Descending pronation patterns

Accepted Manuscript Descending Pronation Patterns Dr. Matt Wallden PII:

S1360-8592(16)30195-4

DOI:

10.1016/j.jbmt.2016.09.006

Reference:

YJBMT 1423

To appear in:

Journal of Bodywork & Movement Therapies

Please cite this article as: Wallden, M., Descending Pronation Patterns, Journal of Bodywork & Movement Therapies (2016), doi: 10.1016/j.jbmt.2016.09.006. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Descending Pronation Patterns Abstract This practical paper is a continuation of previous papers presented in this section discussing over-pronation. The focus of this article is the way that the body has evolved to handle pronation forces in a descending manner from trunk to foot. It was written to accompany the “Toe-tal Function” editorial in the 20:2 edition of JBMT, but didn’t make it in for publication. ---

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The bipedal design of the human body means that, in standing, humans spend most of their time on two feet, in walking they spend most of their time on one foot, and in running they spend 100% of the load-bearing time on one foot.

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Essentially, bipedal gait requires is some rather high-level neural control and, in addition, it requires high-level efficiency, high-level strength and significant coordination; which is why it takes an infant about 7-8 years to get good at it; and may explain why humans have the highest density of spindle cells (in certain of their tissues) of any creature on the planet. Because hominids put themselves upright, the human biomechanical frame must be able to effectively manage loads akin to a nail being hammered into the ground when running and jumping, in contrast to the greater spread of load that a quadruped utilizes across two or more limbs per step. Indeed, a Boeing engineer once received a call from a cargo company enquiring about transporting an elephant. “Will we need to reinforce the floor?” the cargo executive asked. The engineer laughed and replied, “Don’t worry. We design our floors for a woman in a stiletto heel.” He went on to explain that a 100-pound (50kg) woman standing on a heel that tapers down to a quarter-inch (5mm) diameter exerts a force of 1600lb/square inch, far more than the amount an elephant exerts on its broad foot pads (Yancey & Brand 1997). Humans, as bipeds, are more like stilettos than elephant pads when it comes to gait.

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The upshot is that in order to be an effective bipedal creature humans have developed various mechanisms to stabilize the body, to resist, overcome and harness gravity. In the ancestral environment the consistent requirement to perform significant levels of walking and running, plus the inevitable lifting and carrying of objects would have resulted in what, in this day and age, would be termed “functional exercise”. Back then, of course, it would have been termed “life”. Either way it is and was a key ingredient to provide sufficient conditioning of the anti-gravity musculature. For example, picking up something heavy from the ground, whether that be a child and walking with it (rather than putting it in a push-chair) or carrying home a log or a downed animal or building with heavy stones; these activities would all condition the lifting muscles. These lifting muscles are the same muscles to both lift these extrinsic loads, and also to lift the body from the ground. As such, the lifting muscles are our anti-gravity muscles. Our pro-gravity muscles are those used for generating downward forces towards the ground, such as when hurling a stone or punch downward, serving a tennis ball, striking a hammer, and even in throwing in general. For most sports, however, the body needs to generate upward power, which is why it’s so common to see athletes of many disciplines practicing lifting-based techniques. In terms of foot mechanics, what is rarely discussed in any detail is that the musculature in the human leg is focused towards the proximal end, so there is very little muscle mass in the foot and ankle; although there are lots of tendons and connective tissues; tissues capable of transferring significant load and providing significant information. The question then becomes what is the function of these tiny, insignificant muscles of the foot? And the probable answer is that they serve a fine control function as opposed to a gross movement function, because the kinds of loads that are passed through the foot are extreme – multiples of bodyweight as discussed in previous papers. In terms of the larger muscles - those that are used to counteract gravity and to move the body through space, which of these are key in controlling the loading through the foot? It depends to some degree on what motion is being conducted. Running down a hill for example, the quadriceps are being heavily recruited as anti-gravity muscles, but, at the same time, the rectus femoris as part of the quadriceps group will be pulling on the pelvis tilting it

ACCEPTED MANUSCRIPT anteriorly and driving a pro-gravity pattern – ie working with gravity to pull the trunk toward the ground. This seems contradictory. So, to prevent this from occurring there has to be a balance between the front and the back body musculature (in this case the hip flexors versus the hip extensors) which, when working together, will create “lift”. In much the same way that when the transversus abdominis contracts all around the body wall it creates a kind of erectile “lift” through the trunk (Beach 2010). Lift will always occur when an attempt is made to compress a non-compressible object (such as viscera or synovial fluid) when it is held in a contained space (such as the abdominal cavity or joint capsule)

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Classically, however, what is commonly observed clinically is that the typical gravity pattern through the lower limb is adduction, internal rotation, flexion and pronation. The reciprocal movement patterns, abduction, external rotation, extension and supination are anti-gravity motions. So when a bi-articular musculature, like the rectus femoris, is utilized to extend the knee (anti-gravity), but to flex the hip (pro-gravity), appropriate synergistic co-contraction of antagonists (such as gluteus maximus) must occur in the hip extensors to counterbalance this.

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The medial rotational pull of gravity through the lower limb that can result in over-pronation at the foot is counteracted by the external rotators of the hip, in particular the gluteus maximus (which also resists hip flexion), and the posterior fibres of gluteus medius. However, far from being simply a hip extensor and lateral rotator of the hip, some 80% of the fibres of gluteus maximus insert into the iliotibial band; making it debatable – in fact, reasonable – to suggest that the iliotibial band is actually better termed the gluteus maximus tendon (in much the same way that the sacrotuberous ligament is really the conjoined tendon of the biceps femoris and semitendinosis) (Stecco et al 2013). Since anatomy has traditionally been viewed from the neutral “anatomical position”, the gluteus maximus’ insertion onto the ITB seems to have been somewhat overlooked from a functional perspective, as it would only seem to dampen its efficacy in exerting an external rotational pull on the femur in the upright neutral position – versus its bony insertion into the greater trochanter. However, as soon as the hip and knee are flexed, as occurs in running and, especially, in deep squatting and lunging (cutting and planting maneuvers in sports), the gluteus maximus’ insertion into the ITB suddenly has major ramifications for controlling medial rotation of the knee and the descending pronation pattern that will be perpetuated down into the foot as a result.

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If an upright stance is assumed, then it is clear that the gluteus medius posterior fibres and the piriformis have a strong mechanical advantage in external rotation (or preventing internal rotation) of the hip. Since an inability to resist this internal rotation allows the femur to rotate inwards, which drags the tibia medially and draws the foot into pronation, it would seem prudent to first address tensions and conditioning in the hip musculature before placing an extrinsic “block” to pronation under the foot as a form of orthotic. In this author’s clinical experience, close to 100% of over-pronation issues at the foot are part of a descending pattern; which is exactly what a simple awareness of the evolution of vertebrate design would anticipate (Radinski 1988). But then if we look above the leg towards the pelvis, not only do muscles like the gluteus maximus and the hamstring control the leg, but they also control pelvic tilt. Osteokinematically, anterior pelvic tilt will drag the femurs into internal rotation, which drags the tibia and subtalar joint medially causing pronation. This is not a problem, in fact, a quick review of the anatomy of the lower limb identifies that the connective tissue structures are well developed to resist this gravity pattern. The sacrotuberous ligament, the ischiofemoral ligament, the medial collateral ligament of the knee, the deltoid ligament of the ankle and the plantar fascia are all both beautifully aligned to effectively resist gravitational loading, and are also significantly thicker than their laterally placed or antagonistic counterparts (if, indeed, they have them at all). Since all extant living organisms successfully exploit an energetic niche, the ability to be efficient in movement is a key evolutionary driver. So not only does the lower limb passive subsystem resist the effects of gravity, it also captures any descending loads in the form of potential energy energy from the superincumbent mass; recoiling it for the next step as the supporting limb supinates, externally rotates, abducts and extends. It is this efficient energy harnessing that would have been key to the very survival of the species.

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However when this system is undeveloped or deconditioned (mainly neural or active components), the passive subsystems described above may receive excessive loading. Since creep to the passive tissues is both load and time dependent then, across time, creep, stretching and insufficiency of the energy capture mechanism will occur; the end result being over-pronation. A key part of the connective tissues’ role, of course, is to feedback information, via the mechanoreceptors to the nervous system to let it know when the leg is under gravitational load; this allows the nervous system to respond by activating the appropriate musculature, maintaining function and conditioning. However, creep in the connective tissues means that greater stretch is required to trigger mechanoreceptors embedded within them, and hence a delay in firing of appropriate musculature ensues. This becomes a vicious cycle of spiraling dysfunction. New Research Directions

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Since most of the field of gait research is completed in sagittal plane motion, in a very “sterile” environment, such as on a treadmill or on a flat, clean floor in a lab, clinic, gym, or on a track, so the notion that the results attained provide some kind of “real” understanding as to how the foot works is somewhat romantic. What this means is that much of the published data, that ultimately may result in fairly major interventions from surgeries to orthotics to “motioncontrol” sports shoes, may be inappropriate for the much of activity the patient actually wants to utilize them for. One of the potential issues with such interventions is that they are a relatively dramatic and instantaneous change to the way people move. On the other hand, one of the beauties of a corrective stretching and exercise-based approach is that it actually works with the body’s own pace of adaptation. In other words, the body will only change at the speed it is ready to change; nothing radical – no years of walking or running in a certain way to then find that, suddenly, in an instant, the gait pattern is mechanically altered by an extrinsic device. [INSERT FIGURE 1]

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Of course, there is an argument to say that a dramatic change in the “right” direction could be a good thing if the movement pattern is bad, inefficient or injurious, and this is the conventional way of looking at it, but the body’s ability to adapt to a sudden change, when it is already in a weakened and often pain-generating state, is something that the cognizant therapist must carefully consider.

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What the more traditional model of foot function doesn’t tend to take into account is a more natural environment; which is exactly the environment that stimulated the development of the foot in the first instance. So there is this very detailed comprehensive understanding of how the foot functions on a flat surface, yet the reality is that human beings, just like any animal, are highly adapted to locomote over cambered surfaces, rough surfaces, slippery surfaces, hard surfaces and soft surfaces… the list is extensive… and in multiple directions. Yet the foot is very well-adapted for most of these surfaces, which is why it is highly complex. The simple notion of not moving in a straight line, is something that is rarely considered in the literature and when you look at how the foot moves when turning, for example (see figure’s 1 & 2) then, if turning left, the left foot will tend to supinate, while the right foot will tend to pronate, and since it’s more effective to turn off the outside foot (due to the bulk of the hips muscle mass being external rotators and the fact that the centre of mass is on the “inside” of the turn) it is ideal for the right foot to pronate maximally so that it will generate maximal recoil via the plantar fascia and accommodate the very high drive of the body into the ground through that leg. Additionally, a more pronated foot provides greater ground contact area against the ground and therefore greater traction – in much the same way that a sports car has wider tyres, than an economy-focused car – something that is important to effectively turn (as anyone who has attempted to turn on ice or mud will attest to). Postural Considerations To transfer this understanding to simple standing posture, it is easy to see how when the body rotates to the left (as it would do in turning left), the right foot will pronate and the left

ACCEPTED MANUSCRIPT foot will supinate. When an asymmetrical pronation pattern is observed clinically it is almost invariably associated either with this contralateral trunk rotation described or, when under load, the muscle systems that stabilize and mobilize the trunk in that (say, leftward) direction, are dominant over the muscle slings that take the trunk in the other direction (for more details see Wallden 2014 “The Middle Crossed Syndrome”). [INSERT FIGURE 2]

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It is very common to see this asymmetric pattern, most commonly with over-pronation in the “dominant” or kicking foot, and then under-pronating (supinating) or optimal on the standing leg “non-dominant” foot. So if a patient has greater pronation through the right leg, a common finding is that they have deficits in their right trunk rotation (either range of motion or strength) which can be tested through assessing a “twist” pattern under load – a wood chop style of movement and, ideally, a reverse woodshop (see Figure 2) as it is more “anti-gravity”*, So, this reverse woodchop exercise can be built in as part of a corrective program that can be either exclusively, or can be biased, toward the side that is over-pronating.

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*while the woodchop still exhibits a similar foot profile it is pro-gravity. Concluding Remarks

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While an understandable focus of over pronation has been the foot and the associated musculature and how they interact on a uniform surface in sagittally oriented gait, a kinesiology-based and evolutionary biomechanical view suggest that a greater focus might be fruitfully placed on the proximal musculature especially those muscles controlling the pelvic position, and the various neural mechanisms in place to provide input to the nervous system informing that musculature of how, when and to what extent to engage. References

Beach, P., 2010. Muscle & Meridians – the manipulation of shape. Elsevier

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Preece et al (2008) The influence of gluteus maximus on transverse plane tibial rotatio Radinski, R. 1988. The Evolution of Vertebrate Design. Stecco et al 2013. The anatomical and functional relation between gluteus maximus and fascia lata. Journal of Bodywork & Movement Therapies (2013) 17, 512e517

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Wallden, M., 2014. The Middle Crossed Syndrome. JBMT

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Yancey, P., & Brand, P., 1997. The Gift of Pain. Zondervan pp171

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