Contributed By: Ian Golden
Brunnstrom’s Clinical Kinesiology, in an introduction to the topic, divides walking gait into stance and swing phases. They indicate that in the stance phase contact is made first with the heel strike, and only in pathological conditions do other parts make first contact. Walking is often characterized by a period of double-support or stance characterized by a period of simultaneous toe-off and heel-strike in the feet. They further that a typical walking cycle, from heel strike to heel strike, or stance to stance, lasts approximately 1-2 seconds and yields 30 to 60 strides per minute.
When transitioning to the analysis of running, we see that the double stance phase of a walking gait is eliminated and replaced in some cases by a float phase in which both feet are in the air. With greater speeds the rate increases from 30-60 strides per minute while walking to upwards of 180-190 while running in those with efficient forms, or approximately 0.7 seconds at a 6:00 minute mile. Norkin and Levangie in Joint Structure and Function indicate that the forces move from an average of 75% of body weight placed through one extremity while walking, to upwards of 250% with running. Half of this force may be transmitted through and absorbed by the Achilles and foot tendons. Norkin and Levangie further indicate that the relative percent of the cycle spent in the float phase increases proportionate to running speed.
In both of these Kinesiology texts, the focus on movement in the ankle and foot is in the linear plane of dorsi and plantar flexion. Eccentric firing of the calf and quadriceps are required to maintain alignment of the knee and ankle, and are crucial to providing a braking counter to the downward forces. Efficient gaits will limit the degree of forces acting in the vertical plane in favor of quicker and more forefoot-oriented strike patterns that may foster horizontal displacement and recoil. Minimizing the downward force acting through the calcaneus and paired with a recoil force in the upward plane not only makes the gait cycle more efficient, but also better able to absorb the magnified forces.
II. Application to Running Shoes
The focus with shoe development and with running related injuries has followed the assumption that the heel-strike is the normal gait pattern for running. Thus the primary focus of the industry has been on the impact of this gait, namely the impact of under or over pronation and the necessity of requiring the subtalar joint and arch to absorb the brunt of running-related forces. Although pushes have existed to overhaul the notion of characterizing heel-strike patterns as normal or desirable in favor of a more efficient midstance strike with quicker turnover, we will maintain this focus on heel-strike gait patterns. (See article entitled Biomechanics of Running also from the Finger Lakes Running Company)
At impact, and in normal gait patterns, the hind foot will land in approximately 5-10 degrees of inversion. By midstance the runner will have assumed approximately 10 degrees of eversion. The normal gait cycle will demonstrate the foot reversing its course, supinating back approximately 5 degrees to establish a stable platform for toe-off. With this focused on heel strike patterns, pronation is not only normal, but a necessity to absorb the forces of running.
Injuries, if related to these biomechanics, should only occur when extremes are demonstrated, i.e. over-pronation or under-pronation/supination. Those whose gaits may be defined as under-pronating or supinating will demonstrate a consistent wear from the inverted heel strike zone, across the lateral border of the foot and through to toe-off. These individuals often have high arches and rigid feet with a limited capacity to absorb the force of impact. These individuals are best suited to “cushioned” shoes that will not further exaggerate the under-pronation, and that will provide a greater degree of shock absorption to an otherwise rigid foot.
Those demonstrating over-pronation may demonstrate the typical degree of 10 degrees of pronation by midstance, but not the necessary supination for a desirable toe-off. In these individuals, often those with low or collapsed arches, supporting the arch through stability features is necessary. This can be accomplished via the use of dual densities or posting on the medial sides of shoes and in shoes that are defined as stability.
In only those cases of severe over-pronation, i.e. moving into 20 degrees of eversion at midstance or in those individuals with larger frames, potentially greater than 160 pounds wherein the forces on the shoes are further magnified, may shoes defined as “motion control” necessary.
Further to consider when applying these concepts to running shoes is the shape of the shoe construction. Companies construct shoes according to the above described pairings, i.e. low arches with over-pronation, medium arches with normal pronation, and high arches with neutral, supinating, or under-pronating mechanics. Shoes in each of these categories most often are constructed along relevant “lasts” or foundations. Cushioned trainers most often are constructed with curved lasts, assuming the wearer to have higher arches and a resulting curvature to the foot. Stability trainers are most often constructed along semi-curved lasts, assuming the individual will have a medium arch, some curve to the foot, and a need for some degree of pronation control. Motion Control shoes are most often constructed along straight lasts that assumed that the runner will have flatter feet and issues associated with severe over-pronation.
III. Selecting Running Shoes Based On Shoe Design and Individual Biomechanics
The two primary factors in considering which shoes will be appropriate for runners thus become category of shoe (cushioned, stability, motion control) based on dynamic gait patterns, and last of shoe construction based upon arch type and foot curvature. Dynamic gait patterns should be considered via simply observing the person walk without the influence of a shoe, and at a plane that permits direct and unobstructed viewing. Analysis of the wear patterns of shoes will also help a great deal. When analyzing such wear patterns it becomes necessary to factor in the type of shoe in hand. A cushioned, stability, and motion control shoe, if successful in doing their jobs, should impact the gait of a runner as well as yield differing gait patterns than would occur in an unsupported or barefoot. For example, a person with a neutral toe-off wear pattern in a cushioned trainer may indeed demonstrate a neutral gait. A person demonstrating a neutral toe-off wear pattern in a motion-control most likely will demonstrate excessive over-pronation if unsupported.
Although in time such characteristics will become evident to the eye without further testing, it is possible to use testing procedures to analyze arch flexibility and foot curvature. One rough method often cited and used is the wet bag test. An individual is asked to step in a pan of water and immediately step onto a brown paper bag. The prints created are predicted to differ according to arch type and foot curvature.
The “normal” foot, possessing a medium arch and semi-curvature may leave a print similar to the one to the left. A semi-curved stability shoe may be warranted as it is assumed that some degree of normal over pronation will occur as the arch descends to accommodate the weight of the body.
The low-arched flat foot may appear as the diagram to the left with minimal curvature in the medial arch. The runner is assumed to over-pronate and the most appropriate running shoe may be straight-lasted and offering motion control. It should be noted that not all individuals with flat feet actually pronate excessively. In some cases if an individual has been born with flat feet their skeletal alignment will have self-corrected and balanced itself out in the course of development. For those individuals a straighter cut shoe without pronation control components would be appropriate.
The pattern to the left may indicate that the individual has a high-arched and rigid foot. It is assumed that this foot will under-pronate or supinate. It is assumed that in having a more rigid foot this individual already has a stable or rigid platform and may be best be supported with a cushioned curved-lasted shoe. Shoes that provide pronation control may force this individual further to the outside. This would destabilize biomechanics and increase the risk for overuse injuries.
An additional test to measure for the curvature of the foot in isolation can be used as follows. The individual’s foot should be traced while in a weighted-stance. The print should be cut out and folded on itself according to a bisection of the heel. A line should be drawn along this bisection through to the toes. A mark should be placed corresponding to the center of the individual’s toebox. If the longitudinal bisection line falls within ½ inch from the toebox center, the individual most likely has a straight-lasted foot. If the bisection line is lateral to the medial toebox marking by ½ to 1 inch the individual most likely will require a semi-curved lasted shoe. If the bisection line falls 1 to 1.5 inches lateral to the toebox center, the individual most likely requires a curved-lasted shoe.
A further test may be used to measure the flexibility of the individual’s arch. The individual can place their unweighted foot (either resting in standing, or via sitting) on a piece of paper. A line should be made at the forward most point on their foot. They should then weight the foot, or stand, and another mark made along the forward most point. The individual with a high arch or rigid foot will display minimal if any shift in the weighted marking. An individual with a medium arch and often having a normal degree of pronation will demonstrate a discrepancy up to ¼ of an inch. Those with flexible arches, flat feet, and often over-pronation will demonstrate shifts of greater than ¼ of an inch.
IV. Tying It Together and Tips for Buying Running Shoes
Much like Cinderella, the shoe most appropriate for your foot and biomechanics will be that one that fits like a glass slipper. Every quality running shoe is designed with a specific function and foot type in mind. Individuals with flatter feet most likely have very different biomechanics than those with high arched feet and therefore will be best suited to shoes designed to not only accommodate the shape of that foot, but also the biomechanic that usually plays out. These two variables, foot type and biomechanics are often consistent, but not always. It therefore becomes useful to not only know the type of foot that you have, but also what your body does on those feet once you start moving.
If you have a flat foot chances are your body could use more help in finding a stable platform through a straighter cut shoe falling in the Motion Control category. A normal or medium arch that doesn’t change a whole lot when weighted often equates to a shoe in the Stability or pronation control category. A foot with a higher arch, or one that does not change when weighted is often best suited by a shoe curved in at the midfoot and in the Cushioned category. Because foot type does not always equate to a certain biomechanic it is recommended that individuals spend some time at a Running Specialty Store with staff not only familiar with the construction and function of shoes, but also who are trained to analyze gait.
Try on several models that are in the appropriate category but do not feel pressured to buy a shoe recommended by a salesperson as a appropriate if it doesn’t feel right on your foot. You need a good fit and an appropriate function. The arch of the shoe should line up with the arch in your foot and your foot should not hang over the base of support nor have excess width in the heel and midfoot. Your feet should not feel bound or cramped in the toeboxes and you should have at least ½ of a thumbnail’s width from your longest toes. The heel doesn’t need to be vice-tight, but you don’t want to be walking out of the shoes either. Use socks similar to what you’ll be wearing and try the shoes on with your orthotics if you have them. Above all spend some time in the shoes and if at all possible, take them for a test run outside the store or on a treadmill if provided. Stick with what works (until they change them) and be sensitive to listening to your body telling you the shoes are spent (usually 350 – 550 miles). Thanks for reading this far and give us a call or stop in if you have any questions. Happy feet make for happy souls and happy running!
Ian Golden is owner and operator of The Finger Lakes Running Company
Photo By: Andy Myers