Well, if I was to do the task I would definitely split up the sprite into two pieces. One lower part for the legs and a top part for the rest of the body. That way your running animation is only really dependent on the leg section of the sprite. Then making the aim animation would be independent if you're moving or not.
also: Highly suggest looking up inverse kinematics if you want to make a very extensive/advanced animation without needing to draw all the frames and stuff yourself.