ACL injuries are widespread in sports today. While direct collisions certainly can cause ACL tears, the majority of injuries are noncontact injuries. The most “at risk” sports tend to involve jumping, pivoting and cutting such as soccer, basketball, football and volleyball.
It has been widely publicized for some time that females are anywhere from three to eight times more likely to suffer such an injury compared to their male counterparts.. Why so many more injuries in women? One reason may simply be increased female participation.
The 2004 National Federation of State High School Associations participation study revealed that the number of female athletes involved in high school sports increased from 300,000 to 2.7 million since 1971. Here are the top three sports for female athletes in the calendar year of 2006-2007:
- Basketball - 456,967
- Volleyball - 405,832
- Soccer - 337,632
Current ACL Research
According to the American Journal of Sports Medicine, girls soccer and basketball players undergo the greatest number of knee surgeries every year. So what are some of the reasons why females are at such a higher risk for injury? Some of the reasons are as follows:
- Biomechanical differences such as a wider pelvis and increased valgus
- Quad dominance (typically see a 2:1 Q/HS ratio instead of 3:2)
- Poor running, cutting and landing mechanics
- Faulty muscle firing patterns
- Smaller femoral notch and ACL
- Greater overall joint laxity
- Hormonal differences
Researchers have been trying for years to link ACL tears to the menstrual cycle. While no definitive link has been identified, here are some basic truths:
- ACL injury risk is greater during the preovulatory phase.
- Evidence exists for sex hormone receptors on the ACL and on skeletal muscle.
- Hormone profiles vary greatly between female athletes.
- The magnitude of change in laxity across the menstrual cycle varies greatly among females.
- The mechanical and molecular properties of the ACL are influenced by estrogen as well as the interaction of several sex hormones, secondary messengers, remodeling proteins and mechanical stresses.
Even with the aforementioned knowledge, there are still several unanswered questions. How do injury rates vary in females who have normal cycles versus extended intervals between menstruation or those using oral contraceptives? What effects do these sex hormones have on the ACL? What biomechanical changes take place (if any) during the menstrual cycle? For those females experiencing a change in laxity across the cycle, what impact does this have on the mechanical properties of the ACL and knee joint stability?
The list could go on, but the point is there is still much research to be done. Moving forward, there needs to be continued efforts in identifying how all hormones impact the ACL. More studies need to look at individual hormone profiles and include healthy female athletes, not just those who have suffered an injury. Researchers have also suggested, when making female to male comparisons, that factors should be assessed during the early follicular phase of the cycle when hormones are at the lowest point to eliminate potential confounding variables.
Now, let’s turn our attention to the prevention side of the equation. Recent research has linked anterior knee joint laxity or increased ACL injury risk to these biomechanical factors:
- Lower anterior pelvic tilt
- Increased knee recurvatum (hyperextension)
- Decreased hip external rotation
- Decreased ankle dorsiflexion
- Navicular drop
This tells us, as exercise specialists, we need to address the entire kinetic chain of the lower leg. No real surprise there, right? Individually or together, these factors all affect the frontal plane mechanics of athletes as they plant, cut, pivot and land.
Timothy Hewett, PhD., has authored several studies relating injury risk to a drop landing from a box. Athletes with increased risk exhibit increased valgus and single leg dominance in his studies. Much of his work advocates teaching athletes how to properly eccentrically control body motion, stay low during cutting maneuvers and land softly when jumping.
Drop Landing from 18” Box
Bad Drop Landing with Significant Valgus
Acceptable Drop Landing w/Neutral Positioning
Single Leg Squat Assessment
Bad Single Leg Squat
Acceptable Single Leg Squat
I agree with Hewett’s findings and have built much of my prevention programs around his research. Limited work has been done thus far to document the direct impact that foot pronation has on injury risk. Keep in mind that as pronation occurs, there is believed to be inherent internal rotation of the tibia on the femur, leading to increased ACL strain. Even so, there is limited research between rear foot eversion and internal rotation of the tibia with respect to ACL loading.
The take away message here is to recognize limited dorsiflexion or significant pronation in your clients. Consider having them stand barefoot for the initial assessment. This will allow you to observe resting alignment and dynamic movement with respect to squatting, walking, jogging and jumping. It is also important to screen both legs together and individually to detect any side to side abnormalities.
ACL Prevention Screening
Prior to beginning an ACL prevention program, it is important to include a comprehensive screening for each participant. While many programs have been found to work in reducing injury risk, there are certain things you must look at to properly evaluate clients such as:
Proper Plant and Cut Position
- Observe general postural alignment (varus, valgus or neutral alignment)
- Observe pelvic tilt (side view)
- Test two feet and single leg squat
- Assess static and dynamic balance
- Measure lower limb flexibility
- Assess drop landing form
- Evaluate running and cutting technique
Based on the results of this testing, you will immediately identify the areas of greatest need and deficits. Be prepared to find fault with most of your female athletes. With this in mind, delicately pass along the feedback to her and her parents, if applicable. It is never wise to tell a young athlete she is about to tear her ACL. However, it is important to relay your findings in a professional way, assuring the athlete and the parents that properly directed training will significantly reduce injury risk. Hewett has reported that ACL prevention programs may reduce injury risk by as much as 62 percent.
Perhaps the best tool at your disposal is video. I highly recommend using video analysis in your ACL prevention programs. We utilize Dartfish software at my facility, as this allows us to catalogue videos, supply immediate feedback to the client and compare athletes side by side on the screen. You may also use less expensive means such as a Flip Mini Camera or traditional camcorder and upload the video to your PC and play with Windows Media Player or QuickTime for Macs as well. In the end, this tool will allow you to store assessments for future reference and raise the professionalism of your program.
The Prevention Program
Armed with all of the research and assessment findings, you are ready to implement a safe and effective exercise program. Whether educating a coach or parent to carry out this effort or working one on one with the athlete, there are certain components that should be included. The flow of a successful program should consist of the following (in progressive order):
1. Dynamic Warm Up – Begin with a general warm up, using gross motor movements to properly loosen up the entire body (jogging, shuffles, carioca, etc.) and then progress to a more specific warm up that more closely mimics the sport specific and position specific demands of the athlete.
2. Plyometrics – Integrating a proper jump landing and power training regimen is critical to preventing ACL injuries. Begin with simple in place jumps using both feet and then progress to linear jumps. As the athlete demonstrates good form with these drills, you may add in lateral hopping and then eventually rotational jumps as well. I like to include at least one vertical, horizontal and lateral jumping drill in each session. Always count foot contacts as you go or have a system for monitoring both volume and intensity to ensure safety and proper progression.
Once the athlete has mastered the jumps, consider adding in single leg hopping drills. Using a single leg hop and stick drill is a great way to teach proper single leg eccentric control. The athlete stands on the right leg and then gently hops forward and lands on the left leg, controlling the landing. Once this becomes easy, the athlete can advance to hopping from the left leg and landing on the right leg. Emphasize form over height and distance. Perform one to three sets of three to five repetitions on each side.
Single Leg Stick – Start Position
Single Leg Stick – Finish Position
Be sure to emphasize no valgus and a soft, bent knee landing with a low center of gravity. A recent study published in the Journal of Athletic Training revealed landing styles that placed the center of mass of the whole body anteriorly may be an effective way to decrease quad contraction and the knee extensor moment, while increasing hamstring and plantar flexor contraction. This, in plain terms, means less strain on the ACL.
3. Strengthening – The strength program should include multiple hamstring exercises to balance the often over dominant quadriceps and reduce ACL load. Such exercises include single leg bridges and curls with a stability ball, Nordic hamstring (assisted), stiff legged dead lifts (single and double leg) and even prone hamstring curls for pure strength development. Dynamic reaching and closed chain exercises such as multi-directional lunging, box step-downs and step-ups and single leg squatting are effective ways to improve strength and neuromuscular control. It is also advisable to include single leg calf raises on a box to improve closed chain dorsiflexion and increase plantar flexion/inversion strength to help reduce the effects of pronation.
The other critical piece is working the gluteus medius muscle. To reduce ACL strain, we must reduce frontal plane excursion. The gluteus medius provides pelvic stability and resists the femoral rotation that leads to valgus loading. Be sure to include lateral reaching progressions, resisted band work (closed chain) and even monster walks to recruit the gluteus medius and improve hip control. A 2000 study published in the Journal of the American Academy of Orthopedic Surgeons reported that females exhibit a shorter duration of gluteus medius activation in stance phase during cutting maneuvers, so remember to work the gluteus medius.
Lateral Band Walk
4. Athletic Movement Drills –These drills should teach young athletes how to execute safe, effective motor patterns. The main idea is to provide a feed forward mechanism for the brain to handle harmful potential loading that occurs at high speeds in sport.
Drills should follow these parameters:
- Focus on deceleration
- Stress low, bent knee cutting
- Discourage lazy banana cuts/runs
- Cue butt down and athletic position
- Employ repetition, technique and specificity
- Work sport specific energy systems
Sample athletic movement drills involve a similar progression as the plyometric program moving from linear to lateral and then to rotational patterns. Begin with larger intervals or distances between cones to allow for easier deceleration and change of direction and then gradually decrease the distance between cones to increase difficulty and heighten demand on the central nervous system. Be careful not to overwhelm an athlete with too much complexity. It is far better to do a few drills perfectly rather than get fancy and lose form and technique along the way. Be sure to demonstrate exactly what the drill should look like and then provide appropriate physical, verbal and visual feedback and cues throughout to ensure proper motor learning.
5. Balance Training – Teaching young athletes how to control their own bodyweight may be one of the best things we can do as fitness professionals. Beyond simply standing on one leg, we need to train them to control momentum, rotation and perturbation that may lead to harmful stress loading. Again, a progressive loading approach moves sequentially from the frontal to sagittal plane and then to the transverse plane with these types of exercises. Examples include:
Lateral Lower Extremity Reach
Cross-over Reach to Left
Cross-over Reach to Right
- Forward reaches (using lower and upper body)
- Lateral reaches (using lower and upper body)
- Rotational reaches (using lower and upper body)
Personally, I like to perform these exercises at the end of my sessions to challenge the athletes when they are fatigued. However, if you have a client with substantial balance deficiencies, consider implementing this training earlier on as it may need to be a bigger emphasis in your program and require a higher level of contribution from the central nervous system. Use time or repetitions to measure progression with balance training, and cease or correct the drill once form begins to suffer.
The research has indicated that ACL prevention programs do in fact lower injury risk. However, there are many questions yet to be answered. Why do these programs work? How much time is required for effective adaptation to take place? Is the effect of training transient? When do we implement such programs for maximal benefit, and how do we tailor them accordingly?
The exciting part is we can positively contribute to reducing these injuries together. Understanding the research, accurately assessing athletes and implementing a program with the components described in this article will allow you to make an immediate impact with your training. Counsel your athletes to perform off season and preseason prevention drills two to three times per week and continue no less than once per week, in season.
Continued participation by the athlete will help to ensure improved motor learning and more consistent performance using pre-programmed motor patterns. While we cannot prevent every ACL injury, using the proper training approach will in fact save many athletes from a season or career ending injury.
- Griffin LY, Agel J, Albohm MJ et al. Noncontact Anterior Cruciate Ligament Injuries: Risk Factors and Prevention Strategies. J. Am. Acad. Ortho. Surg. May/June 2000; 8: 141-150.
- Hewett TE, Lindenfeld TN, Riccobene JV et al. The Effect of Neuromuscular Training on the Incidence of Knee Injury in Female Athletes. Am J Sports Med. November 1999 27:699-706
- Hewett TE, Stroupe AL, Nance TA et al. Plyometric Training in Female Athletes. Am J Sports Med. 1996;24(6):765-773.
- Powell JW and Barber-Foss KD. Sex-Related Injury Patterns Among Selected High School Sports. Am J Sports Med. May 2000;28:385-391
- Sigward SM, Ota S, and Powers CM. Predictors of Frontal Plane Knee excursion During a Drop Land in Young Female Soccer Players. J Orthop Sports Phys Ther. November 2008;38(11):661-667.
- Schultz SJ, Nguyen A-D, and Levine BJ. The Relationship Between Lower Extremity Alignment and Anterior Knee Joint Laxity. J Sports Health Jan/Feb 2009;1(1):54-59.
- Schultz SJ, Schmitz RJ, and Nguyen A-D. Research Retreat IV: ACL Injuries-The Gender Bias, April 3-5, 2008, Greensboro, NC. J Athl Train. 2008;43(5):530-537.
- Shimokochi Y, Lee SY, Schultz SJ et al. The Relationships Among Sagittal-Plane Lower Extremity Moments: Implications for Landing Strategy in Anterior Cruciate Ligament Injury Prevention. J Athl Train. 2009;44(1):33-38.