Physical activity is an inclusive term that refers to any expenditure of energy brought about by bodily movement via the skeletal muscles; as such, it includes the complete spectrum of activity from very low resting levels to maximal exertion. exercise is a component of physical activity. the distinguishing characteristic of exercise is that it is a structured activity specifically planned to develop and maintain physical fitness. "exercise" britannica school. encyclopaedia britannica, inc., 2013. web. 21 oct. 2013. how is the word spectrum used in this excerpt?