The effects of an unanticipated directional stimulus on lower extremity kinematics and ground reaction forces during a drop-landing and sublateral cut

INTRODUCTION: Female athletes' anterior cruciate ligament (ACL) injury rates are four to six times higher than male (Ford et al., 2005; Hewett et al., 1999). Investigations into non-contact ACL injuries suggest that many ruptures occur during a landing or side-cutting motion (Boden et al., 2010). The decision, about which direction to cut, may alter the biomechanical procedures of the lower extremity when performing landing or cutting motions. These alterations may potentially increase the risk of ACL injury.;PURPOSE: The purpose of this study was to determine the biomechanical effects of rapid decision making during a diagonal cut in a female athlete during a drop landing.;METHODS: Fourteen collegiate female recreational athletes (age = 21.4 +/- 1.8 yrs, height = 170 +/- 4.1 cm, mass = 64.9 +/- 5.4 kg) participated in this study. All subjects performed a drop landing (height = .5m) with an anticipated right and left directional cuts (ADC). The participants then performed trials of unanticipated directional cuts (UDC) in both directions as generated by random order. The three best trials of all conditions were collected and analyzed. Kinematic and ground reaction force (GRF) data of the dominant side were examined during cuts away from the dominant leg, and compared between ADC and UDC. Three dimensional biomechanical data were recorded with 6 high speed cameras (240 Hz) and two AMTIRTM force plates (960Hz). We compared ADC -- UDC differences scores (p <0.05) for lower-extremity joint kinematics and ground reaction forces (GRF) using one sample t-tests.;RESULTS: The results demonstrated that less maximum knee flexion angle (4.42° +/- 7.59) and knee flexion displacement (4.51° +/- 6.0) were exhibited during UDC, compared with ADC. Furthermore, at initial contact, more hip and knee adduction angles (2.34° +/- 2.84, and 1.03° +/- 1.22, respectively) were exhibited during UDC. There were no differences in GRF for any of the conditions.;CONCLUSION: Based on our data, the kinematic changes displayed during UDC may increase the vulnerability of the knee during landing. However, the examined GRF data does not show any significant difference between conditions. We see that a reactive decision making process may put the ACL at greater risk based on our kinematic results. The effects of a decision making process during a drop landing on the ACL injury mechanisms will need to be substantiated.