The awkwardness with which her leg buckled in conjunction with the grimace on her face as she clutched her knee lying on the soccer field said everything – ACL tear. An increase in the number of women participating in athletic activities has consequently led to a rise in the number of non-contact anterior cruciate ligament injuries. It has been shown that female athletes are up to four times more likely to sustain a season, and possibly career ending ACL injury compared to males participating in the same sport. Every year approximately 7,500 female athletes (nearly 1 in 1,000) between the ages of 15 and 25 sustain a non-contact ACL injury. Those most at risk participate in sports that require cutting or jumping. More specifically, soccer and basketball may be responsible for up to 2/3 of all ACL injuries.
A non-contact ACL tear is most likely to occur when the foot is fixed on the ground and there is a large eccentric load in combination with either excess anterior tibial translation or rotation of the femur (upper leg) on the tibia (lower leg). In other words, deceleration of the body in conjunction with a fixed foot on the playing surface can lock the lower leg (tibia) in place. If the upper body and leg then rotate in a different direction (i.e., planting and cutting) there are rotational forces that can significantly load the ligaments of the knee. Further, it is typical for female athletes to decelerate from sprinting with one large step while keeping their center of gravity behind their knee. The fixed foot from the planting action causes the upper leg to slide forward (anterior translation) on the lower leg and creates a tremendous amount of shearing forces. In either case the loads generated may be too great for the ligaments to withstand and thus cause an ACL tear.
Fortunately there are exercises to help change mechanical inefficiencies, train the neuromuscular system, and help strengthen and stabilize the lower body when landing and changing directions. These exercises can be coached to young female athletes in order to reduce the likelihood of suffering a non-contact ACL injury.
This article is the first of a two part series which will describe three biomechanical techniques used to help reduce the risk of suffering a non-contact ACL injury as well as detail a multi-directional and multi-planar plyometric drill progression that can assist in teaching proper deceleration mechanics.
Compared to men, women tend to land from a jump with a more erect body posture. To avoid this, teach your female athletes to land with flexed knees and hips using cues such as “landing softly”. First perform sub-maximal, single vertical jumps in place. Then allow the athletes to complete several (3-5) jumps in succession. Next instruct the athlete to rotate 180 degrees while in the air. Another alternative is to perform jumps linearly (i.e., broad jumps) or laterally. Again, begin with a single jump before progressing to multiple jumps. Performing the jumps on different surfaces, such as grass (dry and wet), a hard court (wooden or rubber, not concrete), or even sand will provide an even greater proprioceptive challenge for your athletes.
It has also been reported that women use a large step to decelerate while simultaneously keeping their center of gravity behind the knee. This is thought to tighten and load the ACL. The alternative is to use multiple short steps while maintaining the center of gravity over or in front of the knees when coming to a stop, especially when sprinting at or near maximal speeds. It is important to understand that the skill of decelerating the body at various speeds is a prerequisite to planting and cutting (or simply stated as agility actions). With that said, begin by instructing your athlete to run at half speed and upon either hearing a whistle or running a prescribed distance (15-20 yards) decelerate within in 1-1.5 yards using several small steps. Next perform the drill at a faster speed and halt within 2 yards. The drill could culminate with the athlete decelerating from full speed using many short steps.
The third technique will couple deceleration (above drill) with re-acceleration. Using the short multiple steps to decelerate at half speed, but prior to coming to a complete stop, continue the fast action of the feet to re-accelerate in the same direction. Progress to higher speeds until the athlete can accelerate to full speed, decelerate, and then re-accelerate into full speed. Variations can then include accelerating and re-accelerating at different speeds and in different directions. For example, the athlete could accelerate to full speed for 15 yards, decelerate, and re-accelerate to full speed 45 degrees to the right for 5 yards. The variations are limitless and should be similar to the patterns performed in your athlete’s sport.
Decelerating the body at high velocities requires the neuromuscular system to respond to rapid eccentric loading. When properly trained, the muscles responsible for stabilizing the knee joint will absorb a majority of the forces, reducing the amount of stress placed on the ligaments. Several neuromuscular factors appear to contribute to female athletes having a greater risk of non-contact knee injuries compared to their male counterparts
- The quadriceps-to-hamstring strength ratio is typically less in untrained female athletes than in males, meaning the hamstring strength is underdeveloped compared quadriceps strength.
- Electromechanical delay (the difference in time between neural activation and actual force development within a muscle) has been found to be longer in women than men.
- Recruitment patterns have also been reported to differ between genders. When landing from a jump the quadriceps appear to activate prior to the hamstrings in female athletes, which may add to the stress placed on the ligaments of the knee due to anterior tibial translation.
- Functional joint stiffness has been found to be less in women compared to men. Functional joint stiffness describes the tension developed in the muscles which act to stabilize the knee joint during landing or rapid changes of direction. Increased tension by the muscles of the hips and legs can create more stabilization about the knee joint (high functional joint stiffness), whereas lax muscles (low functional joint stiffness) allows the brunt of the forces created by deceleration to be placed on the ligaments.
The combination of weaker hamstrings, slower electromechanical delay, recruitment of the quadriceps prior to the hamstrings, and less functional joint stiffness combine to diminish the hamstring’s ability to assist in knee stabilization when a rapid eccentric load is placed on the lower extremities.
An athlete should have the ability to land or stop, with control, in various positions (multi-planar) and stances (one leg and two legs). The following drill progression includes multi-directional, plyometric actions combined to replicate the numerous possible stresses placed on the knee joint during deceleration. By performing the closed kinetic chain exercises in the progression at various speeds the athlete will train the neuromuscular system to increase functional joint stiffness, decrease the electromechanical delay, and possibly alter recruitment patterns.
Each of the four steps may take two to four weeks (or longer) to master before the athlete can combine multiple steps in sequence. Be sure each step can be performed alone with proper mechanics and control. Once the progression can be performed in its entirety (steps one through four) an athlete may use the exercises 2-3 times per week in the preparation phase of training, and less during the competitive phase of a training cycle. The athlete’s training age and competition schedule should dictate the speed of progression and volume of work performed.
Step One – Depth Drop
The athlete begins by standing on top of a step or box set at four to six inches. Next, she steps off (do not jump) (Figure 1a) and lands on both feet simultaneously. Proper landing mechanics for the depth drop include flexing at the ankle, knee, and hips in order to absorb the eccentric loads (Figure 1b). Be sure the athlete contacts the ground beginning with the ball of the foot and progresses to the heel, avoiding a flat-footed landing.
|Fig. 1A. Stepping off
|Fig. 1B. Proper landing
from the step
To increase the eccentric loads the height of the step or box can be raised incrementally during a four to six week build-up period up to 12 to 18 inches. The athlete also needs to be instructed to consciously increase the tension of the hip and upper leg muscles upon landing, therefore improving stability around the knee joint (high functional joint stiffness). This will help reduce the tension placed on the ligaments and prepare the muscles for subsequent movements by reducing amortization time during the stretch shortening cycle.
Step Two – Lateral Jump to One Legged Landing
The athlete will jump laterally approximately two to three feet immediately after completing the depth drop and land only on the outside leg. To increase the intensity of the landing the athlete should gradually jump greater distances, increasing to a yard or more over a two to four week period. As the athlete lands from each lateral jump, apply the same landing mechanics for the depth drop described above. Also, be sure the upper body remains inside the landing leg. The landing leg will always be the outside leg, regardless of rotation (Figures 2a and 2b).
|Fig. 2A. Proper one-legged landing from lateral jump
||Fig. 2B. Improper landing mechanics following lateral jump
A variation can be added by instructing the athlete to rotate 180 degrees while in the air, and by changing the direction of the lateral jump (right or left). Use visual and verbal cues to dictate the direction of the lateral jump. Give your athlete these cues while he or she is in midair after stepping off the box for the depth drop. This is a great way to increase the reactive nature of the drill.
Step Three – Acceleration
Before beginning this step, be sure that your athlete can perform the depth drop, followed by a quick lateral jump, and land with control and stability. Once this is achieved, have the athlete perform a five to ten yard sprint using proper acceleration mechanics (Figure 3).
FIG. 3. Acceleration mechanics
Begin these short sprints slowly (1/2 speed) and gradually increase the speed over several training sessions to full speed. The athlete should slow down from the sprint by jogging to a stop. Instruct the athlete to accelerate in different directions in order to more closely mimic the characteristics of athletic events. For example, instead of accelerating straight ahead, the athlete could open up to a 45 or 90-degree angle. Use verbal and visual cues to dictate the direction of the movement and add a reactive component to the exercise.
Step Four – Deceleration
This step is designed to teach your athletes how to decelerate properly and quickly in preparation for an immediate re-acceleration in another direction. Instruct the athlete to use a series of multiple, short steps to come to a quick, but controlled stop. The number of steps required to decelerate will be directly related to the speed of acceleration. Also teach the athlete to maintain ground contact with the ball of the foot during deceleration, which should help keep the center of gravity in front of the knee. Finally, the athlete should keep the knees flexed and avoid a stiff legged stop.
Each athlete will respond differently to these drills and their variations, so be sure to progress to more challenging exercises on an individual basis.
Not all ACL injuries are preventable, however making the necessary adjustments to your athletes movement skills by teaching proper deceleration mechanics using multi-directional and multi-planar drills may reduce their chances of becoming that 1 in 1,000.
- Garrick, JG and Requa, RK. Anterior cruciate ligament injuries in men and women: How common are they? In: Prevention of Non-contact ACL Injuries. LY Griffin (Ed.) Rosemont, IL: American Academy of Orthopaedic Surgeons, 2001, pp. 1-10.
- Lephart, S. and Riemann, BL. The role of mechanoreceptors in functional joint stability. pp. 45-52.
- Hutson, LJ and Wojtys, EM. The influence of the neuromuscular system on joiont stability. pp. 53-62.
- Kibler, WB. The neuromuscular contribution of the hip and trunk to ACL injury. pp. 63-68.
- Griffin, LY. The Henning Program. pp. 93-96.