Marathon runners who are not fully fit should take heed – they can cause damage to their heart that will take three months to repair, according to researchers.
Scientists studied the heart function of a number of healthy amateur runners before and after the 26mile run using magnetic resonance imaging.
The researchers from the Heart and Stroke Foundation found the less time the competitors had prepared for the race beforehand, the higher their risk of heart damage.
‘Marathon runners can be a lot less fit than they think,’ Dr Eric Larose told the Canadian Cardiovascular Congress 2010.
He said that lack of real aerobic fitness may directly impact the ways the heart organises itself to survive the stress of marathon running.
The research revealed that the magnitude of abnormal heart segments was more widespread and significant in a group of less fit runners.
‘Without proper training, marathon running can damage your heart. Fortunately the exercise-induced injury is reversible over time,’ said Dr Larose.
‘But it could take up to three months to completely recover.’
They studied the effects on the heart using MRI measurements. The left ventricle of the heart is divided into 17 segments that make up the heart as a whole. When a segment is injured – or stressed out – during the marathon, its neighbours on either side can take over to perform the function of the damaged area.
This makes the heart as a whole appear stronger and fitter than is really the case when considering each individual segment.
It also makes it practically impossible for doctors to arrive at an accurate assessment of the heart health of the marathoner when only considering the whole heart.
‘The heart isn’t simply playing tricks – this may be an important adaptive survival mechanism, like the way the brain can switch function after a stroke,’ said Dr Larose from Laval University.
‘Unfortunately, as a result, the data produced by traditional means may be inconsistent and misleading.’
Heart and Stroke Foundation spokesperson Dr Beth Abramson said that marathons were becoming popular with older runners who had it on their ‘to do’ lists.
She stressed that runners need to train properly, stay hydrated and most importantly, speak to their doctor about what is right for them.