# Comparison of Countermovement and Preferred-Style Jump Biomechanics in Male Basketball Players
## 2 Materials and Methods  
Ten male basketball players (age: 19 \(\pm\) 1 year; height: 1.84 \(\pm\) 0.14 m; mass: 92.8 \(\pm\) 11.4 kg) from the same National Collegiate Athletic Association Division I level team were recruited to participate in a cross-sectional study. Four of the recruited players were guards, five were forwards, and one was a center. All players signed an informed consent document, which was approved by Marquette University's Institutional Review Board for human subjects testing. Twenty-eight spherical markers were attached over several anatomical landmarks of the lower body and torso [8]. Once markers were attached, players performed a general warm-up that consisted of calisthenic exercises (e.g., squat and lungs) and several sub-maximal effort jumps. After the warm-up, each player performed a series of jumping tasks, which included three maximal effort CMJs and three maximal effort Pref during which each player could choose the approach and jump strategy. Players were given up to 30 s rest between each jump to minimize the effects of fatigue. The CMJ were performed with hands akimbo (i.e., placed on their hips with elbows pointed outwards). For the Pref, all but two players chose a jump strategy that consisted of a short approach run and a double leg take off with a lead and trail leg footfall pattern (Figure 1). The other two players chose a single leg take off strategy. For the purposes of the current study only the players who used the double leg take off during Preff were included (\(n=8\)). During each type of jump, the positions of all markers were recorded with a 14-camera motion capture system (T-Series Cameras, Vicon, Denver, CO, USA) at 100 Hz. Ground reaction force (GRF) data were simultaneously recorded with two force plates (Models OR6-6, Advanced Mechanical Technologies Inc., Watertown, MA, USA) at 1000 Hz. The marker and vertical GRF data were imported into OpenSim software (v3.3). The marker and GRF data were both smoothed with a 4 th order low-pass Butterworth filter with a cut-off frequency of 12 Hz, which was determined based on a residual analysis. A musculoskeletal model that was specifically developed for movements with large flexion motions (e.g., squat, countermovement jump) was used in this study [20]. The model was scaled to each participant by adjusting anthropometric parameters (e.g., segment length and mass) within the model. Data were processed with a standard pipeline where joint angles were calculated with inverse kinematics (IK) and NJM were calculated with inverse dynamics (ID). The NJM were calculated as internal NJM and presented so that positive moments reflect extension moments at each joint. Joint angular velocities, net joint powers (NJP), and net joint work (NJW) were also calculated. All joint kinetic data were normalized by body mass of each participant. In addition, the vertical position and velocity of the pelvis segment were calculated and used to represent the vertical position and velocity of the COM. Discrete peak variables were extracted from each jump trial. For the CMJ, peaks were extracted during the movement phase, which was defined as the time interval between when the summed vertical GRF fell below 95% of body weight and when both feet left the ground (i.e., summed vertical GRF \(<\) 10 N) (Figure 2). For the Preff, peaks were extracted during the ground contact phase, which was defined as the time interval between when the lead foot made contact with the first force plate and when both feet left the ground (i.e., summed vertical GRF \(<\) 10 N). Vertical jump height was calculated from the vertical velocity at the instant of take-off. The difference between vertical pelvis position at the beginning of each respective jump and at its minimum was used to represent the COM displacement during the lowering phase. The discrete peaks from each type of jump were averaged across trials to create within-subject averages, which were then used for statistical analysis.