Especially during an intensive workout, more blood and oxygen are required to the peripheral tissues of the arms and legs in highly trained athletes' bodies.

This sound can be heard as the diastolic pressure of the irregularly shaped heart creates a disordered blood flow.

An S4 gallop is a stronger and louder sound created by the heart, if diseased in any way, and is typically a sign of a serious medical condition.

Over time, the body will increase both the chamber size of the left ventricle, and the muscle mass and wall thickness of the heart.

With a larger left ventricle, the heart rate can decrease and still maintain a level of cardiac output necessary for the body.

Dynamic exercises include running, swimming, skiing, rowing, and cycling, which rely on oxygen from the body.

Both static and dynamic exercises involve the thickening of the left ventricular wall due to increased cardiac output, which leads to physiologic hypertrophy of the heart.

[12][13][14] Regarding differential diagnosis, left ventricular hypertrophy is usually indistinguishable from athlete's heart and at ECG, but can usually be discounted in the young and fit.

[20][21] The medical history of the patient (endurance sports) and physical examination (bradycardia, and maybe a third or fourth heart sound), can give important hints.

Because of several well-known and high-profile cases of athletes experiencing sudden unexpected death due to cardiac arrest, such as Reggie White and Marc-Vivien Foé, a growing movement is making an effort to have both professional and school-based athletes screened for cardiac and other related conditions, usually through a careful medical and health history, a good family history, a comprehensive physical examination including auscultation of heart and lung sounds and recording of vital signs such as heart rate and blood pressure, and increasingly, for better efforts at detection, such as an electrocardiogram.

[citation needed] An electrocardiogram (ECG) is a relatively straightforward procedure to administer and interpret, compared to more invasive or sophisticated tests; it can reveal or hint at many circulatory disorders and arrhythmias.

[citation needed] If sudden cardiac death occurs, it is usually because of pathological hypertrophic enlargement of the heart that went undetected or was incorrectly attributed to the benign "athletic" cases.

Among the many alternative causes are episodes of isolated arrhythmias which degenerated into lethal VF and asystole, and various unnoticed, possibly asymptomatic cardiac congenital defects of the vessels, chambers, or valves of the heart.

However, one long-term study of elite-trained athletes found that dilation of the left ventricle was only partially reversible after a long period of deconditioning.

Because his research occurred throughout the 19th century, technology was limited, and it became difficult to devise appropriate ways to measure the hearts of athletes.