The claim that individual participation in adequate amounts of regular physical activity can improve health and prevent disease is fully justified. There is excellent evidence that regular exercise reduces ones risk of most major causes of premature death. Exercise is linked with decreases in heart disease, breast and colon cancer, osteoporosis and depression, to name a few.
Exercise benefits the immune system, digestion, detoxification and oxidation systems. There is no question that regular moderate exercise is the lynchpin of good health.
Studies also indicate that it does not matter much what type of exercise you do or whether you do the exercising all at once or scattered throughout the day. You will get the benefits of exercise either way: enanced physical function, strong reserve capacities, ability to fight disease, and lessened effects of age and chronic disease.
The American Heart Association has tips for helping you get started and stay going with an exercise program. If you have not exercised in a long time and need help getting started, your insurance will often pay for you to have some visits with a physical therapist.
American Heart Association exercise tips
American Family Doctor page on exercise: http://familydoctor.org/015.xml