Exercise as medicine. In the 19th century, most work involved physical activity; in the 20th century, exercise became a leisure pursuit; today, it's an urgent medical necessity.
D015444:Exercise; D005260:Female; D006266:Health Education / Q000266:history*; D006293:Health Promotion / Q000266:history*; D049672:History, 19th Century; D049673:History, 20th Century; D006801:Humans; D008019:Life Style; D009043:Motor Activity; D013178:Sports Medicine / Q000266:history; D016387:Women's Health / Q000266:history*