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.
Further, Coghill noted that the partial patterns of the limbs affect the total pattern – the weighted foot, for example, demands different opposition from the spinal musculature than does the swimming foot, or indeed the limb of an arboreal ape that suspends the body. If you lift a weight, for example, as the weight increases, the spinal action of support for the arms increases.
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. Thus, the limbs amplify movement that originates in the musculature of the spine and trunk.
The arms, in running, amplify spinal movement to counterbalance leg movement and to assist in raising and lowering the body’s center of gravity to support the stride. Arm movement is digressive and sequential, such that it begins with spinal movement, then follows with movement of the shoulder girdle from the sternum, then scapular movement, then the movement of the segments of the arm.
There is also lateral movement of the spine – sideways bending in opposition to the tilting of the pelvis in running — which is disguised by the vertical counter movement of the shoulders, because, as the arm swings forward, the scapula moves down and out from the spine; as the arm swings back, the scapula moves upward and in towards the spine, so the lateral curving of the spine does not appear as an inclination of the shoulder girdle.
In faster running, we see more extension and flexion at the elbow, because the weights of the forearm and hand are useful in raising the body’s center of gravity when the body has reached its maximum lift. This is the arm equivalent of what we see in basketball players and ballet dancers: the basketball player will leap, and then draw his legs up to extend “hang” time. A ballet dancer, in a grand jeté, leaps, then lifts the knee and, finally extends the leg, which gives the illusion of suspension, as, while the leg is still lifting upwards as it extends forward, the upper body remains at the same level. Actually, the same thing happens in the legs in the running stride, but in a less pronounced way: the lower leg is still traveling upwards even as the upper leg begins to swing back before footstrike. However, in leg extension, the biarticular muscles of the leg are strongly engaged to transfer the work of the mono-articular gluteus muscles through the leg, so we don’t see the same digressive sequence in extension that we see in leg recovery. The Biarticular muscles in running
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.
The innate behavior of crawling establishes how spinal extension can be amplified in the limbs to create the learned behaviors of swimming, cross county skiing, and even kayaking. The extension of the arms and legs is generated by spinal extension.
More recent research: