With aerobic exercise, the heart muscle improves in at least three ways. The muscle itself grows thicker and stronger much the way skeletal muscles are changed by weight lifting. Secondly, the size of the chamber (or ventricle) inside the heart enlarges so that more blood is pumped with each heartbeat. In the past, some physicians made the error of diagnosing as pathological the heart enlarged by exercise Ė confusing it with enlargement due to heart failure. The third improvement involves the capillaries that feed the heart muscle its own supply of blood. With increased aerobic exercise, existing capillaries that branch off the heartís coronary arteries dilate Ė allowing blood to pass through heart muscles more freely so that remote areas of the heart receive blood more easily. Itís as if small towns and villages suddenly had more roads coming to them from other towns. It isnít the size of the roads (or capillaries) thatís significant; itís the number because they provide alternate routes. Applied to villages, we might call this phenomenon encroaching civilization; in our heart we call it increased vascularity decreasing the possibility of heart attack and speeding recovery if you do have one.

The incidence of heart attack during exercise is so rare that when one does occur it hits the newspapers. In contrast, the number of heart attacks in sedentary individuals is so common as to be a national disgrace. It becomes obvious that a sedentary life is far more dangerous than an athletic life. To insist on a stress elector-cardiogram before undertaking an exercise program misses the point. Instead, perhaps we should take stress elector-cardiograms if we plan not to exercise because we know that if we are not in perfect physical condition a sedentary lifestyle will kill us.

Aerobic exercise also increases the number of capillaries in the muscles so that oxygen and fuel are delivered more easily to the individual muscle cells which in turn decreases the work load of the heart and lungs. Most people feel that their lungs are what limit them when they run. It is a natural reaction to blame your lungs when your chest is heaving during a run but the lungs are only trying to compensate for poor oxygen uptake in the muscles. Oxygen rich blood is red when it enters the muscles. As the blood passes through the muscles, oxygen is removed so that the blood is blue when it flows into the veins. Increased vascularity of fit muscles brings more muscle cells into contact with capillaries allowing for rapid oxygen absorption. In other words, it isnít necessary for oxygen to profuse among cells to reach remote cells.

The increase in capillaries in the body as the result of aerobic exercise has far reaching effects:

  • The heart doesnít have to work as hard during exercise.
  • The lungs donít puff so hard.
  • Every individual muscle cell is more likely to get immediate oxygen when needed.

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