A run cycle has the same basic animation principles as a walk cycle - but with a lot more force.
Instead of just propelling our mass forward, we need to push it entirely off the ground.
These are the basic key frames for one step of a running cycle:
Keyframes for a running cycle
This illustration shows only one step - remember to animate the second leg!
This is running at 14 frames per step (one leg), at 24 fps.
The body MASS going up and down
The legs bending in perspective
The feet flipping
Moves up and down as it does in the side view.
If you wish to elaborate - show the hips swinging - the foot that's forward brings its side of the pelvis down.
Most of the foreshortening happens to calf.
The thigh gets fore-shortened as well but unless your character brings its knees up very high - don't shorten the thighs too much.
If you are animating Flash or After Effects Cut Outs, you have no choice - You need to draw the foot from three angles and switch between them as you animate:
It's not very convincing otherwise.
For different kinds of characters, play with
Modify these simple key frames to fit your character.
Gotta' run :-)