MUD Mired in time...

MUD: Walking ? [from the bottom – up] Where is the bottom? Right here... in the mud. ==================> From so long ago, that nobody has a clue as to who first used footprints for a defined purpose. Probably it was trackers armed with clubs and spears? Let's face it, many of those really old foot prints look a bit like hands. Our footprints evolved as we did. The enlightened need to tack specificity onto just about everything led to a tsunami of measurements generating sciency walking terms. Those terms were spiced with more than a pinch of conjecture, especially when foot prints were odd looking. Stop here. Go to the internet and do a search for footprint measurements. You will find endless mud tracks, inked foot prints on rolled out paper, prints on pressure sensitive paper, digital sensor walkways taking pixel type footprints, and on & on and on. There's even AI footprints. Had to be. Did you see all that? Crazy huh? All that measuring and terminology to every minimal nuance of mud prints... wow. And what has it given us? Well, mostly (hunters aside) some good detective novel content which captured bad guys who seem to always have a peculiar walking footprint oddity - as seen in the mud.

Let's review, just to see how useless it is aside from suggesting height & weight of the walker.

1 Gait cycle : Walking is “ periodic ”, as with a clock, it repeats as it goes round again, and again... A value series that repeats. It has two features, distance traversed and speed (time required for each cycle).

Fist, we identify ONE specific walking cycle. Here, A is at the back edge of the right heel.

C is similar in that it is the back edge of the right heel once again. That defines a typical single unit of the repeating cycle . The whole thing we call ‘gait’ (not jumping or making funny faces). But not all gait is ‘walking’ [more about that later]. If only we knew how how much time it took for right heel to next right heel mud print to happen, we would then also know the PERIOD (the name for the time it took for one full cycle).

Ooo, if only this mud had come from a magnetic magic gush where the crystals form as they cool to tell us that it was 1.2 seconds from A to C [a right heel strike to the next right heel strike]. Period=1.2s If the distance from A to C indicates a relaxed walk, then we know the height of this walker. One full walking cycle length is 75% of the walker's height ( stature ). This assumes a relaxed walk in a person who is not wounded nor carrying a load. From one gait foot-print detail to the next occurring same side same detail is called a STRIDE. Teaching stuff nearly always uses a right heel strike to the next right heel strike as defining one STRIDE. We can see that 1 stride contains 2 STEPS - A to B then B to C. A left step and a right step = one cycle. So, although we chose to begin with a right heel strike (at A), our first mud documented step is the LEFT step, the one swinging and then landing (A to B). Yes, everybody measures this distance and then they call it the “left step length”. You see this everywhere. They will give you the left step length and the right step length. They will list every % thing that can be made of any two mobile things. (Following this? Sorry. It is all wrong, but we'll let you suffer a bit.) Now, we jump ages ahead. Instead of mud we go to the computer lab seeking GIGO. The big improvement is the absence of gnats & mosquitoes though bugs persist. The terminology now being used is still stuck in that mud along with those muddy implications. This means that the thinking of possibilities is also mired. The lab also tells you the knee had one angle over here and then had another angle over there with a continuous graph of knee angles through the whole cycle.

Wow! So many numeric details! The swing of each leg takes 62% of the period... or whatever it shows? “Abnormal” = bell curve deviation from what persons of the same age are doing ... on the average . Age? Did we get that from the mud prints? Size, maybe. But age normals? Are equally set metronomes of different age going to have differing periods? THAT seems a bit muddy to me.

But what does it mean? If not an average case, is what we see a deviation or is it a correction? Looking at many different ills and beating the standard deviation into dust we find that a variety of unlike maladies are associated with similar foot prints, typically called ‘shortened stride length’.

Shortened stride length is the result conclusion of so many studies. Stride is shorter. This disease makes the stride length shorter. How? Why? No no. It just does. Close the lights. Go home. But wait 62% + 62% = 124%. Two legs swinging at once? What is that functionally a % of? Percent of time? Of length? Length of what? Do you feel it welling up and over your shoes? Let's begin again. This time we won’t just measure things because they are easy to measure. We want to know what does what ? And how much? And if not, then what else? When we see something is wrong, is what we see a bad thing to do? Or, maybe the next best choice? We go back to Verne Inman and his determinants – things that you can see that accomplish something positive . His goal was prosthetics for neurologically intact soldiers with missing leg parts. There is only one good outcome in the military – return to duty. For us it is RESTORATION of ability, to match our peers. Inman focused on what the whole body does. He sought (& found) the why. What does each thing that the body parts do together functionally that a prosthetic can also do (maybe in a different way or by different means)? Is the functional goal attained despite a missing part of the anatomy? ‘What is normal’ is a wrong question. What details of movement do good? Ah. Better.

If we had no knees and the legs were just stiff rods, then the body trajectory would trace a portion of a circle for each leg. The two arcs cross steeply to each other which needs an abrupt reversal . Hey! That’s not SMOOTH. Nooooooooooooooo.

Nature does not like THAT! Also, the bigger the angular arc of the circle used, the more upward and then following downward the travel. More up and down engages gravity? Noooooooooooooooo. That is not efficient. Skateboard UP a hill? Better have extreme inertia. What is best, theoretically? A========================>B A dead straight horizontal line at uniform speed. Without wheels, this is nearly impossible and actually impractical. Wheels without roads are not so good. Wheels are a one trick pony. Jointed limbs have contour options. Legs win. But the laboratory is flat and so this huge distinction gets little mention. The yellow arrows might be a wheel solution. But sine waves are what legs can do. A big sine wave (green line) uses much more energy than a low amplitude sine wave (red).

The biologic target is a nearly flat low amplitude sine wave travel of our center of mass.

Legs are designed to do exactly that. They can allow, on the fly, alterations to offset ground irregularities. The coordinated tricks to attain the flattest uniform travel are called the ‘determinants of gait’. This was a great advance in thinking, but keep in mind that, as good as this was for amputees, it had no allowance for neurologic abnormality. The 6 movement tricks (‘determinants’) allow compensation for missing parts or rigid ankles when replaced by prosthetics. [Psst...You can’t say ‘tricks’ in medicine!!!]

The ankle foot link meanwhile adapts to the smaller ground contours while also diverting inertial thrusts from above acting like a capacitor, filling and smoothing the sharp reversals at the crossing of the intersecting arcs.

The pelvic determinant contributions are interesting. Roll, pitch, and yaw – but these perfectly appropriate terms are not used - ever. Requires a pilot’s license I suppose. Body mass, not over either leg but between them can rotate horizontally to increase the two step lengths of each stride with no anti-gravity cost. Arm swing allows the right/left/right/… alternating rotational torque to be offset (neutralized). Is that why we swing the arms? Yup. Although the hip is still riding upward and then downward even after the knee/foot tricks, the center of mass stays more level as one hip upthrusts. It simply lifts one side of the pelvis centered on the center of mass as the other side is dropping. No vertical cost.

The distance from center of mass to each hip center is just about equal to the ankle to forefoot roll over length. This means that both share this ground adaptive allowance. If you waste one of these? High heels... Wearing high heels requires more up & down fanny motion about the center of mass to offset the ankle arc loss (to fashion). Lumbar spinal fusion to the pelvis kills this pelvic tilt contribution and makes wearing high heels, or anything that constrains ankle movement, quite uncomfortable and exhausting.

Are there alternates to Inman’s determinants? Yes, a big one. A very large radius single wheel using a smaller arc that is centered vertically also mimics this and (an alternative discussed in our ebooks that follow). Inman did not include this nor what happens when neurology is amiss (not from missing anatomy).

Back to MUD.

This is a good time to suggest another book in our series: It will discuss a tool (HARP Line Measurement Tool) built so as to better track Hip-Ankle Relative Positioning. It treats the thigh-shin angle (knee angle) as a Harp frame and an invisible hip-ankle line is the longest (virtual) string** of that harp. [= simplified radians]

______________________________________________________ ** This tool was added to SportsCAD, Seaside Software TM, and is useful for general evaluation of many additional things.

Step length is the distance that the BODY travels with each step. We project it to the ground to make the distance easier to relate to the two steps (as seen in the mud). Side to side weight transfer

happens on the WHEEL at two points one heel & other side toe. Seeing this = intact sensation. This is lost early when proprioception makes safe transfer of weight less certain, the trailing heel stays planted until AFTER the feeling of safe transfer is confirmed.

Looking at footprints in the mud, we gravitate to distances between what we see there. Size (length and width) of each foot and any wounds or oddities. If there is only a left

and a right footprint then we take double the step length (assuming the other side step is similar) to get the full stride length (which, again, is wrong – sorry – we’ll get to that). This is 75% of the person's height if the prints don't look hurried. Deeper heel and smeared edges might suggest hurried gait so we then guess using ? 85% ? If there was some way to know WHEN the heels hit the ground and when each heel left and when the forefoot came down and when the toes left to swing, as is possible with electronic mud having footprint tracking digital running pads, then we have TIME EVENTS such as: right heel strike, heel off, toe strike, toe off & left heel strike, heel off, toe strike, toe off etc...

Those in turn allow time intervals derived from timed events: Right stance = the total time any part of the right foot is on the ground Left stance = the total time any part of the left foot is on the ground Swing phase (right or left) is when that whole foot is off the ground (follows on toe-off until swinging heel strike. Good? (Sorry, this too is wrong – we’ll get to it later...) See? THIS ==> IS <== what is used in the bulk of what you read. These are the key time markers of Braun & Fischer and Inman and the followers thereof. It's everywhere.

Above we see a series of connected wheels. Each wheel has a radius (like a spoke of a wheel). The green center-of-mass to hip-center wheel is seen here rotated 90 degrees for size comparison. It matches the red radius of the ankle-metatarsal wheel. Thus we have additive circumferences that each travel at best speeds. “Harmonics have two parts which are the wheel rolling distance per turn and the rotational time for a full cycle (the ‘period’). The interaction of these 5 wheels produce the very low (nearly level) sine wave that the body travels when walking. The body can weld portions together to create other (especially very large radius) wheels. Such joining is often called joint stiffness and is commonly attacked with chisels and other weapons of center-of- mass destruction .

Stiffly held joints create new spokes to make new wheels. Could be bad. Could be good. Also, combination locking tricks need to be vertical rise centered. This adjustment to avoid body rise creates another observer perceived ‘abnormality’ which then becomes a surgical target. We will detail this later. You may have noticed the absence, in our discussions, of angle plots of all the joints except for the double bump knee curve. ?? They add NOTHING to our understanding of combined effect. Seeking joint by joint angular plots, each within bounds of ‘normal’, is the source of outrageous misinterpretation. EVERYTHING that ALL the joints are contributing to function is seen and seen best in the knee angle curve [single stride of 2steps]. There, the functional interactions are obvious once you learn how to see them, and you will. I promise.

So, here it is. The knee angle graph (so they call it a graph – they lie). Our Y axis allows 0 to 80 degrees. The X axis shows time as % of one complete stride. About 1.2 seconds is the period for an average height adult. This X axis could be 0 to some long enough time as needed. We see an obvious two curve graph. A small one, ‘stance’ where a foot lands and stays in the mud while about 15 degrees of knee range happens green zone] called ‘stance’. The big curve is about 70 degrees but only the part after ‘toe off’ [looks like a saxophone] is called ‘swing’ [blue zone]. The red boxes on the Y axis show common range for the two flexion peaks. The X axis red boxes are where certain ‘events’ occur during walking as determined by mud. In particular note the box straddling 50% as is quoted everywhere (from mud). That is ‘toe off’ and is the beginning of ‘swing phase’ [where the lifted foot is no longer seen in the mud]. Everything before this is ‘stance phase’… after is ‘stance phase’. Totally bogus. As the knee is at the key center of walking (it is) we will follow the knee angle progression through a full stride (left step + right step or LHS to next LHS). Inman dove deep on the stance details as prosthetics were his target. Swing phase was not his immediate big concern aside from weight distribution etc. So, maybe we need more determinants to get a better handle on stance/swing phase which is a big issue in neurologic conditions. Hmmmmmm….. Could this be better????

Recap: the vertical [Y] axis is 0 degrees at the top and 80 degrees at the bottom. The orange vertical rectangles show typical reported peak/low angle ranges for “stance” and “swing” phases. Commonly, a few degrees of flexion exist throughout (from how markers are placed). Notice that the knee curve after toe off in the blue area looks like a saxophone, a swing instrument! Hmm.. nice mnemonic to remember a falsehood. ?? Left heel strike to left toe-off ... Looking at what the left leg does, the mud version of things has the green zone as left stance phase; the heel lands = contact until the left toe leaves the ground. This works for mud, but is that THAT all functional stance ? For those who choked on this, a “preswing” was allowed as a latter part of stance phase. Mmmmm? You think?

Mud seems to stick as this is the current terminology you see in print. Look. We see about 10° to (pushing it) 15° of knee flexion in green stance phase. Crazy fact: Even in tall snug cylinder casts from groin to ankle directly on skin (of thin gymnasts) we get ~ 10° of flexion (inside the cast!) [This was not easy to measure ]. We conclude that stance flexion is highly momentum & inertially driven and hard to make not happen, aside from surgically fusing the knee joint. Stance curve is trampoline-like yielding to the weight above.

You ask, ‘Does that 10° accomplish anything?’ You can't tell from angle graphs. But direct visualization shows that it shortens the leg as the hip forward trajectory passes from behind the ankle to above it. There is less hill to climb against gravity saving energy. That is one of Inman's 'determinants', a why for the what – shorten required vertical rise approaching verticality nor leave a debt on passing. This is only functional if the hip to ankle line* is passing through vertical. The knee ANGLE graphs do not even hint this. You have to infer it from – oooooooh – those mud prints (orange rectangles at the bottom of the graph). HARP* does tell you. This is mentally exhausting. So, let’s take a break from why old terminology is bad. Let’s look at a common, for us, functional “abnormality” as we clinicians see regularly. An insincere apology: These books are written with language acquiring methods - lots of repetition and small variations. We are learning a new language of walking so we can communicate a new way of seeing which is often devoid of accepted terminology. We are dodging ‘standard’ but conceptually damaged labels so as to not get mud all over our new floor. - rmn

------------------------------------------------------------------------------------------------------------------ * Hip Ankle Relative Position ( HARP , a vector in space & relative to the room & ground)

Above are examples of spastic diplegia with medial leg rotation ‘crouch gait’. The reasons for seeing doctors are typically about this wrong angle and that angle… this bent twisted look vs “nice and straight”. You can’t say “straight” without saying “nice and..” – this was not allowed. Detailed histories disclose that these kids can do just about anything. But, they do not want to. They can’t do it quite well enough or to keep doing (whatever it is) long enough to be satisfying. Free tickets to a theme park? Only if carried or wheeled. Too exhausting -for everybody. FATIGUE is the bush they beat around. More energy required than can be sustained. We see two main patterns of movement in what we do. 1. CONCENTRIC – Each muscle does what it’s name implies. Biceps, a flexor, flexes. Quadriceps, an extensor, extends. Move this thing from here to there? OK. Each muscle does its part CONCENTRICALLY (gets shorter when in action). ATP is required to elongate the muscle AFTER the action – like a crossbow. Nerve trigger unlocks the number of muscle fibers needed to release their already predelivered muscle energy. Heat of RELAXATION = resetting by elongating actin/myosin (ATP). Dead = rigor mortis = contracted everywhere. 2. ECCENTRIC – The muscle trigger unlocks the muscle mechanism to a greater external tension which actually further elongates the muscle. The flexors are extended by eccentric ‘activation’. The extensors are flexed. This has BIG energy savings. In human walking, only the psoas is concentric. It is the cue stick that hits the cue ball. Everything else is ricochet. Leg muscles act eccentrically to divert the energy source as a billiard ball bounces off cushions. All the energy was delivered in the pool stick hit. In gait, the energy savings is immense. This is why we have hips at all!! … to allow eccentric control of walking progression. Less energy. Period! So, when we climb steep stairs? There is no ‘MO’. We go CONCENTRIC, just like the kids with spastic crouch gait whose actual abnormality is that pendulum energy is dampened. The killer: ATP delivery is during RELAXATION (elongation of actin/myosin units) which requires blood flow. Sustained contracted states make blood delivery stop. Muscle ‘activation’ is best when brief with relaxed time to follow for replenishment and removal of pre-Krebs anaerobic waste (muscle will get some of it done anaerobically until O2 is again supplied). If not, cramps. Some odd stuff we see is cramp avoidance.

So, maybe we stop calling it ‘abnormal’ (not a bell shaped match to an age population at large). Maybe, instead, we call it “stair climbing” gait, which is essentially what it is (though missing a catchy name) – the millennia old concentric way to get any muscle job done minus any energy saving tricks. Hey, I just crawled out of the ocean. I don’t have land tricks yet. The above marathoner is toe walking with very short steps, that are inwardly rotated and with a quite obvious crouch. It is exactly similar to spastic diplegia even in the emg recordings which looked obviously spastic - though not actually so. This is NOT a spastic person. This mud is an avalanche. The key abnormality is not to be found in the RANGE of any joint motion. It is in the energy cost of the range that is still being used and is measurable. (In the book Range vs Resistance we will beat this into you. Maybe wear padding for that book). OK? Another?

Stepping video frames through this girl’s knee flexion curve showed that there was no significant knee flexion (Hip-to-ankle shortening during verticality of stance). Flexion seen above was mostly for cramp relief. It is totally absent in forward progression. Remember? Blood flow during active contraction is poor? Can’t recharge. Cramps. To get technical, knee angle, as such, has magnitude but not direction. The HARP line which is another way to measure knee angle & additionally has magnitude & direction. It is also linked to stature. HARP uses the same positions of hip, knee & ankle in space as does knee angle. It tells you both WHAT and the WHY at the same time. So, swing seems suspicious. And knee flexion comes from what? Knee flexors? In normal gait, knee flexors are not used to bend the knee. What does? Hip flexors, center of mass inertia to rise against gravity, planted foot ankle resistance, heel descent, effective foot length to forward roll over and maybe things worn while walking… Eccentric gait is normal gait. Key to rehabilitation is the WOBBLE ZONE often, unfortunately, smudged away when graphs are smoothed.

In this segment of “stance phase” of the knee angle graph there is a wobble zone. Here we come to grips with an unsung but vital reality. Knee flexion is not about the KNEE flexing – it is passively the thing being bent – from afar. So what flexes the knee? 1. knee ‘flexor’ muscles are not ‘flexor’ in normal walking. 2. Quadriceps relative weakness (not holding back the landing force that we found to be so dynamically driven by body momentum). 3. The knee can hyper-extend if the tibia is held back. A resisting ankle joint with parents stressing to get those heels down can destroy the knee by a slamming knee extension of compression (on landing). There is a different kind (extension in tension/distraction) which is not damaging. Discuss this later. 4. Hip flexors [initiating thigh swing which has no terminology at all in anything you read] with the foot planted are responsible for everything between the first orange arrow and toe off [green to blue]. This is dampened or increased by 1, 2, & 3 above. So, what are the actual knee flexors in normal gait? The hip flexors. Psoas /Iliacus -not even in the ‘leg’. MUD! We do NOT swing our leg. We swing the thigh . With the toe grounded, the flexing thigh bends the knee and lifts the heel. We don't need a saxophone mnemonic for swing anymore. FUNCTIONAL SWING begins between the two up pointing orange arrows illustrated above – [creepy music goes here] - Welcome to the WOBBLE ZONE!

Seriously. How can we escape the visually obvious fact that swing phase begins at the topmost point of the wobble zone where ground reaction and stance support are at play? Polar graphs (gray inset) show 5 contributors to this one knee curve. If you jam everything into mud swing at toe-off , then that is when NOTHING is happening . If you use polar graphs of this same data (color dashes carry time info), we see the many different but interacting forces that make this full stride knee curve what it is. We can use a thing called Fourier transforms to draw similar shapes as seen above. We only need 5 harmonics for most knee curves of any normal or pathological circumstance. Each harmonic (= numerical representation of a

circle having both size & speed of rotation) represents a different body part or interacting thing (eg. Ground) contributing to the composite knee flexion curve. One double bump graph line drawn by 5 linked gears. You can’t draw much of anything if the gears are all similar. Using a series of gear sizes allows combos that are best suited to the task. Hmm, what size series would nature select?

Hmmmmm… nah.. maybe… Start with a really obvious wheel to test: But SURPRISE !!!!!

Stride or step lengths ?

We are showing it wrong as it is seen everywhere. Actual FUNCTIONAL step or stride length is not in the MUD! A step or stride length is how far the body goes (use center of mass or even neck center is easier) during a stride or step. We commonly project this trajectory line on to the ground where it is easier to relate to the mud that just won’t go away. Unequal step lengths? For example, in hemiplegia – no matter how stiff. Both step lengths measured in the mud must be the same or the body would be ripped apart. How far the body travels with each step vs the other step is where we see the functional travel difference. So, the “step to” gait = one side is put forward as a step then the other side carries the body forward to catch up.

The Wheel Use a wheel (a circle) with a diameter the size of the subject. Wheel diameter = 1 stature

When dealing with a full stride (one full period made from two steps, R & L) we use statures (= diameter) for length measurements. It’s OK to carry cms or inches along for the ride. Pretend scientists like that. If dealing with one side of the body, one leg, or one step then it is very convenient to use the circle’s RADIUS as our measure rather than the diameter. Same circle. So a 75% stature stride would have a 75% half stature step. Makes everything easy. We can also use arm span or mid neck to finger tips.

Notice that the radius wheel center is rather close to the center of mass. If you also measure everything else in statures including the walkway ground, then those wide graph envelopes shrink like heated electrical wire coating. Data gets very tight. A ½ mile walk by 4 subjects, one a monster wrestler, another a slim but 7 month pregnant woman, her husband short but totally muscular and me – a schlub… walking data looked the same when using statures whereas it was all over the place in metric or royal measurement. ?? The ½ mile becomes something else for each subject.

Notice (medial rotation crouch gait) & that the knee angle is unchanged in the three frames indicating early stance to midstance to preswing. This girl is a super athlete. Why is she spontaneously doing this? … and toe walking ? We can restate this a little differently for clarity… These mechanisms can be approximated using 'harmonics proportioned in a Fibonacci series starting with a stature matching 'power' (wheel radius = ½ stature). It is tempting to assume these proportions as the bone sizes. It kind of works. Interestingly, these harmonics tickle the edge of being in a Fibonacci series. Forcing Fibonacci harmonics into a Fourier-like summation series comes close. Close, but no prize. Our muscle bulk is more proximal with tendons reaching to the target limb insertions. In this way the pendulum periods are NOT quite those of the bone lengths but more like a metronome . The period is derived from lengths between a moving joint center to the segment’s center of mass but power or distance uses the full radius length. For this reason, harmonic size (‘power’) and speed of rotation (‘period’) are somewhat disconnected. We'll call it skewed. This gains more distance without being slowed by it as would happen with a longer pendulum. This is why speed runners flex so severely … to shorten the forward leg’s pendulum inertia which allows faster hip flexion for the next step’s outreach. Besides, running is concentric. For every thing, turn turn, there is a time and a purpose…

Momentum compression

swing

^Transition^

^slow both: hip flexion & knee extension

Brief psoas here.

Stiff AFO toe plate or heel planted + stiff equinus kills psoas’s thigh nudge. No energy to drive eccentric mechanism. Walker becomes a stepper.

The psoas briefly inserts the needed energy at the real swing beginning. Everything else is deflection. Think pool cue as psoas. Balls bouncing off cushions deflect but add no new energy. The more things that impede the supple swing of the double pendulum the vastly more energy the psoas has to supply. Establishing suppleness to swing phase can quiet the seemingly overactive hip flexors. When he stance leg harp line H_A approaches vertical the dampening of the opposite swing leg provides a boost to the stance to reach the top of its trajectory. Incomplete swing arc robs the opposite leg of the energy boost it needs to get to the top. Deflecting momentum is eccentric. If energy is lost due to whatever is awry, then concentric muscle (the primitive obvious this-does-that muscle approach) takes over at a much higher energy cost. When we walk UP steep stairs we have no momentum to run the process and so we become concentric. The medial rotation crouch is not THE problem. It is a stair climbing movement that works when eccentric inertial mechanisms are dampened. Get that? As the swing leg extends at the knee, the full swing is TERMINATED (by hamstrings limiting extension) and thus diverting the momentum to the pelvis which pulls the other leg over its hill approaching verticality. This is a VITAL target of corrective surgery. Terminal knee extension needs a link to transfer momentum and at the right time – and not too early. The ‘fast/slow’ knee extension exam is looking at this.

RECAP: These bones can be thought of as spokes … radii of connected wheels. Their radius sizes and angular speed, when in motion, provide a nice Fourier harmonic similarity. But the speeds are a bit off expected series based on radius alone. Nature cheats. Muscle mass is moved proximal in each segment by using tendons to reach the insertions.

This means the pendulum speed (period) comes from the centers of mass of each leg segment. This matches the polar graphs. The pendulums are metronome-like. Segmental centers of mass were detailed by Braun & Fisher over a century ago!! Were they on to this????? Kinds of motion were computed...

This is the clockworks. Limb parts as spokes of linked wheels. What we do well - we do with this. What we do badly - we ALSO do with this.

Abnormality and normality are similarly constrained. This eccentric based clockworks is attuned to efficiency, moving flat ahead in air rather than every which way in water. By having the two hips virtually connected to the body’s center of mass (via ONE pelvis + 2 hip joints) rather than the more primitive limb sling suspension from fish to this... we have a more energy efficient and easily adapting mechanism of travel that can boost output - at will - when needed, often maintaining efficiency by modulating one segment or another drawing on another determinant we here propose – expectation. Done this before – context relevant motor memory. Hips are not to allow walking. Many ancient beasts without hips could easily outrun us. Quadrupeds, today, only have two hips of the four legs. Articulated hips properly spaced relative to center of mass, allow an insane degree of energy conservation by juggling the periods of several pendulums passing energy between them. This stuff is useless in the absence of intact sensory mechanisms attuned to inertial and acceleration events. Add a machine to our legs and we find similar considerations: Adjust the foot levers badly and the the man pumping the machine will expire before the job is done.

Walking is not the only user of eccentric motion tricks. Apprentice driven machines require it. Interesting adjustment rules basically come down to avoiding epicycles which divert energy from the energy minimized desired task. So too in bicycle foot driven linkages.

MUD:

Step lengths Stride lengths [a recap] All sorts of measures derive from measuring mud print distances. Can the left step length be twice the size of the right step length? Well after enough steps the feet would be miles apart if THAT were true. FUNCTIONAL step length is how far the center of mass travels for each step. That is what both walking and stepping are for, to move the body from hither to thither. A video exam tool that lets you pull lines and automatically gives you the center of that line makes tracking centers easy which is good for knee centers and mass centers also. . This point gives you a point in space ____ as does this line (using its center). BEWARE Step length (“shortened stride length”) error is everywhere. Every malady “causes” shortened stride length… no … compensation for energy insufficiency uses a shorter body travel to get by. Restated: Shortened arc of travel over an elongated center of mass to ground wheel spoke (radius) has small vertical rise and so isn't a malady but rather a compensatory mechanism to get some distance with least up/down (= least energy) cost. Human interfaces can be modified such that the linkages are 'IN TUNE” with the body linkages. Minus that, people powered things tend to kill. A Tour de France competitor, who never finished , finally placed once his pedal lengths were changed to harmonize with his leg segments. We observed epicycles at the top & bottom of each pedal stroke & fixed that by altering length of pedal from pedal axis. A spinal fusion to the pelvis kills lumbar centered vertical hip oscillation. As the center of mass to hip center distances are nearly the same as the ankle to metatarsal heads... you cannot wear high heels with that fusion. Wearing high heels (limits available ankle modulation) makes the two hips alternately rise & fall more, thus leading to marriage and babies.. sometimes.

Shortened stride length? Almost no knee angle change in stance. Toe walking?

The big circle is built from fusion of the smaller circles. Bigger wheel but smaller angle of rotation. Stiff plantar flexion centers the roll at midstance. Avoids a cam. She is normal (an athlete Irish step dancer) [working against drag we inflicted on her – elastics… see the book on our shelf]. “THE WHEEL” (the big circle with a diameter equal to stature) is beautifully useful in seeing something invisible – sensory loss. Like the movie where ‘I see dead people.’ With the wheel you can see dead sensation. This may be the single most important visual thing that isn’t implemented anywhere!

SENSORY LOSS masquerades as motor problems:

Beware of this!!! When both heels stay planted at same time – both feet flat to ground – and no 'wheel' transfer of momentum side to other side – we have a trust problem.

This is the back-knee (recurvatum) in tension as the patient lacks the SENSORY assurance that the receiving leg is ready to support. This indicates sensory deficiency. Not a surgical target. Sensory deficiency is lack of detection OR the inability to apply what is perceived to the task. Walking involves KNOWING & expectation (such as how the ground will behave when loaded). Conditions that foul the sensory contribution of what is or the expectation of what will happen on loading (ankle foot varus) cripple gait far out of proportion to the mechanical incapability. Driving a Porsche stuck in reverse [doable] vs Drive any car with the windows all covered with metal foil [nooooooo].

Post injury and with surgical repair with some residual calf weakness but no sensory loss, the heel-toe transfer wheel is still intact. This reflects KNOWING. Left energy is being passed to the right BEFORE the right is fully secured. In the absence of KNOWING, the trailing heel stays planted until certainty of the leading foot security. If you see an intact wheel, even if strength is diminished somehow, means that KNOWING is intact. Sensory is present and working. NEVER – never never ever give this up. In disorders where sensory is lost we hear walking go SLAP SLAP SLAP – here comes a syphilitic… Using sound and jaring impulses to know when to transfer weight and momentum to the other side.

Bracing strategies Bracing for stability – if energy conserving skills are absent then this eases stance Bracing for mobility – requires sensory with quick adaptability but is hurt by stability. Bracing choice prescriptions are related to the wobble zone, where stance must give way to swing. What swings is NOT the leg. It is the thigh flexing while the foot is on the ground which makes the thigh bend the knee. Most of the energy of walking is injected by the psoas at this transition. Extra stability here poisons the essence of walking – energy conservation. But, clinically we need to bow to reality. The eccentric energy saving mechanism requires a very fast adjusting and inertially sensitive neurology as the driver. There is where we must make separate strategies 1. can neurologically adjust quickly and proportionately 2. can not

Treatment strategy across the board derives from this:

Two groups

for distinct surgical interventions or for kinds of braces & walking aids.

Always have the TRANSITIONS in mind between step stance to swing to step stance...

Body progression is of two types. Continuous & halting. Halting flushes all energy in the system down the energy drain. If the center of mass moves steadily forward then the d istance to t ime graphs generate straight lines (slope depends on speed and the units used to measure distance. If the center of mass stops & starts, slows & speeds by lower resistance or is otherwise irregular then the progression graph forms steps as slowing flattens the curve. These are called “STEPPERS”. The straight continuous graph represents “ WALKERS ”. Walkers conserve and use energy and momentum. Steppers do not have efficient energy transfer in their recipe for ambulation and so jar from one island of stability to the next in step-wise progression. High energy usage is made worse if they have to also use active power to maintain anti-gravity to the stabilizing legs. So steppers need stability islands with reasonably easy allowance of initiation of a next step. AFOs can provide these stability islands if well thought out.

The casual clinician does not recognize the huge differences of needs of these two groups nor shortcuts in repair related to these differences.

Braces for 'walkers' must be set for transitions (not slow, not stable). They might even be used to speed up a slow or locking transition. Stepper braces should NOT mask sensation the lack of which increases instability and coordinated energy transferal. Whether using Inman's determinants to progress or a substitute to get around a deficiency, an easy gauge of functional efficiency is simply to follow the head, even blocking the body from view. Smooth forward progression? Halting progression? At the end of stance with the hip extended (10 deg or so?) there is stretch of the proximal rectus femoris (RF) which the body should note but ignore. If spastic reflex is set such that this stretch TRIGGERS a reflexive contraction of the RF (or even the whole quadriceps), then at the moment when the psoas is to flex the thigh, this abnormal

reflex acts to extend it. Side sway and stiff full leg swing follows. Making this more difficult is that high hamstring activity and contracture requires compensatory quadriceps output to overcome hamstring excess for function to occur. This RF peculiarity is thus hidden in a sea of quadriceps stimulation. Manual testing using slow and then fast movements, with skill, help sort it out. But is is another kind of mud as abnormalities and reactions to them pile on. There is a lot to know, but step-wise viewing of the walk frame by frame is super handy.

Plantar flexion contracture (or device) in stance retro-pulses. One would fall backward. Getting the center of mass over support center requires a 'jack-knife' posture. This flexed hip posture is far more likely to reflect an uncompensated (by wedge) equinus. Simple wedge correction in the shoe restores stance ease with less 'stability' required. That ease is reflected in high function. Extending the heel backward in a shoe with an AFO prevents ataxic back knee. But note, that back knee is a stabilizing trick. It bangs straight such that the patient feels it as secure before swinging the other leg. Nice trick, but damaging to the knee. Again stability vs mobility. Mud. So much for mud. Let's recap, so far but more directly.

For STRIDE, we use height as our ruler. On a circle with a diameter of one stature, the feet will 'wheel' align during right-left and left -right weight transfer which includes energy transfer.

Swing phase is NOT the leg but rather the swinging thigh which is a concentric and a brief act of the psoas. The iliopsoas muscle is not IN the leg. It is in the body with segmental arteries serving it as the source of almost all the energy of walking which is briefly put into the swing – similar to pushing a child on a swing. The oomph it provides is brief as with pushing a kid on a swing. The swing and return follow from pendulum related momentum etc. A stride is two steps.

When considering only one STEP, we use the same stature circle but the radius of that circle is now the ruler. We use stature and half stature for stride and for step measurement. In symmetric gait we expect the stride and step numbers to be about the same. Easy. Don't go back in the mud to measure FUNCTIONAL step lengths. Although the mud measure of heel to heel is convenient -WHEN NORMAL, it becomes misleading when dissecting abnormalities. Mud step lengths MUST always be the same. If not, the body would be ripped apart by unequal steps. Abnormality such as 'step to' has one leg claim new ground and the other catches up. They are equal in length but not in what they do.

For functional purposes we measure the trajectory (path) of the center of mass. Our favorite video analysis programs can select points directly [click] or use an average of two or more points by pulling a line out [click press- pull-release]. So, pulling a line across the body at the c of g level uses the line's center point. You can do the same thing with knees etc. We can easily get useful measurements from emailed home videos by grabbing stature from the video and (if actual height is known) typing in the known metric size of one stature. Here we are shown the 5 'wheels' that generate the single knee angle graph. The upper green one actually from the side would be seen more squished because it is actually leaning away from us and thus foreshortened as seen from the side. This is the center of mass to hip as radius of a wheel nearly the same size as the forefoot to ankle wheel. For this reason you cannot immobilize BOTH at the same time without adding jarring momentum epicycles to take their place. These smaller wheels adapt to the irregularities of ground surface and are driven by movement about their centers of inertia. An untethered talus allows inertial accommodation to ground driven foot postures as the talus moves within an envelope of tension and resistance created by the musculature forces that surround it.

If the foot can't do it then the smaller ground irregularities inertial force drives the hip upward pivoting around the center of mass of the body. In normal walking on level ground one hip rises and the other lowers alternately.

The undulating mountains and valleys that the hips travel thus average the center of mass through a tunnel in those rising falling paths. This pelvic tilt as seen from the front is often confused with Trendelenburg gait which it isn't. High heel shoes, by preempting the full forefoot wheel arc, cause a great increase in hip hiking stimulating the boys on the corner to whistle. (mud?)

If momentum is drained by resistance, then a plan B evolves. The several anatomic spokes of wheels lock into a rigid single but quite large wheel. That big wheel only uses a short arc at the top of that wheel – the flattest most centered arc. This is another way to have forward progression with low vertical rise & fall (energy saving). This interpretation is over & over missed as just about every malady discussed having a gait abnormality is said to have “SHORTENED STRIDE LENGTH”. That is, shortened step & stride length as a hallmark of the malady . It is NOT an abnormality. It is a clever work around for loss of momentum or resisted motion.

Do you want to easily experience what walking is like when momentum is dampened continually? Walk up steep stairs. We have adopted the name “stair climbing gait” for what many call crouch gait. The difference? Crouch is just a word for the obvious look. Stair climbing sheds light on what is actually happening – absent momentum. A most common example is spastic diplegia's medial rotation crouch gait. As if the brain is messed up into that abnormal pattern? No. This gait is the work-around for dampened momentum and gross energy loss. The crouch releases as much tension as possible short of collapse while generating a next best alternative. Single big wheel with short turn arcs (flat) centered over the floor rolling point (which requires equinus to center it).

This is NOT CP. It is an athlete dancer with the swing dampened by elastics. Gait labs suggested 'shark bite' surgeries and a variety of osteotomies and muscle/tendon fillets which were simply cured by removing the elastic gizmos dampening her swing inertia.

Again, an athlete whose gait was dampened by applied elastics has shortened stride length and a mild crouch and is toe walking. Toe walking??? To get a tall wheel and use the shortened arc the wheel center must be centered below the arc otherwise it becomes a CAM (a 'lifter') which has its own nasty energy and wear & tear consequences.

A HARP line shows that her knee flexion is unchanged through all of stance phase. The wheels lock and form a very large wheel turns on the forefoot pivot of the ankle in equinus. So, now we find that we need to distinguish pathological equinus from functional equinus. More mud. Groan. Hey. This is medicine. You want easy? Go be a rocket scientist.

Rocket science? That's where we started!

Our Vanguard (Rocket) tracking system had etch-a sketch wheels that allowed points to be located. Took forever!!!! A pair of microphones (left and top of screen) instead locate the squeak of a mouse pointer. Menus for the computer back then were adhesive

tape with drawn on script. This was not video but rear projection of film at 1000 fps. Mud didn't seem so bad. No keyboards. Programming and bootstrapping in binary. First clinical patient? Familial spastic para-paresis. So much has changed but the key, as seen here, is to not disconnect the visual patient from the data by stacks of graphs without insight... mud. We have come a long way. Cellphones can now capture most of what we need to clear the mud from our seeing what is going on. So now, as here, we need to help get the mud out of our eyes and see what is wrong versus what is making-do in order to not be left behind in life. That's why we are here.