Rationale and Clinical Techniques for Anterior Cruciate Ligament Injury Prevention Among Female Athletes

Abstract

OBJECTIVE: To present the rationale and detailed techniques for the application of exercises targeted to prevent anterior cruciate ligament (ACL) injury in high-risk female athletes. BACKGROUND: Female athletes have a 4- to 6-fold increased risk for ACL injury compared with their male counterparts playing at similar levels in the same sports. The increased ACL injury risk coupled with greater sports participation by young women over the last 30 years (9-fold increase in high school and 5-fold increase in collegiate sports) has generated public awareness and fueled several sex-related mechanistic and interventional investigations. These investigations provide the groundwork for the development of neuromuscular training aimed at targeting identified neuromuscular imbalances to decrease ACL injury risk. DESCRIPTION: After the onset of puberty, female athletes may not have a neuromuscular spurt to match their similar, rapid increase in growth and development. The lack of a natural neuromuscular adaptation may facilitate the development of neuromuscular imbalances that increase the risk for ACL injury. Dynamic neuromuscular analysis training provides the methodologic approach for identifying high-risk individuals and the basis of using interventions targeted to their specific needs. CLINICAL ADVANTAGES: Dynamic neuromuscular training applied to the high-risk population may decrease ACL injury risk and help more female athletes enjoy the benefits of sports participation without the long-term disabilities associated with injury.

Figure 1. Free-body diagram of forces acting on the tibia, showing the frontal-plane equilibrium between external valgus load (V), articular contact force (C), quadriceps force (Q), medial hamstrings (MH), and anterior cruciate ligament (ACL) force

Under external valgus loading, contact shifts to the lateral compartment. The moment balance with respect to the contact point shows that Q and MH both help the ACL (and the medial collateral ligament, not shown) stabilize the joint against valgus loading. Under a given valgus load, any reduction in these muscle forces increases ligament loading

Figure 2. The athletic position is a functionally stable position with the knees comfortably flexed, shoulders back, eyes up, feet approximately shoulderwidth apart, and body mass balanced over the balls of the feet

The knees should be over the balls of the feet and the chest over the knees. This athlete-ready position is the starting and finishing position for most of the training exercises. During some exercises, the finishing position is exaggerated with deeper knee flexion in order to emphasize the correction of certain biomechanical deficiencies

Figure 3. Wall jumps

The athlete stands erect with the arms semiextended overhead. This vertical jump requires minimal knee flexion. The gastrocnemius muscles should create the vertical height, and the arms should extend fully at the top of the jump. Use this jump as a warm-up and coaching exercise, as this relatively low-intensity movement can reveal abnormal knee motion in athletes with poor side-to-side knee control

Figure 4. Tuck jumps

The athlete starts in the athletic position with her feet shoulderwidth apart. She initiates the jump with a slight crouch downward while she extends her arms behind her. She then swings her arms forward as she simultaneously jumps straight up and pulls her knees up as high as possible. At the highest point of the jump, the athlete is in the air with her thighs parallel to the ground. When landing, the athlete should immediately begin the next tuck jump. Encourage her to land softly, using a toe-to-midfoot rocker landing. The athlete should not continue this jump if she cannot control the high landing force or if she uses a knock-kneed landing

Figure 5. Broad jump and hold

The athlete prepares in the athletic position with her arms extended behind her at the shoulder. She begins by swinging her arms forward and jumping horizontally and vertically at approximately a 45° angle to achieve maximum horizontal distance. The athlete must “stick” the landing with her knees flexed to approximately 90° in an exaggerated athletic position. If she cannot stick the landing during a maximal effort jump in the early phases, have her perform a submaximal broad jump, sticking the landing with her toes straight ahead and no inward motion of her knees. As her technique improves, encourage her to add distance to her jumps but not at the expense of perfect technique

Figure 6. The 180° jump

. The starting position is standing erect with feet shoulderwidth apart. The athlete initiates this 2-footed jump with a direct vertical motion combined with a 180° rotation in midair, keeping her arms away from her sides to help maintain balance. When she lands, she immediately reverses this jump into the opposite direction. She repeats until perfect technique fails. The goal of this jump is to achieve maximal height with a full 180° rotation. Encourage the athlete to maintain exact foot position on the floor by jumping and landing in the same footprint

Figure 7. Single-leg hop and hold

The starting position is a semicrouched position on a single leg. The athlete's arm should be fully extended behind her at the shoulder. She initiates the jump by swinging the arms forward while simultaneously extending at the hip and knee. The jump should carry the athlete up at an angle of approximately 45° and attain maximal distance for a single-leg landing. She is instructed to land on the jumping leg with deep knee flexion (to 90°) and to hold the landing for at least 3 seconds. Coach this jump with care to protect the athlete from injury. Start her with a submaximal effort on the single-leg broad jump so she can experience the level of difficulty. Continue to increase the distance of the broad hop as the athlete improves her ability to “stick” and hold the final landing. Have the athlete keep her visual focus away from her feet to help prevent too much forward lean at the waist

Figure 8. Squat jumps

The athlete begins in the athletic position with her feet flat on the mat and pointing straight ahead. She drops into deep knee, hip, and ankle flexion; touches the floor (or mat) as close to her heels as possible; and then takes off into a maximal vertical jump. The athlete then jumps straight up vertically and reaches as high as possible. On landing, she immediately returns to the starting position and repeats the initial jump. Repeat for the allotted time or until her technique begins to deteriorate. Teach the athlete to jump straight up vertically, reaching as high overhead as possible. Encourage her to land in the same spot on the floor and maintain upright posture when regaining the deep-squat position. Do not allow the athlete to bend forward at the waist to reach the floor. She should keep her eyes up, feet and knees pointed straight ahead, and arms to the outside of her legs

Figure 9. X hops

The athlete faces a quadrant pattern and stands on a single limb with the support knee slightly bent. She hops diagonally, lands in the opposite quadrant, maintains forward stance, and holds the deep knee-flexion landing for 3 seconds. She then hops laterally into the side quadrant and again holds the landing. Next she hops diagonally backward and holds the jump. Finally, she hops laterally into the initial quadrant and holds the landing. She repeats this pattern for the required number of sets. Encourage the athlete to maintain balance during each landing, keeping her eyes up and the visual focus away from her feet

Figure 10. Single-leg balance

The balance drills are performed on a balance device that provides an unstable surface. The athlete begins on the device with a 2-legged stance with feet shoulderwidth apart, in athletic position. As she improves, the training drills can incorporate ball catches and single-leg balance drills. Encourage the athlete to maintain deep knee flexion when performing all balance drills

Figure 11. Bounding

The athlete begins this jump by bounding in place. Once she attains proper rhythm and form, encourage her to maintain the vertical component of the bound while adding some horizontal distance to each jump. The progression of jumps advances the athlete across the training area. When coaching this jump, encourage the athlete to maintain maximum bounding height

Figure 12. Jump, jump, jump, vertical jump

The athlete performs 3 successive broad jumps and immediately progresses into a maximum-effort vertical jump. The 3 consecutive broad jumps should be performed as quickly as possible and attain maximal horizontal distance. The third broad jump should be used as a preparatory jump that will allow horizontal momentum to be quickly and efficiently transferred into vertical power. Encourage the athlete to provide minimal braking on the third and final broad jump to ensure that maximum energy is transferred to the vertical jump. Coach the athlete to go directly vertical on the fourth jump and not move horizontally. Use full arm extension to achieve maximum vertical height