Athlete’s Heart: Why Bigger is Not Always Better, or Worse

Alberto Contador Velasco is a Spanish former professional cyclist. He is one of the most successful riders of his era, winning the Tour de France twice, the Giro d’Italia twice, and the Vuelta a España three times.

What doesn’t kill you does not always make you stronger.

But it doesn’t necessarily make you weaker, either.

At least when it comes to exercise and your heart.

Most data indicates that in the short-term, exercise doesn’t cause heart damage, even if it makes your heart a little tired.

However, this doesn’t tell us how it affects your heart in the long-term.

In this article, we’ll look at one of the last stages of the cardiotoxicity cycle — how exercise changes your heart over time, and how these changes affect your health.

How Exercise Changes Your Heart

During exercise, your cardiovascular system has to pump more blood to supply your working muscles.

With enough training, this increased demand for blood changes the shape, size, and function of your heart and blood vessels — a condition called “athlete’s heart syndrome.”

Genetics, gender, age, body size, and other factors also determine your heart size, but exercise is the main one.(1)

There are four main features of athlete’s heart:(2-20)

  1. Increased mass, thickness, and volume.
  2. Changes in filling rate, elasticity, and compliance.
  3. Increased blood vessel width, capillarization, elasticity, and blood volume.
  4. Altered electrical activity, heart rate, and heart rate variability.

The four main features of athlete’s heart.

 

It would probably be more accurate to call this “athlete’s cardiovascular system,” since it also affects the blood vessels and nervous system, but “athlete’s heart” is easier to say.

This is a huge topic, so we’ll focus on the structural changes of athlete’s heart in this article. We’ll look at how exercise changes the electrical activity of the heart later.

The Anatomy of an Athlete’s Heart

Every sport changes your heart in slightly different ways, depending on the demands.(21-24)

Endurance sports like running and cycling tend to produce eccentric hypertrophy (growth). The walls of the heart become thicker, and the chambers become wider to allow more blood inside.

On the other hand, strength and power sports like weight lifting and sprinting tend to increase the thickness of the heart walls, rather than their volume. Researchers call this concentric hypertrophy.

Sports that require both strength and endurance like swimming, rowing, and triathlon tend to produce changes somewhere in the middle.

There are some caveats to this, as heart size is also largely determined by how much you train.(25,26) Elite cyclists, rowers, and swimmers, who train more than most power athletes, can actually develop thicker hearts than weight lifters, despite being more endurance focused.(27)

Any athlete that participates in a demanding sport is likely to develop some changes in heart size. These changes can start to worry doctors if they become too great.

Is Your Heart in the “Gray Zone?”

Athlete’s heart is a spectrum.

It ranges from small, almost insignificant changes to extreme abnormalities.

In the latter cases, it’s often hard to tell the difference between athlete’s heart and heart disease, or if there is a difference.(28-29) This is especially true for endurance sports which tend to produce the largest changes, yet bodybuilders, throwers, and Olympic and power lifters can also develop enlarged hearts.

These extreme cases of athlete’s heart are in what researchers call the “gray zone” — a range somewhere between normal and abnormal.(30)

In some cases, exercise can increase the size of the heart enough to make it appear similar to heart disease. These cases of athlete’s heart are in the “gray zone.”

 

Most recreational athletes have hearts that are within the normal, safe range of healthy people.(32-35)

There is a small increase in heart size after almost any training.(36-38) This effect starts after you go past about three hours of exercise per week and stops soon after.(39-40) It takes a lot of intense training to make the heart much larger.(41-46)

In fact, only about 50% of trained athletes develop significant changes in heart size.(47-49)

Among elite endurance athletes, about 15% develop changes large enough to get close to what might be considered a sign of disease — the gray zone.(50

Most athletes don’t get close to the gray zone, but when they do, some authors believe this might be dangerous.(51-55)

Why an Enlarged Heart Might be Dangerous

Most of the time, heart enlargement (cardiac hypertrophy) is caused by heart disease.(56-58)

People with enlarged hearts have a higher risk of coronary artery disease, cerebrovascular disease, dangerous arrhythmias, cardiac failure, sudden cardiac death, and an early death from all causes.(59-66)

Studies have also shown that athlete’s with larger hearts and more training sometimes have higher levels of atherosclerosis and heart damage.(67-71)

Despite these concerns, most data indicates that athlete’s heart is safe for the majority of athletes, and may have some benefits.

Why Athlete’s Heart is Probably Not Dangerous for Most Athletes

Athlete’s heart and heart disease are both compensatory mechanisms, but with different causes.

Heart enlargement caused by heart disease is usually caused by either a genetic condition called hypertrophic cardiomyopathy (HCM) or hypertension.

It’s not clear what causes the heart to grow in HCM. In hypertensive heart disease, the heart grows larger as a way to manage the chronic increase in blood pressure. This works for a little while, but the heart often fails.(72)

Athlete’s heart is also caused by increased pressure and expansion, but it’s intermittent as opposed to chronic. The heart grows thicker, wider, and stronger to better pump blood to the working muscles.(73,74)

After a workout your heart is fatigued from the effort, and but it has time to recover and adapt, in contrast to chronic hypertension. There’s also little evidence that your heart is damaged after even the most brutal workouts.

Dr. Aaron Baggish, the author of a recent review on this topic, believes athlete’s heart is a “beneficial physiologic adaptation” to exercise.(75,76) This is opposed to a pathological adaptation, as in heart disease.

Most data suggests that athlete’s heart and heart disease are two distinct conditions, and “most authors… believe that athletic left ventricular hypertrophy [heart enlargement] is a purely physiological [safe] condition.”(77,78)

The idea that athlete’s heart is a sign of heart disease “has resurfaced numerous times over the last 110 years of scientific inquiry despite the fact that there is no clear evidence to substantiate its validity,” continues Dr. Baggish.

This doesn’t mean that athlete’s heart is completely safe, but “there is no evidence at present showing that athlete’s heart remodeling leads to long-term disease progression, cardiovascular disability, or sudden cardiac death,” writes Dr. Barry Maron, the author of another excellent review on athlete’s heart.(79)

Nevertheless, the idea that extreme athlete’s heart could be harmful in some cases “is perhaps unlikely but at this time cannot be excluded with certainty.”

There’s also little evidence that having an enlarged heart is going to make you much healthier. It’s unlikely that a marathon runner is going to have a healthier heart than someone who lifts weights a few times a week and stays active with other light activity.

In the end, there’s not much evidence having a large, athlete’s heart is bad or good for you.

In the next few articles, we’ll look at the main reasons why most researchers believe that athlete’s heart is safe, and the evidence it may be harmful. We’ll also look at ways to make sure your training does not damage your heart.

These articles are not meant to prove or disprove whether or not athlete’s heart is safe. The goal is to provide a clear view of the current evidence so you can make an informed decision about your exercise levels.

You’re reading Part 6 of a series on whether or not exercise damages your heart. Click here to read Part 7.

You can read the first post in this series by clicking here.

 

References

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2. Maron BJ, Pelliccia A. The heart of trained athletes: cardiac remodeling and the risks of sports, including sudden death. Circulation. 2006 Oct 10;114(15):1633-44. Abstract: https://pmid.us/17030703 | Full Text: https://goo.gl/qirCb | Author Contact: <hcm.maron@mhif.org>

3. Baggish AL, Wood MJ. Athlete’s heart and cardiovascular care of the athlete: scientific and clinical update. Circulation. 2011 Jun 14;123(23):2723-35. Abstract: https://pmid.us/21670241 | Full Text: https://goo.gl/fWiEj

4. Prior DL, La Gerche A. The athlete’s heart. Heart. 2012 Jun;98(12):947-55. doi: 10.1136/heartjnl-2011-301329. Abstract: https://pmid.us/22626903 | Full Text: Received from author.

5. La Gerche A, Taylor AJ, Prior DL. Athlete’s heart: the potential for multimodality imaging to address the critical remaining questions. JACC Cardiovasc Imaging. 2009 Mar;2(3):350-63. Abstract: https://pmid.us/19356581 | Full Text: https://goo.gl/K6iT2

6. George K, Spence A, Naylor LH, et al. Cardiac adaptation to acute and chronic participation in endurance sports. Heart. 2011 Dec;97(24):1999-2004. Epub 2011 Nov 5. Abstract: https://pmid.us/22058283 | Full Text: Received from author. | Author Contact: <K.George@ljmu.ac.uk>

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8. Bhella PS, Levine BD. The Heart of a Champion. J Am Coll Cardiol. 2010;55(15):1626-1628. doi:10.1016/j.jacc.2009.12.030. Abstract: https://pmid.us/20378082 Full Text: https://goo.gl/TYG6W

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22. Spence AL, Naylor LH, Carter HH, et al. A prospective randomised longitudinal MRI study of left ventricular adaptation to endurance and resistance exercise training in humans. J Physiol. 2011 Nov 15;589(Pt 22):5443-52. doi: 10.1113/jphysiol.2011.217125. Epub 2011 Oct 3. Abstract: https://pmid.us/21969450 | Full Text: https://goo.gl/W1Otl

23. Baggish AL, Wood MJ. Athlete’s heart and cardiovascular care of the athlete: scientific and clinical update. Circulation. 2011 Jun 14;123(23):2723-35. Abstract: https://pmid.us/21670241 | Full Text: https://goo.gl/fWiEj

24. Prior DL, La Gerche A. The athlete’s heart. Heart. 2012 Jun;98(12):947-55. doi: 10.1136/heartjnl-2011-301329. Abstract: https://pmid.us/22626903 | Full Text: Received from author.

25. Pelliccia A, Culasso F, Di Paolo FM, et al. Physiologic left ventricular cavity dilatation in elite athletes. Ann Intern Med. 1999 Jan 5;130(1):23-31. Abstract: https://pmid.us/9890846 | Full Text: NA

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34. Baggish AL, Wood MJ. Athlete’s heart and cardiovascular care of the athlete: scientific and clinical update. Circulation. 2011 Jun 14;123(23):2723-35. Abstract: https://pmid.us/21670241 | Full Text: https://goo.gl/fWiEj

35. La Gerche A, Taylor AJ, Prior DL. Athlete’s heart: the potential for multimodality imaging to address the critical remaining questions. JACC Cardiovasc Imaging. 2009 Mar;2(3):350-63. Abstract: https://pmid.us/19356581 | Full Text: https://goo.gl/K6iT2

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74. Green DJ, Naylor LH, George K. Cardiac and vascular adaptations to exercise. Curr Opin Clin Nutr Metab Care. 2006 Nov;9(6):677-84. Abstract: https://pmid.us/17053419  | Full Text: https://goo.gl/hj036

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76. Baggish AL, Wood MJ. Athlete’s heart and cardiovascular care of the athlete: scientific and clinical update. Circulation. 2011 Jun 14;123(23):2723-35. Abstract: https://pmid.us/21670241 | Full Text: https://goo.gl/fWiEj

77. Hildick-Smith DJ, Shapiro LM. Echocardiographic differentiation of pathological and physiological left ventricular hypertrophy. Heart. 2001 Jun;85(6):615-9. Abstract: https://pmid/11359735 | Full Text: https://goo.gl/kr8wy

78. Maron BJ, Pelliccia A. The heart of trained athletes: cardiac remodeling and the risks of sports, including sudden death. Circulation. 2006 Oct 10;114(15):1633-44. Abstract: https://pmid.us/17030703 | Full Text: https://goo.gl/qirCb | Author Contact: <hcm.maron@mhif.org>

79. Maron BJ, Pelliccia A. The heart of trained athletes: cardiac remodeling and the risks of sports, including sudden death. Circulation. 2006 Oct 10;114(15):1633-44. Abstract: https://pmid.us/17030703 | Full Text: https://goo.gl/qirCb | Author Contact: <hcm.maron@mhif.org>

80. Maron BJ, Pelliccia A. The heart of trained athletes: cardiac remodeling and the risks of sports, including sudden death. Circulation. 2006 Oct 10;114(15):1633-44. Abstract: https://pmid.us/17030703 | Full Text: https://goo.gl/qirCb | Author Contact: <hcm.maron@mhif.org>

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