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The aims of this project are to successfully identify and resolve the problem faced by football participant when it comes to metatarsal injuries. The aim of the research is to design a new sporting accessory that will increase protection against these injuries, with an aim to eradicate the injuries from the game all together.
Identify the problem
Research into relevant areas such as materials and biomechanics.
Support the theory using materials research and impact testing.
Produce a range of concept designs and embodiment
Produce a prototype of the final design
Discuss the findings of the project
Give any recommendations for improvement
The scope of a project sets out the limits and boundaries of a project to ensure the project stays on track and within its timescale.
The scope of the project will not exceed the set objectives unless they are deemed vital to the project.
Keeping within the scope of the project is vital to ensure all objectives are completed on time and within budget.
The project will only concentrate on breaks in the metatarsal bones during football and not any other sports.
As Metatarsal injuries are becoming more apparent due to football footwear becoming less protective, there is an ever growing need for a solution to reduce metatarsal injuries. Such a solution should allow the wearer to still perform to the highest standards without hindrance, be comfortable and not cause secondary injury to a player through friction. The potential users of the solution are anyone who plays football and holds their personal safety in high regard.
A selling price for this product should be between £12 and £17 so not to out-price itself from the football accessory market.
Problems arising in the form of aesthetics and ergonomics include:
The conflict between perceived protection and actual protection.
The natural differences from human to human foot.
Research and Literature Review
Metatarsal breaks have been amongst some of the high profile injuries that have recently affected professionals. Wayne Rooney is just one of the latest high profile players to suffer a metatarsal break in the last 4 years, each coming immediately before a major international championship and making it onto the front pages of most of the newspapers.
Wayne Rooney suffered 2 metatarsal breaks in 4 years through an impact from another players boot on top of the foot, causing the bone to break through the impact force. Other high profile players who have suffered metatarsal breaks include Steven Gerrard, Michael Owen and David Beckham, all of which occurred during impact from another players football stud on the top of the foot. These injuries take on average 12 weeks for a professional to recover from using oxygen tents to sleep in and having the highest medical advice possible. For the amateur player these recovery times can be a lot longer and can put the player out of action for a considerably longer amount of time.
There is another type of metatarsal injuries caused by stress fractures, these stress fractures occur in the bone after long periods of repeat high impacts on the bottom of the foot, typically over stud locations on the first and fifth metatarsal. This period could be months or even years. Various measures have been taken to reduce these injuries but research still shows that there are high concentrations of pressure still around the stud locations on the first and fifth metatarsal heads if the player is wearing the traditional 6 stud boot configuration.
These stress fractures have developed in the past into very serious injuries forcing players to retire from the game due to constant pain in the foot. A good example of this is Gary Lineker who had to retire because of a stress fracture in his first metatarsal. Gary now has a metal rod in his foot to prevent the injury from returning.
"d3oâ„¢ is a patented technology combining enhanced chemistry, engineering and design to produce an intelligent shock absorption system that flows freely when moving slowly, but on shock, locks together to absorb energy, before instantly returning to its flexible shape" - www.d3o.com
d3oâ„¢ is a new smart material, created and engineered in the UK it offers high levels of shock protection whilst remaining free flowing under normal conditions. d3oâ„¢ is a highly secretive material and there is very little documentation regarding its composition. Information that is available includes its current uses. d3oâ„¢ is currently used in a wide range of sporting and leisure goods and work based footwear. These range from knee and elbow protectors, to full body armour and even ballet and heavy work shoes.
d3oâ„¢ comes in 3 different types, a sheet material, a manufactured component type 1 and manufactured component CE.
The sheet material is available in 2 different geometries, d3o mesh and d3o contour.
"d3oâ„¢ Mesh is a perforated textured sheet which has been specifically designed for comfort and breathability for applications requiring good flexure. It can be used as a component within a design and die cut to shape." - www.d3o.com
The d3oâ„¢ mesh comes in thickness's of 4 and 6mm and comes in sheets of size 330 x 400mm.
Figure 1 - d3o Mesh Sheet
"d3oâ„¢ Contour solid sheet is used when breathability is not important. Its impact performance is also higher than the mesh product." - www.d3o.com
The d3oâ„¢ Contour solid sheet comes in 3, 4 and 6mm thickness and sheets of size 255 x 295mm and 295 x 369mm for 4 and 6mm large sheets.
Figure 2 - d3o Solid sheet
The manufactured components type 1 are designed to be integrated into clothing or products for a range of sports. d3oâ„¢ T1 pads are 7mm thick and very soft and flexible so they are almost invisible in products. T1 components are lightweight, breathable and unlike conventional protection methods when integrated into clothing products are almost invisible.
"Type 1 components are designed to be directly integrated into garments such as snow sports trousers & jackets and mountain biking garments to provide a flexible, breathable, washable and lightweight alternative to conventional rigid hard shell systems" - www.d3o.com
Figure 3 - Type1 d3o component
The d3o manufactured components CE are a range of protectors certified to EN1621-1. These products are all designed specifically to conform to each part of the body, and be as soft and flexible as possible providing complete comfort and freedom of movement.
CE components are thicker and larger than type 1 and are designed to absorb an increased level of shock for more demanding applications.
Figure 4 - d3o CE Component
d3o can be placed in the washing machine at 40° C and can be used over and over again.
Shockwaves are caused with every step we take, these shockwaves can be harmful to the body and reverberate around the body at 70mph, damaging joints and muscles with every stride.
"Sorbothane is proven to absorb an outstanding percentage of these shockwaves, repeatedly without performance degradation." - www.sorbothane.co.uk
On impact Sorbothane deforms laterally, dispersing these shockwaves before returning to its original form immediately.
Sorbothane is a liquid pushed to its maximum viscosity until it possesses all the physical properties of a solid.
"Under the pressure of an impact Sorbothane deforms to disperse the shock waves then retakes its initial form immediately to be operational at 100% of its efficiency on the next impact." - www.sorbothane.co.uk
Sorbothane as a solid deforms away from the impact (proportional to the force applied) which reduces the speed of the impact therefore reducing the net impact force over time.
Figure 5 - Sorbothane
Currently Sorbothane is only used in insoles for running shoes. The same technology however could be applied to a pad that attaches to a sock/insert to protect the metatarsals from impact. It wouldn't matter what type of impact, whether its running or by being stamped/kicked, the material would still react in the same manner and disperse the impact laterally away from the metatarsals.
Sorbothane, like d3o, is a non-newtonian material, these materials have been discussed in detail in the supporting theory section of this project.
Traditionally, designers seeking performance textiles have had to make trade-offs between hard armour and soft armour choices when developing high performance apparel. DEFLEXIONâ„¢ protection textiles provide the benefits of both and minimize the drawbacks.
High protection while remaining comfortable
Good fit with freedom of movement
Keep working across temperature extremes without becoming rigid
A variety of DEFLEXIONâ„¢ impact materials with different thicknesses, weights, flexibilities, breathability and levels of protection exist to provide the designer many choices to create protection items which have the right look and feel for the particular application.
The DEFLEXION impact material series that fits the use of this project best is the TP-series.
The TP-Range combines the properties of silicones with thermoplastics to give designers unique impact protection materials with high levels of protection. The base technology is available as flat sheets in two formats - either with holes for maximized airflow or as a solid sheet. The tremendous versatility of the technology enables different surface effects, allowing the impact protection system to have the right look and feel for targeted applications.
Figure 6 - DEFLEXION TP Series
There are five metatarsal bones in the foot. A metatarsal fracture is when one of these is broken. There are two main types of metatarsal fractures: acute fractures (due to sudden injury) and stress fractures (due to overuse injury). The most common type of metatarsal injury is an acute fracture of the fifth metatarsal because of its placement on the lateral side of the foot and the tendons that connect to it.
Football injuries are commonly divided into traumatic injuries with an acute onset and overuse injuries with a gradual onset (Ekstrand et al., 2003).
"Traumatic injuries are caused by an external force on one specific occasion (e.g., during a tackle or a burst of speed) exceeding the maximum durability of a tissue such as a ligament, a bone or a muscle tendon." (Ekstrand and Torvesit., 2010.)
Acute metatarsal injuries are caused by direct impacts on the foot, these can be a sudden impact (someone kicking or standing on the foot), or twisting of the foot. Twisting generally causes injuries towards the base of the metatarsal. During twisting, the mechanism pulls on a large ligament that attaches to the base of the metatarsal, when twisted the ligament pulls of a fragment of the bone. This twisting injury usually occurs when landing from a jump. These twisting injuries are something I will need to take into account as well as the direct impact injuries.
Acute metatarsal injuries can take between 6 and 8 weeks to recover from however, the table below shows the amount of time it took for high profile football players to fully recover.
Table 1 - Recovery Periods from Metatarsal Injuries
Predicted Recovery (weeks)
From Table 1 we can see that despite it generally taking 6-8 weeks for a player to recover from the injury the actual recovery period in terms of regaining match fitness is usually more than the predicted amount.
Metatarsal Stress Fracture
Overuse injuries are caused by repetitive low-grade forces exceeding the tolerance of the tissues (Bahr, 2009).
Stress fractures result from repeated submaximal loads causing fatigue of the bone structure (Orava, 1980; Warden et al., 2007).
A stress fracture is a type of incomplete fracture in a bone. Stress fractures tend to occur as a result of overuse and are known as 'overuse injuries'. Historically, a metatarsal stress fracture has been called a march fracture because it was seen in soldiers who were marching for long periods of time. However, metatarsal stress fractures are not only seen in military recruits. They are commonly seen in athletes (especially runners), ballet dancers and gymnasts. Metatarsal stress fractures can affect anyone: not just Olympic athletes. They are seen in runners of all levels. The same occurs in football, but due to stud locations on the first and fifth metatarsal heads, the forces are magnified in these areas, leading to an increase in stress fracture frequency.
Overuse injuries tend to occur more if the participant has recently changed their training and increased the intensity, duration or frequency of their training. I will be taking into consideration the high pressure points around the first and fifth metatarsal heads during the development of my football sock.
From the table labelled Appendix 1 we can see that in Ekstrand Torveists research into stress fractures, in 1,180,000 hours of participation only 51 stress fractures occurred, resulting in 0.04injuries/1000hours. They discuss in there research how even though these fractures are quite a rare occurrence, the average time it takes for a player to recover is between 3 and 5 months, putting the player out of action for a considerable amount of time.
The feet are a highly complicated piece of natural engineering, they support our entire body weight throughout our lifetime. So how do they work?
How do our feet work?
Each foot has 26 bones, one less than in our hands. The phalanges form the toes, calcaneus (heel), between these bones are the tarsals and metatarsals.
Over 100 different ligaments are needed to hold together the bone's in the foot and its 33 joints.
All of the intricate muscles and ligaments come into action every time we take a step. In a normal, healthy gait, the heel hits the ground first. The calcaneus and a layer of fatty tissue underneath it absorb some of the impact. As the foot rolls forward on its outside edge, the intrinsic muscles of the sole of the foot give way a little and a band of tissue along the bottom of the foot, called the plantar fascia, stretches out. Then the weight moves to the ball of the foot and over the joints formed by the metatarsals and the first, or proximal, phalanges. Finally, we get leverage by pushing off on our big toes, while the Achilles' tendon lifts our heel.
Stress's during the foot when running
"During a typical game of football a player may run over 6 miles with thousands of ground contacts, each with a force of two to three times body weight" - Lake et al. (2010
A football boot has to distribute these loads throughout the time it is being worn during running and rapid movement moments.
"With studded footwear, this can be problematic and pressure hot spots under the foot have been measured at stud locations. Many footballers have foot pain in forefoot stud areas (first and fifth metatarsal heads). Prolonged trauma to these joints at the ball of the foot can result in chronic injury, with and loss of mobility" - Lake et al. (2010)
When running and wearing football boots, we need to make sure that our footwear is correct. We need to ensure that the footwear is the right size and that they fit properly, we need to match the footwear we use to the ground conditions. The use of orthotics and inserts can reduce the likely hood of injury as well as bespoke footwear modifications.
How the foot works, stress's in the foot during impact, running and striking the ball.
"There are five Metatarsal bones in each foot. They are the relatively long bones which are located between the 'Tarsal' bones of the hind-foot and the 'Phalanges' bones in the toes. Functionally, the ankle and foot have two principle functions: propulsion and support. The Metatarsal bones play a major role in these functions. For propulsion they act like a rigid lever and for support they act like a flexible structure that aids balance, thus holding up the entire body." - www.physioroom.com
Figure 7 - Bones of the Foot
Looking at the image above, "The metatarsal and Foot structure", we can see the layout of the bone structure in the foot. In particular the metatarsal bones numbered 1 to 5.
The muscles and tendons that control the foot's movement are divided into two groups, extrinsic and intrinsic. The extrinsic muscles and tendons start in the lower leg and wrap around the ankle in various ways before attaching the tarsal bones. They form a sock, constructed out of crisscrossing straps of muscle and tendon tissue, which joins the leg to the foot and enables the foot to move in several directions. The intrinsic muscles start and end in the foot. Most of them are arranged in several layers across the sole of the foot to form the arch.
Figure 8 - Major muscles of the foot
The image above "Muscles of the foot", shows the muscles used in the foot that allow us to jump, sprint, run and walk.
"Most of the motion of the foot is caused by the stronger muscles in the lower leg whose tendons connect in the foot. Contraction of the muscles in the leg is the main way that we move our feet to stand, walk, run, and jump.
There are numerous small muscles in the foot. Most of the muscles of the foot are arranged in layers on the sole of the foot. These muscles move the toes and provide padding underneath the sole of the foot." - www.sportspodiatry.co.uk
Makeup of the foot, diagrams of the metatarsal layout
Look at existing products (metasox), advantages, disadvantages.
Every time a football player steps out onto a football pitch they risk injury, football is a fast paced contact sport and because of this injuries frequently occur. Reducing the frequency of injury is a top priority for any football club, particularly those injuries that cause the player to be side lined for a considerable amount of time. Ekstrand and Torstveit performed research into Stress fractures in male elite football players, they found that 78% of recorded fractures were that of the fifth metatarsal and caused absences as long as 3-5 months.
The introduction of a non-newtonian material as a barrier to protect the metatarsals will reduce the frequency of metatarsal injuries in football players. Theory that supports this hypothesis is presented in the next section.
The term, non-Newtonian is used to classify all fluids in which shear stress is not directly proportional to deformation rate. Such fluids commonly are classified as having time-independent, time-dependent, or viscoelastic behaviour (R.W. Fox, 1985).
Non-Newtonian materials act in different ways when a force is applied to them. Their stresses vs. strain graphs are non-linear, unlike Newtonian materials whereas the stress in the material increases, the strain rises proportionally. With a non-Newtonian material, as the stress on the material rises, the strain either increases drastically or decreases drastically.
There are two types of non-Newtonian materials, sheer-thinning and sheer-thickening. Sheer-thinning materials become more fluid as force is applied. Examples of this are things like tomato sauce and toothpaste, when it is in the tube, toothpaste is a thick gel, as we squeeze the tube we apply a force which makes the toothpaste become more fluid and flow out of the end. Shear thickening is a non-Newtonian flow behaviour often observed in concentrated colloidal dispersions characterized by significant, sometimes discontinuous increase in viscosity with increasing shear stress (YOUNG S. LEE, 2003). A good example of this is custard. Videos on the internet show people running across swimming pools full of custard without sinking into the liquid, instead as they apply the sharp downward force of the foot strike to the material, the material close to the foot locks together producing a solid.
The materials I propose to use in my design are all sheer-thickening fluids. They are materials that push the viscosity limits of a liquid to its maximum until they observe some properties of solid materials. Shear-thickening materials have long chain molecules, they are soft and flexible under low sheer forces, but if we increase the force via a sharp impact, they instantly lock together, dissipating the impact force whilst absorbing it at the same time (Woodford, 2009).
Figure 9 - Graph showing the different typical shear stress rates in different materials
From Figure 9 we can see just how the different non-Newtonian materials work. Sheer-thinning materials have a sharp increase in there shear stress as shear strain is applied, in contrast to sheer-thickening that has low values of shear stress as strain is applied. In between the two is the linear curve for a Newtonian material. For a newtonian material the viscosity can be given by the slope of the line and therefore its viscosity determined by a single measurement. A non-newtonian material does not have a single value for viscosity, it is common practice to use the term apparent viscosity, which is simply the ratio of shear stress to shear rate at a specified shear rate (Halling, 1975).
One of the models used to describe non-Newtonian materials is the Ostwald-de Waele model, or more commonly known as the Power Law model (Schramm, 2005).
Information about non-newtonian fluids (d3o, sorbothane and deflexion).
Method of proposed impact testing (explanation of results I can get)
Market research shows there is a gap when it comes to metatarsal protection. Existing products are of poor quality and offer very basic protection using basic silicon material as the protective material.
Figure 1 - d3o Mesh [image] 2010. D3o labs.
Available from: http://d3olab.com/i/img-mesh.gif
Accessed on 07/10/2010
Physio Rooms (2010) Metatarsal Fractures in Depth.
Available at: http://www.physioroom.com/injuries/ankle_and_foot/metatarsal_fracture_full.php
[Accessed 27th October, 2010]
LAKE, M. and WILSSENS, J. (2010) Football Boot Selection: Five Take Home Messages
Figure 5 - The metatarsal and Foot structure [Image] 2009. PhysioWeb, USA.
Available from: http://www.physioweb.org/IMAGES/foot.jpg
[Accessed 1st November 2010]
Figure 6 - The Muscles of the Foot [Image] 2010, Sports Podiatry, UK.
Available from: http://www.sportspodiatry.co.uk/images/images/anatomy5.jpg
[Accessed 1st November 2010]
Available from http://www.d3o.com/d3o_products/sheet-plain/
Abstract from d3oâ„¢ website.
Available from http://www.d3o.com/d3o_products/sheet-plain/
Abstract from d3oâ„¢ website.
Available from http://www.d3o.com/d3o_products/t1-limb-and-head-protectors/
Table 1 - Recovery period from Metatarsal fracture.
Lecture Notes supplied by Dr Mark Lake
J,EKSTRAND and M.K. TORVESIT (2010) Stress fractures in elite male football players. Scandinavian Journal of Medicine and Science in Sports.
Ekstrand J, Karlsson J, Hodson A. Football medicine. London; Martin Dunitz (Taylor & Francis Group), 2003: 562.
Bahr R. No injuries, but plenty of pain? On the methodology for recording overuse symptoms in sports. Br J Sports Med 2009: 43: 966-972.
Orava S. Stress fractures. Br J Sports Med 1980: 14: 40-44.
Warden SJ, Creaby MW, Bryant AL, Crossley KM. Stress fracture risk factors in female football players and their clinical implications. Br J Sports Med 2007: 41Suppl. 1: i38-i43.
Abstract from Sorbothane website.
Available from http://www.sorbothane.co.uk/index.php/produits.html
Figure 7 - Illustration of how Sorbothane works [Image] 2010, Sorbothane.
Available from http://sorbothane.co.uk/images/science-sorbothane-lrg.gif