5 facts about a runner’s heart

Like any muscle, the heart adapts to exercise by getting bigger and stronger and, therefore, better at delivering blood to your working muscles. The illustration above (in black) show some of the adaptations you can expect to find in a runner’s pump compared with a ‘normal’ heart (in blue). Here are five facts about a runner's heart: 

1. It's bigger 

An endurance athlete’s heart can be up to 50 per cent bigger than a non-athlete’s heart.

2. It can pump more blood around the body

The atria, the upper two ‘filling chambers’ where blood arrives in the heart, are enlarged, as are the ventricles, the two lower chambers that pump blood around the body.

Related: Amby Burfoot on running and the heart disease diagnosis that threatened to stop him 

3. It has more flexible coronary arteries 

The vessels that supply blood to the muscles of the heart are able to expand more to allow more blood flow during exercise even when there are some cholesterol deposits. This ability to dilate makes it easier for blood to get around any partial blockages.

4. It has wider, more abundant coronary capillaries 

The secondary network of vessels that distribute blood to muscles of the heart may be two to three times bigger than normal.

5. It has denser plaques in arteries 

Left: A cross-section of a coronary artery shows the plaque accumulation of atherosclerosis: blobs of cholesterol (yellow) with dots of calcium (blue).

Right: In patients taking statins, plaques tend to have less cholesterol but more calcium, which hardens into dense bands. This leads to high coronary artery calcium scores, but dense plaques may be less likely to rupture and cause a heart attack. Emerging evidence suggests that plaques in runners, too, may be denser and more stable.

Related: Running - heart healthy or a heart risk?