First, there's the back breaking lifting and carrying and toting and rocking and walking of the baby or babies. My back hurt like hell during the first few months! I still don't now how women wear those baby carrier things, my shoulders would ache for days after. Sure, I had huge babies but people wear those with their babies all kinds of sizes and I just don't see how.
Next, at some point you baby proof and baby gates are in half the doors in the house. Baby gates are not for keeping kids in or out of a room, they're for torturing parents! Every time I walk in or out of a door I get a new bruise from knocking my thigh against the frame. I can't even open the things fast enough to keep from kicking the stupid gate on the way through. Unbelievable. Where's the stupid remote control that opens the door and slides the frame into the wall?
Then, inevitably, the kids decide you're a trampoline, punching bag, gym mat or whatever and start jumping on you, pounding on you, crawling all over you and generally treating you like a great big stuffed animal. Try telling them to be gentle when they realize that when they pound on your belly it jiggles in a very amusing way. Try getting them to stop jumping on you when they realize it's such a soft place to land. It just doesn't work.
Not to mention the endless round of unintentional head butts, book corner to cheek hits, plastic hammer whacks and random full on kicks by children not entirely sure how to coordinate their body parts yet. I have bruises all over, especially on my face, but that's probably because I'm stupid enough to lean in again and again while making smoochy smoochy noises to kiss bellies and faces and feet of flailing children. I suppose I'll never be able to resist. The learning curve is defeated by sheer hormonal attraction to baby belly. Ach.
I'm sure I've missed a few, but you get the general idea. Raising children is cause for many injuries, bruises, strains, headaches and general malaise. And I'm not even talking about the illnesses they give you. Cold after cold after flu after cold. Good gracious. I need a vacation.