This paper presents a model that addresses mechanical exposure with regard to the development of musculoskeletal disorders, defines exposure concepts, unifies a variety of exposures, and includes the concept of human activity. When force is used as an agent, concepts related to the measurement, transformation, and interaction of the agent with tissues can be developed for use in epidemiologic exposure assessment and hazard assessment. The importance of tissue response in the exposure modeling process and in the creation of exposure indices is highlighted. Unfortunately, the response of tissue to forces of varying amplitudes and time variation patterns are largely unknown and thus reduce the possibility to develop optimal exposure assessment metrics. Although the paper argues that an exposure index at the tissue level may be the most powerful, considerations of resources and current knowledge make exposure indices based on external exposure or internal exposure preferable choices.