Research has shown that athletic women’s muscle recruitment patterns differ from men’s and that they have different muscle imbalances than men. Both of these factors can lead to an increased risk of injury, especially to the knee, and specifically to the anterior cruciate ligament, or ACL.
What do these women have in common: a 40-year-old runner, a 20-year-old collegiate volleyball player and a 16-year-old soccer player?
They are all female athletes, and as such, they are predisposed to certain injury patterns and anatomical weaknesses. Because of these predispositions, female athletes have different training needs than their male counterparts.
Research has shown that athletic women’s muscle recruitment patterns differ from men’s and that they have different muscle imbalances than men. Both of these factors can lead to an increased risk of injury, especially to the knee, and specifically to the anterior cruciate ligament, or ACL, an important stabilizing ligament in the knee.
It has also been found that 20 to 30 percent of women have one leg that is weaker than the other, which can increase injury risk by 2.6 times the normal rate. Therefore, specific training strategies need to be aimed at improving these weak/poorly functioning muscles.
There are four main issues that affect a woman’s athletic performance: excessive flexibility; decreased hamstring (back of the thigh) strength and recruitment time; decreased strength of the hip abductors and external rotators (the muscles that move your leg out the side and rotate your hip outward); and sub-optimal jump landing position.
Everyone wants to be flexible, but female athletes are often too flexible. This can reduce stability of the joints around the stretched muscle. Consider the hamstrings. You may often hear, “My hamstrings are so tight, I really need to stretch them.” Many people tend to overestimate the need for increased hamstring length and, therefore, stretch too much. In fact, excessive flexibility in this area in females is common.
Now, consider how overstretching of the hamstrings is encouraged in the setting of yoga, for example. Often, it is suggested to pull the thigh close towards the chest, far surpassing the “normal” flexibility mark. This causes excessive slack in the muscle and may make it harder for the hamstrings to react and activate quickly as in necessary in athletic activities. If excessive flexibility is an issue, the female athlete needs to focus on increased strength and stability to protect and support the surrounding joints.
Hamstring activation time and strength is another area of concern. Studies have shown that, unlike males, females do not significantly increase their hamstring strength after age 11. There is also a delay in recruitment and activation of the hamstring muscle in female athletes versus males, which is thought to be a main source of heightened ACL injury risk.
Because of this inherent timing delay and hamstring weakness, women tend to overuse their quadriceps muscles (front of the thighs) to compensate. Thus, there is over-recruitment of the quadriceps and under-recruitment of the hamstrings, even if they are strong, resulting in a muscle imbalance. This imbalance, combined with decreased hip and core strength in females, can significantly alter the body mechanics and alignment during sports activities, increasing injury risk.
Hip abductor (side of hip) and hip external rotator strength deficits are also common in female athletes. In fact, studies have shown that females begin to exhibit decreased functional hip abductor strength at the beginning of adolescence. This weakness can have a negative impact on landing mechanics, which is thought to be a major contributor to ACL injury in women.
These altered mechanics lead to changes in the position of the hip, knee and ankle upon landing from a jump. Simply stated, the leg and knee rotate inward, when they should remain well aligned over the foot and ankle. It has been found that after puberty, girls’ landing mechanics change to a stiffer, straighter-leg landing, with this increased inward angle at the knee, whereas boys’ landing style does not change.
Studies have indicated the same poor landing alignment in female runners. Not only can this poor functional alignment lead to increased ACL tears, but it can contribute to other orthopedic complaints, such as plantar fasciitis, shin splints and hip pain, due to the abnormal stresses that it places on the lower extremity.
The statistics regarding female athletes and ACL injury risk are startling. One study looked at the injury rate in over 30,000 high school and 13,000 collegiate female athletes and compared them with male athletes.
The ACL tear risk in high school girls was 1 per 100, while the collegiate rate was 1 per 10. High school female soccer players had six times greater risk than males, while collegiate female soccer players had a three times greater risk than males, and basketball players an eight times greater risk than males.
It is important to note that 70 percent to 80 percent of ACL injuries are non-contact and, instead, occur during deceleration, lateral pivoting and jump landings, where alignment, muscle recruitment and timing are important.
What can be done to decrease the risk of these injuries? Generally, successful ACL injury prevention programs include training in balance, lower extremity and core strengthening, plyometrics and sport-specific agility exercises performed two to three times per week.
Targeting hip abductor and external rotator strength specifically in functional positions is important. This means limiting machine use, which tends to promote non-functional, single-plane motion. Training in functional, sport-specific positions and multiple planes of motion is important to promote proper muscle response during athletic activities.
This training can increase performance and decrease injury risk by correcting typical muscle imbalances and biomechanical deficits commonly seen in the female athlete.
Nicole Tomasino is a physical therapist at the Spaulding Outpatient Center Framingham, Mass., and received her doctor of physical therapy degree from the Massachusetts General Hospital Institute of Health Professions. She has a special interest in the evaluation and treatment of female athletes.