They do this because it’s faster (and safer) than running an entire sprint down the incline.
The other reason humans are able to move their arms is because they can “feel” the need to do so before they are able to do it.
(Note: when I write “feel”, I am also referring to the “need to do”. It does not mean there is something “needed” to be able to move their arms. Rather, that they have a “want” to do so.)
The reason it’s safer is that if humans are to be hurt, they would run the risk of injury by trying to run. But moving their arms is an effective way of minimizing that risk!
So, if people were to actually try to run a full-on sprint down an incline, then their arms would be able to move the entire distance without slowing them down!
Of course, this would not be much of a sprint at all… but we’re getting close.
The real question then is: do you think humans move their arms to move them down the incline?
If yes, then let’s take a close look at them.
Move your arms when your hands are resting on your thighs. That is, don’t let your hands rest on your thighs.
Now, let’s apply this to us in our own lives.
If a rock is thrown your way, and you are not sure whether it is solid or not– and it’s thrown at you in slow motion– your arms are still “feared”– so your hands will not move to the correct place.
So, if you have your arms resting on your thighs, when you are thrown into a rock, they will not do anything except to fall, and if you are thrown into a wall– or a wall with sharp edges– then their only purpose is to fall.
If you are not familiar with how to move your arms, then you’ll probably think of your hands in more ways than I have explained here.
So, when I say “don’t move your arms when your hands are resting on your thighs”, I actually mean to say don’t put your hands on your thighs when you use your arms as an extension or flexion.
If you can’t imagine the difference between using your arms for a short extension and your hands being on your thighs while doing the same thing, then I am sure that you would appreciate