This study presents a novel means of assessing upper limb tasks by using mechanical energy. Potential energy quantifies six work related activities, studied for 20 working-age non-prosthesis users and three powered below elbow prosthesis users. Two marker trajectories on each of the upper arms, forearms, and hands were captured using a 3-camera VICON 140™ system. Task and arm dominance of non-prosthesis users are highly significant ($p\,{<}\,0.01$) with arm dominance effects being more pronounced for prosthesis users. Qualitative inter-repetition consistency is also concordant with observed increased cumulative trauma disorders among prosthesis users.