Men may bonk more—Berlin data points to biology

men may – A large analysis of Berlin Marathon finishers from 1995 to 2025 finds male runners are about twice as likely as female runners to “hit the wall.” Faster men—especially those finishing under three hours—show an even sharper risk. Researchers say the gap may not

For marathoners, the worst part of the race isn’t the noise or the effort—it’s the moment the body stops cooperating. Runners call it “hitting the wall” or “bonking,” when glycogen stores run critically low and a sudden wave of overwhelming fatigue makes it nearly impossible to keep pace.

This week’s research adds a new. uncomfortable detail for anyone who’s ever tried to figure out why that moment hits some people harder than others. In a study published on Thursday in Scientific Reports. researchers analyzed how often runners bonked—and when—and found that male marathoners may be significantly more likely to do it than women.

The study drew on race records from the Berlin Marathon spanning between the years 1995 and 2025. In total, 873,334 runners who completed the race were included. The researchers then used a clear rule to flag “hitting the wall”: a runner was considered to have bonked if their pace slowed by at least 20 percent during the second half of the race compared with the first half.

That pattern is known among runners as positive splitting, where the first half is run faster than the second half.

When the data was sorted by sex, male runners stood out. Male runners were about twice as likely as female runners to hit the wall, according to the study’s results. The difference didn’t just show up at average levels of performance either. Faster male runners appeared to be even more prone to bonking.

Male runners who finished the marathon in less than three hours—around the qualifying time for men for the Boston Marathon and far less than the qualifying time for women—were six times more likely to hit the wall than their fast female counterparts.

For Aldo Seffrin, an exercise physiologist at Nova O2 Sports Science in São José dos Campos, Brazil, the most surprising part was not the fact that a difference existed—it was how wide it became.

“This was the most surprising finding,” Seffrin said. “I expected experience and training to flatten the difference at the top, and instead it widened,” he added. “That tells me pacing failure is not simply a beginner’s mistake.”

The physiology behind bonking starts with glycogen. Glycogen is the body’s stored form of glucose and a preferred fuel for powering muscles. Once glycogen becomes critically low. the body shifts toward fat for energy—but converting fat into a usable fuel isn’t fast or easy. That lag can leave runners feeling as if their race has abruptly been replaced with something harder.

Scientists are still working out exactly what drives bonking from person to person. But the study points to something many runners already understand from hard-earned experience: pacing matters. Running at a steady. sustainable pace helps the body use energy more efficiently—mostly glucose drawn from glycogen stores—reducing the odds of burning through stored fuel before the finish line.

Seffrin and his team note that their findings suggest men might be able to reduce bonking by running slower in the first half of a marathon and then gradually getting faster as the race progresses, a pacing strategy known as negative splitting.

Still, pacing alone may not be the whole explanation. Seffrin put it plainly when discussing why women might be less likely to hit the wall.

“The honest answer is that a lot of foundational exercise physiology was built on male subjects, so several mechanisms are simply less well characterized in women,” he said.

He described known differences in how the body fuels endurance exercise. Women tend to oxidize fat at higher rates and run at a lower respiratory exchange ratio during submaximal endurance exercise—conditions like marathon running at steady. moderate intensity. The study also points to muscle-fiber differences: women have a greater relative proportion of type 1 muscle fibers. also known as slow-twitch muscle fibers. These fibers use oxygen efficiently to resist fatigue, making them well suited for endurance.

Hormones may play a role as well. Seffrin said women’s use of estradiol, a hormone that plays a role in burning fat and conserving carbohydrates during prolonged exercise, could be part of the reason.

If these mechanisms really do help explain the marathon results, they may also connect to a pattern seen in longer events. Seffrin noted that the performance gap between men and women in ultramarathons is often smaller.

Yet he also emphasized that more evidence is needed—especially because research has historically leaned too heavily toward male bodies.

“Better characterization of female-specific physiology, in datasets that actually include it, is what would let us move from ‘what’ to ‘why,’” Seffrin said.

Looking ahead. Seffrin said his team wants to combine race data with other information about each runner. including psychological factors as well as physiological ones. The goal is to sort out whether differences in pacing and hitting the wall are mainly driven by race strategy—or by biology. They also want to study runners who do not finish. because analyzing only finishers likely underestimates how often runners actually bonk.

The research doesn’t just reframe a runner’s fear of the finish line. It turns a familiar race story—fuel runs out, fatigue takes over—into something that may depend, in part, on factors runners can’t always control.

marathon hitting the wall bonking glycogen positive splitting negative splitting Berlin Marathon Scientific Reports exercise physiology sex differences estradiol type 1 muscle fibers