Walking vs running  The curve shows the power cost of sustaining a given velocity while either walking or running.  At the 'transition point' walking or running is equally efficient, above it running is more efficient and walking becomes unsustainable (top speed), while below that walking is more efficient for a given velocity.  In order for running to be more efficient than walking, the runner must sustain a minimum average speed over the distance.   Fats cannot exceed velocity of the transition point for more than a few seconds, and are incapable of using running to extend their capabilities.  It is literally only a way for them to burn fat.  Also the damping effect of the lard blanket cannot be understated. Also injury of course:  Injury usually occurs because of an overload to the musculoskeletal system. It is essential that we understand the forces involved in producing athletic movements as well as the features of these forces and movements that are associated with injury.   ~ Source