Myer GD, Hewett TE et al. The Relationship of Hamstrings and Quadriceps Strength to Anterior Cruciate Ligament Injury in Female Athletes. Clinical Journal of Sports Medicine. Vol. 19, No. 1, 2009; 3-8.
Female athletes participating in sports that carry higher risk for ACL tear (eg. Basketball, volleyball, soccer) have a 4-6 fold higher rate of ACL injury than their male counterparts. Much research has been attempted trying to determine the reasons for the difference in injury rates among the sexes. One of the group of possible causes that has shown the most promise in this area are specific muscle weakness patterns in the hips and thigh. Good muscle control is essential to protect the leg during activities involving jumping, pivoting and landings. Hip weakness can result in a lack of proper control of the femur during landings, allowing the knee to drop into a position that excessively tensions the ACL, putting it at risk for rupture. Women also tend to come down from landings more straight-legged than men. When this is combined with a forceful contraction of the quadriceps, the shin bone (or tibia) is pulled sharply forward. If the hamstrings (which provide a counterforce to the tibia) fail to prevent this forward movement, and if the ACL is excessively tightened for the reasons outlined above, the ligament can tear. For this reason, investigators have looked at the ratio of hamstring strength to quadricep strength as a possible predictor of the risk of ACL tear (Low hamstring strength and higher quadriceps strength equals a low Ham-to-Quad ratio [H:Q] and correlates to a higher risk for tears), and when the uninjured legs of females who have suffered an ACL tear are evaluated, generally these athletes have lower H:Q than uninjured peers. Male athletes as a group have a higher H:Q ratio than their female peers.
This study followed athletes prospectively, meaning that the strength measurements were taken before injury occurred in approximately 1700 athletes, who were then followed for up to two years. Athletes who sustained an ACL injury during this time were then compared with four selected uninjured (previously screened) athletes (the control group) who were otherwise similar with respect to sport, developmental stage, height and weight. The strength of this study is the control group, since the uninjured controls are more closely matched to injured athletes than in previous studies. This increases the likelihood that any differences observed in leg strength are meaningful.
The findings of this study showed that female athletes who went on to tear their ACL had significantly lower hamstring strength at baseline than athletes who did not injure their ACL when both groups were compared to male peers. Quadricep strength did not differ between the two groups. Thus, the decrease in hamstring to quadricep strength ratio came from weak hamstrings, not over-strong quadriceps.
We also know from prior research that while male athletes tend to increase hamstring strength past puberty, female athletes tend to remain plateaued. This results in a lower H:Q in females with sports activities as they move past puberty, indicating an increased risk starting around 12 to 13 years of age. Thus, strengthening programs aimed at increasing hamstring strength in females should be targeted to females just entering their teens or older.
There are simple ways to increase hamstring strength in young athletes. One of the most effective is an exercise developed by the Norwegian National Soccer Team’s strength and conditioning coaches, known as “Nordic Hamstrings.” This exercise has been shown to significantly decrease the risk for hamstring injury in-season, and has also been shown to result in better hamstring strength gains than traditional hamstring curls in the gym. Go to the following URL (http://stadiasportsmedicine.com/info/2017/hamstring-injury-prevention-nordic-hamstrings/#.WimzUUqnHIU) to access a free copy of the Nordic Hamstring Strength protocol or links to Tim Hewett’s ACL risk reduction program (http://www.usatoday.com/sports/gallery/acl/flash.htm). If you would like to discuss screening for ACL injury risk or have specific questions about injury risk reduction, contact Stadia Sports Medicine at (515)221-1102. We’re happy to help!