Many walkers overstride in front of the body. Overstriders typically reach far in front of their bodies, straightening legs before impact. A straightened leg with nowhere to go hangs briefly, neither pulling nor pushing the body forward. Then gravity pulls it down, sending the foot crashing to the ground. Aside from adding unneeded stress to the body, this crash also gives the appearance of lifting.
Old school race walkers talk about pulling their bodies forward through the heel. This not only adds stress, it’s inefficient.