Hamstring extensibility and transverse plane knee control relationship in athletic women

Athletic women are at particular risk for sustaining a noncontact anterior cruciate ligament (ACL) injury. The hamstrings are vital to providing dynam ic knee motion control in the sagittal and transverse planes during running stance, and some have suggested this function is enhanced when they are le ss extensible. This study attempted to determine the correlational relation ships between hamstring extensibility and transverse plane knee kinematics and from these data to describe the dynamic transverse plane knee motion co ntrol capabilities of the hamstrings. Twenty normal athletic women (mean +/ - SD; aged 21 +/- 1.6 years; height 163.3 +/- 5.7 cm; weight 60.1 +/- 3.6 k g) were evaluated for active hamstring extensibility and transverse plane k nee kinematic relationships during crossover-cut stance phase. Following cr ossover-cut training (3 weeks) using the left (preferred) lower extremity a s the stance limb, hamstring extensibility was measured. Following this, su bjects were fitted with 9 retroreflective markers denoting the local segmen tal coordinate systems (3 markers each) of the left foot, leg and thigh. Ki nematic (3-dimensional, four phase-locked cameras, 200 Hz) knee and ankle d ata were sampled and analyzed. Descriptive statistics and Pearson correlati ons between hamstring extensibility and knee and ankle kinematic variables were calculated. Statistical significance was set at P less than or equal t o 0.05 with Bonferroni adjustments. Hamstring extensibility (12 degrees +/- 8 degrees terminal extension) revealed low but significant positive correl ations with tibial external rotation (6 degrees +/- 10.7 degrees) at heelst rike (19.3 degrees +/- 8.5 degrees knee flexion) (r = 0.62, P = 0.004) and tibial internal rotation (-13 degrees +/- 8.4 degrees) at peak knee flexion (57.8 degrees +/- 9.3 degrees) following heelstrike (r = 0.47, P = 0.01). Increased hamstring extensibility resulted in increased tibial external rot ation at heelstrike and decreased tibial internal rotation at peak knee fle xion. Increased hamstring extensibility may improve knee extensor efficienc y at heelstrike by enabling greater tibial external rotation and protect th e ACL at peak knee flexion by decreasing the tibial internal rotation magni tude.