Neuromechanics Weekly:

Gait Noise

Think of “Gait Noise” as those things which alter the sum total of all neuronal activity acting at a specific locus. Gait noise is all of the aberrant signals that distort the correct and most functionally desirable signal necessary for a clean gait.  Think of noise as the static found between radio stations, that irritating white noise that blurs out the perfect radio station from coming in clearly.  Gait noise is thus anything that impairs a clear sensory and motor signal to and from the central nervous system required for clean uncompensated gait. These definitions will help you understand where we are going with this.

1. Communication: Anything that interferes with, slows down, or reduces the clarity or accuracy of a communication. Thus, superfluous data or words in a message are noise because they detract from its meaning.

2. Quality control: Variability that may be caused by changes in the ambient conditions, faulty machine performance, or uneven quality of the material or human factor inputs.

3. Telecommunications: Random disturbance introduced into a communication signal, caused by circuit components, electromagnetic interference, or weather conditions. Also called line noise.

Gait noise is therefore very undesirable. It could be interpreted as seeing a foot turned out more than normal, more than the other side. Seeing that compensation is a motor impairment and an undesirable motor pattern, but it also sends aberrant sensory information back into the nervous system. Bad information in, bad information out, and a viscous cycle ensues.  Gait noise can occur from a total knee replacement, from a scar, from a sprain, a broken bone, from the numbness of a diabetic neuropathy etc.  These all cause impairment of the sensory-motor-sensory loop.  Gait Noise theoretically could occur anywhere along the neuraxis (spinal cord and brain-brainstem) or even the peripheral nervous system, but it makes most sense to think of it happening where neurons congregate; most likely at synapses, especially at the spinal cord level. The wiring of the nervous system extends to all tissues, so the noise can occur anywhere for almost any reason.

In the words of Dr Ted Carrick, “Is the lesion at the receptor, the effector, the peripheral nerve, the spinal cord, the brainstem, the thalamus, the cerebellum or cerebrum?”  Where is the problem in otherwords ?  Lets explore how this relates to “Gait Noise”.

Today lets look at the receptor. Receptors are the information gatherers of the nervous system. Think of your 5 senses (vision, smell, taste, sound and touch). These are all subserved by receptors. Vision and touch seem to most affect gait and movement. This post will concentrate on touch.

Touch encompasses not only physical touch but also proprioception (see here for review of proprioception and receptors). These receptors: Pacinian corpuscles, Merkel discs, end bulbs of Krause, bare nerve endings, joint mechanoreceptors, muscle spindles and Golgi tendon organs are all included here. These sentinels provide the central nervous system (CNS) with mechanical environmental information, for comparison with that same information (there is much redundancy in the CNS) and other environmental information (balance, vision, hearing, etc), so that you can formulate (consciously or subconsciously) a response.

In short, there are multiple systems converging, in this case, on the peripheral receptor. Remember, receptors can be activated in may ways. A touch receptor could be activated not only by touch, but also by heat, cold, pressure, or even chemical (metabolic or toxic) means. Just like you may be a great tennis player, you could probably play racquet ball, handball, or football, even if you never played before. You may not excel, but you could get by. Receptors are no different; they may be BEST activated by touch, but other means could certainly do the job. This inadvertent activation creates receptor bias, as we like to call it “noise”, and that information is sent to the CNS for processing. If a touch receptor is activated, it is activated, and the CNS  sees it as an activation, whether it is intentional or not. These mixed signals are then processed along with everything else, creating “noise”.  And the noise might not be a desired signal. And these signals can be what initiates a gait change, a compensation, whether it be from information mis-processing or a strategy to cope.

Think of the application to your gait analysis, next time you are seeing something that you think you shouldn’t be seeing.  This is the problem with video gait analysis (as we take a moment to pound the wall on this topic ONE MORE TIME !).  What we see on a video analysis is not necessarily the problem, nor does what you see warrant a correction or a specific shoe. What we are seeing on video is their coping strategy after all of the CNS signals (noise and non-noise) have been processed, it is what they can do with what is available to them and with what makes most sense to the brain.  We have said before, as a classic example, that an over pronating foot might be a necessity to compensate for lack of internal hip rotation because the brain deems that functional pathology as more damaging at the hip than the hyperpronation at the foot.  Who are we to deem that the foot needs an orthotic or a stability shoe because of what we see?  Who are we to think that we can outsmart all the sensory-motor calculations of that persons brain without knowing all of the functional limitations of their body ? Perhaps if we take an hour to assess our client, and then see them for another visit or two, we can then correlate the gait video, our findings and our corrective work and then truly qualify a logical reasoning.  But this is a far more difficult game that this simple gait video or foot plantar pressure digital foot mapping nonsense.

Ivo and Shawn; the voices in your head, helping you sift out the noise.