“Pregnancy is the longest duration and highest energy expenditure that humans can experience. Mothers probably aren’t surprised by this.”
-Herman Pontzer

How fast you can run depends on why, for how long, and, more importantly, the drive that sets the purpose for why you are running in the first place. In all emergencies, trying to avoid becoming a tiger’s lunch does not take long: You either run as hard as ever to clearly demonstrate to the charging tiger that it’s not worth the effort to burn its limited energy for an uncatchable running “human bullet” that you are, or it would be over within minutes, with the eternal loss of the right to brag about how you outran a tiger.

Needless to say, physical activity is metabolically expensive, which explains why humans are inherently lazy. However, we would go out of our way to let people know that we “walk or exercise all the time” and that we actually “don’t eat much.” It’s easy to remember the details of the last time we took a long walk in the neighborhood or the intense sweating session at the gym. However, unlike exercise that requires energy expenditure, hardly anyone remembers their meals in the last 24 hours because eating provides energy gain. That being said, energy is not limitless, and there is a hard limit to human endurance before exhaustion sets in. The brain shuts down intense activity as mental fatigue battles with the deep, inaudible but increasingly loud inner voice stating, “I am too exhausted to run another mile, and I do not want to do this, it is not worth it.” This is why athletes need coaches.

A 2019 study reported that the metabolic ceiling for all humans is 4,000 kilocalories per day, roughly 2.5 times the basal metabolic rate. The basal metabolic rate (1,000 to 2,000 kilocalories for most people) can be described as the energy required to keep the body alive at rest. The study noted that prolonged activity above this metabolic ceiling would require burning energy reserves, which is not sustainable indefinitely as the digestive competence of the gut is maxed out.

The Ironman triathlon event only lasts less than a day but involves swimming (2.4 miles), bicycling (112 miles), and running (26.2 miles). The record time for the Western States 100-mile Endurance Run is currently 15 hours, 7 minutes, and 4 seconds. According to bicycling.com, the total mileage for the Tour de France is about 2,200 miles over the 21 days of racing. In 2015, Scott Jurek hiked the 2,189-mile Appalachian Trail in 46 days, 8 hours, and 7 minutes. Finally, the longest-ever man-made endurance event is the 3,000-mile Race Across the USA, where runners, from Southern California to Washington, DC, complete one marathon (26.2 miles) a day, six days a week for 140 days. To say the least, these are insanely unsustainable activities, and it’s no wonder they don’t last several months.

However, here comes the pregnant mama who sets out on a solo 9-month endurance trip with no pre-coaching and still outlasts all known voluntary man-made athletic endeavors in the history of life. She thrives on 2.2 times the basal metabolic rate, near the edge of the human metabolic ceiling, for 270 days! As declared by Herman Pontzer, the author of Burn, “pregnancy is the ultimate ultramarathon.” Just as you don’t forget the details of your recent energy-expensive workout or perhaps how you gallantly outran a tiger, mama remembers your pregnancy history too, if you ask her, or it might come up unprompted, as it did during my recent visit to Nigeria. I learned about the loss of my mom’s first pregnancy, the years it took to conceive me, and some events that occurred during my stay in the womb.

Beyond that, as I went out for a walk in the street every day, it didn’t matter whether it was for 40 or 120 minutes. It was as if someone was still protecting her almost 60-year-old, energy-expensive womb investment. Mama would step out of the house and anxiously sit outside by the gate, watching the street for me to show up.

To my mama, the mama of my children, and all mamas out there, Happy Mother’s Day.

Mukaila Kareem is a physical therapist and physical activity advocate.