America is the country on the move. In unheard of numbers, people of all ages are exercising their way to better health. According to the latest figures, 59 percent of American adults exercise regularly-up 12 percent from just two years ago and more than double the figure of 25 years ago. Even non-exercisers believe they would be more attractive and confident if they were more active. It's hard not to get the message. The advantages of physical fitness are shown on magazine covers, postage stamps, and television ads for everything from beauty soaps to travel books. Exercise as a part of daily life did not catch on until the late 1960s when research by military doctors began to show the good points of' doing regular physical exercises. Growing publicity(宣传) for races held in American cities helped develop a strong interest in the ancient sport of running. Although running has leveled off in recent years as Americans have discovered equally helpful and sometimes safer-forms of exercise.

    As the popularity of exercise continues to increase, so does scientific evidence(根据) of its health benefits. The key to fitness is exercising the major muscle group strongly enough to almost double the heart rate and keep it doubles for 20 to 30 minutes at a time. Doing such physical exercises three times or more a week will greatly improve physical health in about three months.