Science confirms what moms have long known: Pregnancy is the ultimate experience of human endurance.
Findings from a Duke University study — that looked at some of the world’s most energy-intensive and long-duration activities — suggest all humans have a specific metabolic limit or maximum amount of energy output they can sustain over a long period of time. In other words, we all have the same cap on how hard we can physically push ourselves over time. Trained, elite, ultra marathoners hit that limit, and so do pregnant women.
Researchers analyzed runners in a 140-day, 3,000 mile-long race from California to Washington DC, and combined it with previously collected data from long-distance triathlons, Arctic expeditions and Tour de France competitions. In all cases, they found that after about 20 days, athletes were able to maintain energy use up to 2.5 times their resting metabolic rate. Because of the way the human body processes calories, it simply cannot sustain higher energy use, resulting in the cap. Anything more than that, and the body begins to pull from fat reserves, eating away at its own tissue.
In a secondary finding, the study measured the energy expended by expectant moms to that of athletes.
Speaking to Parentology, co-lead author Herman Pontzer, an evolutionary anthropology professor at Duke University, says “We were curious to see how pregnancy compares in a formal analysis of long term endurance.”
The findings show pregnant women almost reach the human endurance limit at 2.2 times their resting metabolic rate. And they sustain that rate over their entire pregnancy and well into the lactation period — a longer time span than competitive sports events.
“People burn more calories per day in ultramarathon, triathlon, Tour de France, etc., but none keep it up for as long as a pregnancy,” Pontzer says. “Sure enough, it’s the longest, most intense thing the body can do.”
Furthermore, many obstetricians now encourage women with complication-free pregnancies to get additional exercise daily.
The study didn’t just look at the pregnancy period, but also three months post gestation for nursing mothers. A normal 40-week pregnancy spans about 270 days. An added 90 days means moms are pushing themselves to the brink for a total of about a year.
While the study initially aimed to discover the limit of endurance by way of looking at athletes, the link to pregnancy gives scientific proof to just how demanding the human gestation period is on a woman’s body.
Pontzer concedes in a Today’s Parent interview, “Mothers probably aren’t surprised by this.”