The conventional gait model (CGM) refers to several closely related biomechanical models used in the objective analysis of human motion. Their use has become popular in the analysis of change of direction tasks to inform best practice in the prevention and rehabilitation of anterior cruciate ligament injury. As externally-placed markers define segment axes origins and orientations, kinematic and kinetic outputs from the CGM are sensitive to marker placement. The aim of this investigation was to quantify the sensitivity of lower extremity kinematics and knee moments to systematic differences in marker placement across the stance phase of a change of direction task. Systematic anterior/posterior displacements were applied to the lateral thigh, femoral epicondyle and tibia markers in software. One-dimensional statistical parametric mapping was used to determine the effect of marker placement across the entire stance phase of a 90° change of direction task. Marker placement error within previously reported inter-tester variability ranges caused significant differences in knee abduction moment, hip rotation angle, knee rotation angle, ankle rotation angle and ankle abduction angle across various periods of stance. Discrete measures of these variables have been associated with increased frontal plane knee loading during change of direction, considered a key mechanism of anterior cruciate ligament injury. Systematic differences in marker placement may lead to incorrect group statistical inferences in such discrete measures.

Background: Deficits in knee strength after anterior cruciate ligament reconstruction (ACLR) surgery are common. Deficits in the single-leg drop jump (SLDJ), a test of plyometric ability, are also found. Purpose: To examine the relationship between isokinetic knee strength, SLDJ performance, and self-reported knee function 9 months after ACLR. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Knee isokinetic peak torque, SLDJ jump height, contact time, and reactive strength index (RSI), as well as International Knee Documentation Committee (IKDC) scores were assessed in 116 male, field-sport athletes at 9.2 months after ACLR. SLDJ testing took place in a 3-dimensional biomechanics laboratory. Linear regression models were used to analyze the relationship between the variables. Results: A significant relationship was found between ACLR-limb isokinetic knee extensor strength and SLDJ jump height ( P < .001, r 2 = 0.29) and RSI ( P < .001, r 2 = 0.33), and between ACLR-limb isokinetic knee flexor strength and SLDJ jump height ( P < .001, r 2 = 0.12) and RSI ( P < .001, r 2 = 0.15). A significant positive relationship was also found between knee extensor asymmetry and SLDJ jump height asymmetry ( P < .001, r 2 = 0.27) and SLDJ reactive strength asymmetry ( P < .001, r 2 = 0.18). Combined ACLR-limb jump height and contact time best predicted IKDC scores ( P < .001, r 2 = 0.12). Conclusion: Isokinetic knee extension strength explained approximately 30% of SLDJ performance, with a much weaker relationship between knee flexion strength and SLDJ performance. Isokinetic strength and SLDJ performance were weak predictors of variation in IKDC scores.

Inter-limb asymmetry refers to differences in movement and performance between limbs during voluntary motor tasks. 1 In the absence of pathology, asymmetry is believed to be driven by differences between dominant and nondominant limbs, though ambiguity remains with respect to the appropriate method for classifying limbs as dominant and non-dominant. Limb dominance is attributed to functional difference in the two hemispheres of the