Declines in physical activity that accompany an admission to an intensive care unit (ICU) represent a significant stress to the body. Decreases in physical activity have been demonstrated to result in losses in functional capacity of the musculoskeletal and cardiovascular systems. These two systems are central to achieving and maintaining functional independence, which is a prerequisite for discharge from a healthcare facility, as is independent functioning of the individual in the community setting. Whereas a decrease in physical activity will result in an attenuation in the functioning of the cardiovascular and musculoskeletal systems, increases in physical activity can stimulate gains in their functional capacity. The concept of improving the functional capacity of the body to withstand anticipated musculoskeletal stressors has had limited application to the effects of inactivity associated with an ICU admission. By increasing an individual's functional capacity through increased physical activity prior to an ICU admission, it seems reasonable that the patient would retain a higher level of functional capacity over their entire ICU admission. The process of enhancing functional capacity of the individual to enable them to withstand the stressor of inactivity associated with an admission to ICU is termed prehabilitation. A generic program of prehabilitation includes warm-up, aerobic, strength, flexibility, and functional task components. The initial level of prehabilitation training and the progression of the training will be different for each individual based upon their initial functional capacity and the degree to which they individually respond to increases in physical activity. Declines in physical activity among ICU patients represents a significant health risk that may be reduced through introducing prehabilitation interventions.