It's true... a lot of the time.  Of course, what really moves the hips is the legs pushing it around, but generally the feet are planted on the ground so you see the motion in the hips and it radiates from there through the spine, the neck, the arms.

The side-step is  a classic exercise for that.

"Motion starts from the hips" is a way of getting you to think about the overlapping action present in all body motion.

It's often subtle.

Even for a character that is sitting there is a slight roll of the butt needed to get the shoulders moving.

I though about this for a while now, and I think the best way of illustrating this is point to the physics of the movement:
If you want to move an object, you always have to move its mass center to move everything else with it. On humanoid characters, this is usually the torso, but depending on where the driving force is applied, the pivot is moving to the nearest point available on the mass's center. (Edit: as long as it's in balance, move it outside and it loses its balance)
This pivot is mostly at the hips, since the driving force usually comes from the legs, but if you pull the character at one arm, this pivot suddenly moves towards his hand, e.g. leaves the center of mass and the legs are struggling to keep up with it as to move it back to the hips and regain the balance.
Or, if the character has wings and starts flying, this pivot suddenly centers around the shoulders. On my last gig I had a lot of this, we animated insects, and they had two cog's, one for walking on the hips, and one for flying on the shoulders, with a reversed spine.
Hope this makes sense. I never was very good at physics

Last edited by wolfor (06-13-2012 3:16 pm)

I get it wolfi thanks. But i need to do some personal tests based on this physics. I even found a document on center of mass at animationphysics.com if u guys would want a look.

The other docs are also very usefull. U should check them out. And thanks for the help.

You can also think of it like this, what is the person doing with his/her balance? For example, when we start walking, we tend to being with moving the hip so far out that we lose our balance. And that's when we take the first step, to catch ourselves from falling.

So next time you look at someone doing for example parkour, martial arts, or just plain running, take note of when they are in balance, regaining balance and when they deliberately move themselves out of balance.