I think that it is not uncommon for runners to treat their feet as passive instruments. We strap on the appropriate running shoe, and expect it to compensate for anything we perceive as innate structural anomaly in our feet. We “land” on our feet, and imagine that we are running with our legs, and that our feet, if they don’t behave properly, will need cushioning and motion control, and that a rocker sole will get us to toe-off more efficiently.
In fact, the foot is very important as a sensory organ. In good running form, the foot finds the ground before the weight of the body is upon it. Once on the ground, the foot has a fraction of a second to sense the surface that the body is about to descend upon, and to relay to the brain messages that will serve to orient the body to deal with variations in terrain – if the ground inclines laterally, for example, there is elaborate adaptation that must take place for the body to balance itself and for it to continue successfully extending forwards.
No matter what surface you are running on, it is always worthwhile to imagine that you are running barefoot. How would you run shoeless on a cement sidewalk? You would certainly not land on your heels, unless you are taking little baby steps. A relaxed ankle allows the forefoot to reach for the ground before the body falls from the arc of the stride. [see The Arc of the Running Stride] If you are running on rocky terrain, and you land on your heels, you are very likely to turn an ankle because a) the adaptation that could occur to deal with an irregular surface hasn’t time to unfold unless the foot finds the ground before your weight does, and b) because the foot has very little lateral strength when the body’s weight is on the heel – when the weight of the body arrives nearer to the ball of the foot, there is much more possible lateral adjustment, as well as strength, as the first and fifth metatarsals are more laterally distant from the midline of the leg, and the muscles that control eversion and inversion have their origins in the metatarsals and toes — they simply work more effectively when the weight is on the forefoot.
As your body’s weight comes onto the foot, the leg prepares to extend through a process that is primarily governed by reflex. As your weight reaches the metatarsal or ball of your foot, your foot spreads upon the ground and the subsequent stretch imparted to muscles between the metatarsal bones stimulates an extension in the leg. This reflex is called the interosseus reflex of the positive supportive response, and it is active when you are simply standing unless your weight is too far back on your heels. But when your weight moves more over the ball of the foot, the reflex will stimulate extension more powerfully, and will facilitate the extension that occurs in walking and running.
Then, as you continue to move forward, your leg begins to extend at the hip, knee, ankle, and metatarsal. This extension of the metatarsal joints of the feet stretches the plantar fascia, and makes the foot more rigid for push-off. A rocker sole on your running shoe prevents this by allowing you to transfer your weight to your toes without extending the toes! Running at faster speeds, the flexors of the toes are come into more evident use, and one begins to push strongly off of the toes.