McNair/Gateway Scholars Program USC

Brian Nguyen

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Major and Classification

Kinesiology

Faculty Mentor

  • Jill McNitt-Gray, Ph.D.

Department

  • Kinesiology

McNair Project

Satisfying the Laws of Motion by Analyzing Human Movement Dynamics: a Kinematic Comparison Between Segmental Analysis and the Force Platform Method

Human movement dynamics is governed by Newton's laws of motion, which form the basis for classical mechanics. The purpose of this study is to determine if kinematic and kinetic data acquired during segmental and force data analyses satisfy the laws of motion. The horizontal velocity of the center of mass at force plate contact were computed and compared using the segment kinematics and force based methods. Segmental analysis has been the primary kinematic method for this study in the field of biomechanics. However, when forces acting on the system can be measured using a force plate, the center of mass trajectory using measured ground reaction forces can be computed using the relationship between the net impulse and the change of momentum. In theory, the kinematic and kinetic based measures of center of mass velocity at an instant are hypothesized to be equal. To test this hypothesis, 9 female participants (ages 18-23) volunteered to participate in accordance with the institutional review board for human subjects. Each participant performed a three-step blocking motion along a volleyball net as quickly as possible. A pair of force plates measures the force generated by each foot during contact as the subjects convert their horizontal momentum to vertical momentum during the task. It is shown that with the resulting digitization of the subjects in which the total body center of mass (TBCM) is calculated, the horizontal velocity at jump take off varies among participants and between methodologies. Since the results do not comply with the Newtonian laws of motion, the experiment requires further investigation. In research that investigates human movement, these laws must always be satisfied during the initial step. This comparison between the two processes enables one to verify at the beginning of the study that the kinematic and kinetic data used to characterize human motion fulfills the laws of motion.