Completing a marathon can be triumphant — but also heart-rending, in a surprisingly literal sense. Immediately after a race, many recreational marathoners have been found to have high levels of enzymes in their blood that indicate cardiac damage. These runners have “stunned” their hearts, as some exercise cardiologists put it. Enzyme levels generally return to normal within a week or so, suggesting that hearts recover quickly, but some experts have still wondered if there are less-stressful ways to get through a marathon. For example, should nonelite runners deliberately walk part of the way?  Exercise scientists in Germany took up this question for a study published earlier this year in the Journal of Science and Medicine in Sport. They recruited 42 recreational runners training for their first marathon and then, just before the race, randomly split them into two groups. Half the runners were told to walk for a minute after roughly every mile and a half, the others to run the entire race. Everyone set their own running and walking paces.  Both groups felt some trepidation about their assignments, according to Kuno Hottenrott, a professor of sports science at Martin Luther University in Germany, who led the study. The nonstop runners “were worried that they would not be able to finish the entire race without having to walk for a bit,” he says, while the walkers fretted that their times would suffer. In fact, almost all of them finished in a little more than four hours, a relatively respectable time for nonelite runners. The walkers tended to speed up when they resumed running, producing faster average miles than those in the other group.  Everyone also showed elevated levels of the enzymes in their blood that signal damage to the heart, however. Dr. Hottenrott says that by the time of follow-up tests four days later, those enzymes had returned to normal — the stunned heart does not seem to be permanently affected — but the results demonstrate that intervals of walking during a marathon will not eliminate the stress endured by a participant’s heart.  What the walkers did show, though, was much less strain on the rest of the body. Despite running faster or harder than the other subjects when running, this group reported less fatigue and little muscle soreness at the end of the race. None of the walkers dropped out. Most of the nonstop runners, on the other hand, had very sore legs and felt intense fatigue, they told the researchers. Two of them were unable to finish.  Fast, fit and experienced marathoners will probably not find much benefit in a run-walk program, Dr. Hottenrott says; their bodies should already be inured to the physical demands of running 26 miles. But he recommends the approach for beginners and runners whose goal is a finishing time of four hours or more. And Dr. Hottenrott points out that almost all of the study participants who were in the walk-run group said that they planned to run another marathon while using the strategy again.  A version of this article appears in print on October 30, 2016, on page MM36 of the Sunday Magazine with the headline: Give Yourself a Break. Today's Paper|Subscribe
Marathon participants who walked part of their course were fresher and had faster average miles than those who ran all the way.