By Jason D. Vescovi and Todd Brown
Jason Vescovi, MS, CSCS, and Todd Brown, CCS, are co-founders of the Essential Element, a facility for training athletes in Northern Virginia.
Training & Conditioning, 12.2, March 2002, http://www.momentummedia.com/articles/tc/tc1202/decelerating.htm
Deceleration training will never eliminate non-contact knee injuries, but it can go a long way toward reducing the susceptibility of female athletes to these debilitating events.
This article discusses some of the biomechanical and neuromuscular factors that can contribute to non-contact knee injuries and then describes a multi-directional and multi-planar plyometric drill progression that you can incorporate into your training program. The plyometric progression is designed to reduce an athlete's chances of incurring non-contact knee injuries by teaching proper deceleration mechanics and by training the muscles responsible for stabilizing the knee. While the prime concern is for women athletes, men can also benefit from this training.
WHY IT HAPPENS
There are several underlying neuromuscular factors that place female athletes at a greater risk of non-contact knee injuries compared to their male counterparts. To begin with, the quadriceps-to-hamstring strength ratio typically is less in untrained female athletes than it is in males, meaning that hamstring strength is underdeveloped compared to that of the quadriceps.
Other underlying neuromuscular factors include gender differences in electromechanical delay, recruitment patterns, and functional joint stiffness. Electromechanical delay defines the time from neural activation to actual force development within a muscle. This delay has been found to be longer in women than in men.
Recruitment patterns have also been reported to differ between genders. For example, when landing from a jump, the quadriceps will activate prior to the hamstrings in female athletes, which may add to the stress placed on the knee.
Furthermore, functional joint stiffness has been found to be less in females than in males. Functional joint stiffness describes the tension developed in the muscles that act to stabilize the knee joint during landing or rapid changes of direction. By increasing the tension in the muscles surrounding the knee (high functional joint stiffness), overall stabilization is increased. Conversely, lax muscles (low functional joint stiffness) allows the brunt of the forces created by decelerating to be placed on the ligaments. Increased functional joint stiffness stabilizes the knee, reduces the tension placed on the ligaments, and helps prepare the muscles for subsequent movements.
In female athletes, 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. The susceptibility of a significant load being placed on the ligaments is therefore greatly increased during deceleration, which will heighten the risk of an ACL injury occurring.
There are also biomechanical factors that may contribute to the higher incidence of knee injuries among female athletes. For instance, women tend to land from jumps with a more upright posture than men. In addition, video analysis has shown that women appear to have their center of gravity behind the knee during non-contact knee injuries--seemingly from a more flat-footed position. Therefore, drills used to help prevent ACL injuries should be designed to focus on proper landing mechanics while assisting the athlete in controlling her center of gravity at various speeds.
Training for deceleration can help increase the stability of the knee and reduce the forces placed on the ligaments during the frequent, rigorous deceleration that is common in several sports, including basketball, soccer, and volleyball.
The late Chuck Henning, an orthopedist and researcher, discovered three important aspects of deceleration-related, non-contact ACL injuries for which he formulated preventive techniques. These techniques include changing the plant-and-cut to an accelerated rounded turn, using a bent-knee landing instead of a straight-knee landing, and replacing the one-step stop with the knees straight with a three-step stop with the knees bent.
We have developed a four-step drill progression implementing some of Henning's suggestions. It can be used as a preventive tool for non-contact knee injuries. The drill 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 help train the neuromuscular system to increase functional joint stiffness, decrease the electromechanical delay, and possibly alter recruitment patterns by allowing the hamstrings to act prior to the quadriceps.
Our deceleration-training progression includes four steps: depth drop, lateral jump, acceleration, and deceleration. When an athlete performs the entire progression, she or he will step off a box (depth drop), landing on both feet with legs and ankles flexed. Upon landing, the athlete immediately performs a lateral jump, landing on one leg, then quickly accelerates for five to 10 yards before decelerating in a series of short steps.
Each step of the progression 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, an athlete may use the exercise two to three times per week in the pre-competitive training schedule and less during the competitive phase. A single training session may contain one to three sets, with six to 10 repetitions of the entire progression. However, 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 a height of six to eight inches. Next, he or she steps off 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. Be sure the athlete contacts the ground beginning with the ball of the foot and progresses to the heel. It is important to avoid a direct, flat-footed landing.
Increase the height of the step or box by three to four inches per week, so that at the end of four weeks, the athlete is stepping off a platform that is approximately 18 inches high. By gradually raising the height of the box, the eccentric loads placed on the muscles around the knee progressively increase.
Another factor that can be manipulated during a landing is functional joint stiffness. The athlete needs to be instructed to consciously increase the tension of the muscles in the hips and upper legs during landing, which will improve stability around the knee joint.
Step two: lateral jump to one-legged landing. Have the athlete begin by laterally jumping two to three feet immediately after completing the depth drop. 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 as for the depth drop. Also, be sure the upper body remains inside the landing leg. The landing leg will always be the outside leg, regardless of rotation.
You can add variation to this exercise 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 from the box for the depth drop. This will increase the reactive nature of the drill.
Step three: acceleration. Before beginning this step, be sure that your athlete can competently perform the depth drop, followed by a quick lateral jump, and then land with control and stability. Once this is achieved, have the athlete add a five-to-ten-yard sprint using proper acceleration mechanics to the sequence. Begin these short sprints slowly, and gradually increase the speed over several training sessions. For example, have the athlete begin at half speed, and in subsequent workouts, increase to three-quarter speed, and then to full speed. The athlete should slow down from this sprint by jogging to a stop instead of trying to stop abruptly.
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. To add a reactive component, try implementing verbal and visual cues to dictate the direction of the movement.
Step four: deceleration. This step is designed to teach your athletes to decelerate properly and quickly in preparation for an immediate re-acceleration in another direction. Instruct the athlete to substitute the jogging stop described in Step Three with 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 keep the center of gravity in front of the knee. Finally, instruct the athlete to keep the knees flexed and avoid any stiff-legged stops, which will help reduce the chance of injury.
While not all non-contact ACL injuries are preventable, teaching proper deceleration mechanics using multi-directional and multi-planar drills may assist in the reduction of season- or career-ending knee injuries in all of your athletes.