THE HIPS, SPINE & SHOULDERS
The bodyís center of gravity is at the hips -- all balance starts there, as does the rest of the bodyís motion. During a walk, itís best to think of the hipsí motion as two separate, overlapping rotations. First, the hips rotate along the axis of the spine, forward and back with the legs. If the right leg is forward, the right hip is rotated forward as well. Second, at the passing position, the free leg pulls the hip out of center, forcing the hips to rock from side to side. These two motions are then transmitted through the spine to the shoulders, which mirror the hips to maintain balance.
When the feet are fully extended, the hips must rotate along the axis of the spine. To keep balance, the shoulders swing in the opposite direction. From the front, the spine is relatively straight, but from the top, you can see how the hips and shoulders twist in opposite directions to maintain balance.
At the passing position, the front view shows the hip being pulled out of center by the weight of the free leg. This causes a counter-rotation in the shoulders. From the top, however, the hips and shoulders are nearly equal angles.
At the extension of the second leg, the hips and shoulders again are flat when viewed from the front. From the top, however, you can see the rotation of the hips and shoulders has completed.
Unless the character is using itís arms, theyíll generally hang loose at the sides. In this case, they generally act like pendulums, dragging a few frames behind the hips and shoulders.
Even at full extension, try keeping the arms slightly bent at the elbows. This will keep them looking natural.
In a standard walk, the head generally tries to stay level, with the eyes focused on where the character is going. It will then bob around slightly to stay balanced. If a character is excited, this bobbing will be more pronounced. The head may also hang low for a sad character, or may look around if the scene requires it.