ACL injuries: How they happen and what you can do to miminimize them


ACL Injuries: How They Happen, and What We Can Do to Reduce Them

The dreaded ACL tear is one of the worst phrases an athlete can hear in sports. It is a devastating injury that can take months to rehab and rebuild muscle strength, and years to return to full capacity. Many athletes do not ever play at the same level again after an ACL tear, and training can be an arduous and confusing process to rebuild muscles that have atrophied and re-learn the movement patterns that made them a great athlete prior to injury.

However, while it is impossible to fully prevent an injury from occurring, a large percentage of ACL injuries occur in at least somewhat controllable (non-contact) circumstances. Thus, it is possible through a variety of interventions and training to reduce the chances of an ACL injury occurring. We have seen incredible improvements in the performance field in technology, and a diaspora of information available to help athletes and coaches understand how ACL tears often happen. This includes what the physiological or muscular and bio-mechanical needs for athletes are to reduce the chances of tears, and incredible data gathering applications that can help inform decisions before injuries occur. 

With more information often comes more confusion trying to make sense of which information is helpful. In order to break this down further, we need to understand what the ACL is and what it does, how these injuries tend to happen, and what we can do to reduce the chances of this devastating injury occurring through assessment, training and utilizing technology.

What is the ACL?

ACL is short hand for the: Anterior (Front side of the human body), Cruciate (Cross, as in they cross each other), Ligaments (Fibrous tissue that connects bones to other bones). To be more specific, any ligament is a fibrous yet somewhat elastic connective tissue in the body that connects bones together, which in turn helps joints to function. In the case of the ACL, it connects the femur, or thigh bone, to your tibia, or the largest bone in your lower leg. This connection allows you to flex and extend your knee; the quadriceps and hamstring muscles are the primary muscles that create this motion. From a biomechanical perspective, the brain gives a message to the Central Nervous System (CNS) that it wants to make a certain movement (like a jump), and the CNS sends a signal to the muscles needed to make that movement happen. The intersection of our muscles producing force and working effectively to initiate movement intersects with the need for the ligaments and other connective tissues to facilitate that movement. In the case of our ACL, when the quadriceps, hamstrings and other leg muscles want to make an explosive jumping, running or other athletic motion, the ACL facilitates that movement by connecting our upper and lower leg together.

Anatomy of an ACL Tear: How Do They Occur?

There is no single way for an ACL tear to occur, thus there is no 100% fool-proof method for preventing them. However, we can see patterns in the movement of athletes in a variety of sports that show us the most common occurrences. Additionally, we can rely on research and statistics to surmise additional patterns of ACL tears that tend to happen the most.

  • Approximately 70% or more of athletic ACL injuries that occur in the United States are considered non-contact, or they occur during a play in sport without any physical contact from another athlete or entity other than the ground.
  • Female athletes are more likely than male athletes, statistically speaking, to tear an ACL.
  • One of the fastest growing segments or demographics of ACL tears in the last two decades has been youth sports or youth athletes.

Based on these statistics, and studying how an ACL tear might look in real-time, we can begin to identify what some of the physical patterns or tendencies are that might lend themselves to ACL tears. Unless contacted by an outside force it is rare for an athlete to tear an ACL if they move effectively and have developed their muscular strength and endurance to the appropriate level for their sport. More often these tears occur most likely from some combination of the following factors:

  • Valgus Collapse: Especially prevalent in female athletes though it can be seen across the athletic spectrum, the Valgus Collapse has shown a strong statistical correlation to ACL tears. The Valgus Collapse refers to one or both knees of an athlete gliding or bowing inwards or towards each other, particularly in a squatting or jumping motion. This often stems from weak stabilizing muscles such as the adductors or glute muscles.
  • Asymmetry in Strength Between the Quadriceps and Hamstring Muscles: The hamstring muscle is crucial as a deceleration tool for athletes when landing and cutting (more on this later). Many athletes, especially those with either poor training habits in the weight room or none at all, tend to be quad-dominant which can lead them to poor habits in deceleration and landing.
  • Poor Landing Mechanics: Many athletes in sports that require jumping such as basketball or football have a tendency in competition to land with poor mechanics. In basketball there are many examples, Derrick Rose, Shaun Livingston, and Kevin Ware to name a few, who landed on a leg that was too straight sending impact to the joints rather than absorbing force through their muscles. It is that force that caused the knee and ACL to buckle and tear.
  • Poor Ankle Mobility – Athletes with very stiff ankles, or who have limited dorsiflexion range of motion, tend to have knee injuries due to their inability to flex and load their landing mechanics properly. Dorsiflexion, or the ability of the foot to flex upwards towards the shin at the ankle joint, is crucial to the ability to absorb force when landing, sprinting and cutting. When an athlete has limited range of motion at the ankle in dorsiflexion, the knee has to absorb the excess force, which can overstress the knee and lead to injuries and ACL tears.
  • Poor Hip Strength and Mobility – Most ACL injuries occur in deceleration or landing situations in sports; one of the key tenets of effective landing and deceleration is the ability to absorb force via loading at the hips, however athletes with weak or immobile hips have great difficulty with higher levels of force and will tend to land on a stiff leg or with an over-bent knee, both of which can lead to excessive force on the knee and a potential ligament tear.

Movement Patterns and Training to Reduce the Chances of ACL Tears:

It is clear based on some of the points above that quality of movement along with muscular strength and endurance is the key to reducing the chances of an ACL tear. In order to improve both movement and muscular strength, athletes first need to consult with a coach or professional and have an assessment conducted. It is imperative that they identify which movement patterns could be contributing to any potential indicators of future injuries as well as deficiencies in muscular strength, endurance or symmetry. This could include range of motion at the ankle and hip joint, asymmetries in their movement, and mechanical issues in key movement patterns such as squatting, hinging at the hips, lunging, landing, slowing down or decelerating (to name a few). Coaches need to look for key indicators such as a valgus collapse or asymmetries in movement, and how athletes utilize their muscles to absorb and create force in athletic motions.

Often it can be difficult to assess or diagnose this with pure observation; however, utilizing wearable tech that provides bio feedback and analysis can bridge the gap and provide the right data to identify and fix risk factors. By using tech that can provide real-time feedback, it can provide insights to a coach, trainer and athlete on how they are using force in athletic movements such as jumping or sprinting, and absorbing force during landing or decelerating. It is incredibly difficult for a coach to adequately assess an athlete’s ability to recruit and utilize muscles effectively based purely on observation. Luckily there is technology available now that can provide real-time data that can inform better training choices and interventions.

For example, as previously mentioned the hamstrings play a key role in decelerating; their function is to flex the knee or bend it, while the quadriceps extend or straighten the knee. When an athlete needs to land or decelerate effectively, they need adequate hamstring strength and recruitment to resist the knee over-extending forward, which is one of the primary causes of non-contact ACL tears. Athletes also utilize a number of different muscles to stabilize the knee, if any of these are a weak link, the athlete will be more pre-disposed to injury and less prepared for competition. This can be hard to identify through simple range of motion testing, however utilizing wearable tech that can provide instant analysis on how an athlete stabilizes when landing can help coaches pinpoint muscular weak links, or identify a poor movement or muscular pattern that leads athletes to compensate and could cause an injury or other issues down the line.

An effective coach who is utilizing technology can perform an in-depth assessment, identify these risk factors and provide an effective training program to reduce the chances of injury while monitoring the data to track their progress and make adjustments throughout the program as needed. These types of well-informed training programs can greatly reduce the risk of ACL injuries.

Putting It All Together: How Do We Prevent ACL Injuries?

Compressing all of the information above, simply put the best recipe for preventing ACL injuries is a quality training program that builds muscular strength, power, endurance and stability. This should be done with a professional coach or trainer who can utilize an effective assessment, feedback technology and data to inform athletes on the correct movement patterns and techniques. The knee is a complex joint with a plethora of muscles that interact with ligaments and tendons to create movement. Athletes must develop the appropriate muscular strength, endurance and stabilization to prepare for play and performing at their peak potential. Through effective and training they must prepare their bodies for the rigor of sports and explosive, dynamic movements. With a qualified coach or trainer and technology that can create well-informed decisions, athletes can become stronger and faster and use their muscles effectively to perform with confidence!