Ultra-endurance events can be bad for your heart. Or maybe not.

That undefinitive statement comes courtesy of contradictory studies both reported Aug. 31 on the Science Daily site. We’ll start with the up(heart)beat report.

The Karolinska Institutet and the Swedish School of Sport and Health Sciences studied 15 athletes (12 males, three females) at the Adventure Racing World Championships. The event covered 800 kilometers in the disciplines of mountain biking, trekking, kayaking and in-line skating and took about six days, with competitors essentially going nonstop for 150 hours at an average work intensity, measured in terms of VO2 peak, of 40 percent. Before and after the event, the athletes were assessed to see how their hearts responded. While some of the athletes registered increased levels of certain blood markers, suggestive of cardiac damage, immediately after the race, those markers were back to normal within 24 hours. Researchers believe the spike wasn’t the result of cardiac damage, but rather the body’s way of protecting and regulating growth. Further, the athletes who finished strongest and did the best had the least affected hearts.

Conclusion: Long, hard bouts of exercise good for your heart.

Then there’s the study conducted by the Liverpool John Moores University and the Countess of Chester Hospital, which suggests just the opposite.

In this study, 45 runners who participated in the Lakeland ultra trail run were examined. Like many ultra trail runs, this one consisted of a 50-mile and a 100-mile course. The average finisher in the 50-miler took 15 hours, the average finisher in the 100 took 36. Ages ranged from 24 to 62. However, only 25 of the 45 runners examined — 16 in the 50-miler, nine in the 100 — completed their race.  Again, the runners were checked before and after the race, this time for levels of cardiac Troponin I (an indicator of cardiac damage) in their blood. They were also administered electrocardiograms before and after.

This time, however, there were “significant electrical changes” in more than 50 percent of the ECGs (some classified as “bizarre”), and cardiac Troponin I levels rose “significantly” in 21 of the 25 runners, and in three it was deemed high enough “to suggest significant cardiac damage.”

Conclusion: Long, hard bouts of exercise bad for your heart.

The authors of the first study acknowledge that their findings are not consistent with the findings of similar studies — studies such as the Lakeland ultra study — which have found signs of cardiac damage. They hypothesize that the shorter events — yes, those would be the the 50- and 100-mile ultra runs — are more intense and thus place more strain on the heart. There’s no denying that ultras are intense. But there’s also no denying that in most ultras, few participants run the entire event. Even strong runners have strategies for walking certain sections (tough uphills, for instance).

What to make of the studies’ contradictory findings? Not much, until more research is done. We’ll keep you updated.

Photo: A runner passes the start/finish at this year’s Umstead 100, held in April. Photo courtesy Joe Lugiano Studios.