The Fitness Paradox: How Can Someone Be Extremely Fit and Still Have Plaque in Their Arteries?

You can be exceptionally fit, exercise for hours every week, have excellent cardiovascular fitness and still have a significant amount of plaque in your coronary arteries.

It sounds contradictory. Exercise is one of the most effective ways to improve cardiovascular health and reduce the risk of premature death. Yet research involving endurance athletes has found that some have more coronary artery calcium and a greater prevalence of coronary atherosclerosis than people who exercise less.

This raises an important question: if exercise is so beneficial, why do some highly trained athletes develop substantial coronary plaque?

The answer is more complicated than simply assuming that all plaque is equally dangerous, or that a high level of fitness protects someone from coronary artery disease.

What researchers have found in endurance athletes

A 2017 study published in Circulation examined 284 middle-aged male athletes and compared their lifetime exercise volumes with coronary artery findings.

The researchers found that athletes with the highest lifetime exercise volumes were more likely to have coronary artery calcium and detectable coronary plaque than those with lower exercise volumes.

The highest exercise group reported more than 2,000 MET-minutes of activity per week.

For context, a MET is a measure of energy expenditure. MET-minutes are calculated by multiplying the intensity of an activity by the time spent doing it. Around 2,000 MET-minutes might represent approximately four hours of vigorous running per week, although the equivalent time varies considerably with the activity and its intensity.

Importantly, the researchers also found differences in plaque composition. Among athletes with detectable plaque, those with higher exercise volumes were more likely to have exclusively calcified plaque and less likely to have mixed plaque.

This was an observational study. It identified an association between exercise volume and coronary findings; it did not establish that exercise caused the plaque or that the additional calcium was harmless.

Why the type of plaque matters

Coronary artery calcium is a measure of calcified plaque in the walls of the coronary arteries. It is a useful marker of atherosclerotic burden, but it does not tell the whole story.

Plaque can contain different proportions of calcium, fat, fibrous tissue and other material. Some plaque is predominantly calcified; some is noncalcified; and some is mixed.

These distinctions matter because plaque characteristics can influence the likelihood of rupture and the development of a heart attack.

A heavily calcified plaque is not automatically harmless. Nor does a lower calcium score guarantee that someone has no potentially dangerous plaque.

The 2017 athlete study raised the possibility that some of the additional plaque found in highly active people may have a different composition. But subsequent research has shown that the picture is not quite so simple.

The Master@Heart study: a more complicated picture

The 2023 Master@Heart study examined 558 men, including lifelong endurance athletes, athletes who began intensive training later in life, and healthy nonathletes.

The researchers found that lifelong endurance athletes had a higher prevalence of coronary atherosclerosis than healthy nonathletes. This included not only calcified plaque but also noncalcified and mixed plaque.

That finding challenged the idea that coronary plaque in endurance athletes is consistently more benign simply because it is associated with long-term exercise.

The study did not establish that endurance exercise caused the plaque, nor did it demonstrate that the athletes would experience more heart attacks. It did, however, show why plaque composition should not be oversimplified.

What the 2025 review found

A 2025 systematic review and meta-analysis by Guarnieri and colleagues examined coronary artery disease findings in people undertaking extreme endurance training.

Its results provide an important distinction between the amount of coronary calcium and the characteristics of the plaque detected through imaging.

The review found:

• No statistically significant difference in continuous coronary artery calcium scores between endurance athletes and comparison groups.
• Higher odds of having a CAC score above 100 and above 400 among endurance athletes.
• No higher prevalence of high-risk or obstructive coronary plaque among endurance athletes.

These findings are not contradictory. A group can have higher odds of crossing particular calcium-score thresholds without having a statistically significant difference in average or continuous calcium scores.

The review offers evidence that greater coronary calcium in endurance athletes does not necessarily correspond to a greater prevalence of high-risk or obstructive plaque.

However, there is an important limitation: the review examined imaging findings, not long-term clinical outcomes. It did not establish whether the differences in calcium scores translate into more or fewer heart attacks, cardiovascular events or deaths.

That distinction matters. Imaging can tell us a great deal about what is happening in the arteries, but it cannot by itself settle the question of long-term risk.

Does exercise volume or intensity make a difference?

The MARC-2 study, published in Circulation in 2023, followed 289 middle-aged and older male athletes for approximately 6.3 years.

The researchers observed that coronary calcium became more common over the follow-up period. The proportion of athletes with detectable CAC increased from 52% to 71%.

They did not find that total exercise volume was associated with the progression of coronary calcium or plaque.

However, they did observe different associations with exercise intensity. A higher proportion of vigorous-intensity exercise was associated with less progression of coronary calcium, while a higher proportion of very vigorous exercise was associated with more progression of calcium and plaque.

These findings are interesting, but they should not be interpreted as proof that very vigorous exercise causes coronary plaque progression. The study was observational, involved men only, and cannot establish cause and effect.

It also did not establish that the imaging changes led to more cardiovascular events.

Does a high calcium score mean exercise is dangerous?

Not necessarily.

A 2019 study published in JAMA Cardiology examined 21,758 generally healthy men enrolled in the Cooper Center Longitudinal Study.

Men reporting very high levels of physical activity were more likely to have a CAC score of 100 or higher.

But among participants with CAC scores of at least 100, high physical activity was not associated with a statistically significant increase in all-cause or cardiovascular mortality.

There are important limitations. The study was observational, involved men, and had relatively few deaths in the most active group. It examined mortality rather than providing a complete picture of nonfatal heart attacks and other cardiovascular events.

The findings offer some reassurance, but they do not prove that high levels of exercise make substantial coronary plaque harmless.

What about people who are not endurance athletes?

Research from the Multi-Ethnic Study of Atherosclerosis (MESA) provides another useful perspective.

A 2022 analysis of 6,777 MESA participants examined physical activity, coronary calcium and cardiovascular outcomes.

Among people with CAC scores below 100, those in the highest physical activity group had lower rates of cardiovascular events and all-cause mortality than those in the lowest activity group.

Among people with CAC scores of 100 or higher, the highest activity group had lower all-cause mortality, but there was no statistically significant reduction in cardiovascular events.

The results do not suggest that physical activity increases cardiovascular risk in people with higher calcium scores. They do show that the relationship between activity, calcium burden and outcomes is not identical across all groups.

This was a general-population study, not a study of lifelong endurance athletes.

What a calcium score can—and cannot—tell you

A coronary artery calcium score is useful, but it is not a complete assessment of coronary health.

It measures calcified plaque. It does not directly measure all plaque, determine exactly how much an artery is narrowed, or establish whether blood flow is being restricted.

Different tests answer different questions:

• CAC scan: Measures the amount of calcified plaque.
• Coronary CT angiography (CCTA): Shows coronary artery plaque, including calcified and noncalcified plaque, and can assess narrowing.
• Stress testing: Evaluates how the heart responds to increased workload and can identify evidence of exercise-related ischemia.
• CT-derived fractional flow reserve (CT-FFR): Estimates whether a coronary narrowing is likely to restrict blood flow.

A person can have substantial coronary plaque and still have a normal stress test. That is because the presence of plaque and the presence of exercise-induced ischemia are not the same thing.

Likewise, a high level of fitness does not establish that the coronary arteries are free of disease.

Should highly active people stop exercising?

The evidence does not support that conclusion.

Regular physical activity remains one of the most important ways to improve cardiovascular health. It helps regulate blood pressure, blood sugar, body weight and cholesterol, and is associated with lower cardiovascular and all-cause mortality.

The research on endurance athletes does not overturn those benefits.

What it does suggest is that exercise capacity and coronary artery health are two different things. Someone can have excellent fitness while also having coronary atherosclerosis.

For people with known coronary plaque, the appropriate level and intensity of exercise should be considered in the context of their overall cardiovascular assessment, symptoms, medical history and test results.

New chest discomfort, unusual breathlessness, faintness or a marked change in exercise tolerance should not be dismissed simply because someone is physically fit.

Evidence strength: MODERATE

The findings are supported by multiple observational studies and a systematic review, but important questions about cause and effect and long-term clinical outcomes remain unanswered.

For reliable information, insights and peer support, visit The High CAC Score Club on Facebook(opens in a new tab). The group is not a substitute for personal medical advice or care.