Researchers, part-funded by us, have shown that even just a few hours of exercise each week can enlarge the heart. This is a normal and beneficial response to exercise which can make the heart stronger and more efficient. It had, until now, only been seen in athletes but these findings could affect diagnosis of heart conditions which also affect the heart's size and shape.
The researchers, from the MRC Clinical Sciences Centre based at Imperial College London, studied the MRI scans of over 1,000 people in one of the largest studies of its kind. They recorded the participants' activity levels over the past year, according to how many hours exercise they did each week.
Around one third of the volunteers reported doing three to five hours exercise a week and one in five of these people subsequently developed an enlarged heart. In people who did more than five hours exercise, almost half had similar heart adaptations.
Developing an 'athlete's heart'
Doctors can use MRI scans to diagnose heart conditions, which can appear as an enlarged heart on the scan. This would be normal if the person was an elite athlete. But these findings indicate that just moderate physical activity can affect the heart enough to impact on diagnosis.
Dr Declan O'Regan, one of the lead researchers on the study published in Circulation: Cardiovascular Imaging, explained: "It's well known that the hearts of endurance athletes adapt in response to exercise, a phenomenon called 'athlete's heart'. This study is the first to show that healthy adults who do regular exercise may also develop enlarged hearts. As a result, there's a risk that some active adults could be misdiagnosed with heart disease."
Normal heart adaptations
This research suggests that the more exercise you do over a threshold of three hours, the more the heart is likely to adapt in response and the more pronounced the changes. The heart muscle gets thicker and the heart's chambers and the volume of the heart chambers increase.
These adaptations allow the heart to pump more blood, so the body's muscles get the oxygen and nutrients required during exercise. Dr O'Regan said: It's a completely normal, healthy response. It shouldn't be misdiagnosed as heart disease." It would, however, be a concern if the doctor detects changes in the heart's thickness and volume in isolation, rather than in tandem.
Changing clinical guidelines
Across the world doctors use a standard set of values to judge whether a person's heart thickness and volume is in the healthy or abnormal range. This ensures consistent diagnoses in different hospitals. But, according to the researchers, the current diagnostic criteria were set using evidence from a much smaller study with people who were not as physically active. The findings of this study could therefore change how doctors around the world diagnose heart conditions.
Our Research Advisor, Dr Noel Faherty, said: "The events in Rio will undoubtedly inspire many of us to put on our running shoes and get active. And this interesting research shows that even moderate physical activity is associated with changes in the heart's size and shape, which are visible on a cardiac MRI.
"Detectable changes to the heart on an MRI scan are common in elite endurance athletes but some heart conditions, like cardiomyopathy, can be diagnosed by detecting similar changes. This study demonstrates the importance of documenting the MRI appearance of healthy, active people's hearts so normal adaptive changes are recognised by doctors and not mistaken for disease."
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