Characterization of barefoot running - the biomechanical advantage of the foot's nature

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(1)Characterization of barefoot running The biomechanical advantage of the foot´s nature. Alberto Diaz Durana. University of Los Andes Faculty of Engineering Department of Mechanical Engineering Bogotá, D.C. Colombia 2008.

(2) Caracterización de la carrera descalza La ventaja biomecánica de la naturaleza del pie. Alberto Diaz Durana. Universidad de los Andes Facultad de Ingeniería Departamento de Ingeniería Mecánica Bogotá, D.C. Colombia 2008 .

(3) CONTENT Page 1. 2. 3. 4. 5.. 6. 7. 8.. 9.. 10. 11. 12.. 13.. Introduction…………………………………………………………………………………….1 Problem formulation…………………………………………………………………………...2 Objectives………………………………………………………………………………………7 Actual foot deformation models and the purpose of a new model …………………………….8 The toe-hell running technique……………………………………………………………..…11 1) Why to teach how to run barefoot……………………………………………………11 2) How to run barefoot…………………………………………………………………..15 3) Mechanical advantage………………………………………………………………..17 Relevance of the new model in toe-heel running……………………………………………..22 Tests protocol………………………………………………………………………………….23 Capturing the lower locomotion members……………………………………………………26 1. Calculating the random error for the captured measurements……………………….27 1. Procedure to calculate the random error…………………………..….29 2. Markers, definition of the bodies and plane construction……………………...…….31 1. Anatomical landmarks………………………………………….…….32 2. Anatomical reference frames…………………………………………33 3. Relative coordinate systems………………………………….……….34 3. Euler Parameters……………………………………………………………………...35 4. Euler Angles…………………………………………………………………….……37 Results and analysis…………………………………………………………………………..38 1. The Body Hip………………………………………………………………….….….38 2. The Body Femur…………………………………………………………………...…39 3. The Body Tibia…………………………………………………………………….…40 4. The Body Calcaneus…………………………………………………………….……41 5. The Body First Toe……………………………………………………………...……42 6. The Body Second Toe……………………………………………………………..…43 7. The Body Third Toe………………………………………………………………….44 Conclusions………………………………………………………………………………...….45 Recommendations and further projections of this investigation……………………………...46 Appendix……………………………………………………………………………………....47 1) Appendix 1. Random error code……………………………………………………...47 2) Appendix 2. Random error results……………………………………………………51 3) Appendix 3. Matlab code……………………………………………………………..54 References…………………………………………………………………………………..…57. DIGITAL DATA (Programs in the CD) 1. Random_Error_Select_Data + 18 text files at Random Error carpet 2. Barefoot toe-heel running sequence (picture *.JPEG file) 3. Hip (Matlab program *.m file) at Matlab Programs carpet 4. Femur (Matlab program *.m file) at Matlab Programs carpet 5. Tibia (Matlab program *.m file) at Matlab Programs carpet 6. Calcaneus (Matlab program *.m file) at Matlab Programs carpet 7. First_toe (Matlab program *.m file) at Matlab Programs carpet 8. Second_toe (Matlab program *.m file) at Matlab Programs carpet 9. Fifth_toe (Matlab program *.m file) at Matlab Programs carpet.

(4) FIGURE INDEX Page Fig. 2.1 Heel-toe running sequence…………………………………………………………………..…3 Fig. 2.2 Ball of the foot………………………………………………………………………………….3 Fig. 2.3 Imaginary axis at the average ankle joint…………………………………………………..…5 Fig. 2.5 Percentual increase of the bending moment when using footwear…………………………...6 Fig. 4.1 Mitered hinge foot model………………………………………………………………………8 Fig. 4.2 Forefoot-rearfoot coupling patterns …………………………………………………………...8 Fig. 4.3 Intracortical pins drilled into the bones……………………………………………………......9 Fig. 4.4 Coronal plane alignment foot model ………………………………………………….….…..9 Fig. 4.5 Unconsidered movements of the feet…………………………………………………….…10 Fig. 5.1 Fifth toe fatigue fracture………………………………………………………………….….11 Fig. 5.2 Zola Budd Pieterse………………………………………………………………….……...…12 Fig. 5.3 Abebe Bikila……………………………………………………………………………….….12 Fig. 5.2 Post-race plantar pressure increase beneath the metatarsal heads due to toe fatigue……..…14 Fig. 5.3 Femur fatigue fracture…………………………………………………………………….......14 Fig. 5.4 Gordon Pirie………………………………………………………………………………..…15 Fig. 5.5 Foot model……………………………………………………………………………….…....17 Fig. 5.6 Foot model at heel-tow running technique…………………………………………….……...18 Fig. 5.7 Foot model at toe-heel running technique…………………………………………………….19 Fig. 6.1 Foot deformations from an MRI scan……………………………………………………….22 Fig. 7.1 PhaseSpace marker and string configuration……………………………………………..….23 Fig. 7.2 Body planes…………………………………………………………………………….……..24 Fig. 7.3 Plantar and dorsal flexion………………………………………………………………..……24 Fig. 7.4 Inversion and eversion………………………………………………………………………...25 Fig. 7.5 Abduction and adduction………………………………………………………………..…….25 Fig. 8.1 *.OWL achieve………………………………………………………………………..………26 Fig. 8.2a Removing unnecessary columns ……………………………………………………..….…27 Fig. 8.2b Unnecessary columns removed…………………………………………………………...…27 Fig. 8.3 Converting the columns into Number type figures with zero decimal positions………..……27 Fig. 8.4 Copying the columns in a *.txt archive…………………………………………………….....28 Fig. 8.5a Markers as shown in the Recap program…………………………………………………….28 Fig. 8.5b PhaseSpace indicated similar coordinates but not the same………………………………..29 Fig. 8.6 Results from the random error experiment with PhaseSpace………………………..………30 Fig. 8.7 Leg marker distribution ……………………………………………………………….……...31 Fig. 8.8 Foot marker distribution………………………………………………………………..……..31 Fig. 8.9 Newtonian coordinate system……………………………………………………….…...…...32 Fig. 8.10 Leg vector construction……………………………………………………………….……..34 Fig. 8.11 Foot vector construction…………………………………………………………………......34 Fig. 8.12 Leg relative coordinate systems ……………………………………………………….……34 Fig. 8.13 Foot relative coordinate systems…………………………………………………………….34 Fig. 8.14 Relative coordinate system ………………………………………………………………….35 Fig. 8.15 Relative coordinates system at the Newtonian origin………………………………….…....35 Fig. 8.16 Euler Angles…………………………………………………………………………………37 Fig. 9.1.1 Rotation of the Hip about the X Newtonian axis in direction of the Coronal Plane………..38 Fig. 9.1.2 Rotation of the Hip about the Z Newtonian axis in direction of the Sagital Plane…….….38 Fig. 9.1.3 Rotation of the Hip about the Y Newtonian axis in direction of the Transverse Plane…….38.

(5) Fig. 9.2.1 Rotation of the Femur about the Y axis of the Hip…………………………………………39 Fig. 9.2.2 Rotation of the Femur about the Z axis of the Hip………………………………………….39 Fig. 9.2.3 Rotation of the Femur about the X axis if the Hip………………………………………….39 Fig. 9.3.1 Rotation of the Tibia about the X axis of the Femur………………………………………40 Fig. 9.3.3 Rotation of the Tibia about the Z axis of the Femur……………………………………….40 Fig. 9.3.2 Rotation of the Tibia about the Y axis of the Femur………………………………………..40 Fig. 9.4.1 Rotation of the Calcaneus about the Y axis of the Tibia ………………………………..…41 Fig. 9.4.2 Rotation of the Calcaneus about the X axis of the Tibia…………………………………..41 Fig. 9.4.3 Rotation of the Calcaneus about the Z axis of the Tibia…………………………………...41 Fig. 9.5.1 Rotation of the First Toe about the Y axis of the Calcaneus………………………………42 Fig. 9.5.2 Rotation of the First Toe about the X axis of the Calcaneus……………………………….42 Fig. 9.5.3 Rotation of the First Toe about the Z axis of the Calcaneus……………………………….42 Fig. 9.6.1 Rotation of the Second Toe about the Y axis of the Calcaneus……………………………43 Fig. 9.6.2 Rotation of the Second Toe about the X axis of the Calcaneus……………………………43 Fig. 9.6.3 Rotation of the Second Toe about the Z axis of the Calcaneus…………………………….43 Fig. 9.7.1 Rotation of the Fifth Toe about the Y axis of the Calcaneus………………………………44 Fig. 9.7.2 Rotation of the Fifth Toe about the X axis of the Calcaneus……………………………....44 Fig. 9.7.3 Rotation of the Fifth Toe about the Z axis of the Calcaneus……………………………….44. .

(6) 1. INTRODUCTION As natural and spontaneous as running may seem, there is a strong social influence on the technique the runner uses. Besides, the runner almost never asks himself if the way in which he runs is a technique he chose or if it`s a technique he learned. As unusual as it may sound, running is not limited by the styles or techniques most seen every day. The possibilities are many if the running technique is seen as a function of many body positions the runner employs during this physical activity. As mentioned by professional long distance runners “very few runners know how to run correctly” 1 . The most common running technique is the heel-toe technique. As the name suggests, this technique consists of beginning the stand cycle with the heel and finishing it with the toes. A contradiction of this -most used- technique is the fact of the small capacity of the heel as a mechanism to attenuate impact in comparison to the bigger joints` mechanisms, as the ankle and the knee. The human body is composed by several different shock absorbers. “The shock absorbers can be categorized as either active or passive. The active shock absorbers include joint positioning and muscle activity. The passive shock absorbers include synovial fluid, bone, heel pad, and articular cartilage” 2 . The foot heel is a construction of skin, blood vessels, fatty tissue and bone. Realizing that the only component of the heel capable of attenuating impact is the thin fatty tissue, there is an inconsistence between the technique and the physical cushioning properties of the parts involved in running; in particular in the instant the runner is striking the ground. If the running technique isn`t modified and the improvement isn`t focused towards the intrinsic mechanical properties of the human body but rather the running footwear technology, the now existing reliance on running footwear would remain and the true advantages of the shock attenuation mechanisms of the lower locomotion members would never be known. A study about the foot deformations and the lower locomotion positioning while running is an important introduction for the understanding of how proper running should be implemented and taught; with minimal dependence on running footwear. This investigation focuses on quantifying these, through mathematical and biomechanical tools, and on characterizing the toe-heel running technique as the proper method to run without depending on footwear. In the case of enthusiasts who practice this sport and runners with flatfoot pathologies, understanding the proper technique of how the foot naturally attenuates impact might contribute in the reduction of pain as a result of this sport and thus, perform better and prevent injuries. . 1 2. Pirie, Gordon. Running fast and injury free. [*.pdf] (2007) pg. 7. Available at: http://www.gordonpirie.com/. Abbas Zadpoor, Amir. A model-based parametric study of impact force during running. Journal of Biomechanics [*.pdf] (2007) 40: 2012–202. pp 1. .

(7) 2. PROBLEM FORMULATION The human foot being one of the principal members to support the body has created a culture around the shoe that provides a series of necessities and values that have been awarded by the society. Shoes supply the requirements of millions of persons around the world, fundamentally those of protecting the foot against the aggressive surroundings of the city and those of the very strong influences and tendencies imposed by fashion and society. This reliance has obligated the people to stop counting with the possibility of employing the foot in a natural manner, namely barefoot. The civilized foot is a structure that has been seriously altered from its natural form as a result of functions and of anthropometric factors that the shoe has replaced and thus, has tended to deform it. In this manner, the benefits that the shoe technology has proportioned are reflected in a negative way by a general foot deterioration, specifically affecting soft tissues, producing muscular atrophy and inducing chronic diseases and deformations at the joints. An investigation developed by Joseph (1992) analyzing statistical footprints of 2300 children between the ages of four and thirteen years established the influence of footwear on the prevalence of flat foot. “The incidence among children who used footwear was 8,6% compared with 2,8% on those who did not (p<0,001). Significant differences between the predominance in shod and unshod children were noted in all age groups, most marked among those with generalized ligament laxity. Flat foot was most common in children who wore closed-toe shoes, less common on those who wore sandals or slippers, and least in the unshod” 3 . Besides, the artificial cover at the foot´s sole makes the tactile and sensorial properties impossible. “Humans need feedback to maintain balance. Similar to control systems for artifacts […] A minimum of three sensory organs contribute to balance keeping: the vestibular organ (located in the inner ear), eyes, and proprioceptors (nerve endings that detect force and displacement) 4 ”. The information proportioned by the foot´s sensorial feedback describes the type of surface and the manner in which the foot must be planted. “Sensory-induced behavior associated with the physical interaction of the plantar surface with the ground (in the unshod), or the footwear and underlying surface (in the shod) has even been suggested by Robbins as being an important consideration in avoidance response to heavy plantar surface loading 5 ”. Without these sensorial functions the foot´s impact against the floor will be unprepared and aggressive; -similar to the case of trying to ride a bicycle with the eyes covered- there is simply a fundamental source of information that is missing in order to know how to control the movement. “The nerves conveying tactile sensation from the foot are predominantly located in the forefoot. When the ball of the foot touches the ground, these nerves “alert” the muscles of the legs, which involuntarily react to absorb the shock of landing. If a person hits the ground heelfirst, this reaction of the leg muscles will be considerably less, and consequently more shock will be experienced at the point of contact of the foot, and be transmitted to the bones of the leg. This jarring is guaranteed eventually to cause injury to the ankle, knee and/or hip joints 6 ”. In addition to this, footwear changes the natural posture´s alignment of the whole body. The high heels and the thick soles produce a different distribution of the loads, modify the angles of support and add weight of the foot. “Wearing shoes increases the energy cost of running. Burkett (1985) found that oxygen consumption during running increased as the amount of mass they added to the foot increased; shoes and orthotics representing 1% of body mass increased oxygen consumption by 3.1%. Flaherty . 3. Joseph, Benjamin. The influence of footwear on the prevalence of flat foot. A survey of 2300 children. Journal Bone Joint Surgery. [*.pdf] (1992) ; 74-B :525-527. Availabe at: http://www.jbjs.org.uk/cgi/reprint/74-B/4/525.pdf 4 Hidenori, Kimura. Jiang, Yifa. A PID Model of Human Balance Keeping. IEEE Control Systems Magazine. (2006). [*.pdf]. pp 18 5 Robbins, S.E. Hanna. A.M. Gouw, G.J. Overload protection avoidance response to heavy plantar surface loading. Med Sci Sports Exer. (1988). 20:85–92. At: Zipfel, B. Berger, L.R. Shod versus unshod: The emergence of forefoot pathology in modern humans? The Foot. [*.pdf]. (2007) 17: 205–213 6 Op.cit. Pirie. pp 22. .

(8) (1994) found that oxygen consumption during running at 12 km/h was 4.7% higher in shoes of mass ~700 g per pair than in bare feet. An increase in oxygen consumption of ~4% is of little importance to the recreational runner, but the competitive athlete would notice a major effect on running speed 7 ”. A modification in the corporal posture obligates the person to adopt a shod gate that results to be very different to the unshod gate, since the foot will be striking the ground with the heel and the knees will be too extended; as shown in (Fig.2.1) 8 .. Fig. 2.1 Heel-toe running sequence The shock attenuation systems of the shoes contributes even more in changing the natural gate; since the new body position, as a result of the shoe´s sole, is already obligating the body to switch its posture. The damping properties of the shoes confuse the movements involved in gate by giving the impression of diminishing the impacts with the ground and making the person believe that the joints of the legs play a minimal role in attenuating it. In fact, “shoes may detrimentally increase loads on the lower extremity joints 9 ”. This effect is considerately more critical when running. The forces derived from the impact between the heel and the ground when employing the heel-toe technique are from 2 to 4 times the bodyweight depending on the speed, the type of surface and the individual style 10 . Reevaluating the technique when running by stimulating the foot´s structure, allowing it to become stronger, and enabling the body to function with a natural gait -without shoes- is the natural alternative to solve what footwear has deteriorated. By simple observation, it´s evident that the heel of the foot provides nearly no adequate shock absorption. Thereby, any type of locomotion utilizing shoes -whether walking or running- is, since the beginning, inadequate and far from being the biological nature of the human body. Once again, by observation, la way to attenuate the impact with the ground when barefoot is by touching the ground first with the ball of the foot (Fig. 2.2) 11 . The posture plus the additional support of the toes, the deflection of the arc´s structure, the deformation of the metatarsal bones and the movement of the ankle, added to a position of the knees slightly bended and ready to absorb the impact, and an exposed skin supplying constant ground feedback, constitute a locomotion system that is superior to any shoe employed with any type of traditional gate or traditional style of running. Fig. 2.2 Ball of the foot In a large portion of the world´s cultures to use footwear is seen as something normal. It is, as well, a requirement of part of the traditions and the common sense of people. To expose the bare feet might . 7. Warburton, Michael. Barefoot Running. Sportscience. [*.pdf]. (2001) pp. 3. Availabe at: sportsci.org/jour/0103/mw.htm Decker, Leslie. An alternative approach to normalization and evaluation for gait patterns: Procrustes analysis applied to the cyclograms of sprinters and middle-distance runners. Journal of Biomechanics. [*.pdf]. (2007) 40:2078– 2087 9 Shakoor, Najia. Walking Barefoot Decreases Loading on the Lower Extremity Joints in Knee Osteoarthritis. Arthritis & Rehumatims.[*.pdf]. Vol. 54, No. 9, September 2006, pp 2923–2927 10 Nigg, M. Benno. Biomechanics of running shoes. University of Calgary. Illinois. 1986. Pg 18 11 Image taken from: http://www.fazeteen.com/winter2004/nikefree.htm 8. .

(9) result to be a scandal and even offensive to many. Besides, there are many fears and issues regarding the foot´s health, integrity and hygiene. To use footwear is in fact so normal that almost no one asks himself about the existence of any other possibility; at least in urban areas. If what´s normal is to wear shoes outside the protection of home during almost all the time of the daily activities -in many families it is permitted to walk barefoot inside the house- it´s normal to use shoes when doing any actions where the legs are employed. Thus, walking, running, jumping, doing sports, taking a bus, waiting at a line of a bank, etc. are done shod and nearly nobody questions himself why! In social spaces where it is permitted to walk barefoot, as the beach, around swimming pools, saunas, etc. it´s very probable to perceive that something uncomfortable in felt with every step. When someone walks in a normal way- namely, using the gait style as if the shoes were worn- the impact at the heel against the floor is considerately harder. The first thing that usually is wrongly understood is that this has sense since there aren´t any shoes. The shoes represent protection, and when this protection is removed, it is to be expected that something is to occur that will attempt against the integrity of the feet. The same happens when it is attempted to run barefoot on a hard surface i.e. the edge of a swimming pool, just that the impact at the heel is several times harder as when walking, and even painful. By nature the solution to avoid this pain is to run landing not on the heel but on the ball of the foot employing all the articulations of the legs to cushion the impact. In a logical sense, the search to protect the feet has made the human kind absolutely dependent on shoes. There exists just no other possibility than to shod the feet as soon these are implied in locomotion. But still, not even the sense of protecting the feet is the most important issue. It has evolved to a social act, a fashion style and a way of living. The never ending circle of the foot and the shoe is part of the society and the culture in which we live, and precisely for this reason, there are simply no chances to reject footwear. Even so, that it has been affirmed that the true human gait is the one of the shod man 12 . In general the human walks in a specific way. The lower extremities enable, in a cyclic movement, a forward displacement of the body at the same time as they maintain its equilibrium. While the body moves forward one leg provides a support in balance while the other is elevated and advancing towards a new state of support that will replace the standing phase of the previous leg. The body weight is transferred successively from leg to leg along this cycle, always maintaining one of the two members against the floor. Given that there aren´t any pathologies, the normal human gait is defined in clear phases, which through the science of gait analysis have been determined as two principal ones; the stance phase and the swing phase. The stance phase is the term appointed to the whole period in which the foot is supported against the floor. The swing phase is the term appointed as soon the new cycle is began when the same foot is detached from the floor, after the propulsion, and is driven along the whole time span where the foot is lifted executing a forward motion of the member. In a similar way, running has the same principles of locomotion as the gait. The difference lies between the stance phase and the swing phase. Instead of having constantly a foot pressed against the floor providing a forward movement, the transition from stance phase after the propulsion and the new stance phase of the cycle is given by a slight jump; namely the two legs are detached from the ground. The traditional running technique (heel-toe) in the sports culture is the one most used in comparison to other techniques employed by professional and enthusiast runners. This technique consists in executing the forward displacement by first touching the ground with the heel and letting the foot role to the toes in order to generate the propulsion. Besides being an improper technique, many beliefs or misbelieves are present in the sports culture that practically obligate the runners to buy specialized shoes in order to continue with their training. These . 12. . Ramiro, José. Guía de recomendaciones para el diseño de calzado. Instituto de biomecánica de Valencia.1995. pp. 30.

(10) beliefs have been quickly diffused around the globe through tradition and through the most popular sport´s information media, such as: magazines, publicity, products, brands, etc. Most running shoes available in the market are designed for enthusiast runners that employ the traditional running technique. Because the impact with the ground utilizing this technique doesn´t provide a natural attenuation done by the foot´s and the leg´s mechanism, the sports footwear must supply this function by adding cushioning systems such as gel, air, channels, honeycomb, microspheres, super-light materials, foam springs and even micro-chips 13 . These materials with the property of absorbing impact require a thickness to function properly. Thereby, it is indispensable to add this additional layer under the foot´s sole; especially under the heel where the biggest forces are induced. The additional height increases the distance from the zone of impact and the ankle of the runner generating a longer bending arm for horizontal forces, i.e. from right to left of the foot. As a result of this longer bending arm, the chances of injuries due to a greater bending moment about the ankle´s joint in direction of eversion (see Chapter 7) and inversion are higher. If the bending moment applied around an imaginary axis at the average ankle joint 14 (Fig.2.3) (which is the joint responsible of the eversion and the inversion movements without plantar or dorsal flexion) of a shod foot‫ܯ‬௦ , which will be called shod moment, is related with the bending moment ‫ܯ‬ௗ , which will be called barefoot moment; the result is a percentual increase of the bending moment, consequence of a greater bending arm, applied on the shod foot.. 15. Fig. 2.3 Imaginary axis at the average ankle joint The moment is a result of the product of the horizontal force F -in inversion or eversion- multiplied by the height from the ground to the same point when shod and when barefoot. If the height of the shod case is taken as ‫ܪ‬௦ , shod height, and the height of the barefoot case as ‫ܪ‬௕ , barefoot height; the numerical analysis is: Shod moment: Barefoot moment:. ‫ܯ‬௦ ൌ ‫ܪ כ ܨ‬௦ ݁‫ݍ‬Ǥ ʹǤͳ ‫ܯ‬௕ ൌ ‫ܪ כ ܨ‬௕ ݁‫ݍ‬Ǥ ʹǤʹ. The percentual relation between the moments is ‫ܯ‬௕ ‫ܪ כ ܨ‬௕ ൌ ‫ݍ݁ͲͲͳ כ‬Ǥ ʹǤ͵ ‫ܯ‬௦ ‫ܪ כ ܨ‬௦ ‫ܪ‬௦ can be expressed as the sum of the barefoot hight and the aditional height supplied by the shoe´s sole, 13. Anonymous. Athletic footwear and running injuries. Part 1-Introduction and history. Spiridon. August 22, 2006. Available at: http://www.quickswood.com/my_weblog/2006/08/athletic_footwe.html 14 Valmassy, Ronald. Clinical biomechanics of the lower extremities. St. Louis Missouri. Mosloy. (1996). pp 4 15 Ibid. pp 4. .

(11) ‫ܪ‬௦ ൌ ‫ܪ‬௕ ൅ ‫ݍ݈݁݁݋ݏ‬Ǥ ʹǤͶ Since the comparison is done using the same forces F, these can be canceled from eq. 2.3 obtaining the next distance relations ‫ܪ‬௕ ‫ܯ‬௕ ‫ܪ‬௕ ൰ ‫ݍ݁ͲͲͳ כ‬Ǥ ʹǤͷ ൌ ‫ ͲͲͳ כ‬ൌ ൬ ‫ܯ‬௦ ‫ܪ‬௦ ‫ܪ‬௕ ൅ ‫݈݁݋ݏ‬ Defined as: The percentual increment of the bending moment about the talocalcaneal axis at the ankle in direction of inversion or eversion as the result of the shoe´s sole. The range of values for the variable sole was obtained from running shoes available in stores. These values are within the range from 0,5cm to 2,5cm of thickness. For the purpose of this example the value ‫ܪ‬௕ taken as 9cm was measured from a 25 year old male, 1.90 m of height and, 72Kg of weight.. Additional height (Shod). Additional Percentual height increase of (Barefoot) the bending moment. sole [cm] 0. Hb [cm] 0. [%]. 0,5. 0. 6,25. 1. 0. 12,5. 1,5. 0. 18,75. 2. 0. 25. 2,5. 0. 31,25. 0. Fig 2.5 Percentual increase of the bending moment when using footwear Observing the particular case of adding a sole with a height of 2,5cm the bending moment increases 31,25%. This bending force combined with a support with no sensorial feedback, effect of a thick sole and the shoe cushioning system, might not allow the runner to react fast enough to avoid the very common ankle injury –typically called ankle sprain. This last case shows an example of one of the negative factors of footwear. Since the intentions of this investigation is not to show the negative issues of wearing shoes, no further study will be done about this theme. However, it is worth mentioning in terms of the mid distance British world champion Gordon Pirie when referring to running shoes with cushion at the heel: “such shoes make correct technique impossible 16 ”. A well suited description of the effect of running footwear is described by an anonymous author available on the internet published partially in the german magazine Spiridon on August 22, 2006 17 and by an article published on The New York Magazine on April 21, 2008 writen by Adam Sternbergh 18 . 16. Op.cit. Pirie. pp 23 Anonymous. Athletic footwear and running injuries. Part 1-Introduction and history. Spiridon. August 22, 2006. Available at: http://www.quickswood.com/my_weblog/2006/08/athletic_footwe.html 18 Sternbergh, Adam. You walk wrong. (2008). [*.pdf]. Available at: http://nymag.com/health/features/46213/ 17. .

(12) 3. OBJECTIVES. The objective of this investigation is to design a model of the leg and foot in order to characterize the barefoot running technique toe-heel and determine the foot deformations and the mechanical advantage of the mechanism of the locomotion members using a motion capture system to track the position of modeled bodies and the Euler angles to determine the relative angular rotations between adjacent bodies. The objective of investigating the toe-heel technique is to suggest an alternative to the traditional running technique (heel-toe) by considering a different body configuration of the locomotion members which will perform better as a mechanism -especially regarding the impact attenuation properties- than the heel-toe technique. The specific objectives that enable this investigation are: x x. x x x. . Design a model of the studied bodies of the locomotion members that represent and provide an accurate approximation of the movement of the real bodies. Capture the motion of the modeled bodies while running on a treadmill with the motion capture system Phase Space and representing the bodies using a vectorial procedure of plane construction. Determine the random error of the measurements taken with the motion capture system. Calculate the relative rotations between adjacent bodies using the Euler parameters. Compare the mechanical advantage of the locomotion members` mechanism between the toehell technique and the heel-toe technique..

(13) 4. ACTUAL FOOT DEFORMATION MODELS AND THE PURPOSE OF A NEW MODEL Previous investigations have been made on foot deformations and foot deformation models. These models have evolved simultaneously as the technology has enabled more accurate measuring techniques for this purpose. “In previous studies the rearfoot and tibia coupling motion was modeled as a single rigid segment because of technical difficulties associated with evaluating the forefoot motion in a shoe condition 19 ”. The difficulty of measuring experimentally accurate values, in which the foot deformations are numerically identified while walking and running, have limited the foot deformation models to focus on the biggest end most evident deformations. One of the most influencing models called a mitered hinge was proposed by Mann (1993) which described the coordination of ankle and subtalar motion 20 (Fig. 4.1).. Fig. 4.1 Mitered hinge foot model. Eslami, Begon, Farahpour and Allard (2006) suggested a model based on the twisted plate and the mitered hinge models of the foot and ankle. The purpose was to determine the differences of forefoot–rearfoot coupling patterns as well as the excessive excursion of tibial internal rotation in shod versus barefoot conditions during running. This contributed on the representation of the forefoot–rearfoot coupling motion patterns and the amount of tibial rotation under the barefoot and shod conditions 21 . Fig. (4.2). Fig. 4.2 Forefoot-rearfoot coupling patterns. Other resent investigations have reported results where more accurate and sophisticated experimental methods take place. Arndt, Wolf, Liu, Nester, Stacoff, Jones, Lundgren and Lundberg (2006) suggested through an invasive method based upon reflective marker arrays mounted on intracortical pins drilled into the bones a kinematic description of the intrinsic articulations of the foot during running 22 (Fig. 4.3). . 19. Eslami, Mansour. Forefoot–rearfoot coupling patterns and tibial internal rotation. Clinical Biomechanics. [*.pdf]. (2007). 22: 74–80 20 Margareta, Nordin. Basic biomechanicas of the musculoskeletal system. Lippincott Williams & Wilkins. Third Edition. (2001). pp 228 21 Op.cit. Eslami. 22 Arndt, A. Intrinsic foot kinematics measured in vivo during the stance phase of slow running. [*.pdf]. (2007) Journal of Biomechanics 40: 2672–2678. .

(14) Fig. 4.3 Intracortical pins drilled into the bones Non invasive methods such as active LED (Light Emitting Diodes) markers captured by cameras equipped with position detectors 23 , and high resolution / high speed image and video cameras have registered information that 20 years ago were still impossible. A similar technology was implemented by Leardini, Benedetti, Berti, Bettinelli, Nativo, and Giannini (2007) proposing a new protocol designed to track a large number of foot segments during the stance phase of gait with the smallest possible number of markers, with particular clinical focus on coronal plane alignment of the rear-foot, transverse and sagital plane alignment of the metatarsal bones, and changes at the medial longitudinal arch 24 (Fig. 4.4).. Fig. 4.4 Coronal plane alignment foot model The models mentioned above have all in common that the type of motion studied is done with a heeltoe technique. The fact that this technique is the most studied isn’t just for granted. These investigations have been influenced by several factors that have driven the objectives towards particular interests. For example as a result of the jogging boom of the late 70`s in the United States, where the rate of injured joggers was as high as two out of three 25 , several investigations focused on explaining the origin of this injury rate. The solution regarding this, was, and still is, the great scientific efforts from many sports brands on inventing the ideal running shoe. Thanks to this drastic sports tendency most known sports shoe-brands are today in the market 26 . The running technique and the social requirements about using shoes during almost all daily activities are perhaps the biggest influences that have directed the investigations towards the results of a particular type of load with a particular shod motion technique. The four models mentioned have 23. 24. Phase Space. http://www.phasespace.com/productsMain.html. Leardini, A. Benedetti, M.G. Rear-foot, mid-foot and fore-foot motion during the stance phase of gait. Gait & Posture. [*.pdf]. (2007). 25: 453–462. 25 26. . Op.cit. Nigg, pp 2. Op.cit. Anonymous. Athletic footwear and running injuries..

(15) focused on describing the foot´s internal joint motion in heel-toe technique. Thereby, there is still no equivalent foot-model that considers neither internal joint deformations nor the role of the toes or the metatarsal bones in toe-heel running. To perform an experiment to determine the foot deformation while walking or running it`s important to avoid any external factors that might modify the natural behavior of the foot; unless the investigation is particularly directed towards the determination of the foot deformation inside shoes. For example if the intentions are to measure the deformations while barefoot running, the test should be done without shoes on unshod populations. It might seem obvious to regard such an example, but, relating it with the purpose of this paper, the fact that most investigations have been done on people that have lived their entire life shod might have limited the foot deformation properties of these volunteers as an effect of the additional support supplied by the shoes; thereby, there would be a noise variable that would be skewing the final result. The proper conditions for researching the foot deformations should be by studding a population that have never used shoes, assuming that the unshod running technique would be best performed by these subjects. The closest subjects available in a city that might present foot and running characteristics of an unshod person are those who practice the sport of running barefoot. For this investigation it would have been wished to count with subjects 100% unshod. Thus, it is suggested to deepen the running investigation in unshod populations. Regarding the unconsidered movements of which the feet are capable (Fig. 4.5 27 ) and focusing the investigation on the phalanges and the transverse and sagital deformations of the metatarsus under load -which have been matter to limited analysis 28 - are the principles of the new model. Being the perceived stiffness of the ground a function of the running technique, since the ground reaction forces depend on the mechanical advantage of the locomotion configuration (Chapter 5.3), “humans are able to adjust their leg mechanics to compensate changes in running surface stiffness. […] These adjustments in leg mechanics occur rapidly and allow the human system to move in a similar manner despite of large changes in the environmental surface 29 ”. This is considered on the running technique under investigation, which is the one contemplated as the most adequate for barefoot running; namely the toe-heel technique 30 . The particular loads exerted on the foot due to this technique and the different mechanical advantage of the new configuration of the locomotion mechanism will play a defining role on the manner in which the foot will perform. Fig 4.5 Unconsidered movements of the feet . 27. Klenermann, Leslie. The Human Foot, A Companion to Clinical Studies. Cap 6. The Foot in Action. SpringerLink. [*.pdf]. pp 138 28 Ibid. Leardini 29 Karamanidis, Kiros. Adaptational phenomena and mechanical responses during running: effect of surface, aging and task experience. Springer-Verlag (2006). [*.pdf]. 98:284–298 30 Op.cit. Warburton. pp. 3. .

(16) 5. THE TOE HEEL RUNNING TECHNIQUE If the running technique is modified in order to make possible a better mechanical advantage for the lower locomotion mechanisms, by enabling a greater knee angle, a wider range of damping motion of the ankle and an initial impact at the ball of the foot, there would be an enhancement on the impact attenuation mechanism. Thus, a superior mechanical advantage means, as well, a reduction on the stess applied on the feet, ankles, knees, back and hips; contributing on the prevention of injuries. However, a correct technique is not learned by simple observation or by trial and error, a proper running technique must be taught as any sports technique.. 5.1 Why to teach how to run barefoot Statistical results from the German journal FussSprungg indicate that running is responsible of 70% of stress fractures (Stressfrakturen) –injury defined as bone fractures resulting from extraordinary activity, such as repetitive stress, on normal bone 31 - or insufficiency fractures (Insuffizienzfraktur) –injury defined as bone fractures resulting from normal activity on deficient bone 32 - either by fatigue (Ermüdung) or by mechanical overload (mechanische Überlastung) (Fig. 5.1) 33 . Participants in endurance and long-distance activities are at high risk for developing this type of stress fractures 34 . Equivalent results from statistical investigations compiled by the American Medical Association in The United States point out that as many as 70 percent of the more than 30 million ‘serious’ runners of this country can count on being injured every year. This disturbing injury rate is not limited only to beginners and top competition athletes, but applies to runners at every level 35 . Fig 5.1 Fifth toe fatigue fracture The breaking point, where the correct technique is distorted, is as soon as the footwear is included as a device that determines human gate. Humans are natural runners, “although comparatively poor sprinters, they can perform endurance running covering many kilometres for long periods using aerobic metabolism. No primates other than humans are capable of endurance running. Although endurance running is now confined to sport it may have given humans an evolutionary edge, according to Bramble and Lieberman 36 in a recent review 37 ”. However, there is an entire generation of runners who have being seriously misinformed by “shoe manufacturers, and the pseudo-experts who pass themselves off as knowledgeable authorities in the popular running press 38 ”. In that way, ignorance influences inexperienced athletes. In fact, it is believed that running is an unhealthy discipline, in terms of inducing injuries. Thereby, “running ignorance refers to a runner who goes from one frustration to another because he or she knows absolutely nothing about the effects of training on the . 31 Farkas,Tracy A. Zane,Richard D. Comminuted Femur Fracture Secondary to Stress During the Boston Marathon. The Journal of Emergency Medicine. [*.pdf]. (2006) Vol. 31, No. 1, pp. 79 32 Ibid 33 Brukner PD, Bradshaw C, Khan KM, White S, Crossley K Stress fractures: a review of 180 cases. Clin J Sports. (1996). Med 6:85–89 and Matheson, G. O. Stress fractures in athletes. Am J Sports Med. (1987). 15:46–58. At: Leumann, A. Pagenstert, G. Fuß- und Unterschenkel-Stressfrakturen im Sport. FussSprungg. [*.pdf]. (2006). 4:150–157 34 Op cit. Farkas,Tracy A. Zane,Richard D. pp 80 35 Op.cit. Pirie. pp. 7 36 Bramble, D.M. Lieberman, B.E. Endurance running and the evolution of Homo. Nature. (2004). 432: 345–352. Available at: http://www.anthro.utah.edu/PDFs/bramble-n-432-345.pdf 37 Op.cit. Klenermann. pp. 144 38 Op.cit. Pirie. pp 5.. .

(17) body 39 ”. If the body is well understood, perhaps the athlete will respond better to what the body is trying to say though several means such as, pain, tiredness, or lack energy. Another problem is that “most athletes take injuries for granted - as going hand in hand with hard training 40 ”. Injuries can´t be part of this discipline regarding the fact that humans depend on their legs to mobilize themselves and it´s a contradiction to assume that the fast locomotion (running) is harmful. “Running with correct technique (even in prepared bare feet), on any surface, is injury free 41 ”. For instance, the knee is one of the most prevalent cases of running injuries 42 . However, it has been demonstrated that that long distance running – i.e. a marathon– does not cause severe damage resulting from this demanding activity; namely, “acute lesions of cartilage, ligaments, or bone marrow of the knee in well-trained runners 43 ”. Thus, one can imply that running correctly is not a hazardous sport by cause of degenerative changes of these particular tissues during long running trials. Still it is very common to find injured runners after this type of races. The question appears, then: What is causing such common running injuries? International runners such as Zola Budd Pieterse (Fig.5.2 44 ) from South Africa -two times 5000m world record 45 - and the late Abebe Bikila (Fig.5.3) from Ethiopia -gold medalist in the Rome Olympics 1960 setting a new marathon world mark 46 - have competed barefoot very successfully.. Fig.5.2 Zola Budd Pieterse. Fig.5.3 Abebe Bikila. Running in bare feet for long distances is clearly not limiting the performance at the highest levels 47 . If the efforts on footwear technology hasn´t made the injury rates lower, perhaps the solution is not to . 39. Ibid. pp 9 Ibid. pp 21 41 Ibid. pp 6 42 Hamill, Joseph Hamill. A dynamical systems approach to lower extremity running injuries. Clinical Biomechanics. [*.pdf]. (1999). 14: 297-308 43 Schueller-Weidekamm, C. Schueller, G. Does marathon running cause acute lesions of the knee? Evaluation with magnetic resonance imaging. Eur Radiol. [*.pdf]. (2006) 16: 2179–2185 44 Run Barefoot. Available at: http://www.runbarefoot.com/indexOld.php?image=0-811193-GettyImages-001 45 BBC News. 1985: Budd smashes 5,000m record. Available at: http://news.bbc.co.uk/onthisday/hi/dates/stories/august/26/newsid_2535000/2535703.stm 46 Media Ethiopia. Abebe Bikila (1932-1973). Available at: http://www.ethiopians.com/abebe_bikila.htm 47 Op.cit. Warburton, Michael. pp 1 40. .

(18) rely on the highest shoe technology. “Athletes who have access only to the volumes of bad information on technique being pedalled by the running magazines and shoe manufacturers, have no way of discovering the benefits of proper running style 48 ”. The main contradiction regarding footwear is the fact that additional protection and support is diminishing the foot stimulation and thereby preventing the natural strengthening of its structure. “Most running shoes today are designed and constructed in such a manner as to make correct technique impossible (and therefore cause chronic injuries to the people who wear them). It is a common misconception that a runner should land on his or her heels and then roll forward to the front of the foot with each stride. In designing their shoes, most shoe companies fall prey to this incorrect assumption 49 ”. In this order of ideas, it´s worth considering the total opposite of wearing super-shoes. When running barefoot, the runner will notice the effect of switching the running techniques and will have the chance to test several methods until the most comfortable is found. Not only will the runner discover a softer technique for landing the feet, but will, as well, stimulate parts of the foot that are fundamental for a structural integrity of the foot and are highly required in order to prevent this “injury epidemic 50 ”. A parallel optimization of the whole body must be present in order to prevent injuries; “injuries are often caused by this imbalance 51 ”. The simultaneous development of the body is related with every part involved when running. It is important to regard the problem of bone fatigue fractures as an imbalance between the effort demanded and the bone strength. “Ideally, the stress on bone, induced by physical activity should optimize the anatomic structure of the trabeculae by direct impact from weight bearing activity and indirectly by muscle pull 52 ”. To have strong feet is part of the total training, however the feet are never considered as part of the routine. Since “physical activity leads to a higher bone mineral density, especially among sporting events containing high workloads of the lower extremities 53 ”, footwear causes a lack of stimulation on the natural process of strengthening the bones of the foot in a proportional magnitude to the intensity required by the activity; consequently increasing the risk of fracture. For instance, the role of the toes and its local foot strength was studied by Nagel 54 . It was demonstrated that long distance running increases plantar pressures beneath the metatarsal heads due to local muscle fatigue, thus, transferring the load from the toes to the metatarsal heads. The results showed that post-race peak pressure and impulse values were higher in the forefoot regions and reduced under the toes (Fig. 5.2).. 48. Op.cit. Pirie pp 17 Ibid pp. 7 50 Ibid. 51 Ibid. pp 55 52 Wol. V. J. (1892) Das Gesetz der Transformation der Knochen. Verlag August Hirschwald, Berlin, pp 1–152. At: Knobloch, Karsten. Rapid rehabilitation programme following sacral stress fracture in a long-distance running female athlete. Arch Orthop Trauma Surg. [*.pdf]. (2006). DOI 10.1007/s00402-006-0201-y 53 Nielsson, B.E. Westlin, N.E. Bone density in athletes. Clin Orthop Relat Res. (1971) 77:179–182. At: Knobloch, Karsten. Rapid rehabilitation programme following sacral stress fracture in a long-distance running female athlete. Arch Orthop Trauma Surg. [*.pdf]. (2006). DOI 10.1007/s00402-006-0201-y 54 Nagel, A. Long distance running increases plantar pressures beneath the metatarsal heads. Gait Posture . (2007). [*.pdf]. doi:10.1016/j.gaitpost.2006.12.012 49. .

(19) Fig. 5.2 Post-race plantar pressure increase beneath the metatarsal heads due to toe fatigue It was concluded in this article that the results could be associated with an increased dorsiflexion in the metatarsophalangeal joints which would lead to higher peak pressure and impulse values under the metatarsal heads, thus, indicating overloading of the passive structures of the foot- i.e. the metatarsal bones- and possibly leading to stress fractures. This agrees with the statement of Williams III, who points out that the strength loss of the toes in push-off leads to a decrease of the cushioning function of the foot which might be thought to be responsible for metatarsal stress fractures 55 . To have knowledge about a proper running technique is fundamental to any person. Part of experiencing childhood is not being able to contain oneself from running from one place to another. Running makes part of everyone. It becomes even more important to know how to run if the person is adopting this sport into a regular discipline. An example of a critical case of inadequate technique is one documented by Spitz where an enthusiast athlete suffered of a bone fatigue fracture while running a marathon. “The asymmetry of this patient’s femoral cortices (left greater than right) may indicate a protective response by the bones to the repetitive stress of running as the bone remodels in response to increased pressure; an uneven gait or stride may cause the difference in one side more than the other”(Fig. 5.3) 56 . Fig 5.3 Femur fatigue fracture An alternative to avoid such related injuries is running barefoot. It has been observed that in developing countries this activity´s rates indicate significantly lower frequency of severe injuries of the ankle and chronic injuries of the lower leg 57 , “it may be suggested that barefoot running could lead to fewer running injuries than shod running 58 ”. As well, an investigation done in China and India developed by Schulman concluded that people who have never worn shoes have relatively fewer foot disorders 59 . 55. Williams III. Arch structure and injury patterns in runners. Clin Biomech (2001) [*.pdf].vol.16.(4):341–347. Spitz, D. J. Newberg, A.H. Imaging of stress fractures in the athlete. Radiol Clin North Am (2002). 40:313–31. At: Farkas,Tracy A. Zane,Richard D. Comminuted Femur Fracture Secondary to Stress During the Boston Marathon. The Journal of Emergency Medicine. [*.pdf]. (2006) Vol. 31, No. 1. pp 81 57 Op.cit. Warburton, Michael. pp. 1 58 Stacoff, Alex. Nigg, Benno M. Tibiocalcaneal kinematics of barefoot versus shod running. Journal of Biomechanics. [*.pdf]. (2000). 33: 1387-1395 59 Schulman, S.B. Survey in China and India of feet that have never worn shoes. J Nat Assoc Chiropodists. (1949). 49:26–30. At: Zipfel, B. Berger, L.R. Shod versus unshod: The emergence of forefoot pathology in modern humans? The Foot. [*.pdf]. (2007) 17: 205–213 56. .

(20) Thereby, additional knowledge is important to reduce injury risks. If the learning process is left to the mere observation and the adoption of the most used technique, small chances will remain for the runner to encounter himself with the technique which suits him best. When so many factors are behind – or perhaps, (in front: blocking) – something as fundamental and natural as running, perhaps it is time to return to the basics; that is: learn, practice and train. If running properly is learned from childhood, running will be once again independent of fashion and technology. “In the literature it is widely accepted that experience or repeated practice causes a task specific adaptation in young 60 ”, meaning that sooner or later, running with technique will result as a spontaneous activity without constant awareness of the method. “Thefirstthingarunnermustknowishowtorunproperly.Everythingelse followsfromthere” 61 GordonPirie. 5.2 How to run barefoot To begin with this description, it is worth regarding once again the visual effect that modern running shoes have from their design out. “The most common misconception concerning style becomes immediately apparent by looking closely at a typical pair of modern running shoes. […] Any athlete who has grown up wearing these shoes unfortunately comes to the conclusion that it is proper to run by striking the ground with the heel first. This assumption follows from the way the shoes are designed, but is absolutely incorrect 62 ”. Running either barefoot or shod should be done landing with the forefoot. However, “any and all additions to the body damage running skill 63 ”, and, “running with shoes may change foot and leg kinematics compared to running barefoot. Hence, barefoot running is often looked upon as the baseline for normal running 64 ”. It is no coincidence that most runners from developing countries, many of whom grew up never wearing shoes, exhibit the best running technique. 65 “Running equals springing through the air, landing elastically on the forefoot with a flexed knee (Fig. 5.4 66 ) (thus producing quiet feet) 67 ”. On landing, the foot should be directly below the body. (Walking is landing on the heels with a straight leg).” 68 Fig. 5.4 Gordon Pirie (first place left). . 60. Op.cit. Karamanidis. Op.cit. Pirie. pp 8. 62 Ibid. pp 17 63 Ibid. pp 17 64 Clarke, T.E., Frederick, E.C., Hamill, C.,. The study of rearfoot movement in running. (1984) In: Frederick, E.C. (Ed.), Sport Shoes and Playing Surfaces. Human kinetics. Champaign, IL, pp. 166-189. At: Stacoff, Alex. Nigg, Benno M. Tibiocalcaneal kinematics of barefoot versus shod running. Journal of Biomechanics. [*.pdf]. (2000). 33: 1387-1395 65 Op.cit. Pirie pp 22 66 Ibid. pp 3 67 Ibid. pp 6 68 Ibid. pp 8. 61. .

(21) Since no artificial cushioning is added between the foot and the ground, a natural switch at the foot´s position when landing is necessary. “When running barefoot on hard surfaces, the runner compensates for the lack of cushioning underfoot by plantar-flexing the foot at contact, thus giving a softer landing. Barefoot runners also land midfoot, increasing the work of the foot's soft tissue support structures, thereby increasing their strength and possibly reducing the risk of injury 69 ”; taking into account, that the forefoot at stance is flexible, therefore absorbing impact and adapting itself to the irregularities in the ground 70 . A very accurate description of the learning process for the toe-heel running technique is described by Gordon Pirie in his book Running Fast and Injury Free. The following quote explains in a very simple way this procedure. Let us start at the very beginning, with the person standing to attention in bare feet. Raise yourself up onto tiptoes, and overbalance forward. You must take a step forward to keep from falling over. From the position which results (it is impossible to step forward onto the heel), you should begin to run at a slow velocity - but with very light, quick steps making sure to feel the stress on the toes. The runner's legs should remain flexed at the knees. A feeling of “sitting” with the seat down “like a duck” is employed with the body upright. An athlete who runs correctly will actually appear to be shorter than other runners of the same height who are not running properly. By keeping his knees flexed and by landing on the ball of the foot on each step, and with the foot beneath the body, the runner will spring along very quietly. As the weight of the runner's body rides over the foot, the entire sole will rest flat on the ground - do not remain like a ballet dancer on your toes throughout the weight-bearing phase. […] The runner will generate more power and cover more ground with each stride by taking advantage of the springiness and power of the muscles in the feet and forelegs as well as the thighs. The runner's tempo should be at least three steps per second. A person running correctly will make virtually no noise as he moves along. A conscious effort must be made to run as lightly as possible. The runner must be aware of what his or her feet and knees are doing at this early stage. […] Try to maintain a quicker tempo than is natural. Don't lean forward. A runner whose style causes him or her to overstride, striking the ground heel-first with straightened knee joints, is running on a very short road to the doctor's office. During this initial teaching phase, the runner should hold his arms close to the body without any movement at all, and concentrate exclusively on what his feet and legs are doing. The ankles, calves and quadriceps are going to be working much harder than before. 71. In case the runner is interested on still wearing footwear, “the perfect running shoe should be something like a heavy-duty ballet slipper - simply an extra layer of protective material around the foot, like a glove 72 ”. In case the runner wants to introduce himself to barefoot running the whole foot must go through a process of strengthening and the soles must go through a natural process of thickening. At the same time, the muscles of the foot will have to adapt to this type of loads, and the bones will go through an equivalent stimuli course. It is suggested to start walking barefoot and progressively begging to increase the distance and the speed. This process must be taken without rushing into excessive efforts, since it is still very probable that the body is not accustomed to this type of activities. To avoid blisters . 69. Op.cit. Warburton. pp. 3. Eslami, Mansour. Forefoot–rearfoot coupling patterns and tibial internal rotation during stance phase of barefoot versus shod running. Clinical Biomechanics (2007) 22 : 74–80 71 Op.cit. Pirie pp 18 72 Ibid. pp 27 70. .

(22) at the soles, any sensation of soreness must be take in account. This usually means that the skin is not unattached jet, as in the case of a blister, but is in a state where further demand isn´t recommended. However, the positive result of this is the development of tougher soles and so longer and harder running sessions. When running in urban surroundings it is always important to be aware of slippery surfaces, such as brick and polished stone when wet, and of cutting or sharp objects.. 5.3 Mechanical advantage. To make the toe-heel and the heel-toe techniques at the same running speed comparable it will be assumed that the hip and knee angles are the same for the two techniques and that the lineal and angular velocities and accelerations are the same for all the body parts, thereby making the position of the foot at ground contact the only difference. In order to analyze and compare the mechanical advantage of the toe-heel and the heel-toe-techniques some assumptions must be taken to simplify the analyzed part. Taking a previous model of the foot during stance 73 as reference, the foot can be represented as shown in (Fig. 5.4). The model assumes that the weight ‫ݓ‬௕ is applied in the vertical direction towards the ground. Thereby, the Ground Reaction Force (GRF) is equal and in opposite direction of‫ݓ‬௕ . The shank and the foot are connected at the ankle by an ideal mechanical hinge joint. Thus, the movement is restrained to the saggital plane which is asumed to be perfectly perpendicular to the joint´s axis and the sole of the foot is assumed to be parallel to the ground. The horizontal forces are neglected in order to analize the mayor and most critical forces. Point k is the center of pressure making the distance from the heel to the ball in a normal step ݇௠௔௫ െ ݇௠௜௡ ൌ ο݇. In addition, the model is assumed to have a distance ratio for heel projection-pivot to projection pivot-ball of 1:3 (Fig.5.5).. Fig. 5.5 Foot model. 73. . Op.cit. Nigg. pp 73.

(23) This previous model can be slightly modified in order to compare the mechanical advantage of the two running techniques. This model is a representation of the foot during stance. That implies that the heel and the ball of the foot are supporting the force ‫ݓ‬௕ at the same time. While running the first ground contact is either at the hell when running heel-toe or at the ball when running toe-heel. In order to analyze both situations with the same model from (Fig.5.1) let us change the position of the model´s foot and see what´s happening with the GRF. The length of the foot is assumed to be the same without considering the movement of the internal articulations due to the change from dorsal to plantar position 74 neither to the effect of the forces applied to the foot at stance. Assuming the ball is at a height h in the instant of striking the ground the sole of foot model would rotate an angle ș with respect to the ground (Fig.5.6).. ‫ ݈݄݁݁ݐܽ݁ܿݎ݋ܨ݊݋݅ݐܴܿܽ݁݀݊ݑ݋ݎܩ‬െ ‫ ݁݋ݐ‬ൌ ‫ܨܴܩ‬௛௧. Fig. 5.6 Foot model at heel-tow running technique For the toe-heel technique the same height h is assumed at the heel when striking the ground with the ball and the same rotation of the model with an angle ș from the sole to the ground is present (Fig.5.7).. . 74. . Op.cit. Valmassy. Chap. 1.

(24) ‫ ݁݋ݐݐܽ݁ܿݎ݋ܨ݊݋݅ݐܴܿܽ݁݀݊ݑ݋ݎܩ‬െ ݄݈݁݁ ൌ ‫ܨܴܩ‬௧௛. Fig.5.7 Foot model at toe-heel running technique Considering that the analysis is focused towards the purpose of finding the running technique, between the two analyzed, which reduces the impact exerted by the GRF on the body; in order to analyze the mechanical advantage, the force to which the body is subjected is GRF. Applying the definition of the mechanical advantage as 75 ݉஺ ൌ. ி೔೙. eq. 5.1. ி೚ೠ೟. with, ݉஺ = Mechanical advantage ‫ܨ‬௜௡ = Force that is being applied to the mechanism ‫ܨ‬௢௨௧ = Force that the mechanism must exert in order to counteract the entering forces to maintain equilibrium. and being ‫ݓ‬௕ equal to the body weight and the dynamical forces present at running, represented as ‫ܨ‬௢௨௧ , and ‫ ܨܴܩ‬the ground reaction force felt by the ground surface, represented as ‫ܨ‬௢௨௧ . Substituting the variables of the analyzed model ݉஺ ൌ. ‫ݓ‬௕ ‫ܨܴܩ‬. Supposing the moment applied at the ankle is the same using the both techniques, toe-heel and at heeltoe, then the forces can be represented as: ‫ܨܴܩ‬௧௛ ൌ ‫ܨܴܩ‬௛௧ ൌ. ெ ௥೟೓ ெ ௥೓೟. eq. 5.2 eq. 5.3. . 75. . Norton, Robert L. Diseño de maquinaria. McGrawHill. Tercera edición. Chap. 6. Pg. 247.