I remember reading that babies’ arms at birth are strong enough to support their own weight. It went on to say that this is sort of a “leftover” from our evolution in which infants had to cling to their mother’sbody hair.
Not so much their arms as their hands. Newborn’s hands have great gripping strength. But it doesn’t last for very long, which is why baby books ask you to never test the theory.
As for why the strong gripping reflex, the clinging to mum’s hair is just a theory (but it makes sense to me).
Is the loss of strength caused by the fact that babies don’t have to use these muscles? If the baby was required to cling on for dear life, would he/she retain that ability?