This can ultimately lead to further inactivity as the effort and energy involved in moving makes inactivity the easier option, and increases the risk of metabolic disorders such as type 2 diabetes mellitus. Regular exercise tones the cardiovascular system and the heart, which is a muscular pump, becomes more efficient. Blood flow through the blood vessels speeds up as the heart rate increases. The supply of oxygen and nutrients to the tissues, particularly voluntary muscles, is improved and the waste products of metabolism are more rapidly removed. Ultimately a healthy, and therefore fit, person has a greater cardiopulmonary reserve.
Lack of exercise has the opposite effects and the reserves of an unfit person are less.
Taxing the cardiovascular system of an unfit person quickly leads to breathlessness and fatigue, even more so if such a person is also overweight for their height and age. This can be seen for example when someone breaks a bone in one of their limbs and has to wear a plaster cast for several weeks - the muscles of the affected limb waste. Careful exercise under the guidance of a physiotherapist is then needed to regain muscle strength after the cast is removed. One of the reasons why women are advised to take regular exercise before, during, and after the menopause is to encourage the maintenance of bone strength and reduce the risk of developing osteoporosis. This condition can occur in men too, and one of the risk factors is inactivity.