Hippocrates, the father of modern medicine said that, all parts of the body if used in moderation develop and age slowly, but if they are left unused they become defective in growth, susceptible to disease and age quickly. Physical exercise and activity is a pre-requisite for a healthy life. 
Exercise also confers on the elderly, a sense of purpose and achievement. They come to realise that they have more control over their bodies than they imagined. Exercises have a beneficial effect on the course and severity of many diseases.

• The Heart: Regular exercise can prevent the development of high blood pressure Low BP can also be raised. High cholestrol levels which are a major risk factor in heart attack and stroke are reduced by regular exercise. Heart attack is more common in those with sedentary habits.
• Diabetes: The effective treatment of this disease is influenced by the obesity of an individual. Loss of weight helps prevent and treat diabetes. Mild diabetes is often controlled by diet and exercise which is much preferred in the elderly rather than management by drugs.
• Fractures: As one grows older the bones become weak and brittle, especially in women after menopause. This and other age related changes make the elderly prone to falls. Regular physical exercise, not only increases the muscle tone but also helps the bones retain calcium and remain strong, reducing the incidence of fractures.
• Cancer: Studies have shown that cancer of the large intestines is greater in those who are not physically active. Similarly, breast cancer and cancer of the sex organs rarely affects sportswomen.
• Constipation: Daily physical exercise combined with a high fibre diet can help avoid constipation
• Mental Depression: Exercise increases the blood circulation in all parts of the body promoting a general sense of well-being. While exercising, people tend to take their minds off personal and psychological problems and thus avoid anxiety and depression

What are the types of exercises that can be performed by the elderly?
It is the constitution of the individual rather than the age that decides the type of exercise that one can do. Exercises may include

Aerobic exercise: This is vigorous exercise that produces  a heart rate of 60-70% of one's maximum. It strengthens the cardio-vascular system. It includes, jogging, cycling, skipping and swimming. The heart becomes stronger and the person is able to perform the same amount of physical activity with less effort. It is done three times a week in 15 to 60 min. sessions.It includes a 3-5 min warm-up and cool down.

But Aerobic exercise should be done only after taking advice from a physician.

The best form of aerobic exercise for the elderly is walking. You could walk for about 30 mins or 3-5 kms a day.

Low-intensity exercise: This places less stress on the heart but plays an important role in maintaing and improving the health of a person especially for bone mineralisation, joint flexibility and weight control. It includes, stretching and light calisthenics.Yoga and pranayama and other traditional methods of physical discipline can also be put into this category. Even walking, if perfomed with less vigour can be put into this category.