There are now detailed manuals describing the effects of different kinds of exercise on both physical and psychological health. For the elderly, remaining active is a clear source of happiness, whether that means exercising, volunteering, or engaging in paid employment.
相比之下，涉及到具体项目有着大量有力的证据。现在有详尽的手册描述各类运动与身体和心理健康的关系。对老人而言，活跃显然是幸福的源泉，无论这意味着锻炼、志愿服务抑或从事带薪工作。（事实上，加拿大一项调查发现带薪就业是65岁以上人群最富满足感的行为。）