In support of that idea, a few studies in recent years have found that the hearts of lifelong male endurance athletes may contain more plaques or other signs of heart problems, such as scarring, than the hearts of less-active men of the same age. A small study presented at a recent meeting of the Radiological Society of America, for instance, found that among a group of middle-aged male triathletes, those who most often trained and competed showed slightly more scarring inside their hearts than the other athletes.

But, adding still more complexity to the issue, other recent studies have indicated that, even if longtime endurance athletes do develop heart problems such as atherosclerosis, their version of the disease may be different from and more benign than the types of heart disease that develop in less active people.

It was in hopes of bringing more clarity to the increasingly tangled question of how endurance training affects hearts that researchers from the University of Minnesota, Stanford University and other institutions decided, for the new study, to zero in on a unique group of runners: men who had participated in at least 25 consecutive Twin Cities marathons in Minneapolis-St. Paul.

These 50 runners, identified by marathon participation logs, turned out to have completed, collectively, 3,510 marathons, with each runner, individually, having finished anywhere from 27 to 171 of the races.

The men obviously were experienced endurance athletes. They had trained for at least 26 years, and some for more than 50. Many had started competing in high school or earlier, but others had come to the sport much later, often, the researchers report, in hopes of ameliorating the effects of past lifestyle choices, such as smoking or junk food diets. Most were lean at the time of the study, but a few qualified as overweight, based on their body mass indexes.