Cranky pregnant moms, prepare for vindication.

Researchers studying the limits of human endurance have determined that the physical intensity of pregnancy is basically like running a 40-week marathon.

“Every mother who has gone through a pregnancy has experienced that effort themselves,” Duke University evolutionary anthropology professor Herman Pontzer, who co-authored the study, tells Today’s Parent. “Pregnancy is the longest-duration, highest-energy-expenditure thing that humans can do. Mothers probably aren’t surprised by this.”

The report, published in June’s edition of Science Advances, analyzed elite athletes from some of the most demanding races in the world, such as Ironman, the Tour de France and the 3,000-mile Race Across the USA, in which runners complete six marathons a week for four months.

Researchers looked at basal metabolic rates, or how many calories you need in order to function when your body is at rest. The most anyone can sustain, according to the study, is burning calories at 2.5 times the person’s BMR, or about 4,000 calories a day for the average adult. Pregnant women, researchers say, operate at 2.2 times their BMR — almost the maximum possible, every day, for some 270 days. A rate much higher than that and pregnancy would be unsustainable, damaging to the body and potentially deadly.

Marathoners’ energy use peaks at around 15.6 times their BMR, but maintain the exceedingly high rate for only a short period of time, the study revealed. By contrast, Tour de France cyclists move at 4.9 times their resting rate during the 23-day race, and Antarctic trekkers who heave 500-pound sleds across the grueling, snow-covered terrain for 95 days go at 3.5 times their BMR.

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“You can sprint for 100 meters, but you can jog for miles, right? That’s also true here,” adds Pontzer.

The problem comes down not to our heart rate or lung capacity, but our digestive systems. Humans, experts say, simply cannot properly process enough calories to sustain an energy use higher than the 2.5 ceiling. More than that and our bodies would begin eating away at their own tissue.

“There’s just a limit to how many calories our guts can effectively absorb per day,” Pontzer says.

So, pregnant people of the world, next time you feel guilty about backsliding on prenatal yoga or sending your partner out for that gallon of ice cream, remember that having this baby will be the greatest race of your life — and you deserve a prize.