Heart Size Very severe training results in enlargement of the heart beyond the limits commonly accepted as normal for the individual. College athletics apparently do not increase the size of the normal heart, but the heart shadows of older champion athletes are longer than the norms. Endurance sports enlarge the right side of the heart while short, intense exertion produces greater change in the left side of the heart. Hypertrophy of the right heart is attributed to elevated pulmonary circulatory resistance and increased venous return to the right heart during prolonged and repeated exercise. Hypertrophy of the left heart following repeated short bouts of violent exertion may be due to the increased work of the rapidly contracting heart against the elevated blood pressure in the systemic circulation. Heart size is related to constitutional type and thoracic circumference. If a larger than average heart is associated with a high vital capacity the average heart rate and blood pressure arc usually lower and there is a greater than normal capacity for the performance of work and sport. The increase in heart size of racing greyhounds may proceed so rapidly that the activity of the heart is impaired by lack of space. Serial electrocardiographic studies were made on 48 athletes during one entire training season. In 43, there were no changes. In 5 cases there were minor changes of obscure significance; they were not considered pathological in view of the excellent performance of these hearts.		Home Components of Physical Fitness Clinical Examination Differences Between Fit and Unfit Men Physiological Elements of Fitness The Step Test The Effects of Training on the Physiological Systems Work Output Physical Condition of Muscle Application of Muscular Force Maintaining Optimum Strength Tests of Muscular Strength Strength and appearance Strength as a measure of physical fitness Strength as affected by organic problems Strength as prophylaxis Role of inactivity in production of disease Lack of Sociability in Work Lactic Acid System Muscular Form Capillary Growth Heart Size Heart Rate Training produces physicochemical changes Muscular Strength Nervous Stimulation and Muscular Strength Quality of Champions Kinesthesis Balance Reaction Time Muscular Tension Visual Aim