When you reach for something while standing, a spectacular sequence of events occurs that allows your arm to move; all without ever thinking of anything other than the object you want to grasp. In observing this reaching movement, our eyes would be drawn to the primary movement of the arm. Unless there is some difficulty, we would be unlikely to recognize the critical series of events that occurs prior to the arm moving. As researchers have investigated such movements, a “chain reaction” that occurs in the rest of the body has been described. The remote action of muscles, far from the hand, has been described as Anticipatory Postural Adjustments (APA).
These “adjustments”, detected by force plates and electromyography, occur before the arm moves (anticipatory). The remote actions were not perceived as being part of the movement, but rather part of the postural system upon which the arm movement occurred. Since the reaction was different from that which was required to stand quietly, they were seen as adjustments to the normal posture to allow the arm movement while maintaining postural stability. Further research has proven that the APAs are specific to the direction of arm movement.
As study of these APAs continued, there has been a great debate over whether there are separate posture and movement systems. There have been strong research papers that support each side of the one-system or two-system argument. From a practical point of view, it is hard to accept that the same muscles of the hip that provide support to the stability of the leg are also in a different system that helps produce the arm movement. It is much more logical to recognize that the hip muscles (and all others for that matter) are part of a single movement system that must provide both stability and mobility at the same time.
At the Gray Institute, this need for stable movement is termed mobile-stability (MOSTABILITY). It is a necessary component of all functional movements. The 3D Movement Analysis and Performance System (3DMAPS) is built upon this “truth” of human movement. The 6 global movements of analysis have both mobility and stability components. The amount of motion (mobility) throughout the body during the global movement is assessed and then the movements are tweaked in order to determine the ability to control the available movement (stability).
So at the Gray Institute, the posture-movement argument becomes a mute point when it translates into stability and mobility. It is the same muscles and joints that contribute to both. The body’s resources must be sufficient to allow stable movement. If those resources are deficient, the body has an unenviable choice: prioritize stability with loss of mobility, or prioritize mobility with loss of stability. In most cases, the body chooses stability over mobility. The reach (or other task) is unsuccessful but the body maintains the upright posture. Other times, because the cognitive drive to complete the task “wins”, the reach occurs but stability is lost and the person may fall. When resources are deficient and the body prioritizes the mobility, injury may occur. Another way to think of this allocation of resources is safe movement priority versus successful movement priority. Again if the resources are sufficient and the training has been functional, the body discovers and manages the proper allocation.
A simple example may help us to see the challenge. In basketball, when a player grabs a rebound, the coach often extols the virtue of keeping the ball overhead so that it cannot be “stripped” by the opponent. In spite of constant reminders, many players bring their arms down when they land. This is not a case of poor memory, but instead a case of insufficient resources. In order to land safely, the player flexes their hips to use the powerful muscles of the posterior-lateral hip to control the landing and stabilize the leg. If success (keeping the arms overhead) becomes the priority the hip muscle contribution to stabilizing the leg is greatly reduced. If the muscular resources in the rest of the leg are insufficient, or have not been trained properly, then knee or foot injury is more likely. That injury could be a single traumatic episode, or a progressive cumulative trauma condition.
As our training and rehab programs add new resources (motion, strength, power, endurance), they also must emphasize functional movements that help the body to learn how to allocate these new resources to both mobility and stability at the same time. Practitioners of Applied Function Science (AFS) create these movements based on a Principles-Strategies-Techniques process (PST). To learn more about AFS and PST, visit www.grayinstitute.com