Timing of lower extremity frontal plane motion differs between female and male athletes during a landing task.
Joseph MF, Rahl M, Sheehan J, Macdougall B, Horn E, Denegar CR, Trojian TH, Anderson JM, Kraemer WJ. Am J Sports Med. 2011 Jul;39(7):1517-21.
It is well documented that female athletes are at greater risk for anterior cruciate ligament (ACL) injuries than male athletes. One potential risk factor for ACL injuries, that is more common among females, is increased dynamic knee valgus, defined as increased hip adduction, hip internal rotation, tibial abduction, and foot eversion. Preventative and rehabilitative programs try to minimize the amount of dynamic knee valgus during landing. However, there is a lack of research describing the timing of dynamic knee valgus between male and female athletes during a landing task. Joseph et al decided to look at the timing component and hypothesized that there would be gender differences with timing of peak dynamic knee valgus. The study included 10 NCAA female athletes and 10 highly-competitive male athletes, who trained 20 hours per week with a female basketball team. The study was performed during the off-season and participants were free of lower extremity injury. The drop-jump test protocol described by Hewett et al was utilized. Each participant was asked to drop off a 31-cm box, land onto two force platforms, and perform a maximum vertical jump. The force plate identified the stance phase, which was the time from initial contact with the ground until their feet left the ground during the jump. Maximun kinematic values (hip adduction, knee flexion, knee valgus, and ankle eversion) were calculated and each participant performed 3 jumps with 30 seconds rest between jumps. Results displayed that maximum hip adduction, knee valgus, and ankle eversion occurred earlier in women than men. Maximum hip adduction and knee valgus occurred before maximum knee flexion in females; while the females were still decelerating from their landing and before initiating their vertical jump. In contrast, maximum hip adduction and knee valgus in males occurred after maximum knee flexion (while they were performing the vertical jump). Furthermore, angular velocity of knee valgus for females was almost twice the rate of males.
This study is interesting because it indicates that men and women use different strategies and that females collapse rapidly into dynamic knee valgus compared to males. Females not only collapse into valgus earlier, but also during the deceleration part of the drop-jump landing. As noted by the authors this study was limited because the males were not NCAA-level athletes. This data suggests that comparing male and female athletes from similar competitive levels may be helpful to confirm the results. While this study highlights the differences between males and females it is also important to keep in mind that some males experience noncontact ACL injuries and some females may never have an ACL injury. It is therefore important that we consider biomechanical risk factors in all of our athletes, not just the females. This study introduced a biomechanical risk factor that I found very interesting: the timing of the maximum dynamic knee valgus occurred during the deceleration phase (landing phase) among females and the acceleration phase (jumping phase) among males. While many of us know that females demonstrate more knee valgus, the timing component differences and two-fold increase of knee valgus velocity further supports the use of specialized training for female athletes. Specialization may include squat/jump (neuromuscular) training, as well as focus on muscular skeletal imbalances (e.g., quadriceps:hamstring ratio), hip/core strength, and heelcord flexibility. It will be interesting to see if injury prevention programs can delay the onset of dynamic knee valgus during landing.
Written by: Thomas Martin
Reviewed by: Jeffrey Driban