Foot instrinsic dialogue Motor Control. 2014 Jul 15. [Epub ahead of print]
Quantifying the Contributions of a Flexor Digitorum Brevis Muscle on Postural Stability. Okai LA1, Kohn AF.
There are many factors in adults that impair gait. It is not all biomechanical. This is part of our ongoing dialogue on the aging population and why gait impairments and falls are so prevalent. 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.
Remember a month ago when we talked about the basics of gait? If not, please see posts the week of 6/27 for a in depth discussion
Suffice it to say, in stance phase (about 60% of the walking and 40% of the running gait cycles) we have 2 motions occurring: pronation and supination. In pronation (which begins as soon as the foot hits the ground and should end at midstance) the foot is becoming a mobile adaptor, so it can adapt to irregular surfaces and act as a shock absorber.
In supination (which begins at midstance and ends at preswing) the foot is becoming a rigid lever, to assist in transferring muscular forces to the lower limb to propel us forward.
The picture above shows supination nicely. Remember that when one foot is in midstance, the opposite leg (in swing phase) assists in supination.
This study (IOHO) demonstrates the principle of supination nicely and demonstrates the (major) role the foot plays in forefoot stiffness.
Department of Mechanical and Manufacturing Engineering, University of Calgary, 2500 University Drive, N.W. Calgary, Alberta, Canada T2N 1N4.
This study characterizes the stiffness of the human forefoot during running. The forefoot stiffness, defined as the ratio of ground reaction moment to angular deflection of the metatarsophalangeal joint, is measured for subjects running barefoot. The joint deflection is obtained from video data, while the ground reaction moment is obtained from force plate and video data. The experiments show that during push-off, the forefoot stiffness rises sharply and then decreases steadily, showing that the forefoot behaves not as a simple spring, but rather as an active mechanism that exhibits a highly time-dependent stiffness. The forefoot stiffness is compared with the bending stiffness of running shoes. For each of four shoes tested, the shoe stiffness is relatively constant and generally much lower than the mean human forefoot stiffness. Since forefoot stiffness and shoe bending stiffness act in parallel (i.e., are additive), the total forefoot stiffness of the shod foot is dominated by that of the human foot.
Overview: Case study of 40 yo male triathlete who developed R sided plantar fascitis after completing a half ironman (2K swim, 90K bike, 21K run). The study describes the factors contributing to the injury, the rehab process, and shoe construction along with the symptoms of plantar fascitis.
Authors Conclusion: A running shoe manufacturing defect was found that possibly contributed to the development of plantar fascitis. Assessing athletic shoe construction may prevent lower extremity overuse syndromes.
What The Gait Guys Say: Plantar fascitis is something we see clinically many times in our practices. It is often due to overpronation of the midtarsal joint (talo-navicular and calcaneo-cuboid) in midstance, with insufficient supination from late midstance through preswing. Thus, this over pronation causing overloading of the plantar fascia and windlass mechanism, resulting in increased torsional forces and micro-tearing at it’s proximal calcaneal (and sometimes distal) attachments. This causes local pain, swelling and inflammation, particularly at the calcaneal attachment site, which is alleviated by rest, ice and analgesics. As we have shared many times now, this over pronation does not have to be a local cause, it could be necessary from insufficient internal rotation of the hip or from other factors.
In this study, the Right shoe upper was canted medially on the midsoles, believed due to it not being glued perpendicularly (as we often see inspecting a shoe from behind, especially Asics Kayano’s in our experience). The authors state they felt this contributed to excessive inward rolling of the right foot, contributing to overpronation.
The authors make the following recommendations about shoe inspection:
The shoe should be glued together securely
The upper should be glued straight (perpendicular) onto the midsole. The shoe, viewed from behind should have a horizontal heel counter and vertical upper
The sole of the shoe should be level to the surface on which it is resting (ie no medial to lateral motion should be present) You can test this by attempting to “rock” the shoe from side to side
The shoes should not roll excessively inward or outward when resting on a level surface (ie when rolling from P to A) You can test this by rocking the shoe from A to P
Air and gel pockets should be inflated evenly. This can be tested manually by pressing into them and checking for uniformity.
A nice rehab protocol is also outlined over a 4 week period.
Bottom Line: It pays to be shoe nerd. Shoes can help or hurt. We see manufacturers defects in shoes every day and tell clients to return the shoe; in fact some we collect to use to show people. A rearfoot varus in a shoe will help to slow pronation. This may actually be beneficial for overpronators but detrimental for supinators. Some defects can be helpful but try and find defect free shoes. Stay away from “2nds” at cheapie stores and online specials. There is usually a reason they are being sold so cheaply. EVA’s have a shelf life and will break down over time. You must be able to not only recommend the appropriate shoe for your patient, based on their evaluation and gait analysis, but you need to inspect their footwear carefully and teach them to do the same.
If you are truly to be a shoe geek, then you must be familiar with some “shoe anatomy.” Simply put, there is the sole ( the part that contacts the ground), the midsole (the part right between the sole and the last), the shank (the stiff rear part of the midsole), the last (the part on top of the midsole and where the insert or orthotic will sit), the insole (the removable insert), the upper (the part above the last that has the sides, laces, etc)the heel counter (the part that holds the heel in place), and the toe box.
Lets discuss each in turn
The Sole (also called the outsole)
This is the part of the shoe that comes in contact with the ground. It is usually made of rubber and provides for some degree of shock absorption and traction. For running shoes, it is usually cemented to the midsole.
Remember that the heel strikes the ground at approximately a 16° angle lateral from the center of the heel (in a heel strike gait, no we aren’t condoning this, this is how shoes are designed). The force is then transmitted from the sole of the shoe, up the lateral column of the foot and across to the first metatarsal for propulsion.This can be assisted by a “rocker” which is a “drop” put into the front portion of some stiffer trail shoes, to ease walking and assist in toe off.(This is good for people with Morton’s toes or hallux rigidus).
A flare to the sole of the shoe, particularly lateral can be important for stability on uneven surfaces.A lateral flare provides extra stability upon heel strike, but it speeds up the rate of pronation.This may be a bad thing, depending on your feet. This flare must extend the length of the sole, otherwise injury can occur at the mid tarsal joint as the foot comes through mid stance. A medial flare can help to prevent overpronation, as the foot comes through mid stance. Again, it must run the length of the shoe.
Look at the lugs on the sole. Are they beveled or straight? A straight lug or cleat will hold on to mud, whereas a beveled one will shed it. This is an important consideration if running off road. How about the cleat pattern (front vs. back and side to side)? Are they symmetrical or opposing? Opposing patterns will enable you to ascend and descend easier at the expense of a slight amount of speed.
The Midsole (sandwiched between the sole and upper)
Midsole material is very important, as it will accommodate to the load imposed on it from the person and their body weight. It serves as the intermediary for load transfer between the ground and the person.Softer density material in the heel of the shoe softens the forces acting at heel strike and is good for impact and shock absorption. The stiffer the material, the more motion control.Air is an excellent shock absorber, however it does not deform, it displaces. This creates and unstable surface for the foot, promoting ankle injuries. Foam and gel are much better as they transduce the force and dissipate it. Often midsoles are made with something called “dual density”.This means that the midsole is softer on its lateral aspect, to absorb force and decrease the velocity of pronation during heel strike and midstance, with a firmer material medially that protects against overpronation as you come through mid stance and go through toe off.
The Shank (this can be within the midsole)
The shank is the stiff area of the shoe between the heel to the transverse tarsal joint. It corresponds to the medial longitudinal arch of the foot, provides torsional rigidity to this shoe and helps to limit the amount of pronation and motion at the subtalar and mid tarsal joints.
The Last (the part between the midsole and insole)
The last (look inside the shoe on top of the shank) is the surface that the insole of the shoe lays on, where the sole and upper are attached).Shoes are board lasted, slip lasted or combination lasted. A board lasted shoe is very stiff and has a piece of cardboard or fiber overlying the shank and sole (sometimes the shank is incorporated into the midsole or last) .It is very effective for motion control (pronation) but can be uncomfortable for somebody who does not have this problem.A slip lasted shoe is made like a slipper and is sewn up the middle.It allows great amounts of flexibility, which is better for people with more rigid feet.A combination lasted shoe has a board lasted heel and slip lasted front portion, giving you the best of both worlds.
When evaluating a shoe, you want to look at the shape of the last (or sole).Bisecting the heel and drawing an imaginary line along the sole of the shoe determines the last shape.This line should pass between the second and third metatarsal.Drawing this imaginary line, you are looking for equal amounts of shoe to be on either side of this line. Shoes have either a straight or curved last.The original idea of a curved last (banana shaped shoe) was to help with pronation.A curved last puts more motion into the foot and may force the foot through mechanics that is not accustomed to. Most people should have a straight last shoe.
The Upper (the sides and top of the shoe)
This is the part above the midsole that holds your foot on the sole. It is usually made of nylon, Gore-Tex or some other man made material. Pick something light and breathable.
The Heel Counter (the back of the upper)
This is part of the upper. A strong, deep heel counter with medial and lateral support is also important for motion control; lateral support especially for people who invert a great deal or when you’re going to place an orthotic in the shoe which inverts the foot a great deal.The lateral counter provides the foot something to give resistance against.This needs to extend at least to the base of the fifth metatarsal, otherwise it can affect the foot during propulsion. A deep heel pocket helps to limit the motion of the calcaneus and will also allow space for an orthotic. The heel counter should grip right above the calcaneus, hugging the Achilles tendon.
The Toe Box
The toe box should be generous enough to prevent crowding and pressure on the metatarsal heads.The widest portion of the shoe should parallel a line bisecting the metatarsal heads.Excessive pressure can result in bunions and/or hammertoes.The shoe may soften and break down laterally, but it will not increase in length.
When measuring feet and determining shoe sizes, do it both sitting and standing, because the laxity of ligaments can become very evident, especially when the foot is weight bearing or you have the weight of a pack on your back.If the person has greater than one size of splaying in both length and width when going from one position to the other, go for the bigger size.Always use ball length rather than sole length. People usually buy smaller shoes because when you pronate, there is less volume in the mid foot and a smaller size shoe will feel better.
The Insole (the removable inner footbed)
This is the part of the shoe that most people remove to put in an orthotic. They have come a long way in construction and make a big difference in shoe fit. They are usually made of some type of foam or EVA material. Some of the newer ones are even dual density foam.
Well, if you made it through this, you are officially as nerdy as us. We’ll see you in the shoe isle…..