Last Updated Nov 2012
The knee consists of four ligaments which stabilize it, of which the anterior cruciate ligament (ACL) carries the highest risk of injury. The ACL injury may be caused by external factors such as playing surface and weather conditions, or internal factors such as stress impacting the muscles. Most competitive sports require dexterous lower extremity movements involving decelerating, twisting, pivoting, landing, cutting and changing direction.
When the ACL tissue suffers a tear, whether from direct or noncontact injury, the player experiences a loss of control of motion of the knee joint. This is of particular concern to professional athletes, who may lose play time and suffer severe pain requiring surgery and physical therapy rehabilitation.
The good news is that of the multiple factors that affect ACL injury risk, those that affect movement mechanics are modifiable. These include coupled unstable movements such as slowing down while changing direction, landing around a full leg extension, and pivoting while one foot is planted and the knee is fully extended. Such unstable movement mechanisms subject the knee joint to the entire weight of the body which increases the stress on the knee and leads to ACL injury.
By conditioning the knee joint to counter the instability of requisite movements which pose a risk, the athlete is capable of being aware of his limitations while improving proprioceptary responses and thus minimizing stress on the knee ligament structure. While there are several factors that influence the implementation of training mechanisms, sports physical therapy can benefit to athlete's conditioning through a neuromuscular exercise program.
An integrated training program focuses on increasing strength and flexibility using multiple methods including plyometric exercises, stretching, and balance. It could begin with simple physical therapy exercises applying body mechanics with specificity, followed by movement patterns which add power by challenging the extremities. This can be done by focusing on steadily 
increasing the range of motion of knee flexion angles, distance between the knees, and lowering hamstring-quadriceps ratios and knee extension torques, as well as by using closed step and jumping exercises. Following such a regimen on an ongoing basis throughout and outside of the playing season helps maintain the achieved improvements.
It is also imperative that the hamstrings and quadriceps should be conditioned so that their relative strength is in proportion to their conjoined action on the knee joint. When the muscles of the hamstring and quadriceps have relative strength to act together, each complements the other’s functionality by absorbing the stress placed by the other on the knee joint.
You could improve your athletic performance by recruiting prevention strategies into your exercise program. The flexibility and agility achieved by making a committed effort to use multiple exercise strategies to increase the strength and endurance of your lower body extremities will most likely offset risk factors. An exercise plan that integrates biomechanics to benefit the lower extremities and make movement easier, flexible, agile and responsive has been shown to avert the risk of injury to the ACL.
A study in the Journal of Strength and Conditioning Research examined the effects of an exercise program on performance and lower-extremity movement biomechanics of athletes. It found that a focused comprehensive neuromuscular training program combining multiple-injury prevention components such as plyometrics, core, balance, resistance, and speed improved performance and movement biomechanics. Specifically, the training program decreased the knee valgus and varus torques while increasing measurements on speed, jumps, single-leg hop distances, squat and jump presses, and range of motion of the knee while landing. (Gregory, Ford, Palumbo, & Hewett, 2005)
Another study examined kinematics and its associated rotations for the hip and knee based on lower extremity maneuvers. It determined that an increase in rotation of the hip and knee resulted in increased knee abduction measures. It recommended a neuromuscular strength training program for the trunk and hip to i
mprove control of lower-extremity alignment and thus reduce risk of injury by lowering the load on knees caused by increased hip adduction. (Lauren, Myer, Gregory, Ford, Kevin, & Timothy, 2009)
If your sport activity relies on movements such as jumping, pivoting, and making sudden turns, then you may benefit from a strength conditioning program which emphasizes the prevention of risk of ACL injuries. We can offer guidance by helping you follow a program which maintains continuity regardless of the season of your sport which will modify the factors causing ACL injury.
If you believe that such a program may help prepare you to mitigate the risks of knee injury while engaging in athletic activity, call us @ 508-845-3974 and schedule yourself for a FREE fitness assessment. We will design an appropriate exercise plan customized to your needs and discuss options to implement the plan during the in-season and off-season.
References:
Myer, Gregory D., Ford, Kevin R., Palumbo, Oseph P., & Hewett, Timothy E. (2005) Neuromuscular Training Improves Performance and Lower-Extremity Biomechanics in Female Athletes. The Journal of Strength & Conditioning Research. 19(1), 51-60.
Lauren E., Myer, Gregory D., Ford, Kevin R., & Hewett, Timothy E. (2009) Relationship Between Hip and Knee Kinematics in Athletic Women During Cutting Maneuvers: A Possible Link to Noncontact Anterior Cruciate Ligament Injury and Prevention Imwalle. The Journal of Strength & Conditioning Research. 23(8), 2223-2230. Doi: 10.1519/JSC.0b013e3181bc1a02
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