Quantification of lower extremity dynamic capability: implications for anterior cruciate ligament injury and change of direction ability

2012-04-30Anterior cruciate ligament (ACL) tears are serious injuries that occur at a higher rate in female athletes when compared to male athletes. Despite considerable research investigating this complex sports medicine problem, the primary factor(s) that underlie the sex disparity in ACL injury remains unknown. Recent literature suggests that diminished lower extremity control may increase the risk of ACL injury in females. The primary objective of this dissertation was to develop a method designed to quantify the capability of the lower limb to dynamically interact with the ground (i.e., the lower extremity dexterity test, or LED-test), and to evaluate whether this method is reliable and informative of lower extremity function in the context of ACL injury risk and change of direction ability. In Chapter III, the LED-test is described, test-retest reliability was assessed, and the extent to which performance was associated with lower limb strength and anthropometry was examined. Test-retest reliability was excellent (ICC = 0.94) and LED-test performance was found to be independent of strength and anthropometry suggesting that the test was capable of quantifying a unique construct. The purpose of Chapter IV was to compare LED-test performance between female and male soccer athletes. Lower extremity biomechanics during a single limb drop jump also were examined. Results revealed that the female athletes exhibited reduced lower extremity dexterity as assessed by the LED-test when compared to the male athletes. Females also were found to land using a movement strategy that has been implicated as increasing the risk of ACL injury (i.e. increased limb stiffness). Our findings suggest that the movement behavior exhibited by the female athletes may represent a heightened feedforward control strategy to compensate for reduced lower extremity dexterity. The purpose of Chapter V was to determine the extent to which LED-test performance (as opposed to lower limb strength and power) was associated with change of direction ability (i.e. agility) in high school soccer athletes. Results revealed that lower extremity dexterity was highly correlated with agility in both males and females, whereas lower limb strength and power were not correlated with agility. Dexterity was the primary predictor of agility performance, explaining almost 50% of the variance in agility after controlling for sex. Overall, the findings of this dissertation indicate that the LED-test measures a unique construct reflective of dynamic lower extremity control. In addition, data from this dissertation suggest that diminished lower extremity dexterity as quantified by the LED-test may influence lower extremity movement patterns considered to place female athletes at risk for ACL injury. Moreover, the results provide evidence that the LED-test quantifies an experimental construct that reveals a dimension of dynamic function that is informative of change of direction ability. As such, impaired lower extremity dexterity may not only contribute to limb mechanics that increase lower extremity injury risk, but reduced dexterity also may impact sport performance by reducing the ability of athletes to change direction quickly