Running fast doesn’t mean that you are running properly or efficiently. It just means fast. If you drive an old formula 1 (Ferrari 375 ) car with an old engine it will probably drive fast enough, but not efficiently, from either a mechanical or economic point of view. The same happens with runners, both runners in the video are elites. But with differents styles. On the left, the runner shows very efficient technique, landing on front foot, very compact and leaning a lot. The opposite happens with the runner to the right, landing on heel, collapsing the body when it takes contact with the ground and not falling. In both these cases the engines (runners bodies) are the same but it “runs” differently and with difference results.