In human-robot collaboration (HRC), robots operate alongside humans within a shared workspace. During collaborative handling tasks, human movements are often highly individual and variable. To ensure smooth collaboration, the robot must adapt its trajectory to align with the motion of the human co-worker. Therefore, this work proposes a dynamic motion planner that enables the robot to track a dynamically changing reference trajectory. The motion planner is evaluated based on its ability to track the trajectory while respecting joint velocity and acceleration limits and avoiding kinematic singularities. When these constraints are at risk of being violated, the robot temporarily assumes a dominant role and attempts to approximate the reference trajectory as closely as possible. An evaluation using a KUKA iiwa in a laboratory setup demonstrates that the proposed motion planner can effectively track dynamically changing, physically feasible reference trajectories. Assuming that the reference trajectory can be human motion, the motion planner can harmonize human and robot movements during collaborative handling tasks.