Background: Repetitive light assembly work is associated with an increased risk for developing work-related musculoskeletal disorders. More exposure variation, for instance by redesigning the workstation, is generally proposed as an effective intervention. Purpose: We investigated the effect of upper arm posture variation in a one-hour repetitive pick-and-place task on shoulder muscle activity, heart rate and perceived exertion, measured on the Borg CR-10 scale and in terms of maximal acceptable work pace (MAWP). Methods: Thirteen healthy participants performed the task in three workstation designs where the hand was moved either horizontal (H30/30), diagonal (D20/40), or vertical (V10/50) with a mean upper arm elevation of ~30°. In a fourth design, the hand was moved horizontally at ~50° mean arm elevation (H50/50). Results: As intended, upper arm posture variation, measured by the upper arm elevation SD and range of motion, differed between H30/30, D20/40, and V10/50. However, MAWP (10.7 cycles·min^-1 on average across conditions; determined using a psychophysical approach), average upper trapezius activity (54% reference voluntary exertion [RVE]), and heart rate (69 bpm) did not differ between these workstation designs. In H50/50, MAWP was lower (9.3 cycles·min^-1), while trapezius activity (78% RVE) and perceived exertion (Borg CR-10) tended to be higher. Conclusions: Our results indicate that posture variation to the extent achieved in the current experiment leads to less effects on muscle activity and perceived exertion than a moderate change in working height.