I’ve always wondered, why do babies in a waking state (especially very young ones) always have tightly bunched-up fists and flexed legs, especially when lying on their backs? The only reason I could think of for it is it could be some kind of mechanism to conserve warmth. Any theories/explanations on this?
Well, a very young baby takes a bit of time to, er, “unwind”. They come wadded up, you know.
One of my bosses was explaining to me that very young kittens and puppies don’t have their myelin sheaths (the fatty insulation on nerves that helps conduct impulses) fully formed, and that’s why they’re kind of shaky and and neurologic-looking when they try to move around the first few weeks. It might be that baby humans also have insufficient myelination, and the scrunching up is just a transient neurological kind of thing.
IIRC the retraction limb muscles are somewhat stronger than the extension muscles. As a guess, for babies, the strength difference may be enough to overcome the small amount of resistance of short and light-weight limbs to make the flexed limb position the default. Once exercise and growth reduce the strength difference the default curled-up position is less likely to happen.