Pregnant women have just as much endurance as extreme athletes, study shows

There are some athletes who live to push the limits of the human body, and while it would seem that extreme athletes are unmatched in peak human performance, a study now confirms that pregnant women are, too.

A new study published in the journal "Science Advances" found that when it comes to pushing the limits of human endurance, pregnant women come in right behind those who participate in extreme herculean activities.

In fact, the study found that the max energy expenditure of some athletes was only "slightly higher" than the metabolic rates women sustained during pregnancy.

For the study, the team measured daily calories burned by a group of athletes who competed in extreme physical activities such as several marathons per week as well as a 3,000-mile race from California to Washington, D.C.

Researchers also considered other feats of human endurance, including punishing 100-mile trail races and pregnancy.

According to a press release about the study, when it comes to physical activities lasting days, weeks and months, the researchers found, humans can only burn calories at 2.5 times their resting metabolic rate.

Not even the world's fastest ultra-marathoners managed to surpass that limit, the researchers found.

So unless you plan on running several marathons regularly throughout the week, the average person has no hope to reach those limits. Pregnant women, along with extreme athletes, do come close, though.

A nine-month pregnancy truly pushes the body to its limits, similarly to week-long endurance races, burning calories beyond the rate at which the body can keep up with.

This research shows that there is something scientific to the "eating for two" adage pregnant women often repeat.

"It's a great example of constrained energy expenditure, where the body is limited in its ability to maintain extremely high levels of energy expenditure for an extended period of time," said co-author of the study Caitlin Thurber.