The Two Activities That Can Actually Shrink Your Heart

We all know that exercise is good for our hearts. Whether you're running, hiking, biking, or dancing, vigorous physical movement has plenty of benefits for our cardiovascular health. Exercise can strengthen the heart just like any other muscle, but can it cause it to shrink?

When we exercise regularly, we prevent having a sudden heart attack and "modify many of the risk factors for heart disease," Dr. Kerry Stewart, director of Clinical and Research Exercise Physiology at Johns Hopkins Bayview, told Johns Hopkins Medicine. Habitual exercise guards against diabetes, helps us maintain our weight, reduces inflammation, lowers blood pressure, and reduces stress hormones that can put an extra burden on the heart.

Moreover, exercise actually can make your heart grow bigger (via NewScientist). It shouldn't be surprising that the more exercise you do, the larger your heart — which is, after all, a muscle — can get. But what might be shocking is that some activity can cause the opposite to happen.  

When the heart doesn't have to work as hard

A 2021 study published in the American Heart Association's journal Circulation found that both spaceflight and long-distance swimming can in effect cause the heart to shrink. Because the pressure of gravity isn't as strong on the heart during these two activities, the heart doesn't have to work as hard (via LiveScience). And when the heart muscle isn't working as hard, it shrinks.

The study looked at the heart of retired astronaut Scott Kelly, who spent 340 days in space and exercised regularly, and that of endurance swimmer Benoît Lecomte, who swam 1,753 miles across the Pacific Ocean. Data showed that both men lost between 19% and 25% of mass in their hearts' left ventricles. Dr. Benjamin D. Levine, study author and internal medicine professor at UT Southwestern Medical Center said, "The heart is remarkably plastic and especially responsive to gravity or its absence. Both the impact of gravity as well as the adaptive response to exercise play a role, and we were surprised that even extremely long periods of low-intensity exercise did not keep the heart muscle from shrinking," (via The American Heart Association). Researchers concluded that high-intensity exercise by astronauts in space may be necessary to maintain heart health.