DS2 is 14wks and is very strong. When they put him on my chest after he was born he lifted his head 45deg and looked straight at me 
He's been pretty much holding his head up for several weeks now.
He's also very tense for want of a better word. When you hold him or pick him up in particular he goes very rigid - almost like a skydiver with arms down by his side and legs curled up behind him. Or more recently like a flying squirrel - legs splayed and knees up, arms down my side slightly behind him. It's quite funny to look at but also rather odd. He's quite an uncomfortable baby to hold. It's mostly his right arm and even when he's sitting on you lap this is often straight out slightly behind him.
When I pick him up out of his crib his arms go rigid and I have to twist him out so his arms don't get caught in the slats.
Other than this his arms are 'normal' and he's started batting things in front of him, he can bend both arms, bring his fists together and put both hands in mouth. He's got full movement in both arms just seems that when he's being handled or carried his arm adopts this position.
Has anyone ever seen this?
Is this something I should get checked out?