Short answers, pulled from the story.
Exercise helps maintain a healthy weight, regulates the digestive system, builds bone density, muscle strength, and joint mobility, reduces surgical risks, and strengthens the immune system. People with moderate to high levels of physical activity have a lower mortality rate than those who are not physically active. Worldwide, physical inactivity is behind 9 percent of premature mortality.
About 150 minutes, or two hours and thirty minutes, of moderate-intensity exercise per week is recommended to reduce the risk of health problems. Most benefits are reached around 3500 metabolic equivalent minutes per week, with diminishing returns above that. Even half the recommended level still lowers the risk of early death, cardiovascular disease, stroke, and cancer.
The three main types of exercise are aerobic, anaerobic, and flexibility. Aerobic exercise such as running and swimming builds cardiovascular endurance, anaerobic exercise such as push-ups and weight training builds muscle strength, and flexibility exercises such as stretching improve range of motion to reduce injury.
Physical inactivity is an independent risk factor for coronary artery disease, and low levels of exercise raise the risk of dying from cardiovascular disease. The greatest reduction in mortality is seen in sedentary people who become moderately active. After a myocardial infarction, survivors who took up regular exercise had higher survival rates.
Continuous aerobic exercise can induce a transient euphoria known as a runner's high or rower's high, driven by increased biosynthesis of anandamide, beta-endorphin, and phenethylamine. Exercise also reduces levels of cortisol, a hormone tied to many physical and mental problems.
A team led by Jerry Morris established the link in a study begun in 1949 and reported in 1953. Morris found that sedentary bus drivers had a higher incidence of heart disease than bus conductors, who moved continually at work. The Roman lawyer Marcus Cicero had praised exercise much earlier, in 65 BCE.