This run cycle by Toshiyuki Inoue is made up of only the essential drawings in a run cycle. There are no "cushioning" drawings, nor are there any arbitrary inbetweens where the drawing merely features the parts of the body exactly in the middle or favoring one key over the other of where they would be when going from A to B.
The essential drawings themselves are:
1. Contact
2. Down Position (squash)
3. Passing Position In which the foot in the air from the drawings before now passes the foot on the ground, hence PASSING position. Spoilered cause I just figured that out.
4. Up Position (stretch)
I believe the proper exposure of this animation is on twos at 24fps.
I am certain that any less than these essential drawings per side of the run breaks the run, and therefore this is the bare minimum. Whether any more than these are even necessary (considering how great this looks) is up to your personal animation aesthetics, morals, values, and current project's needs.