Crossing the finish line of a marathon brings many things: a finisher's medal for your wall, an awesome picture to post on Facebook, a blister or two, and an overwhelming sense of accomplishment. However, a pair of new studies from Australia wants to add blood poisoning to that list. Yes, you read that right—researchers found that long-distance runners showed signs of sepsis after a big race. But before you hang up your running shoes, experts warn that these studies may not tell the whole story.

For the studies, published in International Journal of Sports Medicine and Exercise Immunology Reviews, researchers recruited endurance athletes and took blood samples before and after an ultra-marathon. They discovered that after running 100-plus miles in 24 hours, runners had high levels of biomarkers consistent with what doctors usually see in people with septicemia (also called sepsis), a dangerous infection of the blood that affects over one million people in the U.S. each year—and kills nearly half of them.

Exercise over a prolonged period of time causes the gut wall to change, allowing endotoxins—a dangerous byproduct secreted by gut bacteria—to leak into the bloodstream, explained lead author Ricardo Costa, Ph.D., a professor of nutritional immunology at Monash University in Australia. "This then triggers a systemic inflammatory response from the body's immune cells, similar to a serious infection episode."

But even though the study found increased markers of sepsis, they didn't find an increased risk of an infection—which is why you shouldn't ask for a refund on that triathlon just yet, says Bert Mandelbaum, M.D., an orthopedic surgeon at Santa Monica Orthopaedic and Sports Medicine Group and author of The Win Within: Capturing Your Victorious Spirit. "This is alarmist research and it isn't backed up by the data. The extrapolation that people who exercise a lot are more susceptible to infection is simply unfounded," he says. "If this were true, we'd be seeing pro athletes with four times the rate of infection as normal people, and that is just not seen."

The disagreement seems to stem from the fact that Costa's research focused on a broad biomarker that can indicate septicemia in sick people but thus far hasn't been shown to do the same in healthy people.

"There is absolutely no reason to worry about this. There's no real scientific basis," agrees Nicholas Grosso, M.D., sports medicine specialist and president of The Centers for Advanced Orthopaedics. "I talked to several of my partners in sports medicine, and none of us had ever heard of any such thing. The language 'inflammatory biomarkers' is very non-specific; there are a lot in the body. One would expect that after doing an extreme workout or marathon, you would certainly have a release of them in the body. But the body is designed to combat this—that's what the immune system is for."

He adds that sepsis is not something doctors take lightly, so if this were a risk for endurance athletes, the medical community would be on it. "You don't see marathoners dropping dead. People have been doing extreme exercise, ultra-marathons, and crazy things for years, and we've never heard of anyone getting sepsis from it," he says. (Want A Real Fitness Challenge? Try Running 3 Races In One Weekend.)

Mandlebaum agrees, saying the biomarker the researchers tested for is not specific to blood infections and is in fact a product of cell turnover, a natural process that happens every day in our bodies. "Exercise does cause inflammation, but not all inflammation is bad. What this research really shows is the body's adaptive response to the exercise," he explains. "Cell death and rejuvenation are a natural part of exercise and part of what makes it so good for us—by increasing our resiliency."

You can have too much of a good thing, however, and that includes exercise, adds Mandlebaum. While he doesn't think these studies should scare you away from running a marathon, he does point out that how you run it is important. One thing Costa noted in his findings was that the runners who were better trained showed lower levels of inflammation, presumably because their bodies were better adapted to the stress of such long workouts. The take-home message, then, is really about the importance of being prepared for a big race. (Try the Top 25 Marathon Training Tips.)

This is why Mandlebaum advises following a cyclical progression when training. "You need to determine your base fitness level and then cycle up and down in your training, building in rest days. This will help your body adapt to the exercise and reduce your risk of stress fractures and other injuries," he explains. He adds that if you're planning on doing any long endurance races, it's a good idea to get a basic check-up done by your doctor first to screen for any underlying issues you may have that could compromise your immune system.

"Exercise has so many proven advantages—lower blood pressure, a better mood, and, yes, lower rates of sickness. Meanwhile, not exercising is overwhelming harmful," Mandlebaum says. And, he points out, as a group, obese people have far more health problems than ultra-marathoners.

In the end, he says it's about keeping perspective, training properly, and listening to your body. So if you feel sick, don't be afraid to take a rest, but don't let the fear of getting sick keep you from crossing that ultra off of your bucket list!