My baby is a few days shy of 5 months old, but 4 months adjusted age (he was prem).
I've noticed for a while that when he's picked up, like just under the arms or whatever, his body stiffens and his back arches slightly - his legs are dead straight. And when I pick him up like that and hold him up to me with his head looking over my shoulder he doesn't relax and conform to my body like a baby usually would for cuddles/comfort, his tummy is against me and his legs are sticking out away from me. I have to actually use my other arm to push his legs into me and he's still stiff even then.
I only really became somewhat concerned about it at Gymbaroo today when we were doing an exercise with the babies where we held them under their arms and swung them gently between our legs. All of the other babies of varying ages were basically floppy and relaxed, just swinging gently, and my baby was stiff as always.
.. any ideas?
(I cross-posted this in the special needs sub-forum as well)