Английский Этимологический словарь - exercise (n.)

- c.1340, "condition of being in active operation," from O.Fr. exercice, from L. exercitium, from exercitare, frequentive of exercere "keep busy, drive on," lit. "remove restraint," from ex- "off" + arcere "keep away, prevent, enclose," from PIE *ark- "to hold, contain, guard." Original sense may have been driving farm animals to the field to plow; meaning "physical activity" first recorded in Eng. c.1390. The ending was abstracted for formations such as dancercise (1967); jazzercise (1977); and boxercise (1985).