11/16/2025
Based on a Duke University study published in Science Advances in 2019, growing a baby is energetically comparable to or more demanding than running a marathon every day for 9 months. The study found that pregnancy pushes the human body to its metabolic limits over a long duration, in a way that is similar to elite endurance events but sustained for much longer.
Energy costs during pregnancy:
Pregnancy is an extreme feat of endurance because the body works constantly to grow a new human, even at rest.
📑Total calories: Pregnancy requires an additional 50,000 dietary calories over nine months. The mother’s body provides 96% of this energy.
📑Cardiovascular demand: To support the growing baby, a woman’s blood volume can increase by 30 to 50 percent, and her heart rate increases by 10 to 15 beats per minute.
📑Metabolic demands: The body’s resting energy use can rise by up to 30%, meaning it works much harder even when stationary.
While a marathon is a discrete event, pregnancy is a continuous process of biological transformation. The comparison highlights the total metabolic output over the long term. A woman’s heart, lungs, and metabolism work overtime every day for nine months, making pregnancy one of the most intense and sustained physical challenges a human body can undergo.
SOURCE: https://www.therunningweek.com/post/growing-a-baby-takes-more-energy-than-running-marathons-for-9-months-straight
