The ACL is one of four major ligaments in the knee and its function is to stabilize the knee keeping the lower (tibia) and upper (femur) leg bones from moving too far from each other, either forward or to the side. Sports such as basketball, volleyball, and soccer, which require starting/stopping, cutting, jumping, and other high force maneuvers, have the highest incidences of ACL injuries. More than seventy percent of these injuries are non-contact. Several studies have found that girls have three to eight times more ACL injuries than boys, depending on the sport. However, the good news is that proper training can reduce the number of these injuries. In fact, a two year study (PEP) performed by the Santa Monica Orthopaedic and Sports Medicine Research Foundation during 2000 and 2001 found that ACL injuries were decreased by 88% and 74% respectively, when female soccer players performed certain exercises and drills during their warm up.
Many studies have attempted to discover why women have more ACL injuries than men. There is no definitive answer. However, there are several factors that seem to predispose women to this injury:
· Anatomically, women have a greater Q angle (the angle formed by the femur and the tibia when viewed from the front) at the knee which can allow the knee to internally rotate to a greater extent than their male counterpart.
· Girls tend to have quadriceps that are too dominant and hamstrings that are too weak.
· Females are not as efficient when it comes to cutting, decelerating, and landing due to muscle reaction time disparity.
· Women have “looser” knee joints than men.
The knee joint is at risk regardless of gender. It is imperative that athletes learn how to apply and absorb forces properly (starting/stopping, cutting, landing, core strength, etc.), strengthen muscles that support the knee (especially the hamstrings in girls), increase agility, and enhance their proprioceptive awareness (plyometrics, coordinated movements at fast speed, control position of limbs during potentially vulnerable situations).
Many organizations have implemented successful knee injury prevention programs. These programs share several key components including understanding and improving proper movement skills, increasing power/core strength, and enhancing proprioception. The Velocity Sports Performance staff has implemented these components in the following units: mobility/flexibility, balance, power, and agility.
Several of the mobility, power, and agility exercises are plyometric in nature. Plyometric exercises involve stretching a muscle followed by a rapid concentric contraction of that muscle which engages the serial-elastic and proprioceptive components of the muscle tissue. The result is a more powerful force application. Plyometric exercise bridge the gap between strength and speed. They must be carefully introduced into the training regime insuring that the intensity of these exercises is increased gradually throughout the season.
Note that static stretching is not included as part of our recommended pre-training or pre-event warm-up. Several good studies suggest that static stretching tends to shut down the mechanisms that enable the human musculature to produce large forces. Motoneuron excitability is definitely decreased during and after static stretching protocols. Because of these studies, and based on results from our own experience, all of the exercise units are used to increase muscle temperature and flexibility. If static stretching is to be used for increasing joint range of motion, we recommend that it be performed as a post-training or post-event activity.
There are hundreds of exercises and drills that athletes and coaches can choose from to augment sports training. Most ACL injury prevention programs use the same 4 to 15 exercises throughout the training cycle. We have chosen a larger set that specifically addresses the needs of female soccer players, adds variety, and increases intensity as the program progresses. These exercises and drills should be done at least three times a week for a period of 20 to 30 minutes during the warm up phase of training. They should be continued throughout the entire season. The emphasis must be on quality of effort, not quantity. If done properly, the potential for ACL injury will be reduced and the training program will be enhanced.
