The impact of different trajectory embodiments in terms of velocity profiles on users’ mental stress in close human-robot interaction is investigated. A cooperative assembly scenario is chosen using a standard industrial robot. Conditions are implemented in a repeated measures within-subjects design comparing linear with trapezoidal trajectories. Heart rate variability and galvanic skin conductance are chosen as objective stress markers and evaluated using the average standard deviation of the beat-to-beat intervals (SDNN) and the average skin resistance. Additionally, evaluations of user experience and acceptance are conducted based on evaluated subjective measures. The results of the user study reveal a significant increase of average heart rate variability and average skin resistance in the trapezoidal condition indicating a reduced mental stress level independent of demographical and dispositional factors.