Prior to each data collection session, a global axis system was established along with integration of the force plates according to the manufacturer’s guidelines using the Motion Monitor software. The axes of the global axis system were defined using a right-
hand convention, with the positive x-axis corresponding with the forward direction of the double leg jump movement, the positive y-axis defined by a vector located with a
positive 90° rotation about the z-axis relative to the x-axis, and the positive z-axis defined
by a vector located with a positive 90° rotation about the x-axis from the position of the
y-axis.
Segments of the shank, thigh, and pelvis were defined within the data collection software. The shank segments were defined by the segment endpoints of the ankle joint center and knee joint center, and a third non-collinear point of the shank electromagnetic receiver. The thigh segments were defined by the segment endpoints of the knee joint cent and hip joint center, and a third non-collinear point of the thigh electromagnetic receiver. The thigh joint center was estimated within the software using the Bell method.90 The pelvis segment was defined based on the of the right and left ASIS, and the third non-collinear point of the sacrum electromagnetic receiver.
Local coordinate systems were established based on a right-hand convention and coincided with the orientation of the global axis system such that, the positive x-axis corresponded with the anterior direction, the positive y-axis as the medial direction for the right leg and lateral direction for the left leg, and the positive z-axis as the superior direction. Cardan angles using an Euler sequence were used to calculate joint angles for the knee and hip using the Motion Monitor software. The Euler sequence for both knee and hip angle was defined by a first rotation about the y-axis, a second rotation about the x-axis, and a third rotation about the z-axis. The first rotation about the y-axis
plane motion of the knee (+ varus / - valgus) and hip (+ adduction / - abduction). The third rotation about the z-axis corresponded with transverse plane motion of the knee (+ internal rotation / - external rotation) and hip (+ internal rotation / - external rotation). The sign conventions to define the direction of anatomical motion for the first rotation about the y-axis were consistent for the left leg, but the inverse for the second and third rotations. This factor was corrected in the data reduction process to make all sign conventions indicative of the relative motions listed previously.
Moments for the knee and hip were calculated within the Motion Monitor software using a standard inverse dynamics approach. These moments were calculated as internal moments and are representative of the moment produced within the body to resist the external moments generated on the body by interaction with the environment. Moments in each plane of motion were calculated for the knee and hip, as well as the proximal anterior tibial shear force. The proximal anterior tibial shear force was defined as the resultant force acting on the shank segment calculated at the point of the knee. Prior to exportation of the data, the data were filtered within the Motion Monitor software using a Butterworth filter with a cutoff frequency of 14.5 Hz. The data were filtered prior to exportation to ensure no introduction of a time shift in the data between the kinematic and kinetic data. All data were exported at the sampling rate of 1440 Hz, consistent with that of the sampling frequency of the kinetic data, and the highest sampling frequency of the data collected. This required up-sampling of the kinematic data that was performed during exportation by the Motion Monitor software.
Definition and Calculation of Dependent Variables
The vertical ground reaction force was used to define the stance phase for the double leg jump landing. The point at which the vertical ground reaction force first exceeded 10N was defined as Initial Ground Contact, and the subsequent point at which the vertical ground reaction force value fell below 10N was used to define toe-off. The time period between Initial Ground Contact and toe-off was defined as the stance phase of the double leg jump landing. The time from Initial Ground Contact until peak knee flexion was defined as the Landing Phase of the double leg jump landing. The time period of the 100 milliseconds preceding Initial Ground Contact was defined at the Preparatory Phase. Dependent variables were calculated relative to these time points of interest.
Kinematic Variables
The assessment of kinematic values was performed for the initial trials collected for the original JUMP ACL study (Baseline), and from the follow up data collection (Follow- Up) for all repeated measures analyses. Values for the kinematic variables were
determined for the following phases of the double leg jump landing: Preparatory Phase, Initial Ground Contact, and Landing Phase. Kinematic values for all three planes of knee joint motion and hip joint motion were determined for the Preparatory Phase and Initial Ground Contact. These values were averaged across trials. Maximum and minimum values for all three planes of knee joint motion and hip joint motion were determined for the Landing Phase and averaged across trials.
Kinetic Variables
The assessment of kinetic values was performed for the initial trials collected at Baseline, and from the Follow-Up data collection for all repeated measures analyses. Values for the kinetic variables were determined for the following phases of the double leg jump landing: Initial Ground Contact, and Landing Phase. Values for the moments of the knee and hip for all three planes of motion, as well as anterior tibial shear force were recorded at the point of Initial Ground Contact and averaged across trials. The maximum and minimum values during the Landing Phase for the knee and hip, for all three planes of motion, as well as the maximum anterior tibial shear and vertical ground reaction force was determined, recorded, and averaged across trials.
All moments were reported as internal moments and normalized by the product of the participant’s body weight (N) and body height (m). Vertical ground reaction force was normalized to the participant’s body weight.
Joint Coordination and Variability
Joint coordination was determined using a vector coding method as described by Heiderscheit et al81 and Ferber et al83 as an alteration to the technique proposed by Sparrow et al.79 Angle-angle plots were constructed for each joint coupling of interest during the Landing Phase of the double leg jump landing (Figure 2). The coupling angle for each point was calculated as:
θ! = abs{tan!! y!!!−y!
x!!!−x! ]
coordination value. Variability of joint coordination was calculated as the average between trial standard deviation.82 The joint coordination pairs that were investigated included: Hip Sagittal Plane – Knee Sagittal Plane, Hip Frontal Plane – Knee Frontal Plane, Hip Transverse Plane – Knee Transverse Plane, Hip Frontal Plane – Knee Transverse Plane, and Hip Transverse Plane – Knee Frontal Plane.
All data reduction was conducted using customized MATLAB software programs (Mathworks, Natick, MA, v7.10).