Few of us would pull a Dean Karnazes and run 50 marathons in 50 days. But a multi-stage race like the TransRockies Run—maybe. Such an undertaking might rightly come with worries about blisters or bears, but could it harm your health? A new study tempers such concern.
Researchers in Denmark followed eight runners competing in the Bornholm Multiple-Marathon, a weeklong race consisting of a marathon a day on flat dirt and asphalt roads. Temperatures during the year of the study–2010–were a comfortable 50 to 65 degrees. The subjects were in their 40s and while not competitive athletes, they were experienced; all had completed 80 or more marathons, and at the time were running about 35 miles a week.
Before and within 24 hours of the last race, the researchers measured multiple health indictors, including blood, cholesterol and hormone levels, muscle tissue damage, and markers of stress for the liver, kidney and heart. After comparing the data, the researchers concluded that running seven consecutive marathons did not lead to obvious negative health effects, and in fact, the effort improved health markers in some areas.
Subjects' total cholesterol was lower, and HDL (the good cholesterol) levels were higher overall. Insulin sensitivity, a measure of diabetes risk, improved significantly, and while subjects did not lose weight, they did lower their body fat and increase lean muscle mass.
Markers for inflammation and muscle and liver damage did increase, but were not statistically significant, according the study.
“The overall picture was that very minor changes occurred after the event,” wrote the authors, who published the study in the Journal of Strength and Conditioning Research. “Supporting this is the minimal changes seen in inflammatory markers and the unchanged physical stress level indicated by no differences in cortisol levels before and after the event.”
The authors, however, note that a number of factors–mild temperatures, rest between races, the fitness of the subjects, and the flat course (downhill running produces greater muscle damage)–all influenced their findings and the results could differ under hot or cold conditions, or on a course with lots of elevation change. Still, they add their findings directly apply to "real-world races."