"You might suspect from the emphasis on cardiopulmonary fitness that the major effect of training is on the heart and lungs. Guess again. Exercise does nothing for the lungs that has been amply proved...Nor does it especially benefit your heart. Running, no matter what you have been told, primarily trains and conditions the muscles."
-- George Sheehan, MD, Cardiologist
(Known as the "Guru" of running. He has authored several books on running for fitness.)
"Most of the improvement in functional capacity due to exercise is not even directly related to the heart. It is due to an effect on the peripheral muscle cells whereby they more efficiently extract oxygen from the blood."
-- Henry Solomon, MD Cardiologist
(From his book The Exercise Myth, 1984)
Harcourt Brace Jovanovich, San Diego, ISBN 0151294585.