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?