Amelia Stewart-Short

Pontzer’s team went looking for the ceiling on human endurance. They measured Tour de France cyclists, men hauling sledges across Antarctica, and runners who crossed America at roughly a marathon a day for twenty weeks.

Everything topped out around 2.5 times basal metabolic rate. Push past it and the body starts eating itself.

Pregnancy sits at 2.2. For nine months.

Nobody claimed pregnancy is as hard as the Tour. What they found is that the same ceiling governs both, and that a pregnant woman gets close to it without doing anything at all.

The first trimester is where it starts and it is the part with no evidence attached. Cardiac output up a fifth by week eight. Plasma volume expanding. Blood pressure falling, which is the grey-out when you stand. Thirty to fifty per cent more air moving through you every minute at the same breathing rate, so you are taking deeper breaths all day without knowing it. A whole organ under construction.

The exhaustion has a mechanism. Progesterone breaks down into allopregnanolone, which acts on the same brain receptors anaesthetics do. Researchers in that field call these compounds endogenous anaesthetics.

The sickness has one too. GDF15 comes from the placenta and the baby, crosses into your blood, and acts on the vomiting centre in your brainstem. How ill you get depends on your own sensitivity to it, which explains why one woman is floored and another barely notices.

So you are running an endurance event under sedation, and you look exactly as you did in June.

This is the trimester women are expected to work through without mentioning it.

*A Conscious Pregnancy*, link in bio 🌿