His hips don't appear to be moving at all. The arms are moving forward and back around the torso, but the torso stays still. The moving shadows on the torso help, but the stripes at the edge of the shirt don't move at all. The net result is that the torso and hips appear static, and the arms and legs just look like they are contracting on springs rather than moving forward and back.
Maybe at the left and right edges of the torso, have the stripes curve up by a pixel, suggesting they go around a tube (into the screen). When he walks and one side is pulled forward, have that side curve a bit more forward.
Maybe for the hips, have the bottom edge of his rump slant up towards the leg that goes forward, and back towards the leg that goes back. Not a lot, just something to give the illusion of forward and back.
My two cents.