Athlete's Heart: Why Do Athletes' Hearts Grow Bigger?

Regular and intense physical training leads to significant physiological adaptations in the cardiovascular system. In sports cardiology , the term "athlete's heart" is used to describe the structural and functional changes that develop in the heart as a result of prolonged exercise. This is not a disease, but rather a physiological restructuring of the heart to adapt to increased physical strain .

During exercise, the oxygen demand of muscles increases. To meet this demand, the heart has to pump more blood. As a result of prolonged training, changes occur in the heart such as enlargement of the ventricular chambers, increase in myocardial wall thickness, and growth in heart mass . These adaptations support exercise performance by increasing the amount of blood the heart pumps with each beat, i.e., stroke volume .

However, some structural changes seen in the heart of athletes can resemble early signs of serious heart diseases such as hypertrophic cardiomyopathy or arrhythmogenic cardiomyopathy. Therefore, distinguishing whether the changes observed in the heart of athletes are a physiological adaptation or a symptom of an underlying heart disease is one of the most important issues in sports cardiology.

ADAPTATIONS OF THE CARDIOVASCULAR SYSTEM TO EXERCISE

Regular physical training leads to both structural (morphological) and functional changes in the cardiovascular system . The primary purpose of these changes is to meet the increased oxygen and energy needs of the muscles working during exercise. Because muscles consume significantly more oxygen during exercise, the circulatory system must be able to transport this oxygen quickly and in sufficient quantities. Therefore, over time, the heart becomes a stronger and more efficient pump.

One of the most important physiological indicators of exercise performance is called maximal oxygen consumption (VO₂max) . VO₂max represents the maximum amount of oxygen a person can utilize during intense exercise and is a key parameter indicating the capacity of the cardiovascular system. Physiologically, VO₂max depends on two main factors: the amount of blood the heart pumps and the amount of oxygen the muscles can draw from the blood. The amount of blood the heart pumps is called cardiac output and is determined by multiplying two components: heart rate and stroke volume (the amount of blood pumped with each heartbeat) . Regular training, in particular, increases stroke volume; that is, athletes' hearts can pump more blood with each beat.

The type of exercise can also determine the form of adaptations that develop in the heart. Generally, sports activities are divided into two main categories: endurance and strength exercises. Endurance exercises (e.g., long-distance running, swimming, or cycling) are usually long-duration and aerobic in nature. In these types of activities, the heart is constantly forced to pump a high volume of blood. Therefore, the heart adapts to the volume load over time , and enlargement occurs, especially in the left ventricular cavity. This is called eccentric hypertrophy . Thanks to this adaptation, the heart can pump more blood with each beat and deliver more oxygen to the muscles. In contrast, strength exercises (e.g., short-duration but high-intensity activities such as weightlifting or sprinting) create a different load on the heart. In these types of exercises, blood pressure temporarily rises considerably, and the heart is subjected to a pressure load . Therefore, the heart muscle, especially the left ventricular wall, becomes thicker. This adaptation is called concentric hypertrophy and allows the heart to work against higher pressures. However, since many sports today involve both endurance and strength components, athletes often exhibit a combination of these two adaptations.

Exercise alters not only the structure of the heart but also its control by the autonomic nervous system . Prolonged training increases parasympathetic (vagal) activity in the heart , while decreasing sympathetic activity. As a result, athletes frequently experience sinus bradycardia , or a low resting heart rate. This usually indicates that the heart is working more efficiently because, due to its stronger contractions, the athlete's heart requires fewer beats to pump the same amount of blood.

Most of these physiological adaptations are performance-enhancing changes and are considered completely normal. However, in some cases, this remodeling process in the heart can lead to arrhythmias or changes resembling early signs of structural heart disease . Therefore, the correct interpretation of cardiac adaptations seen in athletes is one of the most important issues in sports cardiology.

HOW IS ATHLETE'S HEART DIAGNOSED?

Most cardiac changes in athletes are exercise-induced physiological adaptations , but in some cases these changes can resemble early signs of heart disease. Therefore, the most important goal in sports cardiology is to differentiate athlete's heart from pathological heart disease . A single test is usually insufficient to make this distinction; instead, a multi-step evaluation approach using a combination of different clinical and imaging methods is employed.

The assessment often begins with the simplest methods. The first step involves taking a detailed medical history of the athlete and investigating symptoms such as fainting, chest pain, palpitations, or shortness of breath, especially those occurring during exercise. Additionally, a family history of sudden cardiac death at an early age or genetic heart disease can be an important clue. This information can help detect certain heart conditions, though rare, in athletes early on.

This initial assessment is usually followed by an electrocardiogram (ECG) . An ECG is a quick and easy test that records the electrical activity of the heart. It is normal for athletes to see some ECG changes due to regular training. For example, a low resting heart rate (sinus bradycardia) or some voltage increases are common physiological findings in athletes. However, some ECG patterns may suggest an underlying heart condition and may require further investigation.

If the initial assessment reveals a suspicious finding, the next step involves tests that examine the structure and function of the heart. Echocardiography is the most common of these. Echocardiography is a method that uses ultrasound to visualize the heart and provides important information about the size of the heart chambers, the thickness of the heart muscle, and the heart's pumping power. In athletes, it is generally observed that the heart chambers expand evenly and heart function is normal. This may be an indicator of exercise-induced physiological adaptation.

In some cases, it is also important to observe how the heart behaves during exercise. Therefore, methods such as exercise stress tests or 24-hour rhythm recording (Holter ECG) can be used. These tests are particularly useful for evaluating exercise-induced arrhythmias or blood pressure responses.

In more complex or uncertain cases, advanced imaging techniques may be used. One of these is cardiac magnetic resonance imaging (CMR). This method can examine the structure of the heart in great detail and reveal certain pathological changes in the heart muscle, such as fibrosis or inflammation. Therefore, it is a very valuable tool in differentiating between athlete's heart and some cardiomyopathies.

In conclusion, the evaluation of an athlete's heart is generally a step-by-step process . First, simple clinical assessments are performed, and then, if deemed necessary, more detailed tests are carried out. This approach ensures the safety of the athletes and prevents normal exercise-related adaptations from being mistakenly interpreted as disease.

THE "GREY ZONE" PROBLEM OF ATHLETE'S HEART - IS IT ATHLETE'S HEART OR A DISEASE?

One of the most challenging aspects of sports cardiology is the striking similarity between athlete's heart and certain heart diseases . Physiological changes in the heart resulting from intense and prolonged training can sometimes mimic the structural changes seen in heart disease. Therefore, some findings in athletes' hearts create a "grey zone" between physiology and pathology .

This gray area often manifests in characteristics such as heart size or wall thickness. For example, in athletes who train intensely, the left ventricular wall may thicken . This is often a normal adaptation related to exercise; however, a similar finding can also be seen in a serious heart condition such as hypertrophic cardiomyopathy (HCM) . Similarly, some athletes may experience enlargement of the heart chambers . While this change is a common physiological condition in endurance sports, in some cases it can be confused with dilated cardiomyopathy .

Another important gray area concerns right ventricular enlargement . In intense endurance sports, the right ventricle can enlarge significantly. However, some heart diseases, particularly arrhythmogenic cardiomyopathy , can lead to similar changes. Therefore, changes in the structure of the right heart in athletes need to be carefully evaluated.

Some athletes also exhibit more prominent trabecular structures on the inner surface of the heart muscle. While this is often a physiological variation, in some cases it can be confused with a rare cardiomyopathy called left ventricular non-compaction (LVNC) .

Therefore, it is not accurate to make a decision based on a single finding when evaluating an athlete's heart. Many factors are considered together to determine whether a change is physiological or pathological. These include the athlete's symptoms, family history, electrocardiogram findings, exercise capacity, and imaging results . Genetic tests or advanced imaging techniques may also be used if necessary.

Consequently, the line between athlete's heart and certain heart diseases is not always clear. Therefore, when evaluating heart changes seen in athletes, it is necessary to carefully analyze the fine line between physiological adaptation and potential cardiac disease . This approach is of great importance both for ensuring the safety of athletes and for preventing unnecessary restrictions on their participation in sports.

MAKING A DECISION BASED ON THE FINDINGS

After evaluating changes in the heart of athletes, the most important step is the clinical decision-making process . The goal at this stage is not only to make a diagnosis but also to determine whether the athlete can safely continue participating in sports. This is because some heart conditions can lead to serious complications, even sudden cardiac death, during intense physical activity.

Therefore, when evaluating the heart in athletes, imaging results alone are not considered. Many different factors are evaluated together when making a decision. These include the athlete's symptoms, exercise capacity, electrocardiogram findings, structural characteristics of the heart, and family history . If the athlete is completely asymptomatic and the changes observed in the heart during examinations are thought to be exercise-related physiological adaptations, they are generally allowed to continue their sporting activities.

However, a more cautious approach is sometimes necessary. Particularly if conditions such as cardiomyopathies, serious arrhythmias, or coronary artery disease are diagnosed, sports activities may need to be restricted. This decision may also vary depending on the type and intensity of the athlete's sport. For example, very high-intensity competitive sports may pose a greater risk for individuals with certain heart conditions.

The goal of modern sports cardiology is not to unnecessarily remove athletes from sports. Instead, the aim is to enable safe sports participation by detecting risky conditions early. Therefore, regular cardiological check-ups are of great importance for athletes, especially those who participate in competitive sports.

CONCLUSION

Athlete's heart is a result of physiological adaptations to the heart caused by regular and intense physical training . These adaptations allow the heart to work more efficiently and contribute to improved exercise performance. However, in some cases, these changes may resemble those of cardiomyopathies or other cardiovascular diseases.

Therefore, a multifaceted approach should be adopted when evaluating the heart in athletes. The combined use of clinical history, physical examination, electrocardiography, and imaging methods helps prevent the confusion of physiological adaptations with pathological conditions.

In conclusion, the concept of the athlete's heart is a significant example demonstrating the powerful impact of exercise on human physiology. A proper understanding of these adaptations is crucial for both athlete safety and the sustainability of athletic performance. Advances in sports cardiology now allow for more accurate assessment of athletes' heart health, increasing the possibility of safe sports participation.

Reference:

Palermi S, Cavarretta E, D'Ascenzi F, Castelletti S, Ricci F, Vecchiato M, Serio A, Cavigli L, Bossone E, Limongelli G, Biffi A, Monda E, La Gerche A, Baggish A, D'Andrea A. Athlete's Heart: A Cardiovascular Step-By-Step Multimodality Approach. Rev Cardiovasc Med. 2023 May 19;24(5):151. doi: 10.31083/j.rcm2405151. PMID: 39076743; PMCID: PMC11273059.