If you think that one needs a cushioned shoe to absorb the impact of running, consider this: the vertical movement in the running stride is so minimal that, were you jumping in place, your feet would not even leave the ground. This is because most of the powerful thrust of extension is dedicated to moving you forward. What does this mean? It means that there need be no real impact involved in “landing” in running. The foot of the recovered leg can be on the ground before the body falls out of its arc, so that there is then minimal impact when that foot is simply placed on the ground. The legs obviously do not carry the body’s weight when it is airborne — flying from the extended leg to the recovered one, and if the leg is recovered quickly without being unduly lifted, the foot will take the body’s weight only after the foot is on the ground. With the right dose of vertical lift in the stride, coming down is not very difficult for the leg.
Neither, on the other hand, does the horizontal movement of the body impose any significant impact on “landing”, as the recovering leg, after it reaches the extent of its forward movement, may begin to move back toward the body at the speed at which the body is moving over the ground. That is, the speed of the body is determined by the speed and amplitude of extension and that extension determines the speed and amplitude of recovery, such that the runner need not move into his legs, but may continue forward movement over the recovered leg. When done successfully, there is no horizontal impact, because the leg allows the body to continue its forward movement. It is not the ground that forces the leg to change direction, in other words — the change in direction has already occurred before contact.
The major forces that impact the body in running are those involved in the powerful extension that drives the runner forward. These forces are not insignificant, but they are distributed throughout the body when the body remains adaptable in movement. Any notion of correct positioning risks interfering with posture’s natural distribution of the work involved in running. Indeed, the work of awareness in running is to avoid the stabilities that we mistake for control.
But… when conditions change, so may the relationship between vertical and horizontal travel. One must work harder on extension to run uphill, and the work of absorbing the “fall” disappears entirely. On the other hand, running downhill poses some difficulties. When vertical travel (drop) increases, the body accelerates rapidly. If the stride remains long, it is very difficult to avoid significant impact. One needs to decelerate the drop. First, leg extension will not be as powerful, resulting in a lower leg recovery. This serves to get the foot to the ground more quickly. A lower midstance makes reaching the foot towards the downhill ground easier, but requires more work. Again, the objective is not to fall upon the foot, but to fall after the foot reaches the ground. On steep declines one may need to stop driving with the legs so that the strides are not excessively long. And, obviously, one does not need lift in the stride while descending. On descents, the logic of using cushioned shoes becomes more apparent if one wishes to use the vertical drop to accelerate. Thus, the barefoot runner may be just fine running a 10K on the track. Running a fast Boston Marathon, with its long down-hills, might just require a bit of cushioning.