Athlete's heart: why the hearts of 291 people grow the same, but remodel differently.

Athlete's heart isn't a metaphor, but a measurable fact. In trained individuals, the heart is literally larger in size. A new study by Hofbauer and colleagues in the European Journal of Preventive Cardiology (2026) measured the hearts of 291 healthy, active individuals using 3D ultrasound. And an interesting asymmetry was found. Heart enlargement depends on endurance levels almost equally in men and women. However, the degree of remodelling at the same VO₂peak turned out to be different.

This is not «news of the day» about another benefit of sport. This is about how the body's main muscle adapts. And why your heart on an echocardiogram might look «too big» without actually being ill. Athlete's heart lives precisely in this grey area between normal and diagnosis.

The study showed that [details of the study's findings] regarding athletes' hearts.

A team from the University of Vienna surveyed 291 healthy individuals aged 27±4 years. Among them were 129 women and 162 men, all of whom exercised regularly. This was not a one-off measurement. Each participant underwent three-dimensional echocardiography – the most accurate method for ultrasound assessment of heart structure. In parallel, a stress test was performed, measuring peak oxygen consumption, VO₂peak. This is an objective marker of aerobic endurance that is independent of subjective assessments of «how much I exercise».

Participants were divided into three fitness levels according to VO₂peak, separately for each sex. The median VO₂peak was 48 ml/min/kg for women and 55 for men. This is a fundamentally important detail of the sample. There are neither Olympians nor couch potatoes here. This is precisely the «recreational» middle ground that most people who go to the gym or run in the park fall into.

Why was this necessary? Athletes' heart has until now been described predominantly in professional athletes. What the heart of an ordinary trained person looks like – there was a lack of data. A doctor, looking at the ultrasound of an active patient, had no clear guidelines. This study fills precisely that gap.

It is worth explaining separately why three-dimensional ultrasound was used, rather than standard two-dimensional ultrasound. Classic echocardiography measures the heart in planes and then calculates the volume using formulas. This introduces an error, especially when the chambers are enlarged in a non-standard way. The three-dimensional method reconstructs the actual chamber volume without assumptions about its shape. For assessing an athlete's heart, where the geometry often deviates from «textbook» limits, this accuracy is critical. This is precisely why the obtained figures can be taken as a reference, rather than an approximate guideline.

The heart grows with endurance

The main result is simple. The higher the VO₂peak, the larger the volumes of all heart chambers. And this works in both sexes without exception.

The left ventricular index was calculated relative to body surface area. This eliminates the influence of height and weight, leaving only pure adaptation. This indicator increased from low to high fitness levels as follows. In women, from 73 to 88 ml/m², i.e. by approximately 21%. In men, from 82 to 99 ml/m². Similarly, the right ventricle, left atrium, myocardial mass and stroke volume increased. Greater endurance — a bigger heart.

An important detail concerns the mechanism. The VO₂peak-dependent increase turned out to be sex-independent. This means the «better endurance equals a larger heart» relationship itself is the same for everyone. Genes, hormones, and body size affect the absolute numbers in millilitres. However, the vector of adaptation is common to men and women. The athlete's heart forms according to a single principle, regardless of sex.

Where does the sex difference hide

And now for the nuance, which is worth reading on for. With the same VO₂peak, men demonstrated more pronounced cardiac remodelling than women.

Let me phrase it differently. Take a man and a woman with identical endurance. The man's heart will rebuild itself more strongly. Women show the same adaptation, but on a softer scale. This does not mean «a woman's heart is weaker». It's a different scale of the same physiological response to the same load. Two people with the same VO₂peak can have differently remodelled hearts simply due to sex.

Why is this important in practice? Historically, standards for assessing the athlete's heart have been built predominantly on men. A woman's heart, assessed by a male scale, risks being incorrectly labelled as either «insufficiently adapted» or the opposite. The research provides separate reference values for each sex. This is precisely the tool that sports medicine cardiologists have been lacking.

Interestingly, the difference in remodelling does not boil down to a difference in body size. The authors calculated all volumes relative to body surface area precisely to eliminate the effect of height and weight. Men are taller and heavier – that's obvious. But even after accounting for size, the remodelling vector remained more pronounced in them. This means that the difference is due to sex itself, not simply «men are bigger». Probable causes include hormonal background and differences in the myocardium's response to the same load. The exact mechanism is yet to be unravelled.

The ejection fraction is unchanged, and that is good.

This is the most beautiful part of the results. The heart chambers grow, myocardial mass grows. And the ejection fraction of the athlete's heart remains stable at all fitness levels. Ejection fraction is the percentage of blood that the heart pumps out with each beat. In other words, it's an indicator of the quality of the pump's work, not its size.

Furthermore, the left ventricular ejection fraction was even higher in women than in men. Median 61% versus 58%. The heart does not «stretch from overload» and does not lose its tone. It effectively increases its stroke volume whilst maintaining the quality of each contraction.

This is the key difference between healthy adaptation and illness. In pathological enlargement of the heart, its function declines. The heart becomes large but weak. Here, it's the opposite. A larger reservoir of blood with unchanged ejection efficiency. Training builds a more powerful pump, not a worn-out one.

There is also simple physiological logic behind these figures. A more resilient heart pumps more blood per beat, so it can beat less frequently at rest. Hence the famous «athlete's low pulse» – not an anomaly, but a consequence of a greater stroke volume. In the study, the stroke volume of the left ventricle increased along with the chambers: a fitter heart delivers more blood per contraction. The pump became larger, so it needs fewer beats for the same amount of work. This works in both men and women.

Athletes heart from illness

This is where the practical value of the work is highest. An enlarged heart on ultrasound lies in a grey area. The boundary between normal adaptation and cardiomyopathy can be blurred. An error in either direction is costly. A healthy person can be frightened by a diagnosis. Or a real illness can be missed, dismissed as being due to sport.

Researchers have found markers that distinguish physiology from pathology. The ratio of left to right ventricle volumes remained constant, around 1.1, across all fitness levels. The same applies to the ratio of ventricle to atrium. The heart grows in a balanced way. All chambers increase proportionally, without a bias to one side.

And here, the remodelling index, meaning the ratio of mass to volume, slightly decreased with increasing trainability. In women, from 0.97 to 0.88. This is a sign of «eccentric» enlargement. The chamber fills with volume, and the wall does not thicken. This is the opposite of hypertrophic cardiomyopathy, where the wall thickens with a small chamber volume. The direction of remodelling is a simple diagnostic clue.

What to do with this

There are three practical conclusions, and they are not banal.

First. If you exercise regularly and your echocardiogram shows «heart slightly larger than normal», this is most likely athlete's heart, not a diagnosis. Especially when the ejection fraction is normal and the chambers are proportionally enlarged. However, it must be interpreted by a cardiologist, not a calculator or an online article. Common sense here does not replace a doctor.

Secondly, women should insist that their hearts are assessed according to female standards. The male scale will exaggerate «deviations» where there are none. Separate reference values now exist – it's a matter of awareness.

Third. VO₂peak is the best indicator of cardiac adaptation, better than «hours per week». Endurance, measured objectively, predicts cardiac hypertrophy regardless of the sport. I wrote about the link between aerobic fitness and vascular health in breakdown of aerobic capacity. And as for why fitness is stronger than heart genetics — in a separate post.

Athlete's heart is proof that the body intelligently adapts to exertion. The heart doesn't wear out from cardio. It becomes a larger and more efficient reservoir. Exactly as much as you train it.

---

Sources

Pelliccia A, et al. Expanding our understanding of exercise-induced cardiac remodelling: the recreational athlete’s heart (editorial). European Journal of Preventive Cardiology. 2026. DOI: 10.1093/eurjpc/zwag001Athlete's heart is not a metaphor, but a measurable fact. Trained individuals have literally larger hearts. New research by Hofbauer and colleagues in the European Journal of Preventive Cardiology (2026) measured the hearts of 291 healthy, active individuals using 3D ultrasound. And they found an interesting asymmetry. Heart enlargement depends on endurance levels almost equally in men and women. However, the degree of remodelling at the same VO₂peak turned out to be different.

Hofbauer T, Heber S, Schoeny H, et al. The recreational athlete’s heart: sex-specific three-dimensional echocardiographic reference values in relation to VO₂peak. European Journal of Preventive Cardiology. 2026;33(8):1379-1388. DOI: 10.1093/eurjpc/zwaf758

Pluim BM, Zwinderman AH, van der Laarse A, van der Wall EE. The athlete’s heart. A meta-analysis of cardiac structure and function. Circulation. 2000;101(3):336-344. DOI: 10.1161/01.cir.101.3.336

This is not «news of the day» about another benefit of sport. This is about how the body's main muscle adapts. And why your heart on an echocardiogram might look «too big» without actually being ill. Athlete's heart lives precisely in this grey area between normal and diagnosis.

The study showed that [details of the study's findings] regarding athletes' hearts.

A team from the University of Vienna surveyed 291 healthy individuals aged 27±4 years. Among them were 129 women and 162 men, all of whom exercised regularly. This was not a one-off measurement. Each participant underwent three-dimensional echocardiography – the most accurate method for ultrasound assessment of heart structure. In parallel, a stress test was performed, measuring peak oxygen consumption, VO₂peak. This is an objective marker of aerobic endurance that is independent of subjective assessments of «how much I exercise».

Participants were divided into three fitness levels according to VO₂peak, separately for each sex. The median VO₂peak was 48 ml/min/kg for women and 55 for men. This is a fundamentally important detail of the sample. There are neither Olympians nor couch potatoes here. This is precisely the «recreational» middle ground that most people who go to the gym or run in the park fall into.

What was the point of this? The athlete's heart has so far been described predominantly in professional athletes. What the heart of an ordinary, fit person looks like – there was a lack of data. Doctors, looking at ultrasounds of active patients, lacked clear benchmarks. This study fills precisely that gap.

It is worth explaining separately why three-dimensional ultrasound was used and not ordinary two-dimensional. Classic echocardiography measures the heart in planes and then calculates the volume using formulas. This leads to errors, especially when the chambers are enlarged in a non-standard way. The three-dimensional method reconstructs the actual volume of the chamber without assumptions about its shape. This accuracy is critical for assessing an athlete's heart, where the geometry often goes beyond «textbook» limits. This is precisely why the resulting figures can be taken as a reference, rather than an approximate guideline.

The heart grows with endurance

The main result is simple. The higher the VO₂peak, the larger the volumes of all heart chambers. And this works in both sexes without exception.

The left ventricular index was calculated relative to body surface area. This eliminates the influence of height and weight, leaving only pure adaptation. This indicator increased from low to high fitness levels as follows. In women, from 73 to 88 ml/m², i.e. by approximately 21%. In men, from 82 to 99 ml/m². Similarly, the right ventricle, left atrium, myocardial mass and stroke volume increased. Greater endurance — a bigger heart.

An important detail concerns the mechanism. The VO₂peak-dependent increase was found to be sex-independent. In other words, the link itself – «better endurance gives a bigger heart» – is the same for everyone. Genes, hormones, and body size influence the absolute figures in millilitres. However, the vector of adaptation is common to men and women. The heart responds to training according to a single principle.

Where does the sex difference hide

And now for the nuance, which is worth reading on for. With the same VO₂peak, men demonstrated more pronounced cardiac remodelling than women.

Let me phrase it differently. Take a man and a woman with identical endurance. The man's heart will rebuild itself more strongly. Women show the same adaptation, but on a softer scale. This does not mean «a woman's heart is weaker». It's a different scale of the same physiological response to the same load. Two people with the same VO₂peak can have differently remodelled hearts simply due to sex.

Why is this important in practice? Standards for assessing an athlete's heart have historically been based mainly on men. A woman's heart, assessed by a male scale, risks receiving the wrong label. Either «not sufficiently adapted» or, conversely, the opposite. The study provides separate reference values for each sex. This is precisely the tool that sports medicine cardiologists have been lacking.

Interestingly, the difference in remodelling does not boil down to a difference in body size. The authors calculated all volumes relative to body surface area precisely to eliminate the effect of height and weight. Men are taller and heavier – that's obvious. But even after accounting for size, the remodelling vector remained more pronounced in them. This means that the difference is due to sex itself, not simply «men are bigger». Probable causes include hormonal background and differences in the myocardium's response to the same load. The exact mechanism is yet to be unravelled.

The ejection fraction is unchanged, and that is good.

This is the most beautiful part of the results. The heart chambers are growing, and the myocardial mass is increasing. The ejection fraction remains stable at all fitness levels. The ejection fraction is the percentage of blood the heart pumps out with one contraction. This means it's an indicator of the pump's performance quality, not its size.

Furthermore, the left ventricular ejection fraction was even higher in women than in men. Median 61% versus 58%. The heart does not «stretch from overload» and does not lose its tone. It effectively increases its stroke volume whilst maintaining the quality of each contraction.

This is the key difference between healthy adaptation and illness. In pathological enlargement of the heart, its function declines. The heart becomes large but weak. Here, it's the opposite. A larger reservoir of blood with unchanged ejection efficiency. Training builds a more powerful pump, not a worn-out one.

There is also simple physiological logic behind these figures. A more resilient heart pumps more blood per beat, so it can beat less frequently at rest. Hence the famous «athlete's low pulse» – not an anomaly, but a consequence of a greater stroke volume. In the study, the stroke volume of the left ventricle increased along with the chambers: a fitter heart delivers more blood per contraction. The pump became larger, so it needs fewer beats for the same amount of work. This works in both men and women.

Athletes heart from illness

This is where the practical value of the work is highest. An enlarged heart on ultrasound lies in a grey area. The boundary between normal adaptation and cardiomyopathy can be blurred. An error in either direction is costly. A healthy person can be frightened by a diagnosis. Or a real illness can be missed, dismissed as being due to sport.

Researchers have found markers that distinguish physiology from pathology. The ratio of left to right ventricle volumes remained constant, around 1.1, across all fitness levels. The same applies to the ratio of ventricle to atrium. The heart grows in a balanced way. All chambers increase proportionally, without a bias to one side.

And here, the remodelling index, meaning the ratio of mass to volume, slightly decreased with increasing trainability. In women, from 0.97 to 0.88. This is a sign of «eccentric» enlargement. The chamber fills with volume, and the wall does not thicken. This is the opposite of hypertrophic cardiomyopathy, where the wall thickens with a small chamber volume. The direction of remodelling is a simple diagnostic clue.

What to do with this

There are three practical conclusions, and they are not banal.

First. If you exercise regularly and your echocardiogram shows «heart slightly larger than normal», this is most likely athlete's heart, not a diagnosis. Especially when the ejection fraction is normal and the chambers are proportionally enlarged. However, it must be interpreted by a cardiologist, not a calculator or an online article. Common sense here does not replace a doctor.

Secondly, women should insist that their hearts are assessed according to female standards. The male scale will exaggerate «deviations» where there are none. Separate reference values now exist – it's a matter of awareness.

Thirdly, VO₂peak is a better indicator of cardiac adaptation than «hours per week.» Endurance, when measured objectively, predicts cardiac structure regardless of the sport. I wrote about the connection between aerobic fitness and vascular health in breakdown of aerobic capacity. And as for why fitness is stronger than heart genetics — in a separate post.

Athlete's heart is proof that the body intelligently adapts to exertion. The heart doesn't wear out from cardio. It becomes a larger and more efficient reservoir. Exactly as much as you train it.

Sources

• Hofbauer T, Heber S, Schoeny H, et al. The recreational athlete’s heart: sex-specific three-dimensional echocardiographic reference values in relation to VO₂peak. European Journal of Preventive Cardiology. 2026;33(8):1379-1388. DOI: 10.1093/eurjpc/zwaf758
• Pluim BM, Zwinderman AH, van der Laarse A, van der Wall EE. The athlete’s heart. A meta-analysis of cardiac structure and function. Circulation. 2000;101(3):336-344. DOI: 10.1161/01.cir.101.3.336
• Pelliccia A, et al. Expanding our understanding of exercise-induced cardiac remodelling: the recreational athlete’s heart (editorial). European Journal of Preventive Cardiology. 2026. DOI: 10.1093/eurjpc/zwag001