The athlete’s heart refers to the normal changes that occur when a person regularly engages in intense physical activity. Among these adaptations, cardiac hypertrophy is often observed—meaning an increase in the size or thickness of the heart muscle.
In most cases, these modifications are beneficial and reversible. They reflect the heart’s ability to adapt to repeated effort and improve its efficiency.
A Muscle Pump in Training
The heart acts like a muscular pump that propels bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood throughout the body. When stimulated regularly and intensely, it can transform—this is the phenomenon of cardiac remodeling.
The analogy with weight training is clear: muscles grow under the effect of sustained exercise. In the same way, the heart strengthens its walls when it must eject bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood against greater resistance. This results in left ventricular hypertrophy.
When Adaptation Crosses the Line
Although athlete’s heart hypertrophy is generally harmless, certain situations can push this natural mechanism into a pathological risk:
- Overtraining, which exhausts the cardiac muscle and may cause rhythm disturbances or reduced performance.
- Doping, which artificially intensifies remodeling and weakens the heart, increasing the risk of severe arrhythmias or even sudden death.
It is therefore essential to distinguish the healthy athlete’s heart—a simple sign of good adaptation—from the excesses associated with inappropriate or dangerous sports practices.
The Athlete’s Heart – A Normal Adaptation
This text presents the normal adaptations of the athlete’s heart muscle and emphasizes the importance of ensuring that it is not a cardiomyopathy, meaning an actual heart disease.
Don’t Confuse Things
Physical activity, when pushed to an athletic level, can lead to remodeling of the heart, particularly of the left ventricle.
But this is not the effect of jogging for an hour three times a week or doing four weekly weight training sessions. These habits are excellent for health, but they are not enough to significantly alter the structure of the heart.
What Do We Mean by an Athlete?
An athlete is defined as someone—young or older, amateur or professional—who trains regularly and competes in official competitions, whether at the local, national, or international level.
However, even within this group, not everyone develops an athlete’s heart. For remodeling to occur, two conditions must be met: a high level of intensity and a high training volume.
- High intensity, meaning sessions where the heart rate reaches about 75% of the maximum for age.
- High training volume, meaning several hours per week (often 7 to 10 hours or more) sustained for at least three months.
Not All Sports Have the Same Effect
Each sport stresses the heart in a different way:
- A weightlifter, focused on pure strength, develops a heart in which the left ventricle thickens concentrically, much like a muscle reinforced by high resistance.
- A marathon runner, focused on endurance, develops eccentric hypertrophy: the left ventricular cavity enlarges, allowing the heart to fill with and eject a greater volume of bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood with each beat.
This adaptation explains why endurance athletes often have a lower resting heart rate. Their heart beats more slowly but pumps more bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood with every contraction.
Sometimes, a slightly reduced ejection fraction at rest may be observed during echocardiography or cardiac MRI. This is not a sign of weakness: as soon as exercise resumes, contraction returns to completely normal values.
Between Endurance and Strength, a Continuum
Between the weightlifter and the marathon runner lies a whole spectrum of sports. Depending on the degree of endurance or strength required, left ventricular remodeling will take on a particular profile, combining enlargement and thickening in varying proportions.
Classifying Sports for Better Understanding
To simplify, specialists group sports into four categories:
- Strength (wrestling, weightlifting, downhill skiing) → thickening of the heart muscle.
- Endurance (cycling, triathlon, rowing) → enlargement of the cavity.
- Mixed (soccer, hockey, American football) → a combination of both types of remodeling.
- Skill (golf, curling, table tennis) → little or no cardiac modification.
Differences by Sex and Origin
Cardiac remodeling is not identical in all athletes. Women generally develop less pronounced adaptations than men. Left ventricular enlargement is more modest, and thickening of the heart muscle is also more limited.
In addition, ethnic differences have been observed. Athletes of Afro-Caribbean origin, for example, often show more significant remodeling in response to training than those from other ethnic backgrounds.
What About Arrhythmias in Athletes?
Even when the heart adapts harmoniously, some high-level athletes may develop rhythm disturbances.
- Ventricular Extrasystoles
Ventricular extrasystoles are premature heartbeats. They are common in athletes but also in the general population. In the vast majority of cases, they are harmless and do not compromise health or the practice of sports.
- Atrial Fibrillation
A more significant issue, however, attracts the attention of specialists: atrial fibrillation. This arrhythmia results in an irregular, often rapid heartbeat and is observed more frequently in endurance athletes than in the general population of the same age.
The exact cause of this phenomenon is still under investigation. It is thought that enlargement of the atriaThe atria are the two upper chambers of the heart. They act as reservoirs for blood that will fill the ventricles., the intensity of repeated efforts, and certain electrical changes specific to the athlete’s heart may play a role.
Atrial fibrillation requires particular attention, since it can sometimes lead to the formation of a bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood clot that may travel to the brain and cause a stroke.
Preventing this potential complication does not apply to all athletes. It is mainly indicated for those with additional risk factors, such as advanced age or certain medical conditions (hypertension, diabetes, heart disease).
- Ventricular Tachycardia
A small subgroup of athletes may develop frequent ventricular extrasystoles that evolve into ventricular tachycardia. This arrhythmia is more concerning because it is sometimes linked to extreme remodeling of the heart muscle or cavity size.
In such cases, it reflects a pathological process and may expose the athlete to a life-threatening risk. Continuing competitive activity then becomes dangerous and must be reassessed by the medical team.
A Diagnostic Challenge
Evaluating the athlete’s heart is complex. The type of sport practiced, the intensity and volume of training, as well as sex and ethnic origin, are all factors to consider.
The real challenge lies in distinguishing between normal remodeling due to training and an underlying heart disease (such as a cardiomyopathy). This boundary can sometimes be difficult to define, and making an accurate diagnosis is essential, since the athlete’s safety during training and competition depends on it.
Distinguishing an Athlete’s Heart from Heart Disease
Cardiac remodeling observed in athletes may sometimes resemble a heart condition, particularly certain cardiomyopathies (such as hypertrophic or dilated forms). For specialists, the challenge is to differentiate between a normal adaptation and a pathological condition that could be life-threatening.
- Electrocardiogram (ECG)
The ECG is often the first tool used. In athletes, certain tracings considered “abnormal” in the general population may be completely harmless: bradycardia (a slow heartbeat), minor conduction blocks, or repolarization changes.
However, more pronounced abnormalities—such as deeply inverted T waves or signs of disproportionate hypertrophy—may point toward an underlying disease.
- Echocardiography
Cardiac ultrasound allows direct visualization of the heart’s structure. In an athlete’s heart, moderate and generally harmonious hypertrophy is observed, with good systolic and diastolic function.
On the other hand, excessive asymmetry, poor muscle contraction, or disproportionate dilation of a cavity suggest a pathological cardiomyopathy.
- Cardiac Magnetic Resonance Imaging (MRI)
MRI provides an even more detailed view. It not only measures volumes and wall thickness but can also detect fibrosis (scarring within the heart muscle). Fibrosis is rarely present in a healthy athlete’s heart but is common in cardiomyopathies and in remodeling associated with doping.
In Practice
Distinguishing a healthy athlete’s heart from a pathological cardiomyopathy therefore requires a combined approach involving:
- Analysis of the sports context (type, volume, and intensity of training),
- Clinical examination,
- Imaging and cardiac function tests.
Careful follow-up is indispensable, since a mistaken diagnosis could either unfairly exclude an athlete from their sport or, conversely, expose someone with disease to serious—even fatal—risks by allowing them to continue competing.
The Reversibility Test
A key element in clarifying the diagnosis is prolonged rest. In athletes, a significant reduction in training often leads to partial or complete regression of remodeling (thinner walls, cavities returning to normal size).
If, on the other hand, hypertrophy or dilation persists despite stopping exercise, this increases the likelihood of a genuine underlying condition.
What About the Right Ventricle?
Remodeling of the right ventricle is mainly seen in endurance sports such as long-distance running, cycling, or triathlon. In these situations, the cavity dilates in a manner similar to the left ventricle—this is referred to as balanced or harmonious dilation.
On the other hand, thickening of the right ventricular muscle is not expected in athletes. When it is present, it represents an abnormal finding that should raise suspicion of heart disease.
Thus, whether on the left or the right side, the athlete’s heart undergoes transformations adapted to the demands of training. But these structural changes are not the only features observed.
In some athletes, these adaptations may be accompanied by electrical disturbances, leading to arrhythmias. These rhythm disorders are sometimes benign but, in certain cases, can become concerning or even dangerous.
Conclusion
The athlete’s heart is a remarkable illustration of the human body’s ability to adapt to effort. The thickening and/or enlargement of the cardiac chambers observed in high-level athletes are most often physiological, reversible, and harmless phenomena when they occur in the context of well-guided training.
These adaptations vary according to the type of sport, the intensity and volume of training, but also according to sex and ethnic background. In some athletes, they may be associated with rhythm disturbances, particularly atrial fibrillation, whose exact causes are still being studied. This condition requires special vigilance, especially in older athletes or those with cardiovascular risk factors.
In summary, the athlete’s heart represents a normal and beneficial adaptation of the body. It reminds us that with progressive and balanced training, sport can transform the heart into a more efficient pump—capable of supporting exceptional performance while remaining an ally for health.
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