Look at the photo, which way am I turning my head ? How hard am I turning ? Perhaps I am turning hard through my neck and thoracic spine to look over my shoulder. The point is, you can see it in my feet and if you know your biomechanics you should easily know which way I am turned.
It should be simple and clear that I am turning my neck and thoracic spine strongly to the left. The left rotation has forced me to find stability over the lateral left foot while driving the rotation with the right foot. Left foot had to supinate, right had to pronate. No rocket science here.
Earlier in the week I posted a brief discussion on the neck and proprioception and the upper and lower limb. I caught some questions on challenging the strength of the neurological linkages to the lower limb, so I promised a simple picture to solidify my point.
Where is what i wrote earlier this week.
"From the study: "Limb proprioception is an awareness by the central nervous system (CNS) of the location of a limb in three-dimensional space and is essential for movement and postural control. The CNS uses the position of the head and neck when interpreting the position of the upper limb, and altered input from neck muscles may affect the sensory inputs to the CNS and consequently may impair the awareness of upper limb joint position."
We say it is not just the upper limb however, the neck and head posture is used in interpreting the position of the lower limb as well. And similarly altered head/neck muscle input can impair awareness of the lower limb posture as well. Think about it, we are trying to stay upright in the gravitational plane while keeping the eyes and vestibular centers on the horizon. Gait is nothing more than a single leg balancing act repeated over and over. Faulty info on where our center of pressure is from a visual or vestibular aspect will alter where we put our foot in space. Just look at how many neurologic diseases end up with a wider based gait, because our proprioceptive centers no longer trust our base of support. It is all connected."
Exp Brain Res. 2015 May;233(5):1663-75. doi: 10.1007/s00221-015-4240-x. Epub 2015 Mar 13.
Neck muscle fatigue alters upper limb proprioception.
Zabihhosseinian M1, Holmes MW, Murphy B.
As in this study, and putting it together with my photo and discussion at the start here today, limb proprioception is an awareness by the CNS of the location of the limb and is essential for proper movement and postural control. If I had rotated to the left and had my CNS not known where the foot was in space and in relation to the rest of my body, I may have fallen over to the left. Instead, my CNS sensed the weight shift to the left from the neck and torso rotation, and moved my foot weight bearing into supination (affording a slightly greater lateral weight bearing on the foot) to accommodate the shift in my center of pressure and mass laterally. So, the CNS used the position of the head and neck, and the weight shift, in interpreting the appropriate positioning of the lower limbs. Sometimes moving the foot into supination to accommodate the lateral load is not enough, and we need to actually step laterally to maintain upright. Altered input from my neck muscles might affect the sensory inputs to the CNS and consequently may impair the awareness of my limb joint positioning in space. This happens often in vestibular challenged clients and in client of aging decline where the system is losing proprioception. If we do not know where a body part is in space, we don't know how to use it or how to load it (think about chronic ankle sprains).
As i said earlier this week, think about it, we are trying to stay upright in the gravitational plane while keeping the eyes and vestibular centers on the horizon. Gait is nothing more than a single leg balancing act repeated over and over. Faulty info on where our center of pressure is from a visual or vestibular aspect will alter where we put our foot in space. Just look at how many neurologic diseases end up with a wider based gait, because our proprioceptive centers no longer trust our base of support. It is all connected.
Think about how amazing this system is when it works right, we can run on a track leaning into the curve, we can ride a bike and lean into turns, we can run forward and yet turn to look behind us, all without falling over -- thanks to our CNS and joint proprioception.
Dr. Shawn Allen, the other gait guy