ist. DeVane said he doesn't discourage people from marathon-distance levels of training, but he doesn't promote that much running either.
"You don't need to do that much to be heart healthy," he said. "I'm usually just trying to get people to move at all."
Dr Todd Weitzenberg, chief of sports medicine with Kaiser Permanente in California, notes that there's a vast field of research proving that running of any kind is healthful. Running has been associated with lower rates of heart disease, diabetes, cancer and ageing-associated disability. Runners live longer than their non-running friends and family.
"You can argue that endurance sports put undue stress on our bodies," he said. "But we're almost genetically hardwired to push ourselves to the limits."
Certainly no one is seriously arguing, he added, that the average marathoner is less healthy than the average couch potato.
What's sparked new debate is recent evidence that a lot of running - a lifetime of running marathons, for example, or the 80-plus kilometres a week demanded by ultra-marathon training - may start to undo some of the benefits of exercise.
Two studies published this year got widespread attention for citing potential negative health effects from exercise - one of them, from long-distance running specifically. One study found that a small percentage of people may have an adverse reaction to exercise that actually increases their risk of heart disease and diabetes. A second study analysed some of the changes to athletes' hearts that could put them at risk.
Yet another study found that, over the course of a year, there were fewer deaths among people who ran up to about 32km a week, and at a fairly leisurely 10-minute-per-1.61km pace, than among people who didn't run at all. That wasn't a shock, of course. What was surprising was that there were fewer deaths among those runners than among people who ran more than 40.22km a week or at a faster pace.
In fact, the longer, or faster, that people ran, the fewer health benefits they seemed to get, until, the study authors joked, a runner could potentially run himself back to couch potato.
That study and others all build evidence for the U-shaped curve of exercise benefits: that greater effort begets greater benefits, but only to a certain point. Then the benefits drop off, suggesting that there's probably a maximum amount of exercise before it starts to become unhealthy.
In another way to look at the U-curve, someone running about 16km a week may actually be healthier than someone running about 96km a week.
While the U-curve is pretty widely accepted, there's disagreement over how much exercise may be too much. Many scientists say, assuming there exists a maximum safe amount of running, it's probably so high that very few runners will ever get there.
"There are probably levels of exercise that are excessive for the average individual," said Dr Anthony Luke, medical director of the San Francisco Marathon. "But we can't arbitrarily say too much is 50 miles (80.45 km) a week, or 100 miles (160.9 km). I don't think everyone has the same limits."
The concern, according to Luke and other sports-medicine experts, is that there does seem to be some small percentage of runners who are at risk for fatal heart attacks when they run at a certain distance or intensity. It's a rare thing - for every 100,000 runners who compete in marathons every year, only one dies - but "no one should be dying at a marathon," Luke said.
But rather than setting safe limits for running, the better approach, many running advocates and sports doctors say, is finding out why those people die, and how their deaths could be prevented.
A middle-aged or older person who's taking up running for the first time should get checked out by a doctor and screened for possible heart conditions.
Plus, doctors and scientists don't yet fully understand exactly what happens to athletes' hearts when they run long distances or at a sustained hard pace. A recent study by the Mayo Clinic, where researchers took care to note the various and many positive health effects f