I've come to the realization that mother's arm muscles must be really strong from holding babies. Every time I babysit and I hold a baby after a while, I feel my arm weighing down and the baby starting to get heavy. Especially when babies sleep, it weighs them down and they become really heavy.
One time while feeding a baby his bottle my arm started hurting after a while, I then understood why they have pillows to use to rest your arm on while feeding a baby.
Then today I babysat a baby and she was good for a half hour, then started crying so I held her. Then she fell asleep on me. In the beginning it was alright, but then my arm couldn't take it anymore, so I sat down.
Its funny, how step by step the baby goes into a different position. First she's laying on my shoulder, then she moves her head down and it lays on my arm, when I sit her head lands on my lap. I sit on the steps so I can have my foot up so her head isn't hanging down. Then I leaned my back against the banister post so my back shouldn't kill. So by the end of the hour of her sleeping on me, I was able to be comfortable too.