Your gait and peripheral vision: Part 2. There is more to it than what you do/don’t see.

Written by Dr. Shawn Allen

Yesterday we did a blog post on the loss of peripheral vision from drooping eye lids leading to the necessity (not vanity based) of a minor surgical procedure called a blepharoplasty.  Here was that blog post (link), it had some important research based points you need to know.

Vision is typically the predominant sensory system used for guiding locomotion. Online visual control is critical for adjusting lower limb trajectory and ensuring proper foot placement, including optimal limb/foot crossing velocity, optimal trail-foot horizontal distance and lead-toe clearance. Research suggests that peripheral visual cues play a large role in this online gait control. 1

We have discussed many of these issues, the conscious and subconscious importance of vision on human gait, in many of our blog posts over time.  Namely, blog posts on dual-tasking attention, negotiating stairs, and even in tandem walking holding hands. These all require a degree of peripheral vision function otherwise gait problems, including falls, rise on the risk list.

According to Timmis and Buckley (2), “although gaze during adaptive gait involving obstacle crossing is typically directed two or more steps ahead, visual information of the swinging lower-limb and its relative position in the environment (termed visual exproprioception) is available in the lower visual field (lvf).”  Their study determined exactly when lvf exproprioceptive information is utilized to control/update lead-limb swing trajectory during obstacle negotiation. 

Their study determined that “when (the) lower visual field (lvf) was occluded, foot-placement distance and toe-clearance became significantly increased; which is consistent with previous work that likewise used continuous lvf occlusion”. Their findings suggest that “ lvf (exproprioceptive) input is typically used in an online manner to control/update final foot-placement, and that without such control, uncertainty regarding foot placement causes toe-clearance to be increased. Also that lvf input is not normally exploited in an online manner to update toe-clearance during crossing: which is contrary to what previous research has suggested.” 2

Elliot and Buckley (3) showed the importance of peripheral visual cues in the control of minimum-foot-clearance during overground locomotion. In their study, 

From their abstract: “eleven subjects walked at their natural speed whilst wearing goggles providing four different visual conditions: upper occlusion, lower occlusion, circumferential-peripheral occlusion and full vision. Results showed that under circumferential-peripheral occlusion, subjects were more cautious and increased minimum-foot-clearance and decreased walking speed and step length. The minimum-foot-clearance increase can be interpreted as a motor control strategy aiming to safely clear the ground when online visual exproprioceptive cues from the body are not available. The lack of minimum-foot-clearance increase in lower occlusion suggests that the view of a clear pathway from beyond two steps combined with visual exproprioception and optic flow in the upper field were adequate to guide gait. A suggested accompanying safety strategy of reducing the amount of variability of minimum-foot-clearance under circumferential-peripheral occlusion conditions was not found, likely due to the lack of online visual exproprioceptive cues provided by the peripheral visual field for fine-tuning foot trajectory.”

These appear to be important studies on the effects of vision and peripheral vision and proprioceptive cues.  How we move our bodies depends much on visual cues, the ones we know we see, and the ones we are unaware that we “see”. Take this to the next level, imagine how the blind must adapt to gait without these cues. That is gait topic we will save for another time.

So, the gait analysis you are doing with your runners, your athletes, your clients takes into consideration their vision right ? Hmmmm, some how we just know that many gait gurus just sat back in their chairs and let out a long exhale. We go even more rogue in podcast 95 when we discuss head tilt and the vestibular system, we know that one is almost always overlooked. Another long exhale we presume.

Shawn Allen … .  one of the gait guys

References:

1. Exerc Sport Sci Rev. 2008 Jul;36(3):145-51. doi: 10.1097/JES.0b013e31817bff72.Role of peripheral visual cues in online visual guidance of locomotion. Marigold DS¹.

2.Gait Posture. 2012 May;36(1):160-2. doi: 10.1016/j.gaitpost.2012.02.008. Epub 2012 Mar 17.Obstacle crossing during locomotion: visual exproprioceptive information is used in an online mode to update foot placement before the obstacle but not swing trajectory over it.Timmis MA¹, Buckley JG.

3. Gait Posture. 2009 Oct;30(3):370-4. doi: 10.1016/j.gaitpost.2009.06.011. Epub 2009 Jul 22.Peripheral visual cues affect minimum-foot-clearance during overground locomotion.Graci V¹, Elliott DB, Buckley JG.

“I keep walking into doorframes,” : A visual aspect of problematic gait you likely have not considered.

Written by Dr. Shawn Allen

Recently i had an elderly client come in to see me, we were working on some arthritic knee problems post-total knee arthroplasty. He mentioned to me that he recently had eye surgery because he was having some gait difficulties. My brain immediately when into age related gait decline, you know, balance kind of stuff.  He mentioned that he was banging into door frames because he was not clearing the sides of the door frames and was also banging up his knees, ankles, thighs and toes on many other things.  He said he had been getting anxious about his gait and thought he might be experiencing some kind of neurologic gait problem. He wasn’t trusting his gait, he feared leaving his house. He happened to mention it to his eye doctor a few months ago and here is what he told him .  

“Your upper eye lids are drooping so much that they are obliterating your peripheral vision. You can’t avoid banging into things that you cannot see. Your peripheral vision is imperative for normal safe gait.”

Drooping eyelids are an inevitable effect of getting older, but the sagging eyelids can impair peripheral vision and magnify gait risks. The procedure known as a blepharoplasty is a simple procedure performed on the upper eyelid when the lid drops down and creates a lateral blind or fold blocking out the lateral eye fields. When looking to the extremes of lateral gaze or depending on peripheral vision this fold blocks the lateral field on the affected eye while the bridge of the nose blocks the same lateral field of the other eye. Effectively, the lateral gaze and peripheral vision becomes progressively narrowed. 

Watch the gait of your elderly clients. Observe how they move about your office, around furniture, tables, door frames. Ask if their gait is uncertain. Ask if they are running into things for no apparent reason.  Think about this next time you are walking in close proximity of the elderly, just because you see them in your peripheral vision, does not mean they can see you.  Remember, their balance and stability is likely not what yours is, it might not take much to knock them over for what appears to be little reason at all.

From the Graci study: 

“However, under CPO conditions (circumferential peripheral visual field occlusion), the doorframe led to a further reduction in crossing velocity and increase in trail-foot horizontal distance and lead-toe clearance, which may have been because of concerns about hitting the doorframe with the head and/or upper body.”

From their conclusions, “exteroceptive cues are provided by the central visual field and are used in a feed-forward manner to plan the gait adaptations required to safely negotiate an obstacle, whereas exproprioceptive information is provided by the peripheral visual field and used online to “fine tune” adaptive gait. The loss of the upper and lower peripheral visual fields together had a greater effect on adaptive gait compared with the loss of the lower visual field alone, likely because of the absence of lamellar flow visual cues used to control egomotion.”

Shawn Allen, one of the gait guys.

1. Optom Vis Sci. 2010 Jan;87(1):21-7. doi: 10.1097/OPX.0b013e3181c1d547.Utility of peripheral visual cues in planning and controlling adaptive gait.Graci V¹, Elliott DB, Buckley JG.

2. http://abcnews.go.com/blogs/health/2013/05/31/eye-lifts-fine-line-between-cosmetic-and-therapeutic/

Foot Clearance: We don't think about it until we are face down in the mud, and we have all been there.

How many times have you tripped over something so small and insignificant you can barely believe it ? We have all tripped over a small elevation in a cracked sidewalk or a curled up rug corner.  But sometimes we look back and there is no evidence of a culprit, not even a Hobbit or an elf.  How can this happen ?

Minimum foot clearance (MFC) is defined as the minimum vertical distance between the lowest point of the foot of the swing leg and the walking surface during the swing phase of the gait cycle. In other simpler words, the minimum height all parts of the foot need to clear the ground to progress through the swing phase of the limb without contacting the ground. One could justify that getting as close to this minimal amount without catching the foot is most mechanically advantageous.  But, how close to vulnerability are you willing to get ? And as you age, do you even want to enter the danger zone ? Obviously, insufficient clearance is linked to tripping and falling, which is most concerning in the elderly. 

Trips or falls from insufficient foot clearance can be related to insufficient hallux and toe(s) dorsiflexion (extension), ankle dorsiflexion, knee flexion and/or hip flexion, failure to maintain ipsilateral pelvis neutral ( anterior/posterior pelvis posture shifting), even insufficient hip hike generated by the contralateral hip abductors, namely the gluteus medius in most people’s minds. It can also be from an obvious failed concerted effort of all of the above. Note that some of these biomechanical events are sagittal and some are frontal plane.  However, do not ever forget that the swing leg is moving through the axial plane, supported in part by the abdominal wall, starting from a posteriorly obliqued pelvis at swing initiation into an anteriorly obliqued position at terminal swing. We would be remiss as well if we did not ask the reader to consider the “inverted pendulum theory” effect of controlling the dynamically moving torso over the fixed stance phase leg (yes, we could have said “core stability” but that is so flippantly used these days that many lose appreciation for really what is happening dynamically in human locomotion).  If each component is even slightly insufficient, a summation can lead to failed foot clearance.  This is why a total body examination is necessary, every time, and its why the exclusive use of video gait analysis alone will fail every time in finding the culprit(s). 

When we examine people we all tend to look for biomechanical issues unless one grasps the greater global picture of how the body must work as a whole. When one trips we first tend to look for an external source as the cause such as a turned up rug or an object, but there are plentiful internal causes as well. For example, we have this blog post on people tripping on subway stairs.  In this case, there was a change in the perceptual height of the stairs because of a subconscious, learned and engaged sensory-motor behavior of prior steps upward.  However, do not discount direct, peripheral and lower fields of view vision changes or challenges when it comes to trips and falls. Do not forget to consider vestibular components, illumination and gait speed variables as well.  Even the most subtle change in the environment (transitions from tile to carpet, transitions from treadmill to ground walking etc) can cause a trip or fall if it is subtle enough to avoid detection, especially if one is skirting the edge of MFC (minimal foot clearance) already. And, remember this, gait has components of both anticipatory and reactive adjustments, any sensory-motor adaptive changes that impair the speed, calculation and timely integration of these adjustments can change gait behaviors. Sometimes even perceived fall or trip risk in a client can easily slip them into a shorter step/stride length to encourage less single leg stance phase and more double support phase gait. This occurs often in the elderly. This can be met with a reduced minimal foot clearance by design which in itself can increase risk, especially at the moment of transition from a larger step length to a shorter one. Understanding all age-related and non-age related effects on lower limb trajectory variables as described above and only help the clinician become more competent in gait analysis of your client and in understanding the critical variables that are challenging them. 

Many studies indicate that variability and consistency in a motor pattern such as those necessary for foot clearance are huge keys for predictable patterns and injury prevention, and in this case a predictor for trips and falls.  Barrett’s study concluded that “greater MFC variability was observed in older compared to younger adults and older fallers compared to older non-fallers in the majority of studies. Greater MFC variability may contribute to increased risk of trips and associated falls in older compared to young adults and older fallers compared to older non-fallers.”

Once again we outline our mission, to enlighten everyone into the complexities of gait and how gait is all encompassing.  There are so many variables to gait, many of which will never be noted, detected or reflected on a gait analysis and a camera.  Don’t be a minimalist when it comes to evaluating your client’s gait, simply using a treadmill, a camera and some elaborate computer software are not often going to cut the mustard when it really counts.  A knowledgeable and engaged brain are arguably your best gait analysis tools.  

Remember, what you see in someone’s gait is not their problem, it is their adaptive strategy(s).  That is all you are seeing on your camera and computer screen, compensations, not the source of the problem(s).

Shawn and Ivo

the gait guys

References (some of them): 

1. Gait Posture. 2010 Oct;32(4):429-35. doi: 10.1016/j.gaitpost.2010.07.010. Epub 2010 Aug 7.

A systematic review of the effect of ageing and falls history on minimum foot clearance characteristics during level walking. Barrett RS1, Mills PM, Begg RK.

2. Gait Posture. 2007 Feb;25(2):191-8. Epub 2006 May 4. Minimum foot clearance during walking: strategies for the minimisation of trip-related falls. Begg R1, Best R, Dell’Oro L, Taylor S.

3. Clin Biomech (Bristol, Avon). 2011 Nov;26(9):962-8. doi: 10.1016/j.clinbiomech.2011.05.013. Epub 2011 Jun 29. Ageing and limb dominance effects on foot-ground clearance during treadmill and overground walking. Nagano H1, Begg RK, Sparrow WA, Taylor S.

4. Acta Bioeng Biomech. 2014;16(1):3-9. Differences in gait pattern between the elderly and the young during level walking under low illumination. Choi JS, Kang DW, Shin YH, Tack GR.

Texting and Walking.  Your gait will change when you are texting on your phone.

You are going to want to put away your cell phone after you read this, or at least hide your parent’s phones. *(the video link attached here has likely been blocked by ABC News, you should see a forwarded link to their youtube feed. If not,

here it is

.  So you think you are a multi-tasker do you ?  Do you know how much cerebral cortex real estate is necessary to walk or drive and text ? Just try texting while walking for 5 seconds in an unfamiliar environment and see what happens.  Dual tasking is difficult especially when one task is cognitive and the other is spacial and motor. At some point something has to give, especially if you are on the edge of tapping out the executive function centers in the brain because of early disease or age related mental decline.  This has never been more prevalent than in the elderly and the number of mounting studies proving that dual attention tasks lead to a dramatic increase in age related fall injuries.  If you look into the literature the fall rate increases from anywhere from 11 to 50%, these are strong numbers correlating falls and dual attention tasking in the elderly.  Certainly the numbers are worse in the frail and gait challenged and fewer in healthier elderly folks, but the correlation seems to be strong particularly when there are even early signs of frontal cortex demise. We have talked about this on several recent podcasts

(check out podcasts 80-85)

and this has been rooted even further from one of our neurology mentors, Dr. Ted Carrick.   Recently in the Journal of Applied Biomechanics, Parr and associated took 30 young able bodied healthy individuals with experience texting on cellular phones. The study used an 11-camera optical motion capture system on a 8m obstacle-free floor. 

The study showed a reduction in gait velocity in addition to significant changes in spatial and temporal parameters, notably, step width, while the double support phase of the gait cycle increased.  Furthermore, and equally disturbing, toe clearance decreased but luckily step length and cadence decreased. 

Thus, it appears that the attention draining texting task generally forced the brain to slow the gait, reduce step length while improving stability via increasing step width and double support phase of gait, keep in mind that these are young healthy experienced individuals with no early cognitive challenges. 

This is not the case in aging adults, or in adults with factors that have either challenged gait stability (degrees of impaired balance, vision, vestibular, proprioception etc) or challenged frontal cortex function where that functionality of the brain is already nearing its tipping point for adequate function.  Sadly, these are all factors in the aging adult and they are why falls are increased and riskier for the elderly. Essentially, what the studies are showing is that dual tasking creates a distraction that can amplify any sensory-motor challenges in the system.  Mind you, there are studies that show that if the dual task is remedial such as talking while walking the effects are more muted, however in those who are at the tipping point capacity of mental executive function, mere talking (cognitive linguistic engagement), can also tip the system into deciding whether to focus on the gait or the talk but not both adequately.  Something will have to give in these folks, safe competent dual tasking is beyond the ability of their system.  As we have eluded to here, there are many factors and variables that can challenge the system. Visual challenges such as low light vision problems or depth perception challenges can act similarly on the system to dual tasking attempts and thus magnify fall risk. What about sensory challenges from a spinal stenosis or peripheral neuropathy such as in advancing diabetes?  Balance and vestibular challenges, let alone factors such as unfamiliar environments (perhaps magnified by vision challenges) as precursors are a foregone conclusion to increase fall risk in anyone let alone the elderly. By this point in this article it should be a given that texting while doing anything else is a dual tasking brain challenge that could lead to a fall, an embarrassing spill into the public pool or into a fountain at the mall let alone driving off a cliff or into a crowd of people.  But are all of these unfortunate people showing signs of frontal cortex/executive function impairment? Perhaps not, especially if they are healthy.  One has to keep in mind that texting is a high demanding cognitive attention task, even though we think nothing of it as a healthy adult. Think about it, one has to engage a separate screen other than the environment they are trying to walk through. Additionally, one has to think about what they are trying to text, engage a seperate motor program to type, then there is spelling, choosing text recipients, sending the message, watching and listening for a response, and the list goes on meanwhile the person is still trying to run the gait subprograms.  We take it for granted but texting is highly engaging and adding walking can tip the system into a challenge or failure if we are in a crowd, unfamiliar environment, low light etc.   So if you have ever wondered why elderly people trip and fall in even the most benign environments, it is likely a compounded result of challenges to situation and spatial awareness and working memory with many possible factor challenges. Again, things like poor lighting, vision limitations, unfamiliar environment, vestibular limitations, numbness in the feet, talking or even if they are simply carrying the afternoon tea to the sun room these things all are dual tasking and some require higher demands from the executive function brain centers.   Any factor(s) which tax the already-reducing executive function centers in the elderly subtract from the most basic elements required for upright posture and gait.  If dual-tasking can impair healthy young individuals, the elderly are a forgone conclusion to have magnified risks.   There can be a plus to all of this however. If the goal were to only reduce falls and fall risks in the elderly, an astute clinician can work this to their favor and do gait challenges and retraining in the office environment while safely stacking dual task challenges to expand and restore some executive function capabilities.  We are never too old to learn and lay down improved motor and cognitive patterns. So, use this information to your advantage to improve function instead of delivering it as a dark cloud to hang over your clients, whether they are elderly or neurologically challenged.  In summary, put down the darn phone, trust us, that text can wait.  Rather, enjoy the sunshine, the smiling faces, the trees.  If you are driving or walking, dump the phone and pay attention to traffic and your environment. Stop and wave to a friend. Teach your kids about this texting problem, they are likely already oblivious to many risks in the world, and this one likely hasn’t crossed their mind either. At the very least, help the elderly lady or man cross the street. By now you should understand all that they are consciously and subconsciously trying to calculate to negotiate the street crossing. Their declining executive function is often a mental feat all on its own, but having to actually add the physical act of walking (which is likely already showing aspects of age related biomechanical decline) might just be their tipping point leading to a fall.  So offer your arm, a warm smile, and think everything of it, because someday it will be you at that street corner with sweaty palms and great fear.  

Dr. Shawn Allen, one of the gait guys

References : 1. 

Eur J Neurol.

 2009 Jul;16(7):786-95. doi: 10.1111/j.1468-1331.2009.02612.x. Epub 2009 Mar 31. Stops walking when talking: a predictor of falls in older adults?

Beauchet O

1, 

Annweiler C

, 

Dubost V

, 

Allali G

, 

Kressig RW

, 

Bridenbaugh S

, 

Berrut G

, 

Assal F

, 

Herrmann FR

. 2. 

J Appl Biomech.

 2014 Dec;30(6):685-8. doi: 10.1123/jab.2014-0017. Epub 2014 Jul 9. Cellular Phone Texting Impairs Gait in Able-bodied Young Adults. 

Parr ND

1, 

Hass CJ

, 

Tillman MD

. 3. 

Gait Posture.

 2014 Aug 20. pii: S0966-6362(14)00671-7. doi: 10.1016/j.gaitpost.2014.08.007. [Epub ahead of print]  Texting and walking: effects of environmental setting and task prioritization on dual task interference in healthy young adults. Plumer, Apple, Dowd, Keith. 4. 

Gait Posture.

 2012 Apr;35(4):688-90. doi: 10.1016/j.gaitpost.2011.12.005. Epub 2012 Jan 5.  Cell Phones change the way we walk.  Lamberg, Muratori 5. 

Int J Speech Lang Pathol.

 2010 Oct;12(5):455-9. doi: 10.3109/17549507.2010.486446.  Talking while walking: Cognitive loading and injurious falls in Parkinson;s disease. 

LaPointe LL

1, 

Stierwalt JA

, 

Maitland CG

.