(7) COMPARISON OF TRUNK AND LOWER EXTREMITY KINEMATICS DURING TWO DIFFERENT COUNTERMOVEMENT JUMP TESTING PROTOCOLS: A PRELIMINARY ANALYSIS

Purpose: Countermovement Jump (CMJ) testing is commonly used in athletics to assess and monitor athletes. Two common CMJ protocols exist to remove the influence of arm swing: placing the hands on the hips or utilizing a dowel across the upper back. Thus, this investigation aimed to examine the differences in joint kinematics between the two CMJ testing protocols using markerless motion capture. Methods: 10 recreationally trained participants (M= 5, F= 5) participated in this pilot investigation (age = 23.5 ± 4.9 years, height =173.7 ± 9.4 cm, body mass = 79.4 ±17.9 kg). All data was collected during a single session. Prior to testing, each participant completed a standard dynamic warmup, including submaximal vertical jumps. Participants completed five CMJs in each condition with their hands either akimbo or holding a dowel across the upper back. Markerless motion capture data was collected at 80 Hz (Qualisys, Sweden). 3D human pose estimation was generated using a markerless motion capture video data software (Theia Markerless Inc., Kingston, ON, Canada). All data was low pass filtered at 6 Hz. 4x4 Pose matrices of each body segment were exported and analyzed in Visual3D (Version 6, C-Motion, Inc., Germantown, MD, USA) to calculate trunk position and hip and knee kinematics. All data was time-normalized to 101 data points from the point of movement initiation to takeoff. Range of motion (ROM), peak flexion angle, time of peak flexion angle, and joint angle at take-off was calculated for the trunk, hip, and knee. Comparisons across CMJ protocol conditions were assessed using a paired samples t-test. An a priori alpha level of 0.05 was used to determine statistical significance. Hedges g effect sizes were calculated for each metric. In addition, mean differences between the two conditions were calculated. Results: Significant differences were observed in hip ROM, peak hip flexion angle, and time of peak trunk flexion angle (p=0.01; p=0.009; p= 0.037, respectively). Large effects for hip ROM (g=-0.961; CI: -1.681, -0.207) and peak hip flexion angle (g=-1.013; CI: -1.748, -0.245) were observed while moderate effects for time of peak trunk flexion angle were observed (g=0.738; CI: 0.041, 1.405). Conclusions: Placing the dowel across the back during CMJ task produced greater ROM at the hip joint and subsequently greater peak hip flexion. In addition, the dowel across the back CMJ condition experienced a shorter time of peak trunk flexion, indicating that performing a CMJ with a dowel potentially influences athletes to keep a more upright torso during the CMJ task. Practical Applications: The influence of CMJ protocol on joint kinematics should be considered by practitioners when selecting a protocol for hand placement during CMJ testing. Given the differences in hip joint ROM, peak hip flexion angle, and time of peak trunk flexion angle between two protocols, practitioners should select a CMJ testing protocol that best fits the specificity of their sport as it applies to the execution of the CMJ. Further investigations into the influence of CMJ protocols on outcome metrics commonly used to assess performance is warranted. Acknowledgements: None