ETIOLOGY OF AN ANTERIOR CRUCIATE LIGAMENT INJURY
The incidence of anterior cruciate ligament (ACL) injuries in female athletes has been well documented. By one account, there have been more than 2,000 scientific articles authored on the subject of ACL injuries (12). Research has suggested that the number of ACL injuries in female athletes is 3 to 6 times higher than their male counterparts (1–3). It has been suggested that a majority of ACL injuries are noncontact in nature (2,5). Many of these injuries occur because of multiplane knee loadings associated with maneuvers in sports, such as decelerating, change of direction, and jump landings (4). Research also suggests that the mechanism for causing these types of injuries is due to knee valgus, hip internal rotation, and tibial external rotation during these types of sports maneuvers (5,6,9).
There have been several theories suggested as to why there exists a relatively large difference in injury rates between genders. These theories include anatomical differences, hormonal changes, and neuromuscular deficiencies (8,9,11). Because anatomical and hormonal factors are not easily modifiable, much research has focused on influencing neuromuscular factors through strength training, plyometrics, flexibility, and balance training (8).
MODIFIABLE RISK FACTORS
Meyer et al. (11,12) have identified 4 neuromuscular deficits that can be modified with the goal of decreasing the incidence of female ACL injuries. These include (a) ligament dominance, (b) quadriceps dominance, (c) leg dominance, and (d) trunk dominance “core” dysfunction. Ligament dominance refers to the use of the ligaments of the knee rather than the musculature of the leg to control the motion of the knee during sports maneuvers. This is often seen as high knee valgus in the frontal plane during landing and cutting moves (11,12). Quadriceps dominance is an imbalance between the knee extensor (quadriceps) and knee flexor (hamstring) strength and coordination (11,12). In addition, research by Zebis et al. (15) has also suggested that the rate of force development of the hamstrings to quadriceps muscles may be an important factor in determining the potential for ACL injuries. Leg dominance is defined as an imbalance in strength, coordination, and control between the 2 lower extremities (11,12). Trunk dominance core dysfunction refers to the inability of the athlete to control the inertial forces on the body because of lack of core muscle function, causing excessive trunk motion (11).
ACL INJURY PREVENTION PROGRAMS
New Egypt High School incorporates strength training and warm-up activities into their daily practices using aspects of the Prevent Injury and Enhance Performance Program developed by the Santa Monica Orthopedic and Sports Medicine Research Foundation (10). The girls soccer team is one example as they take part in a summer training program in addition to a twice a week in-season program.
There were some constraints that needed to be considered in putting together the program. First, there was a time limitation. There were only eleven 1-hour sessions scheduled over a 6-week period. Myer et al. (13) demonstrated that following a 90-minute, 3 days a week neuromuscular training program for 6 weeks can decrease the risk factors for lower-extremity injury and enhance performance. Although the time was limited to 2 hours a week, it was believed that a similar program could be implemented and could achieve comparable results.
As is the case with many high school programs, another limitation was that there would be only one coach in charge of overseeing between 30 and 40 girls in a session. Because of this limitation, it was concluded that the best course of action was to create a circuit type of program, in which the athletes would be broken up into groups and put in different stations. This allowed for better management, monitoring, and feedback. An additional issue was that there would be a diverse group of girls in terms of age and ability.
The girls ranged from incoming freshman players to varsity seniors and many had never participated in a formal strength training program. Because of these limitations, there was a need to keep things simple, focus on specific areas, and emphasize quality over quantity. It would have been ideal to put each athlete through a screening process to access each individual's neuromuscular deficits (4). However, because of the constraints mentioned above, it was decided to implement a program for every athlete that addressed the 4 neuromuscular deficits, with the goal of improving any identified shortfalls as they were performing the exercises. Verbal feedback was used throughout the program to improve techniques of all the athletes and as a method of identifying any deficits.
Each session followed a similar schedule. A 10- to 15-minute warm-up was implemented, which included several static stretches and dynamic warm-up exercises (Table 1). The main part of the session focused on 1 of 2 types of workouts. They included (a) body weight, partner assisted, core strengthening, and balance training and (b) strength training and plyometrics. Specific exercises were chosen for the main session to address the 4 neuromuscular imbalances. The main session exercises were chosen from the list displayed in Table 2. Example workout sessions are shown in Table 3. Athletes were broken up into groups of 4 to 6 and put into 6 stations depending on the number of athletes in the session. Athletes spent approximately 6 minutes at each station before rotating to the next. Depending on the station and number in each group, each athlete performed 2–4 sets of each exercise. In the strength training sessions, they were instructed to gradually increase resistance from one session to the next.
Some primary exercises included the Nordic eccentric hamstring exercise (14). This exercise, done with a partner, is a method of improving hamstring strength while addressing any existing quadriceps dominance issues (12). Plyometric box jumps were also used to address the various neuromuscular deficiencies. Athletes were verbally instructed to “land softly,” “keep the knees in line with the toes,” “sit down when landing,” and “stick the landing.” All these verbal cues were meant to prevent the athlete from landing with knee valgus or varus. In addition, they were also meant to assist the athlete in controlling her ability to absorb the force of the landing through ankle, knee, and hip flexion (12). Single-leg catches with a partner were introduced to improve balance, which several studies have indicated as a way to reduce ACL injury risk factors (4,7). Athletes progressed to standing on a foam pad to increase the difficulty level of this exercise. Expanding this program to 3 days a week for 90 minutes may yield additional benefits as demonstrated by Meyer et al. (13).
1. Agel J, Arendt EA, Bershadsky B. Anterior cruciate ligament injury in national collegiate athletic association basketball and soccer: A 13-year review. Am J Sports Med 33: 524–530, 2005.
2. Arendt E, Agel J, Dick R. Anterior cruciate ligament injury patterns among collegiate men and women. J Athl Train 34: 86–92, 1999.
3. Arendt E, Dick R. Knee injury patterns among men and women in collegiate basketball and soccer: NCAA data and review of literature. Am J Sports Med 23: 694–701, 1995.
4. Bien D. Rationale and implementation of anterior cruciate ligament injury prevention warm-up programs in female athletes. J Strength Cond Res 25: 271–285, 2011.
5. Boden BP, Dean GS, Feagin JA Jr, Garrett WE Jr. Mechanisms of anterior cruciate ligament injury. Orthopedics 23: 573–578, 2000.
6. Boden BP, Torg JS, Knowles SB, Hewett TE. Video analysis of anterior cruciate ligament injury: Abnormalities in hip and ankle kinematics. Am J Sports Med 37: 252–259, 2009.
7. Fischer DV. Neuromuscular training to prevent anterior cruciate ligament injury in the female athlete. Strength Cond J 28: 44–54, 2006.
8. Grindstaff TL, Hammill RR, Tuzson AE, Hertel J. Neuromuscular control training programs and noncontact anterior cruciate ligament injury rates in female athletes: A numbers-needed-to-treat analysis. J Athl Train 41: 450–456, 2006.
9. Hewett TE, Myer GD, Ford KR. Anterior cruciate ligament injuries in female athletes: Part 1, mechanisms and risk factors. Am J Sports Med 34: 299–311, 2006.
10. Mandelbaum BR, Silvers HJ, Watanabe DS, Knarr JF, Thomas SD, Griffin LY, Kirkendall DT, Garrett W Jr. Effectiveness of a neuromuscular and proprioceptive training program in preventing anterior cruciate ligament injuries in female athletes: 2-year follow-up. Am J Sports Med 33: 1003–1010, 2005.
11. Myer GD, Brent JL, Ford KR, Hewett TE. Real-time assessment and neuromuscular training feedback techniques to prevent anterior cruciate ligament injury in female athletes. Strength Cond J 33: 21–35, 2011.
12. Myer GD, Ford KR, Hewett TE. Rationale and clinical techniques for anterior cruciate ligament injury prevention among female athletes. J Athl Train 39: 352–364, 2004.
13. Myer GD, Ford KR, Palumbo JP, Hewett TE. Neuromuscular training improves performance and lower extremity biomechanics in female athletes. J Strength Cond Res 19: 51–60, 2005.
14. Sayers A, Sayers B. The Nordic eccentric hamstring exercise for injury prevention in soccer players. Strength Cond J 30: 56–58, 2008.
15. Zebis MK, Anderson LL, Ellingsgaard H, Aagaard P. Rapid hamstring/quadriceps force capacity in male vs. female elite soccer players. J Strength Cond Res 25: 1989–1993, 2011.