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.
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Study: Low vision affects dynamic stability of gait
Gait Posture. 2010 Oct;32(4):547-51. Low vision affects dynamic stability of gait. Hallemans A, Ortibus E, Meire F, Aerts P. Source
Research group of Functional Morphology, Department of Biology, University of Antwerp, Belgium. ann.hallemans@ua.ac.be
Abstract
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/
