Modified some elements on the legs like the background knee which was too much rised on the second frame.
I started sketching quickly arms :
EDIT : after some minor changes i made a gif.
lot of things must be fixed like arms size. The harder part is for me to represent anatomic stuffs like shoulders getting up and down while running, background arms being smaller than the foreground one.
I also made a mistake that i corrected : when you run on the spot before a mirror
you can see that whenever your left leg get up, the opposite arm get up with it and i think that's an important balance part.
i would like to rotate the chest a few but i can't manage to do it properly because i lack of shading skills.