Things adressed int his edit:
The way i see it, the body should elevate or 'bob' when the legs are most towards the center. becaus at this poin the line from the foot t the head is more upright than it is at any other point. take in mind the cahracter isn't "popping" up, so much as it's a natural motion because of the extension of the leg; and it causes the character to be slightly "taller"
The motion from the front to the back of the run i felt was too extreme and caused a jerkiness in the cycle that, given the number of frames, shouldn't be there.
Things not adressed in this edit:
The hair is too stiff. it should move at least a little bit, as should the position of the face. nothing too dramatic, but the body looks ten times more dyanmic than the face, which is where all the detail and attentive focus should be, considering the body/head size ratio.
---------edit------------
I don't know why i din't see this when i was editing it, but i also thnkthe leg that moves forward should move further out than it does.
not soo sure how i feel about the job i did on that edit, but the basic idea still gets across.
----------another edit-----
neither of my edits consider this, but when the body bobs back *down* that should coincide with the foot hitting the ground.
just to have something to compare to, here's a running animation that i did a little while back. it isn't perfect, and not really finished.