For nearly 40 years, from the beginning of the 20th century until his death in 1941, biologist George Coghill studied salamanders. (See George Coghill) His goal was to find the origins of response and movement in a vertebrate organism. He made many important discoveries, among which was his finding that salamanders have innate reflexes governing locomotion. In salamanders there is a spinal movement that enables swimming, which appears very early in development. It is not learned, and requires no experience in order to function. Further, Coghill observed that, when the salamander later develops limbs, the movement of these limbs is initiated by the innate spinal movement that allowed swimming. And even later, when the salamander develops complex patterns for the moving of its limbs in relation to objects (learned patterns, in other words), the total body pattern of movement initially used only for swimming is necessarily engaged to support the movement of the limbs. In other words, any movement in the fully developed salamander is constructed upon and depends on innate spinal movement.
This is very like Alexander’s discovery that any action involves the use of the whole self.
Later, in the 1980’s, Serge Gracovetsky proposed a novel theory of human locomotion which he called “The Spinal Engine”. (see The Spinal Engine) Remarking that quadruple amputees could, without practice, “walk” on the bones at the base of their pelvises, he reasoned that spinal rotation might be at the base of human locomotion. Studying human babies crawling, he noted that the same kind of spinal movement one sees in lizards (and salamanders), that is, the movement of pelvis against thorax to move opposing arm against leg that George Coghill had studied for many years.
Gracovetsky observed that the lateral spinal undulation employed in crawling becomes, when the human stands, primarily axial rotation. The contra-lateral movement we see in running and walking is a variation on the spinal movement apparent in crawling. Thus, underlying the movement of our arms and legs in running is deep spinal movement.
Now, of course, we cannot create the spinal movement that should be behind the movement of running. That would be like trying to breathe properly, an exercise doomed to failure. However, by observing respiration we can learn to sense things we may do habitually that impede respiration, and we can learn to inhibit them. We can work on the same thing in running. As the arms and legs move, we can sense how their movement winds and unwinds the spine, like a rotary clock spring. We have, of course, developed powerful muscles that extend and augment the spinal musculature: as the right leg extends, and the right arm swings forwards, the extension of the latissimus dorsi of the right arm is continued in the extension of the gluteus maximus of the left leg – there is a spiral in the movement that reaches its apex before returning as the other side extends.
Gracovetsky does not differentiate between heel-strike and forefoot strike in describing the the impact forces delivered through the recovered leg. None-the-less, I believe that a runner landing on the forefoot loads the musculature more effectively for subsequent extension. I think that the manner in which the biarticular muscles are organized in the limbs clarifies the way in which the spinal engine has been extended to produce the power and efficiency of the modern runner. You can feel the way the pelvis rotates in the direction of an extending leg, and how the power of the driving leg is thus used to recover the opposite leg.
Thus, the actions of the legs and arms are linked and coordinated through the spinal musculature. The action of one leg is linked to that of the other through the spinal musculature such that the degree of extension of one leg determines the extent of recovery of the other. Further, as the foot of the recovering leg moves toward the ground, its synchronization with the extended leg allows it to link its return to the speed of the body over the surface on which the body moves.
See The Biarticular Muscles