and hormonal causes in another issue, as well as offer some sample warm-up sequences and plyometric progressions that have been used to successfully decrease the risk of injury in female athletes across the country.

So, continuing on with the anatomical causes, in the Finish First Insider Issue #5, I addressed the topic of quadriceps dominance:

Boys vs. Girls: Quadriceps/Hamstrings Tendencies
The quadriceps (4 muscles in front of leg that are used for straightening the leg at the knee) and the hamstrings (3 muscles in the back of the leg that are used for bending the knee and extending the leg back from the hip) are both very important muscles for preventing knee injuries. In both boys and girls, the quadriceps (particular the vastus medialis) is a knee stabilizer and helps prevent non-contact injuries from occurring. However, if there is a threat of injury when the knee is locked in a leg-straight position, it is not beneficial to have the quadriceps contract. In this position, any impact or blow to the front of the knee area is likely to result in an ACL injury (very high prevalence). At this point, it would be most beneficial for the hamstrings to contract while the quadriceps relaxes. In boys, when in this position, it is a natural reflex for the hamstrings to contract while the quadriceps relaxes, leading to a reduced incidence of ACL injuries. In girls, the exact opposite occurs: the natural reflex is to further contract the quadriceps and keep the hamstrings relaxed, leading to an increased prevalence of ACL injuries. As a result, young female athletes (during and after puberty) have a 2 to 10 times higher incidence of ACL injuries than young male athletes of the same age.

Scientists are currently investigating this phenomenon, but have yet to determine exactly why this happens. This has been known as female quad dominance, and studies have shown that female athletes are more apt to contract their quadriceps over their hamstrings vs. male athletes in many sports movements. The good news here is that all female athletes can reduce their risk significantly through a proper performance training and injury prevention program.

Ligament dominance is when the athlete relies more on the ligaments of the joint for stability than the larger, usually stronger muscles. Tim Hewett, PhD, Director of the Sports Medicine biodynamics Center at Cincinnati Children’s Hospital, in a recent article in ‘Training and Conditioning,’ says that ligament dominance creates an inward collapse of the knees during landing actions. This inward collapse creates torque at the knee joint and increases the risk of ligament injury. This same inward collapse affects cutting movements as well, increasing the torque and subsequently increasing injury risk.

Asymmetric imbalances occur when there is a strength, flexibility, or mobility difference between one side of the body versus the other (right leg vs. left leg, right hamstring vs. left hamstring, etc.). Imbalances can also occur between muscles of the same leg. For example, in female athletes where they are already quad dominant, there may be substantial weakness in the hamstrings. The hamstrings are an important knee stabilizer and need to be strengthened accordingly.

Athletes with a weak core (in athletic performance, the core is top of knee to mid thoracic region) are not only less efficient in their athletic movements, but they are also at an increased risk of ACL injury. A stronger athletic core creates a better use and awareness of one’s center of mass. Ground forces from running, landing, etc. are directed towards the body’s center of mass, and balance and better athletic movements center around the body’s center of mass.

A performance program that includes exercises that address the anatomical causes of ACL injuries can have a huge impact on reducing the risk and prevalence of ACL injuries in female athletes. For specific information about sample exercise routines for ACL risk reduction, please check future issues of the Finish First Insider.

Upcoming Event

**Street Survival Self-Defense Class
November 15, 2008; 8am - noon; $75

As a result of the Street Survival Self-Defense Class on November 15, 2008, the Finish First Sports Performance training center will only be open for workouts from noon to 4pm.

Thanks again for subscribing to this free e-newsletter. I hope you enjoy reading it as much as I enjoy writing it. I look forward to your feedback as I continue to research to bring you the most current scientific training information available.

Should you have any specific article requests or questions, email me at Please visit for detailed sports performance training information and programs offered exclusively by Finish First Sports Performance.

Yours In Training,

Coach Jeremy S. Hoy, CSCS, USAW, Jump Stretch, Inc. Certified,
Elite Performance Scientist

Finish First Sports Performance

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