This is a more favorable distribution of mass.
Work Step by Step
Running involves rotating one’s leg around the pivot/joint where it attaches to the torso. The smaller the moment of inertia of the leg, the easier it will be to change its rotational motion, and the faster the animal can run. Moving muscle and flesh closer to the joint (i.e, higher up the leg) reduces the leg’s moment of inertia, improving the animal’s running ability.