Now that we know women are indeed more susceptible to tearing their anterior cruciate ligaments (ACL) than men, preventing these injuries should be a primary concern. With the knowledge of why these injuries are more prevalent in women, a specific exercise program can be designed to focus on prevention. Although there are some intrinsic and extrinsic risk factors that cannot be changed, like body alignment or joint laxity, many exercises can influence these risk factors and minimize their negative effects. Other risk factors, like decreased muscular strength and endurance, can be challenged head-on and overcome with a proper training program. Exercises designed to increase muscular strength and overall stabilization, to increase muscular endurance, to increase reaction time, and to teach balance, coordination, and proprioception are all aspects that are essential to an ACL injury prevention program.

Exercises to increase strength and dynamic stabilization
Women need increased strength of individual muscles, but even more importantly, need all muscles to work together as a group to dynamically stabilize the knee joint and the entire body. The best way to achieve this goal is to train with compound movements where more than one muscle and joint are involved. These often are basic, functional movements that are performed every day and are incorporated into exercises. Examples of compound movements are squats, forward, backward, and side lunges, wall sits, leg presses, step-ups to the front and side, and step-downs to the back and side. These compound movements require co-contraction of muscles that normally work against each other, like the quadriceps and hamstrings. These stabilization exercises also aid the female athlete by retraining her order of muscle recruitment. Studies have shown that females activate their quadriceps before their hamstrings when trying to decelerate the body, like returning to the ground from a jump [1]. Activation of the hamstrings first prevents anterior translation of the tibia and protects the ACL. Concentrating on keeping the knee always slightly flexed when either extending from a bottom position or placing the foot down like in a lunge or step-up, will allow co-contraction and promote the “position of stability” [2].
Of course, training muscles individually will also promote increased strength. Lower repetitions and heavier weights are associated with strength training. All exercises can be done either bilaterally (using both legs at the same), unilaterally (using one leg at a time), or alternating either on a machine, using ankle cuff weights, or having a partner perform manual resistance. Leg extensions are used for the quadriceps, leg curls for the hamstrings, and straight knee and bent knee heel raises for the calves. Most of the hip musculature is worked in the compound leg movements as well, but they can be isolated on inner and outer thigh machines, performing side step-overs, and using manual resistance. A great low back exercise is the deadlift, and crunches work just fine for the abdominals.

Exercises to increase endurance
Higher repetitions and lighter weights are associated with endurance gains. Of course, this protocol is the opposite of a strength protocol. You can accomplish both of these goals by simply weight training for strength on one day and weight training for endurance on another. You can also choose the compound exercises for strength exercises and the isolation movements for endurance exercises. Or cycle your training by following an endurance program for several weeks and then a strength program for several weeks. In addition, any cardiovascular-type exercise performed for more than 20-30 minutes continuously will increase muscular endurance and benefit your heart and lungs. Choose cardiovascular exercises like walking, bicycling, and stair climbing. Adding balance and proprioception drills to the end of a strength training workout will also help increase muscular endurance [2].

Exercises to increase balance, coordination, and proprioception
Proprioceptors are located in the knee tendons and ligaments and are responsible for detecting joint loads and responding to muscular activity. They give the brain information about the joint without any conscious thought process. Research has shown that training for this unconscious neuromuscular event can decrease the risk of ACL injury. Using stability balls and biofoam rollers are some of the best and most challenging ways to get balance, coordination, and proprioception all in one exercise. The Perform Better website at www.performbetter.com is an excellent source for these products and instructional exercise videos and sheets. Without the use of props there are still many exercises you can do, you just have to be creative. Standing on one leg seems simple enough until you try it with your eyes closed. You can hold the one leg pose and move your arms around rapidly or try to catch a ball a partner throws to you in directions all around your body. Manual resistance can work as well with a partner trying to “push you over” from all different angles and sides of your body and you having to regain your initial upright location. Remember to keep that slightly bent knee “position of stability.” Cariocas are useful for coordination and walking on balance beams or curbs are great for balance. As you incorporate these exercises into your routine, you’ll be sure to devise some of your own challenges.

Exercises to increase reaction time
Because women generate muscular force slower than men, reaction time and quickness must be a part of an ACL prevention program. Backward running, high speed step-ups and step-downs with alternating legs, high speed knee-ups, Stairmaster intervals, plyometrics, and agility drills like side shuffles and shuttle runs are all examples of exercise to increase reactivity. An excellent source for learning about plyometrics is Don Chu’s book and video, “Jumping Into Plyometrics.” http://www.humankinetics.com/products/showproduct.cfm? associate=3101&isbn=0736000925.
No exercise program can guarantee full protection from sports-related injuries. However, proper training can eliminate some risk factors and make others less of a consideration. The exercise suggestions outlined in this article can help solve many of the intrinsic and extrinsic factors that put women at risk for ACL and possibly other sport-related injuries. Be sure to consult with a doctor before embarking on any exercise program, and if you have specific questions or need additional help, seek out professional rehabilitation specialists, certified athletic trainers, strength coaches, and personal trainers.

References
1. Huston, L.J. and E.M. Wojtys, Neuromuscular performance characteristics in elite female athletes. Am J Sports Med, 1996. 24(4): p. 427-436.
2. Wilk, K.E., et al., Rehabilitation after anterior cruciate ligament reconstruction in the female athlete. Journal of Athletic Training, 1999. 34(2): p. 177-193.