Context: Athletes who have undergone an anterior cruciate ligament reconstruction often demonstrate more pronounced interlimb knee kinetic symmetry in comparison with uninjured athletes, even after they have completed rehabilitation. Part of the reason for the persistent asymmetry may be that sports medicine professionals are typically not able to assess knee joint kinetics within the clinic setting. Developing measures to assess knee joint kinetic symmetry could help to augment current rehabilitation practices. Objective: The purpose of this study was to explore the extent to which interlimb vertical ground reaction force (GRF) symmetry can predict knee kinetic symmetry during a drop landing task. Design: Cross-sectional study. Setting: Motion analysis laboratory. Participants: A total of 21 uninjured subjects (9 males and 12 females). Protocol: Three-dimensional kinematic data were collected using a multicamera system while subjects performed double-leg drop landings. GRF data were collected synchronously using 2 adjacent force plates. Main Outcome Measures: Knee joint moments and power were calculated for both limbs during the landing trials. An interlimb symmetry index (dominant/nondominant limb) was calculated for both the peak knee joint moment and power variables, as well as for the peak vertical GRFs. Linear regression analyses were performed to determine if the degree of symmetry in the peak vertical GRFs predicted the degree of symmetry for the kinetic variables. Results: The symmetry index for the vertical GRFs was a significant predictor of the symmetry indices for the knee joint moments (r = .81; P < .001) and power (r = .88; P < .001). Conclusion: Interlimb symmetry in the peak vertical GRFs can be used to predict knee joint kinetic symmetry during a double-leg drop landing task.
Aaron Nelson, Nathan Koslakiewicz and Thomas Gus Almonroeder
Logan A. Lucas, Benjamin S. England, Travis W. Mason, Christopher R. Lanning, Taylor M. Miller, Alexander M. Morgan and Thomas Gus Almonroeder
Lower-extremity musculoskeletal injuries are common in sports such as basketball and soccer. Athletes competing in sports of this nature must maneuver in response to the actions of their teammates, opponents, etc. This limits their ability to preplan movements. The purpose of this study was to compare impact accelerations during preplanned versus unplanned lateral cutting. A total of 30 subjects (15 males and 15 females) performed preplanned and unplanned cuts while the authors analyzed impact accelerations using an accelerometer secured to their tibia. For the preplanned condition, subjects were aware of the movement to perform before initiating a trial. For the unplanned condition, subjects initiated their movement and then reacted to the illumination of one of 3 visual stimuli which dictated whether they would cut, land, or land-and-jump. A mixed-model analysis of variance with a between factor of sex (male and female) and a within factor of condition (preplanned and unplanned) was used to analyze the magnitude and variability of the impact accelerations for the cutting trials. Both males and females demonstrated higher impact accelerations (P = .01) and a trend toward greater intertrial variability (P = .07) for the unplanned cutting trials (vs preplanned cuts). Unplanned cutting may place greater demands on the musculoskeletal system.