A lot of people ask that question, but people usually fall while going up the stairs rather then going down the stairs mainly because they do not lift their leg up high enough.
The answer to this riddle is "a staircase". Of course the staircase does not actually move up and down, but when you refer to a staircase directionally, you are either going "up the stairs" or "down the stairs". Its function in and of itself is to "go" up and down.
More bone usage going down, More musle usage going up.
Theres an invention on strollersandprams.com that sits under a pram and you can slide up or down stairs.
their bodies arent used to going up steps and rocks
No. There are separate stairs for going up and down. The staircase is extremely narrow, it would be impossible to have people going both up and down on the same one.
Yes, accidental falls going up stairs are very common. However once the fall has begun gravity will pull the victim down the stairs!
Going up, you have to overcome gravity with every step.
Stairs go up and come down as well.
So people would not have to walk ALL the way up the stairs, and so they can stay fat and ugly.
The opposite of up the stairs is down the stairs, as the opposite of upstairs is downstairs.
It depends, do you fall down the stairs a lot? (if downward-forward) Do you run into walls consistently after going up? (if upward-forward)