“Non-contact ACL injury rate is 2-10 times higher in female athletes than male athletes”

 Female athletes need to alter their strength and conditioning programs from men for a variety of reasons.  Gender alone predisposes female athletes to musculoskeletal injuries and medical conditions unique to their sex.  It is important for female athletes to understand these conditions and take the necessary steps to try to prevent such occurrences which could greatly impact an athlete’s performance or career. 

The main reason for gender specific strength and conditioning programs is due to the high incidence of anterior cruciate ligament (ACL) knee injuries that are occurring among female athletes.  ACL injury rates are on the rise in the female population.  We are seeing this injury more and more in younger athletes as the years pass.  In some sports women are two to four times more susceptible to injuries of the (ACL) when compared to male athletes.  The National Collegiate Athletic Association (NCAA) gathered statistics over a three-year period in the early 1990’s comparing incidents of injuries of men to women. The NCAA study showed that women suffered ACL injuries four times more often in basketball; three times more often in gymnastics; and two times more often in soccer (1).  Research has shown that the majority of these injuries are non-contact injuries and they often occur while planting and cutting, straight-knee landing, and one-step stop landing with the knee hyper-extended.  Pivoting and sudden deceleration are also common mechanisms of non-contact ACL injury.  At-risk positions during these maneuvers include knee extension, flat foot, and off-balance body position.

A growing body of research suggests anatomic, hormonal, neuromuscular and environmental factors may predispose female athletes to ACL injuries.  Specific factors may include estrogen levels, the shape of the intercondylar notch in the knee, playing style, and neuromuscular control of the quadriceps and hamstring muscles.  The enormous financial burden and emotional toll this type of injury places on the athlete and the families is cause for continuing research in developing prevention strategies.  We are seeing promising results with prevention programs that involve proprioception, plyometrics, strength training, and improved jumping, stopping, and turning techniques (6).

Anatomic

Some studies suggest that women have a narrower femoral notch in the knee joint.  This notch is the space at the bottom of the femur through which the ACL runs.  Instead of a reverse U-shaped notch, women may have a narrow A-shaped notch which may create shearing forces against the bone.  Some experts feel that this tight fit may predispose women to ACL tears.  One other anatomic consideration is the increased Q-angle present in female athletes.  The Q-angle is defined as the angle between a line joining the superior anterior iliac spine and the centre of the patella and the projection of a line from the tibial tuberosity through the centre of the patella.  Anatomically women are wider in the pelvic area which increases the Q-angle and causes the hips to move more during exercise.  The normal angle in males is 13 degrees and 18 degrees in females.  This increased angle causes greater stress on the knee joint between the femur and the tibia due to the torsion applied between the two leg bones.  It also causes the quadriceps to pull on the patella which will encourage it to displace.  Pronated and flattened feet can be a by-product of an increased Q-angle.  Recent studies have shown that custom-made, flexible orthotics will reduce pronation, put less stress on the knee, and improve the Q-angle.  To see an illustration of the Q-Angle, see article “What is the Q-Angle.”  Other anatomical factors that may contribute to ACL injury are ACL size, lower-leg malalignment, abnormal extensor mechanism anatomy, knee joint laxity, and muscle flexibility.

There are other anatomical traits that set women apart from men and may predispose unconditioned women to more injuries.  A woman’s legs are longer and her torso shorter than a comparably sized man, and she has a lower center of gravity, less muscle mass and less dense bones.  I am not insinuating that these traits make women more fragile, weak or malformed.   In fact, I take the opposite view.  Many of our unique traits as females help us in a positive way in our athletic endeavors.  For example, having a higher body fat percentage is seen as an advantage to a female marathoner and a lower center of gravity is advantageous in sports that require a lot of balance, agility and coordination. We just can’t lose sight of the fact that we are different, these differences are good and they make us unique in many ways, but require us to train differently from our male counterparts.  Both male and female athletes have their strengths and weaknesses in their anatomical makeup.  The good news is many anatomical differences can be irrelevant when female athletes take on a different training regime. 

Hormonal

One hypothesis is that at midcycle, (the ovulatory phase) days 10-14 in a woman’s menstrual period, there is an increase in estrogen which can cause laxity in the connective tissue in and around the knee joint. This hormone has receptors on the human ACL and it reduces the collagen synthesis and fibroblast proliferation; thus diminishing the tensile strength of the ACL (7).  Although extrogen and progesterone receptors are found in the ACL, there is insufficient evidence to support any claims that there is an increased risk at any time in the menstrual cycle.  I don’t view the menstrual cycle as a detriment to a female athlete’s ability to excel and reach the highest levels of play in her chosen sport.

The Hunt Valley Consensus Conference on Prevention of Non-contact ACL injuries held in June 1999 consisted of twenty-two orthopedists, family physicians, and athletic trainers.  They agreed on the following statements in regards to hormonal risk factors for female athletes:

1. At the present, there is no consensus in the scientific community that sex-specific hormones play a role in the increased incidence of ACL injury, but further research in this area is encouraged.


2. Hormonal intervention for ACL injury prevention cannot be justified.


3. There is no evidence to recommend modification of activity or restriction from sport for females at any time during the menstrual cycle (Griffin et al, 2000: 7).

Participants also laid out several points regarding prevention strategies:

1. Early data show that specific training programs that enhance body control reduce ACL injury in female athletes and may increase athletic performance.


2. Training and conditioning programs for male and female athletes in the same sport may need to be different (Griffin et al, 2000: 7)

(Source: Croissant, J., and Schmit, E.  Misplaced Focus: Assumptions about Sex Hormones and ACL Injury in Female Athletes. Journal of Interdisciplinary Feminist Thought. 2007, Women and Science. Vol.2, Issue 1, Article 2. Retrieved from: http://escholar.salve.edu/jift.)

Estrogen has been reported to decrease fine motor skills by acting on the central and peripheral nervous systems (8).  Motor skill deficits may diminish the normal neuromuscular protective mechanisms of the knee.  I must point out here that girls and women may have motor skill deficits due to lack of coaching and not getting the proper strength training and conditioning at younger ages in comparison to boys. 

In general women are more flexible than men.  Above average hamstring flexibility may predispose women to ACL problems.  With increased laxity in the hamstrings, the muscle group may lose its protective ability to handle the forces required to stabilize the knee.  Thus, the forces are transferred to the knee ligaments.  

Neuromuscular

Most of the research is centering on neuromuscular performance; the interplay between the neurologic system and the muscles that cross the knee joint (quadriceps and hamstrings).  There is evidence that neuromuscular training not only decreases ACL injury risk, but also that it alters biomechanical risk factors for ACL injury and improves measures of performance in female athletes (15).  Effective neuromuscular training protocols have used plyometric power, biomechanics and technique, strength, balance, and core stability training to induce neuromuscular changes and injury prevention effects in female athletes.  However it is not known which of these components are most effective and efficient or whether the effects of the separate components are cumulative.

It is possible that in non-contact ACL injury expected motor recruitment patterns that control the knee are altered, which leads to injury.  This deviation may result in a faulty or delayed neurologic signal to the knee instead of a protective muscle response.  The balance of muscle power and recruitment pattern between the quadriceps and the hamstring muscles is crucial to functional knee stability (4).  Some investigators have reported that quadriceps contraction increases ACL strain between 10 degrees and 30 degrees of knee flexion even though most non-contact ACL injuries occur with the knee close to full extension.  It is possible that the quadriceps, the antagonists, play an important role in ACL disruption.

The hamstrings, on the other hand, are the agonist or “stress shielders.”  Any weakness, increased flexibility or delayed motor signal to the hamstrings may increase the susceptibility to ACL injury.  A woman’s hamstrings should be 60%-70% as strong as the quadriceps.  In most female athletes the ratio is 49%-55%.  This imbalance needs to be addressed in a strength training program. 

One study by Huston and Wojtys evaluated neuromuscular response to anterior tibial translation in male and female athletes. They found that female athletes demonstrated more anterior tibial laxity and significantly less muscle strength and endurance.  In addition, the female athletes relied more on their quadriceps muscles and took significantly longer to generate maximum hamstring muscle torque after anterior tibial force was applied (9).  This overpowering of the quadriceps over the hamstrings may predispose an athlete to non-contact ACL injury.

It is important to say that historically boys and men have been trained at younger ages in activities that have increased their strength, agility, coordination and proprioception.  When boys started sports at a young age, they were also encouraged to strength train and condition along with their skills training to enhance their sport performance and help prevent injuries.  Boys programs have also traditionally gotten the better coaches, which in turn leads to better conditioning and training strategies.  This hasn’t been the case with girls entering sports, then and now.  Girls and women have been at a disadvantage with quality coaching and quality conditioning.   They start sports later in youth and start strength training even later than that.  There needs to be more of a push from parents and coaches to strength train when they start sports.   Strength training has been viewed to be too masculine and not fit for a female.  These disparities and attitudes still exist today in some sports and in some parts of the country.  This is unfortunate for the female athlete.  We, as educators and conditioning specialists need to continually work to change these myths and negative attitudes about girls/women and strength training.

I have to say I was there and could see first hand what was happening back then, before Title IX and shortly thereafter.  In 1970, I was 9 years old and playing sports in the Catholic school leagues.  I was a true athlete and most sports just came naturally for me.  By junior high I was playing 2 sports and summer softball and soccer, and in 1976, when I entered high school I was beginning to excel in 3 sports along with extensive travel with my softball team.  I never remember any coach stressing the need to strength train.  I don’t ever remember going into my high school weight room.  But I did weight train, at a time when it was not cool and really not accepted.  I just saw all the other boys in my neighborhood doing it for their sports so I thought, “Why can’t I.”  So in my neighbor’s basement I lifted weights and loved it.  I did know one thing; weight training would make me strong and better at my sport and I wanted to hit home runs in softball.   My brothers and the neighbor boys taught me how to strength train, not my coaches.  I am proud to say that I have never had a serious injury in high school or college that sidelined me for any length of time.  I had a sprained ankle in high school once and some tendon swelling in my knees periodically in college when I played Division I volleyball and softball.  I retired from major women’s softball at the age of 30, having put in 15 years, summer after summer on the ball diamond.  I had a shoulder injury once that forced me to miss a few games one summer, interestingly enough the injury was sustained in one of my weight training sessions.  I know first hand the benefits of strength training, creating muscle balance and flexibility; I have lived it and felt it.  I attribute my lack of injuries and sport success to strength and flexibility training as a young girl.  To this day, I still strength train, stretch, play sports and enjoy many outdoor activities.

The lack of coaching, strength training and conditioning has put girls and women at a higher risk for injury.  In the competitive sports world today, it is critical for girls to start early on a proper training program to prevent ACL injuries, enhance strength, power, flexibility and overall proprioceptive function.

Environmental

There are other extrinsic factors that may play a role in ACL injuries, besides the factors such as coaching, training and conditioning.  Gender variations in athletic posture and movement patterns have been studied as possible culprits.  Environmental conditions such as improper shoe wear, uneven playing surfaces and weather conditions, (wet, sloppy surfaces) may also contribute to ACL injuries.   For example, a higher rate of ACL injuries has been reported in athletes who wear cleats that are placed at the peripheral margin of the sole with a number of smaller pointed cleats positioned interiorly.  This cleat arrangement resulted in a higher torsional resistance than the other cleat designs (10). Uneven playing surfaces, such as bumpy grass playing fields or holes or rocks on a grassy surface may stress the knee joint and contribute to ACL tears.  Many athletes at the time of their ACL injury have reported landing or stepping on an uneven surface. 

An athlete’s playing style may have a genetic component that is dependent on environmental parameters such as coaching and training techniques.  Women tend to play sports in a more erect position (11).  A more upright position amplifies ground reaction forces that increase the load transmitted to the knee and maximizes anterior shear forces from the quadriceps, an ACL antagonist.

One cannot write an article about ACL injuries without mentioning the work of Timothy Hewett, Ph.D., the founder of Sportsmetrics, a training program that focuses on the development of factors such as speed, strength, agility, and the practice of complex movements, for the prevention of ACL injuries in female athletes.  Dr. Hewett is the Director of Applied Research at the Cincinnati Sportsmedicine Research and Education Foundation.  He has done extensive research and has conducted numerous studies on female athletes.  His three-part program has become the most prominent training program to prevent ACL injuries in female athletes.  The program consists of stretching, plyometrics and strength training drills.  The program addresses potential deficits in  neuromuscular strength, coordination of the stabilizing muscles about the knee joint, and teaches proper landing technique from a jump.   To get more in depth information about Sportsmetrics, you can visit their web site at www.sportsmetrics.net.

More research still needs to be conducted with female athletes in all of these areas before more definitive conclusions are drawn.  As we further understand the causes of ACL injuries we can better implement prevention strategies.  In my opinion, female athletes may need to start gender specific strength and conditioning programs earlier in their careers (before the height of the growth spurt, typically between eleven and thirteen years of age) to prevent injury and prepare for rigorous skills sport training and competition.  Children as young as six can improve strength when following age-specific resistance training guidelines (12).  Evidence also suggests that a pre-season strength training program can reduce sports-related injuries in adolescents (13,14).  So, coaches and parents please rest assured that with adult supervision, proper equipment, and realistic expectations, strength training programs and ACL injury prevention programs designed for children and adolescents are safe and effective.  At this point in time, prevention programs that emphasize pre-season stretching, plyometrics, weight training and balance and agility training have the most merit.   

To get more in-depth information about strength training youth and ACL injuries, go to our home page and click on the appropriate heading.

REFERENCES:

1. Arendt, E. MD., & Dick, R. MS. Knee injury patterns among men and women in collegiate basketball and soccer. American Journal of Sports Medicine. 1995; Vol. 23(E).


2. Austin, W.M. DC, CCSP, CCRD. Women in Sports, Q-Angle, and ACL Injuries.  Dynamic Chiropractic. Oct. 2003; Vol. 21(21). Retrieved on June 16, 2006 from http://www.chiroweb.com/archive/21/21/02.html.


3. Female Athlete Issues for the Team Physician: A Consensus Statement.  Medicine and Science in Sports and Exercise: Oct. 2003; Vol. 35(10): pp1785-1793.


4. Boden, B.P., Garrett, W.E., Griffin, L.Y. Etiology and Prevention of Noncontact ACL Injury. The Physician and Sportsmedicine. Apr. 2000; Vol. 28(4).


5. Lamb, M.M., Moeller, J.L. Anterior Cruciate Ligament Injuries in Female Athletes: Why Are Women More Susceptible? The Physician and Sportsmedicine. Apr. 1997; Vol. 25(4).


6. Schnirring, L. Training Programs May Lower Women’s ACL Injury Risk. The Physician and Sportsmedicine. Oct. 1999; Vol. 27(10).


7. Liu SH, Al-Shaikh RA, Panossian V, et al: Estrogen affects the cellular metabolism of the anterior cruciate ligament: a potential explanation for female athletic injury. Am J Sports Med 1997; 25(5):704-709.


8. Posthuma BW, Bass MJ, Bull SB, et al: Detecting changes in functional ability in women with premenstrual syndrome. Am J Obstet Gynecol 1987; 156(2):275-278.


9. Huston LJ, Wojtys EM: Neuromuscular performance characteristics in elite female athletes. Am J Sports Med 1996; 24(4):427-436.


10. Lambson RB, Barnhill BS, Higgins RW: Football cleat design and its effect on anterior cruciate ligament injuries: a three-year prospective study. Am J Sports Med 1996; 24(2):155-159.


11. Boden BP, Dean GS, Feagin JA, et al:  Mechanisms of ACL injury.  Orthopedics, in press.


12. Falk B, Mor G: The effects of resistance and martial arts training in 6- to 8-yer-old boys. Pediatr Exerc Sci 1996; 8(1):48-56.


13.  Heidt RS Jr, Sweeterman LM, Carlonas RL, et al: Avoidance of soccer injuries in preseason conditioning. Am J Sports Med 2000; 28(5):659-662.


14. Current comment from the American College of Sports Medicine: August 1993-‘The prevention of sports injuries of children and adolescents.’ Med Sci Sports Exerc 1999; 25(8suppl):1-7.


15. Myer GD, Ford KR, Brent JL, Hewett TE: The effects of plyometric Vs. dynamic stabilization and balance training on power, balance, and landing force in female athletes. Journal of Strength and Conditioning Research, 2006; 20(2):345-353.


16. Griffin, Letha Y. et al (2000), “Noncontact Anterior Cruciate Ligament Injuries-Risk Factors and Prevention Strategies,” Journal American Academy Orthopedic Surgery. 8(3): 141-50.


17. Croissant, J., Schmit, E. Misplaced Focus: Assumptions about Sex Hormones and ACL Injury in Female Athletes. Journal of Interdisciplinary Feminist Thought. 2007, Women and Science. Vol.2, Issue 1, Article 2. Retrieved from: http://escholar.salve.edu/jift.