But it must be understood, that unless designed otherwise, i.e. unless the Units of Analysis are chosen from all people, most studies are generalizable only for a much narrower population of the people w/in a nation, region, city, etc.
exercising - the activity of exerting your muscles in various ways to keep fit; the doctor recommended regular exercise; he did some exercising; the physical exertion required by his work kept him fit. exercise, physical exercise, physical exertion, workout.
Exercising for fitness means that in addition to conditioning the heart, lungs, and circulatory system, you work all the major muscles of the body. The goals are to build strength and endurance, so that you can lift heavier objects as well as using the muscles for longer periods of time before they get too fatigued.