Athletic Heart Syndrome - Cause

Cause

Athlete's heart is a result of dynamic physical activity such as (more than 5 hours a week) aerobic training, rather than static training such as weight lifting. During intensive prolonged endurance or strength training, the body signals the heart to pump more blood through the body to counteract the oxygen deficit building in the skeletal muscles. Enlargement of the heart is a natural physical adaptation of the body to deal with the high pressures and large amounts of blood that can affect the heart during these periods of time. Over time, the body will increase both the chamber size of the left ventricle, and the muscle mass and wall thickness of the heart.

Cardiac output, the amount of blood that leaves the heart in a given time period (i.e. liters per minute), is proportional to both the chamber sizes of the heart and the rate at which the heart beats. With a larger left ventricle, the heart rate can decrease and still maintain a level of cardiac output necessary for the body. Therefore, it is very common for athletes with AHS to have lower resting heart rates than nonathletes.

The heart becomes enlarged, or hypertrophic, due to intense cardiovascular workouts, creating an increase in stroke volume, an enlarged left ventricle (and right ventricle), and a decrease in resting pulse along with irregular rhythms. The wall of the left ventricle increases in size by about 15-20% of its normal capacity. There is no decrease of the diastolic function of the left ventricle. The patient may also experience an irregular heartbeat and a resting pulse rate between 40-60 beats per minute, also known as bradycardia.

The level of physical activity in a person determines what physiological changes the heart makes. There are two types of exercise: Static (strength-training) and dynamic (endurance-training). Static exercise consists of weight lifting and is mostly anaerobic, meaning the body does not rely on oxygen for performance. It also moderately increases heart rate and stroke volume (oxygen debt). Dynamic exercises are running, swimming, skiing, and cycling, which rely on oxygen from the body. This type of exercise also increases both heart rate and stroke volume of the heart. 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. It has been shown that once athletes stop training, the heart returns to its normal size.