my son is 7 months old.. he goes to physical therapy 2 times a week. he CONSTANTLY arches his back and we cant get him to do anything. He hasnt learned how to sit up yet or crawl or even roll over all the time yet(almost). Its because he is always arching. As soon as you put him in a sitting position he aches back and crys. even if your sitting behind him its like he wants you to hold him up like he wants you to support him. His therapist says he has too much "extention" but she doesnt know what could be causing this arching.
BTW he has done this since birth. and no he does not like the craddle position.Thanks guys.