Women and ACL Injuries

Every year, an increasing number of women are participating at sports and doing so at a younger age. Unfortunately, there has been a corresponding increase in the number of anterior cruciate ligament (ACL) injuries. Studies have demonstrated that women have four to ten times more ACL injuries than males.

The main purpose of the ACL is to prevent the tibia from moving too far forward and rotating inward under the femur.
There are numerous factors that contribute collectively to the increased risk in ACL injuries: bio-mechanical differences, ligament laxity due to hormonal fluctuations, and improper strength and conditioning. We'll review the bio-mechanical differences and strength and conditioning aspect of ACL injuries.

Q Angle
One of the most important bio-mechanical differences is that women have a wider pelvis than men, due to women needing additional space for child bearing. The angle at which the femur and tibia meet is known as the Q angle. This increased angle not only concentrates greater stress on the knee, but also exerts an outward pull on the patella. Of the four quadriceps muscles, only one, the vastus medialus oblique (VMO), pulls on the patella medially. To negate the effects of women's greater Q angle, exercises which strengthen the VMO, must be performed.

Strength and Conditioning
Just as reading medical textbooks doesn't automatically make you a doctor, performing a strength and conditioning program doesn't assure you of improved performance and reduced risk of injury. To maximize performance and reduce risk, the exercises which make up a strengthening program must be executed perfectly. Simply going through an exercise without regard to proper form is at best, worthless, and at worst, creates injuries.
One of the best exercises increasing lower body strength, is the squat. However, 93% of people fail to perform the exercise correctly.

Performing a squat with a shortened range of motion actually increases the risk of ACL injuries, as performing the upper part of a squat only strengthens the muscles which exert a lateral pull on the patella. This has the same effect as if you were to magically widen the hips, causing an increase in the Q angle.

A properly executed squat dips down below parallel, until the hamstrings and calf muscles make contact. Only a squat which dips below parallel recruits the VMO, strengthening it and thereby reducing the lateral pull exerted by a female's wider hips. Performing a proper squat is simple, but not always easy. It's even harder to teach properly, which is why the majority of trainers allow their clients to perform squats incorrectly. Which basically means you're paying someone to give you an injury. If you train alone, make sure you perform a full squat, as it's the only way you'll derive any benefit.

The VMO
The VMO is one of the most underrated muscles, which is unfortunate due to it's ability to increase sprinting speed, vertical jump, and decrease the risk of all knee injuries. Focusing on the VMO is best done in the early off season.

The split squat performed on a wobble board is one of the best exercises for developing and strengthening the VMO. The instability provided by the wobble board heavily recruits the VMO, as it is a knee stabilizer. The key to this exercise is performing it with a full range of motion, the further you descend, the great the VMO is recruited.

Aerobic Activity
Aerobic activity is becoming increasing popular with athletes, believing it's the most efficient means for improving cardiovascular performance. Unfortunately, this is not only false, but it actually increase the risk of ACL injuries.
Whether decelerating from a full sprint, quickly changing direction, or landing from a jump, high levels of forces must be absorbed, neutralized and re-directed by the body. In some instances, our body absorbs up to up six times our body weight. For optimum performance and reduced risk of injury, this requires a high level of strength. Performing long duration aerobic activity will cause you to lose strength and muscle mass, as it will cause a muscle fiber shift away from high force to low force endurance.
Numerous types of muscle fibers exists, forming a continuum of fiber types ranging from slowest to fastest. The slowest fibers have the greatest endurance, but lowest growth and strength potential. The fastest fibers, have the least endurance capabilities, but the highest strength and growth potential. Marathon runners possess a high number of endurance fiber and have a physique that doesn't exactly appear healthy. Sprinters possess a high number of the faster, more powerful muscle fibers, and possess a muscular physique.
It's been shown that as little as eight weeks of endurance training will cause the faster muscle fibers to behave like the slower, weaker muscle fibers. Here are some studies to back up me up:

Kraemer WJ, Patton JF, Gordon, et al. Compatibility of high-intensity strength and endurance training on hormonal and skeletal muscle adaptations. J Appl Physiol 1995; 78(3): 976-89

Liu Y, Lormes W, Reissnecker S, and Steinbacker JM. Effects of high-intensity and low-intensity endurance training on myosin heavy chain isoform expression in highly trained rowers. Int J Sports Med 2003; May:24(4); 264-70

Thayer, Collins, Noble, Taylor. A decade of aerobic endurance training: histological evidence for fibre type transformation. J Sports Med Phys Fitness 2000; Dec:40(4); 284-9

Cliff note version: aerobic activity causes the stronger, powerful muscle fibers to atrophy and behave like the slower, weaker muscle fibers. This has vital implications, because when your daughter's body tries to decelerate and change direction on the field, or land from a jump, the slower and weaker muscle fibers will be absorbing those forces. Since these muscle fibers are slower to engage, the ligaments and tendons will take on these forces until the the fibers respond. But whether the muscle fibers are sufficiently strong enough to tolerate those forces is a different matter.

Alternative to Aerobic Activity

If someone still feels they need to improve their aerobic capacity, then I prescribe the Tabata Protocol. It ensures they improve BOTH their anaerobic and aerobic capacities simultaneously, without losing strength. The Tabata protocol was developed for Japanese speed skaters and is extremely challenging.

Tabata et al. Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2 max. Med Sci Sports Exer. 1992 Oct;28(10): 1327-30

As you now know, it's becoming clear that some of the increases in ACL injuries in both males and females is created by faulty strength and conditioning programs. Put these recommendations to use and you'll not only minimize your risk of ACL injuries, but you'll greatly improve your athletic performance as well.

By the way, I'll post the exact Tabata Protocol within the next few days.

Thanks to Mystic Muscle for allowing us to use their facility.