On the subject of manual muscle work…There is more to it than meets the eye….
Following with our last few posts, here is an article that may seem verbose, but has interesting implications for practitioners who do manual muscle work with their clients. We would invite you to work your way through the entire article, a little at a time, to fully grasp it’s implications.
Plowing through the neurophysiology, here is a synopsis for you:
Tactile and muscle afferent (or sensory) information travels into the dorsal (or posterior) part of the spinal cord called the “dorsal horn”. This “dorsal horn” is divided into 4 layers; 2 superficial and 2 deep. The superficial layers get their info from the A delta and C fibers (cold, warm, light touch and pain) and the deeper layers get their info from the A alpha and A beta fibers (ie: joint, skin and muscle mechanoreceptors).
So what you may say.
The superficial layers are involved with pain and tissue damage modulation, both at the spinal cord level and from descending inhibition from the brain. The deeper layers are involved with apprising the central nervous system about information relating directly to movement (of the skin, joints and muscles).
Information in this deeper layer is much more specific that that entering the more superficial layers. This happens because of 3 reasons:
- there are more one to one connections of neurons (30% as opposed to 10%) with the information distributed to many pathways in the CNS, instead of just a dedicated few in the more superficial layers
- the connections in the deeper layers are largely unidirectional and 69% are inhibitory connections (ie they modulate output, rather than input)
- the connections in the deeper layers use both GABA and Glycine as neurotransmitters (Glycine is a more specific neurotransmitter).
Ok, this is getting long and complex, tell me something useful...
This supports that much of what we do when we do manual therapy on a patient or client is we stimulate inhibitory neurons or interneurons which can either (directly or indirectly)
- inhibit a muscle
- excite a muscle because we inhibited the inhibitory neuron or interneuron acting on it (you see, 2 negatives can be positive)
So, much of what we do is inhibit muscle function, even though the muscle may be testing stronger. Are we inhibiting the antagonist and thus strengthening the agonist? Are we removing the inhibition of the agonist by inhibiting the inhibitory action on it? Whichever it may be, keep in mind we are probably modulating inhibition, rather than creating excitation.
Semantics? Maybe…But we constantly talk about being specific for a fix, not just cover up the compensation. Is it easier to keep filling up the tire (facilitating) or patching the hole (inhibiting). It’s your call
The Gait Guys. Telling it like it is and shedding light on complex ideas, so you can be all you can be.
Yesterdays post talked about vision and parallax. Today’s explores some adaptations we have to poor visual quality. (Note 3 pictures today, toggle amongst them.)
In the attached study, we see people with poorer vision quality had 3 particular gait parameters (although probably had many more parameters) which changed with vision quality:
1. shorter step length
2. less trunk flexion
3. earlier heel contact with the ground (which goes along with shorter step length.)
If we think about what we know about the nervous system, this all makes sense. There are 3 systems that keep us upright in the gravitational plane: vision, the vestibular system and the proprioceptive system. If we remove one of the systems, the other 2 become enhanced (or better said, they had better become enhanced).
In this study they took away (or impaired) vision. This left the vestibular and proprioceptive systems to take over. The vestibular system affects position of the HEAD ONLY and measures linear and angular acceleration. It makes sense to say that a more upright posture would do wonders for the stability of the system. The semicircular canals found in the inner ear measure angular motion, or rotation. Placing the body upright shifts the position of the semicircular canals in a different posture (particularly the LATERAL semicircular canal, which sits at 30 degrees to the horizontal; ) and places the utricle and saccule (which measure tilt and linear acceleration) in a better position to appreciate these. Translation, correct upright posture and neutral head positioning are critical for their contribution to detecting and maintaining balance and spacial stability.
The study also suggests that earlier heel contact in gait creates an “exploration” of the ground. This is quite important because the foot has so much cortical representation (see bottom picture) and is important for proprioception owing to its 31 articulations LOADED with joint mechanoreceptors, not to mention 4 LAYERS of muscles, LOADED with spindles and Golgi Tendon Organs. The foot is a highly dense sensory receptor, the problem is we have had it hibernating in shoes for far too long. Imagine the advantage to balance, gait and posture we might have if we hadn’t dampened the mechano-sensory receptors for the better part of our lives.
So, bringing this all full circle with the study; If you have poor vision, you had better make up for it with good upright posture and a sensory system that is unimpaired. Most of us could have better posture and could use some retraining of foot function and sensory reception. Blind people generally have good postural and environmental awareness. They are not slouched over leading their gait head first while wearing oven mits on their hands and rigid steel-toed work boots. They take advantage of these systems and optimize them.
Sometimes the simple answers are not as simple as we like, but it is nice to know there is a reason.
The Gait Guys….Providing both simple answers to complex problems and complex answers to apparently simple ones.
Study: Low vision affects dynamic stability of gait
Research group of Functional Morphology, Department of Biology, University of Antwerp, Belgium. email@example.com
The objective of this study was to demonstrate specific differences in gait patterns between those with and without a visual impairment… . Adults with a visual impairment walked with a shorter stride length (1.14 ± 0.21m), less trunk flexion (4.55 ± 5.14°) and an earlier plantar foot contact at heel strike (1.83 ± 3.49°) than sighted individuals (1.39 ± 0.08 m; 11.07 ± 4.01°; 5.10 ± 3.53°). When sighted individuals were blindfolded (no vision condition) they showed similar gait adaptations as well as a slower walking speed (0.84 ± 0.28 ms(-1)), a lower cadence (96.88 ± 13.71 steps min(-1)) and limited movements of the hip (38.24 ± 6.27°) and the ankle in the saggital plane (-5.60 ± 5.07°) compared to a full vision condition (1.27 ± 0.13 ms(-1); 110.55 ± 7.09 steps min(-1); 45.32 ± 4.57°; -16.51 ± .59°). Results showed that even in an uncluttered environment vision is important for locomotion control. The differences between those with and without a visual impairment, and between the full vision and no vision conditions, may reflect a more cautious walking strategy and adaptive changes employed to use the foot to probe the ground for haptic exploration.
homunculus photo courtesy of : http://joecicinelli.com/homunculus-training/
And now, some light reading for a Saturday….
J Orthop Sports Phys Ther. 2001 Oct;31(10):567-7
What the Gait Guys say about this article:
Aren’t you glad you have mechanoreceptors?
As we have discussed in other posts, proprioception is subserved by cutaneous receptors in the skin (pacinian corpuscles, Ruffini endings, etc.), joint mechanoreceptors (types I,II,III and IV) and muscle spindles (nuclear bag and nuclear chain fibers) . It is both conscious and unconscious and travels in two main pathways in the nervous system.
Conscious proprioception (awareness of where a joint or body part is in space or action) arises from the peripheral mechanoreceptors in the skin and joints and travels in the dorsal column system (an ascending spinal cord information highway) to ultimately end in the thalamus of the brain, where the information is relayed to the cerebral cortex.
Unconscious proprioception arises from joint mechanoreceptors and muscle spindles and travels in the spino-cerebellar pathways to end in the midline vermis and flocculonodular lobes of the cerebellum.
Conscious proprioceptive information is relayed to other areas of the cortex and the cerebellum. Unconscious proprioceptive information is relayed from the cerebellum to the red nucleus to the thalamus and back to the cortex, to get integrated with the conscious proprioceptive information. This information is then sent down the spinal cord to effect a response in the periphery. As you can see, there is a constant feed back loop between the proprioceptors, the cerebellum and the cerebral cortex. This is what allow us to be balanced and coordinated in our movements and actions.
The ACL is blessed with type I, II and IV mechanoreceptors (Knee Surgery, Sports Traumatology, Arthroscopy Volume 9, Number 6) We remember that type I mechanoreceptors exist in the periphery of a joint capsule (or in this case, the periphery of the ACL) and are largely tonic in function (ie: they fire all the time) and type II are located deeper in the joint (or deeper in the ACL) and are largely phasic (ie they fire with movement). Type IV mechanoreceptors are largely pain receptors and anyone who has injured his knee can tell you all about them.
The article does a great job reviewing the importance of proprioception and how it relates to knee function and concludes “A higher physiological sensitivity to detecting a passive joint motion closer to full extension has been found both experimentally and clinically, which may protect the joint due to the close proximity to the limit of joint motion. Proprioception has been found to have a relation to subjective knee function, and patients with symptomatic ACL deficiency seem to have larger deficits than asymptomatic individuals.” Bottom line, never quit on the rehab and training of an ACL deficient knee until the absolute best outcome has unequivocally been achieved with certainty that no further improvement can be achieved…… absolute certainty. Too many stop shy of certainty, and your brain will know it. And it will show it in small gait, running and athletic skills.
Yup, this is some heavy stuff, but hey…you’re reading it, right? If we didn’t explain it in detail you might not believe that WE are The Gait Guys ……. more than just foot and shoe guys. After all, there is a brain attached to the other end calling the shots.
Sorting it out so you don’t have to…We remain…The Gait Guys
Join Dr Ivo as he explores the world of joint mechanoreceptors in this weeks episode of Neuromechanics.