This study examined changes in task performance during performance of simulated overhead assembly task. The study objectives were to better understand the relationship between fatigue development during overhead work and task performance. This relationship is important, considering that performance changes, or decreases in task quality, have the potential for justifying and driving ergonomic changes that can help to improve worker safety. Sixteen people participated in eight experimental conditions (two levels of duty cycles, two work heights, and two hand positions). Four dependent measures based on endurance, subjective, objective, and physiological fatigue were used to quantify shoulder fatigue and were collected during the experiment. An overhead work task required participants to use a hand tool to strike targets at two reach distances above their head. Task performance was measured as a function of the closeness to the target center and the ability to apply a consistent force throughout the experiment. Data collected in this experiment is intended to provide a research basis for creating design guidelines that will help maximize efficiency and quality while reducing the likelihood of developing shoulder fatigue. / Master of Science