In the first study mentioned above, published in the Journal of Applied Physiology in February, researchers recruited a group of extremely fit older men. All of them were members of the 100 Marathon club, meaning athletes who had completed a minimum of 100 marathons. Their ages ranged from 26 to 67, and all of them had trained vigorously throughout adulthood.
The control group consisted of 20 healthy men over 50, but none of them were endurance athletes.
The New York Times reported that:
"The different groups underwent a new type of magnetic resonance imaging of their hearts that identifies very early signs of fibrosis, or scarring, within the heart muscle. Fibrosis, if it becomes severe, can lead to stiffening or thickening of portions of the heart, which can contribute to irregular heart function and, eventually, heart failure.
The results, published online… in The Journal of Applied Physiology, were rather disquieting.
None of the younger athletes or the older nonathletes had fibrosis in their hearts. But half of the older lifelong athletes showed some heart muscle scarring. The affected men were, in each case, those who'd trained the longest and hardest. Spending more years exercising strenuously or completing more marathon or ultramarathon races was, in this study, associated with a greater likelihood of heart damage.