Two hypotheses were formulated to examine the additivity of perceived exertion in repetitive, symmetric, mid-sagittal lifting. "Additivity" has been defined as the means by which a whole-body rating of perceived exertion is composed of a weighted combination of component ratings of perceived exertion. The "task additivity" hypothesis asserts that a perceived exertion rating for the whole body in a floor-to-overhead lifting task can be modelled by the perceived exertion ratings of the component motions, i.e., floor-to-knuckle height lifting and knuckle height-to-overhead lifting. This is an inter-task (subtask) additivity paradigm. The "body-segment additivity" hypothesis asserts that the perceived exertion rating for the whole body in a floor-to-overhead lifting task can be modelled by a combination of the ratings of perceived effort from the arms, legs, torso, and central (cardio-respiratory) body functions. This is an intra-task (regional) additivity paradigm. / Master of Science