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:
This is running at 14 frames per step (one leg), at 24 fps.
Don't be afraid!
Stretch and squash your character to get a convincing sense of force in your run.
To quote Disney's Master Animators Frank Thomas and Ollie Johnston:
"If you think you went far enough - Go Further!"
Stretch some more.
Get the energy into the spring!
It works very well with only one in-between between the squash and stretch.
And it's really snappy without any in-betweens at all!
A running cycle can be as short as 2 frames per leg - one up one down, like Pinocchio on the Japanese TV series.
It can also be the long dreamy strides for a long legged athlete.
Ease out - slow down on the way up
Ease in - gather speed on the way back down
This is a must.
Even if you do nothing else - get the spacing right.
The run cycle will magically look good even if everything else is off.
Try Boundin' for inspiration!
See this sweet Pixar short.
This the sort of animation that is just beyond real physics, just a bit unreal, as to make you laugh and marvel at how well it's done.
Have fun now,
Walk on the wild side: Animate a walking cycle from the side-view
Walking forward: Click here to see how a walk cycle looks from the front