“Skeletal structure counteracts the pull of gravity.
Leaving the muscles free to move.
The nervous system and the frame develop together under the influence of gravity
In such a way that the skeleton will hold up the body without expending energy despite the pull of gravity.
If on the other hand the muscles have to carry out the job of the skeleton,
Not only do they use energy needlessly,
But they are then prevented from carrying out their main function,
Of changing the position of the body,
Awareness Through Movement p68.
Image source wisegeekhealth.com