You’ve heard it before. The brain doesn’t think about turning “on” individual muscles, but rather works in terms movements.
The brain, as was discussed at the Bridging The Gap with Charlie Weingroff, likewise does not speak in terms of “movement quality,” but rather cares only about movement success. The brain does not care how it gets from A to B only that it gets from A to B. This can be supported with what we know about motor maps in the premotor and motor areas.
Many are likely familiar with the Penfield maps that suggest that there are designated areas of the brain that represent specific areas of the body like the arm or foot for both sensation and motion. These maps are constantly changing and are sometimes variable between subjects. For example, in amputees, the brain area for the amputated limb is often overtaken by the adjacent body leading to unique sensory experiences like an itchy phantom hand that is alleviated by scratching the cheek.
Primate literature demonstrates that microstimulation of the motor and premotor areas result in complex functional synergies of muscle activation that ultimately bring the joint to a final posture provided that the duration of stimulation is adequte.
Traditionally, primate research was conducted using short (25-50ms) volleys of microstimulation, which resulted in muscle twitch, however, when Michael Graziano and colleagues at Princeton University used microstimulation for longer durations interesting things about our motor maps were revealed.
A primate stimulated in a particular area for 1000ms resulted in the hand forming an opposition posture, the forearm supinating, elbow flexion, shoulder rotation, and opening of the mouth. The final stimualted posture was that akin to the primate feeding himeself. This complex muscular synergy was also identified by Holdefer and Miller. The authors determined that brain motor areas do not represent a specific direction or velocity, but rather the final posture.
Jaw movement, too, appears to be mapped as movement and not as activation of specific muscles that open and close it. A brain area responsible for the mouth and jaw, when stimulated, would result in a cycle of chewing. If the mouth was biased in the opened position, stimulation would beget a closing of the mouth and vice versa is true.
Providing credence to the neurology of movement variability and the brain’s ability to read only success, when joints were preset in different areas, the final posture was consistently repeated and offered different variability regardless of the route necessary to take it there. Final postures were reached even in the face of various impediments to movement.
It stands to reason that the human motor areas respond in a similar manner. Regardless of whether or not you can move in a particular way or via a specific joint movement during a particular exercise does not necessarily mean that it’s good. It simply means that the brain will access plan B by stimulating a slightly different motor area to achieve the same or similar final posture.
With repeated activation, plan B simply becomes plan A due to impediment, and becomes “normal” and functionally dominant. Changes in the brain’s maps are implicated across a range of function and dysfunction. As is the case, remember, our number one target organ for all intervention is the brain.