Porter & Schon: Baxter's The Foot and Ankle in Sport, 2nd ed.

Section 5 - Athletic Shoes, Orthoses, and Rehabilitation

Chapter 26 - The shoe in sports

Carol Frey


CHAPTER CONTENTS

  

 

General considerations

  

 

Materials

  

 

Lasting techniques

  

 

Upper designs and cuts

  

 

Bottoming process

  

 

The outer sole

  

 

Midsoles and wedges

  

 

Other component parts

  

 

New components and designs

  

 

Shoe fit

  

 

Sports-specific shoes

  

 

Court sport shoes

  

 

Field sport shoes

  

 

Winter sports

  

 

Other sports

  

 

Injuries related to athletic footwear

  

 

Conclusions

  

 

References

The relationship of the athlete and the shoe is extremely important to athletic performance. The desire for improved performance affects all athletes and influences not only training but also equipment research and design. Athletic shoe manufacturers rely on scientific research and prior experience in the development of their products. This chapter covers important aspects of design, technology, sports-specific needs, and medical and orthopaedic considerations in the development of athletic shoewear.

General Considerations

Construction

Although product development and marketing methods are different, manufacturers use most of the major methods of shoe construction in the production of sport shoes ( Fig. 26-1 ).

 
 

Figure 26-1  Generic athletic shoe.  From Reyatt T: The first step: know your feet. SHAPE Magazine, Nov 1992.

 



The last

The last, a three-dimensional ( Fig. 26-2 ) form on which the shoe is made, is considered by many to be the foundation for shoe production and development. Foot shape may vary with sports activities, and this is a major area of concern in the development of the last. The shape of the shoe toe box, instep, girth, and foot curvature are determined by the last. The biggest last variations occur in girth (or widest part of the forefoot) and in heel width.

 
 

Figure 26-2  Different lasts used in athletic shoes.  From Reyatt T: The first step: know your feet. SHAPE Magazine, Nov 1992.

 



Straight and curved lasts

Most feet have a slight inward curve. Most sport shoe companies use a last that is curved inward approximately 7 degrees. The greater the curve, the more foot mobility is allowed, a benefit for the underpronator. The straighter the shoe, the more medial support it will provide; this can help to control overpronation.

Combination lasts

The term “combination lasts” refers to any last that varies from a standard proportional last to lasts that accommodate a combination of fitting or movement requirements.

 

Materials

Upper materials

Leather, rubber, plastic injection molding, soft nylon, mesh nylon, polyvinyl chloride (PVC)-coated fabrics, polyurethane-coated fabrics, and canvas have been used in the manufacture of uppers. Most uppers used in sports shoes are made of soft nylon, mesh nylon, leather, canvas, suede, and synthetic materials such as Kangoran.

Sole materials

Rubber is the most widely used sole material because of its versatility, durability, and performance. The most commonly used forms of rubber are a highly compressed molded form or a blown microcellular form. Carbon rubber and styrene-butadiene rubber are the two most common rubber compounds used in athletic shoes. Often used in running-shoe soles, black carbon rubber is the hardest wearing. Styrene-butadiene rubber also is hard and is used in tennis and basketball shoes.

Microcellular rubber

Microcellular rubber (MCR) is a compound composed of natural rubber plus additives. MCR contains a blowing agent in powder form that decomposes during vulcanization, forming a cellular structure. MCR is used mainly for midsoles and wedges, but in some shoes it can be used as an outsole material.

Ethyl vinyl acetate

Ethyl vinyl acetate (EVA) contains ethylene and vinyl acetate and a powdered blowing agent that decomposes during vulcanization to form a cellular structure. Because of its lightness, flexibility, density, elongation, and impact resistance, EVA is a common material used in good-quality running shoes. EVA is available in prefabricated sheet or compression-molded forms.

Polyurethane

Polyurethane (PU) is a liquid polyester that can be formed into a blown cellular structure. PU is versatile and can be used as a midsole and heel wedge material, and its lightness and durability make it a satisfactory outsole material. PU can be injected directly or used as a unit sole. PU can be used in the blown cellular state and as a hardened elastomer form in multistudded soles such as golf shoes.

Hytrel

Hytrel is a thermoplastic polyester elastomere developed by DuPont (E.I. duPont de Nemours and Company, Wilmington, DE).

Nylon

Nylon is a polyester resin with a high melting point that forms a hard outsole when injected. It is used for spike plates and as a base for screw-in studs. The hardness grade of nylon refers to the number of carbon atoms in the nylon molecule and is graded as nylon 6, 11, and 12 (nylon 6 being the hardest).

Leather

Split-leather and coarse full hides are used in the construction of some athletic shoes.

 

Lasting Techniques

The most common methods of lasting used in shoemaking are slip lasting, board lasting, and combination lasting ( Fig. 26-3 ).

 
 

Figure 26-3  Methods of lasting.

 

 

  

1   

Slip lasting—A slip-lasted shoe is constructed by sewing together the upper like a moccasin and then gluing it to the sole. The last usually is forced into the upper, which then takes the shape of the last. A sock liner usually takes the place of an insole. This lasting method makes a lightweight and flexible shoe with no torsional rigidity.

  

2   

Board lasting—The upper is placed over the last and fastened to the insole with cement, tacks, or staples. This construction promotes stability and torsional rigidity but decreases flexibility.

  

3   

Combination lasting—More than one lasting technique can be used on the same shoe. Usually the shoe is board lasted in the rear foot for stability but slip lasted in the forefoot for flexibility. Combination lasting can offer customized features necessary for some athletes.

 

Upper Designs and Cuts

  

1   

U-throat—The U-throat offers a U-shaped full lacing system that extends down to the toes.

  

2   

Vamp or blucher pattern—This upper has no seam construction across the dorsum of the midfoot, and the tongue piece continues with the uppers. Lace stays are not fixed to the throat.

  

3   

Balmoral or brogue pattern—This design is a low-cut, laced shoe, usually with a long wingtip trimmed with pinking and perforations. The tongue, throat, and lace stays are seamed as one unit. This type of upper construction allows less space for the dorsal aspect of the midfoot and often is used in golf shoes.

  

4   

Lace-to-toe pattern—This pattern offers lacing similar to the U-throat pattern, but in addition both quarters are pulled together across the foot for maximal support.

 

Bottoming Process

Bottoming is the process in which the sole components are attached to the upper. The upper determines the shoe fit and provides support, and the sole provides traction and cushioning.

 

The Outer Sole

The outsole is the most plantar surface of the shoe that makes contact with the ground and usually is attached to a midsole to form a complete sole. Most athletic shoes have outer soles of hard carbon rubber or blown rubber compounds. Blown rubber is the lightest outsole material but is not as durable as carbon rubber. Many outsoles are composed of both blown and carbon rubber, with blown rubber in the forefoot and midfoot and carbon rubber used in the high-wear area of the heel. Gum rubbers are hard wearing and grip well on most surfaces. PU is less versatile but also suitable for outsole material and seems to possess good durability. Nylon, leather, and PVC have specific outsole applications for certain sports.

Outer sole designs

Patterns can enhance stability and traction. They also can improve shoe lightness by exposing the middle part of the midsole, thereby eliminating part of the outsole and the associated weight. The design of the outsole ( Fig. 26-4 ) can provide cushioning, traction, pivot points, flexpaths, and wear plugs.

 
 

Figure 26-4  Outsole patterns.  From Reyatt T: The first step: know your feet. SHAPE Magazine, Nov 1992.

 



Outsoles are specific for surface, weather condition, and sport. Outsole options include:

  

   

Wear-area reinforcement (running shoes).

  

   

Cantilevered designs for shock absorption (running shoes).

  

   

Pivot points (court shoes).

  

   

Herringbone (court shoes).

  

   

Suction-cup designs (court shoes).

  

   

Multiclaw or stud designs (field shoes).

  

   

Radial edges (court shoes).

  

   

Asymmetric studs (field shoes).

  

   

Traction and wear lugs (hiking and climbing boots).

Traction provided by the outsole is an important consideration in the design of a sport shoe and is directly related to the ability of the shoe to develop frictional forces with the playing surface. Traction needs depend on the specific sports needs. Too little traction may have a negative effect on athletic performance, and too much traction may put the athlete at risk for injury.[1]

A running shoe should create a grip firm enough with the ground so that propulsion forces created by the runner will not be lost with push-off. Push-off has the highest traction needs; therefore the forepart of the outsole should provide the most traction. The outsole rubber used in running shoes usually is blown rubber (air injected to lighten it) or hard carbon rubber.

Cleated shoes must address a compromise between performance and protection of the athlete. Rotational traction, which is expressed by the torque about a normal axis that is developed to resist rotation of a shoe on a playing surface, must be reduced to decrease the incidence of injury while providing sufficient traction. Both cleat length and outsole material affect friction. Torg and Quendenfeld[1] concluded that the increased rotational traction characteristics of some football shoes are related to an increase in number of significant knee injuries.

The necessity for lateral movement with court sports makes the traction characteristics of court shoes important. A flat outsole pattern develops the greatest frictional forces, whereas a herringbone pattern develops less.[2] With sprinting, initial ground contact is made with the front of the shoe. At foot strike a large horizontal velocity is created, resulting in a high braking force that can cause a backward slide. Anterior spikes help to prevent slipping. With jumping events, an athlete converts the large horizontal momentum of run-up to a vertical momentum at foot plant. The spikes prevent foot slip and allow the development of large propulsive forces necessary for long jump and triple jump.

With golf shoes, motion is primarily stationary with little horizontal velocity. Golf shoes provide a base of support that allows the performance of coordinated body movements needed in hitting the ball. A nonvertical alignment of the spikes prevents slipping in this sport, which mainly requires anterior and lateral forces.

Boating shoes require a large amount of natural rubber to prevent slippage on wet surfaces.

 

Midsoles and Wedges

Most of the recent advances in the athletic shoe industry have been made in midsole design and materials. The midsole and heel wedge are sandwiched between the upper and the outsole, attaching to both. These components provide cushioning, shock absorption, lift, and control.

Unit soles

Unit soles usually contain the outsole, midsole, and heel wedge as one unit. This design is used for roller-skate boots and for other sports in which the sole does not contact the ground. This design usually is heavy and provides little flexibility but excellent torsional rigidity.

Combination or prefabricated soles

Midsoles are manufactured from a combination of two basic materials: EVA and polyurethane. EVA is light, has excellent cushioning properties, and can be manufactured in various densities. The firmest densities in a multidensity midsole usually are designated by a darker color. These can be placed at critical points in the midsole to aid in motion control. PU is a denser, heavier, and more durable material than EVA. New forms of lighter PU are being developed.

Both EVA and PU are used to encapsulate other cushioning materials such as air bags (Nike and Etonic), gel (Ascics), silicone (Brooks), honeycomb pads (Reebok and Puma), and EVA (New Balance).

Some midsoles can be contoured to the foot and are referred to as more stable, anatomic midsoles.

The effect of shoe midsole composition on the amount of tibial strain produced with walking has been studied by Milgrom et al.[3] Their study was designed to test the hypothesis that shoe sole composition can affect the level of bone strain and strain rates that can lead to a stress fracture. The sole materials tested were various polyurethane midsoles and one of polyurethane with embedded air cells. The sole composed of polyurethane with embedded air cells had significantly lower compression and shear strains and shear strain rates. They concluded that the polyurethane sole with the embedded air cells potentially could protect against stress fractures in a walking shoe.

 

Other Component Parts

Heel counters

The heel counter is a firm cup built into the rear of the shoe that holds the heel in position and helps to control excessive foot motion. Most heel counters today are made of a durable plastic, thermoplastic, stytherm, or polyvinyl. The medial side of the heel counter may be extended or reinforced for additional pronation control. Contoured or notched counters also reduce irritation of the Achilles tendon, especially in plantarflexion.

Toe box

The toe box provides a stiff material inserted between the lining and upper in the toe area to prevent collapse and protect the toes.

Foxing

Foxing is a stripping material that gives medial and lateral support to the outside of the shoe and usually is made of suede or rubber. In running shoes, the most important foxing is at the toe, where it is called the toe cap. In court shoes, the foxing runs completely around the sole for lateral support.

Cantilevered or angled radial outsole

A cantilevered outsole provides a concave outsole design in which the outer edges flare out on impact to dissipate shock. This design is used extensively by AVIA.

Shank

The shank is the bridge between the heel and the ball area of the shoe. It is a reinforcing material that is arched and somewhat narrowed to conform roughly to the narrow underpart arch area of the midfoot. Shanks are not common in wedge-soled shoes but are important for torsional rigidity in shoes with heels to support the metatarsal arch.

Tongues

Tongues are designed primarily to protect the dorsum of the foot from dirt, moisture, and lace pressure. Lacing loops or tongue slits help to prevent the tongue from slipping.

Sock linings, arch supports, and inserts

Sock linings cover the insole and improve comfort and appearance. A prime function of the sock lining is to serve as a buffer zone between the shoe and the foot. Sock linings are molded, soft support systems that can function in aeration, moisture absorption, hygiene, shock absorption, and motion control. Arch supports, heel cups, and other types of padding can be added to provide support, cushioning, and motion control. Custom-molded “foothotics” have been made popular by the ski industry. These semirigid insole devices are custom molded to the foot and may help increase comfort, shock absorption, and performance. Custom insoles can be used in any sport shoe, provided there is enough room to accommodate the insert.

 

New Components and Designs

Air soles

First introduced in 1979 by Nike, this concept used encapsulated air units in the midsole to enhance cushioning. Ambient air (Etonic) or Freon (Nike) also can be used. Depending on the model, the air units may be in the heel, forefoot, or both. Initial reports noted that, although air systems had superior shock absorption and potential energy rebound, stability was poor.[4] Stability in the context of sports refers to the ability of the shoe to resist excessive or unwanted motions of the foot and ankle. Shoes with soft, well-cushioned midsoles allow significantly more motion than firmer shoes, and a poor design can encourage instability. Newer designs have addressed the stability problem with success. Air systems are not as susceptible to compaction as EVA, PU, and other midsole materials and therefore are thought to be more durable.

Energy return

Compression of a viscoelastic midsole material allows a small amount of strain energy to be stored in the compressed elastic components of the midsole. Theoretically, when weight is released the elastic components spring back and stored energy is returned to the athlete. It has been suggested that by increasing the energy return of a shoe, the oxygen cost of an activity can be reduced and performance enhanced. There is little evidence to support these claims. The arch of the human foot is also a viscoelastic system and therefore can return energy. [0050] [0060]

The “pumps”

The pumps are actually inflatable linings in the tongue and other parts of the shoe that are pumped up by a device built into the top of the shoe. This provides a tight, secure fit. Both Nike and Reebok have used this fit feature.

Replaceable plug systems

A heel plug is found in multidensity outsoles, where the most durable rubber is placed in the high-wear area of the heel. Adidas designed a rear-foot plug system that allows three different hardnesses of replaceable plug to be inserted into the heel wedge to improve shock absorption. Brooks marketed a pronation control system that allows pronation to be controlled by inserting medial heel plugs of varying hardness.

Pronation control devices

Control over pronation in runners and other athletes is a major concern of the sport shoe industry. Most of the motion-control features fall into two categories: (1) a harder density material built into the medial aspect of the midsole and/or heel to counteract pronation and (2) an added medial component to the inside or outside of the shoe that limits pronation. In the past, most of the pronation-control devices have focused on the rear foot. More attention now is placed on controlling the entire foot.

Women's shoes

There has been a lot of recent interest in manufacturing women's athletic shoes, but only a few companies have tried to market shoes for women. In the past, most women's models were simply men's models with cosmetic changes. It has been hard to change the common perception that men's shoes are better than women's.

 

Shoe Fit

A last is a three-dimensional facsimile of a foot and the form over which the upper is fashioned. The fit of all shoes depends largely on the shape of the last. In fitting a shoe correctly, the shape of the athlete's foot is important in that the shape of the shoe should match the shape of the foot.

Curved lasts are better suited for athletes with high arches who do not overpronate. These shoes offer less medial support but greater foot mobility. Furthermore, a curve-lasted shoe is desirable for a faster runner who wants a more responsive shoe.

Straight lasts provide more support to the medial side of the foot and are better suited for athletes with low arches or those who overpronate. Shoes should feel comfortable and fit well the first time they are put on. Runners and athletes should shop for shoes after a run or after a training session, when their feet are at their largest. The shoe should be fit to the largest foot. There should be a finger's breadth from the end of the toe box to the end of the longest toe, and the athlete should be able to fully extend all toes.

One should keep in mind that although the most common regular shoe width is C for men and B for women, the average athletic shoe width is a D for men and C for women. This reflects additional allowances for foot expansion and movement during sport. Width fittings are not commonly available in athletic footwear. Athletic shoes generally are built on “universal” lasts, and width adjustments are incorporated into lacing patterns.

When fitting new shoes, the athlete should wear the socks normally used while training. If the athlete normally wears orthotics, these should replace the sock liner of the shoe during fitting.

Laces

Beginning at the bottom, laces should be pulled one set of eyelets at a time to tighten. This provides a more comfortable shoe fit and distributes stress evenly across the eyelets and the dorsum of the foot.

The majority of athletes can use the conventional crisscross to the top of the shoe technique, aiming for a snug but comfortable fit. However, there are many lacing techniques ( Fig. 26-5 ), and shoe manufacturers have added extra eyelets so that athletes can lace them for a custom fit.

 
 

Figure 26-5  Lacing techniques.

 

 

Variable lace patterns ( Fig. 26-5, A and B )

Many sport shoes incorporate a lacing system that provides a variable or wavy eyelet pattern allowing lacing to be adjusted for wider or narrower feet. The eyelets placed more widely allow the lacing to pull the quarters in more tightly and are more suitable for narrow feet. The more narrowly placed eyelets allow for more girth and thus are more suitable for a wider foot.

Independent lacing ( Fig. 26-5, C )

One lace is provided near the throat of the shoe and one for the forefoot, which can be tied at different tensions for a custom fit.

For pain and/or prominences on the dorsum of the foot ( Fig. 26-5, D )

This lace pattern can relieve pressure over prominences and painful areas on the dorsum of the foot. The athlete starts with a conventional lacing system until just distal to the problem area. The lace is then moved vertically to the next eyelet so that it does not cross over the dorsum of the foot. A conventional lacing is used to complete the shoe closure. Many soccer players prefer this lacing pattern.

Square-box lacing ( Fig. 26-5, E )

In this method, the laces never cross over the dorsum of the foot but rather pass under the eyelet. This helps to distribute lace pressure more evenly over the dorsum of the foot than the crisscross lacing system. Square-box lacing is useful for an athlete with a high arch, rigid feet, or a dorsal prominence or for an athlete with a deep peroneal nerve entrapment.

Single-lace cross ( Fig. 26-5, F )

The single-lace cross may help the athlete who is having problems with black or sore toenails. One lace runs from the inside most proximal eyelet to the opposite most distal eyelet. The other end of the lace goes side to side through every remaining eyelet. This pattern pulls up the toe box of the shoe, relieving pressure on the toes.

For heel spillage ( Fig. 26-5, G )

This is a conventional pattern of lacing until the last eyelet. By looping the end of each lace and using the loop as an eyelet, one can obtain a more secure fit around the heel. This method is helpful to prevent heel slippage.

Show lacing

Show lacing is not practical for wearing purposes. Retailers and manufacturers use this method to show their shoes.

Elastic lacing

Elastic laces can be beneficial to athletes with wide or expanding feet. However, with the use of elastic laces, shoes will lose some stability because, as the foot rolls in, the laces will give. The elastic lace eliminates the need for lacelocks used by many triathletes because the extra stretch allows shoes to be pulled on easily.

 

Sports-Specific Shoes

Manufacturers group athletic shoes into the following sales categories:

  

1   

Running, training, and walking shoes—includes most shoes used for running and walking.

  

2   

Court sport shoes—-includes all shoes used for major and minor court sports.

  

3   

Field sport shoes—cleated, studded, and spiked shoes used in most field sports.

  

4   

Winter sport shoes—shoes for all winter sports activities, including skating and skiing.

  

5   

Outdoor sport shoes—shoes for recreational sports, such as hunting, fishing, and boating.

  

6   

Track and field shoes—diverse area of sports that has its own category of shoes.

  

7   

Specialty sport shoes—shoes for all minor specialized sports and some major ones not covered under other groups, such as golf and aerobic dancing.

Running, training, and walking

Hiking, race walking, and exercise walking are included in this category.

Hiking boots

These are used on rugged terrain. The upper of a hiking boot should be water resistant. There should be few seams for both comfort and water resistance. The soles, which are heavily lugged for traction and durability, are made of rubber, PU, or PVC compounds. There should be some flexibility in the forepart of the shoe at the metatarsophalangeal joints. Other features of a good hiking boot include a firm heel counter, a padded area around the ankle area, a smooth or seam-free lining, and a high, wide toe box. A wedge or a heel with a shank is required. Climbing boots are different from hiking boots in that they have inflexible soles and a thicker upper ( Fig. 26-6 ).

 
 

Figure 26-6  Hiking boots.

 

 

Race-walking shoes

The construction of a race-walking shoe is similar to that of a track shoe. A firm, light midsole is important. Outsoles are made from carbon rubber or gum rubber. A firm heel counter is desirable.

Exercise walking shoes

The design of this shoe is similar to a training running shoe that has many of the features needed in walking such as lightness; flexible forefoot; comfortable, soft upper; and good shock absorption ( Fig. 26-7 ).

 
 

Figure 26-7  Exercise walking shoes.

 

 

For the urban walker, weight is not as important a consideration, and leather often is used for the upper material. An ample toe box and soft sock liner are added for comfort. The sole is also different, with a wedge incorporated into the design. The tread has a smooth, low profile with a herringbone pattern. Many outsoles have a rocker profile to encourage the natural roll of the foot during the walking motion. This feature also helps to reduce excessive flex at the metatarsophalangeal joints and will reduce stress on the midfoot.

A walking shoe should have a firmer landing area on the heel than most running shoes. The bias-out or upswept heel of many running shoes does not offer the landing platform needed by walkers. Most walkers also benefit from the use of a more resilient compound in the rear part of the shoe. A heel height of 10 to 15mm is recommended for exercise walking to support the correct walking motion and reduce overstretching of the Achilles tendon.

Running

Spikes

Little body weight is placed on the heel in sprinting. For most track runners, even those who run the longer distances, landing and propulsion are carried out on the ball and middle part of the foot. For this reason, track shoes used in the faster and shorter races have just enough padding at the heel to prevent a contusion ( Fig. 26-8 ).

 
 

Figure 26-8  Spikes.

 

 

A slight wedge in the shoes for longer races gives more torsional rigidity and support. Torsional rigidity often is omitted in track shoes for lightness. Track shoe lasts are designed to hug the foot at the heel, waist, and girth. The toe box is semipointed to prevent the toes from splaying under the pressure of landing and take-off.

Certain specifications for track spikes may vary for different events. A maximum of six sole and two heel spikes is permitted; spikes must not project more than 25mm or exceed 4mm in diameter. Added spike receptacles may be present for optimal adjustment and may be filled with flat screws when not in use. Grooves, ridges, and appendages are permitted on the sole and heel.

With the use of synthetic and rubber tracks, track spikes have shortened to approximately 9mm and reverted to six spikes for better traction. With the use of shorter spikes, shoe manufacturers invented removable plastic “claws.” When used in conjunction with replaceable variable length spikes, track shoes have more versatility for different track surfaces.

Nylon sole plates receive the spike receptacles. These often are covered with textured rubber for added traction. For curve running (200- to 400-m races) adequate torsional stability is recommended. Lightweight MCR, PU, or EVA foams are used to provide some padding, particularly in the heel area. A spikeless track shoe, usually made with a thin rubber outsole covering a midsole with a maximum heel height of 13mm, may be preferred if the track surface is hard.

Following the same pattern as sprint shoes, middle-distance shoes vary only in the midsole area. A thin wedge or shank may help to control overpronation and torque during bend running.

Participants in the short and long hurdles require sprint shoes with lasts that are wider in the toe and shorter front spikes to avoid clipping the hurdle with the lead foot. A more heavily padded heel is desirable to cushion the landing.

Flats

More research and design has been done in this area than in all other areas of athletic footwear.

The features most required in a running shoe used for training on hard road surfaces are shock absorption, flexibility, control and stability in the heel counter area, torsional rigidity in the waist or shank, lightness, traction, comfort, motion control, and good fit.

Because of the specific needs of individual runners, athletic shoewear companies now produce models for specific foot types, gait patterns, and training styles. There are designs for light runners, heavy runners, heel strikers, motion control, stability, lightweight trainers, and rugged terrain. This segmentation of the market is crossing over into other major segments of the athletic shoe market such as tennis and basketball.

Uppers usually are made of lightweight soft or mesh nylon. A rigid heel counter is a requirement because, like walkers, most runners land heel first. The midsoles of training shoes should be lightweight and offer good shock-absorbing properties. PU and EVA are the most commonly used materials, but ambient air, Freon, and silicone also can be used. All these materials have good to excellent shock absorbency and are built into heel wedge and midsole combinations. The shape of the sole is wedged from heel to toe, with approximately a double thickness at the heel to the metatarsophalangeal joint flexion points. A flared heel increases stability in the heel area ( Fig. 26-9 ).

 

 

Figure 26-9  Flats.

 

 

Traction is obtained by rubber outsole materials and a good tread design. To obtain the best traction on loose or open terrain surfaces, a deeper sole tread is desired. On smoother, harder surfaces such as pavement, a lower-profile sole offers better stability and adequate traction. Flexpath designs on the outsole increase flexibility.

Throwing events

Shoes for throwing events, in which athletes tend to be larger, are primarily made of leather or suede for maximal durability and support. Because of tremendous stresses applied to the medial and lateral portion of the shoe, the uppers are made with extra support around the girth. A shot-put shoe should have reinforced leather uppers, a sturdy heel counter, firm toe box, and reinforcement in the quarter for lateral support. A good grip from a rubber sole and adequate shank provides some control for anterior and lateral movements across the circle. Discus shoes are similar to shot-put shoes but have more flexibility in the forefoot and a wrap-up sole for improved turning motion in the circle. Javelin boots are the only throwing shoes made with spikes for run-up and planting. Soles have a heavy-duty forefoot and heel spike plates containing six front and two back spikes, which may be as long as 25mm for competition on grass runways. A buckle or strap may be used across the girth to provide additional support.

Jumping events

For jumping events, the spike placement changes from the asymmetric pattern, with two spikes in front for stability (the International Association of Athletics Federations [IAAF] rules that there may be a maximum of six forepart spikes and two heel spikes). Most long jumpers do not use heel spikes. The forepart spike plate is sturdy for extra support. Heel cushioning is used for shock absorption.

Similar to long-jump shoes, triple-jump shoes vary only in the midsole, where a sturdy wedge gives better support for landing during the midstance and toe-off stress during this event. Most triple jumpers use heel spikes.

Regardless of their style, high jumpers use a one-foot take-off. Because foot plant and take-off are critical for a successful jump, the “jump foot” shoe is emphasized by designers. The take-off shoe is made in right and left foot versions. Forward and backward ascent styles (“Fosbury Flop”) have different spike placements and gradient on the sole for take-off. The jump shoe can be built with a maximal elevation of 10mm in the forepart to aid lift-off. Six forepart spikes and two heel spikes may be used. Most shoe companies now produce counterpart trailing shoes that are lighter, with fewer spikes and more flexibility to assist the run-up.

 

Court Sport Shoes

Racquet sports

These sports require forward, backward, and side-to-side movements. The body must be moved with control in all directions. Wear patterns produced in even a short time show that court shoes used in racquet sports are subjected to heavy abuse.

Tennis

Tennis requires body control with quick side-to-side movement, sprinting, jumping, and stretching. The sport is played on lawn, clay, asphalt, and synthetic and rubberized courts. The selection of an appropriate sole must be made for each surface. On clay courts, soles with too deep a tread pattern may be prohibited because of excessive court maintenance, even though most players would prefer the traction. On artificial or synthetic surfaces, harder soles with high rubber content or dual-density PU are preferred for durability.

A tennis shoe should provide good lateral support; light to medium weight; a flat sole with a good heel wedge; a firm heel counter; a well-cushioned insole and midsole; ample toe box; good ventilation; nonslip traction; a pivot point; and reinforcement for toe drag.

The upper should provide a sufficiently high quarter pattern to provide good ankle and lateral foot support. Over-the-ankle-line midcut models are available for those players who prefer more ankle support.

Manufacturers of tennis shoes recommend more cushioning in the ball of the foot for the serve-and-volley player. For the baseline player, a solid heel counter, strong reinforcement in the heel and midfoot area, and good rear-foot stability are recommended ( Fig. 26-10 ).

 
 

Figure 26-10  Tennis shoes.

 

 

Basketball

Basketball requires backward, forward, and vertical accelerations; quick stops; and side-to-side movements. The playing surface usually is wood but may be synthetic or rubberized material. The shoe should provide good lateral and medial support; light to medium weight; a flat sole; a slight heel wedge; good cushioning; a large, firm heel counter; toe drag reinforcement; ventilation, a pivot point; and good traction. High rubber content in the sole is recommended. Soles with multiple-edge patterns, such as circles, squares, or diamonds offer better traction than herringbone patterns (which are excellent for forward stops but not for good lateral stops). High-cut designs are available for full ankle support. In addition to offering added ankle support, high-cut uppers must not restrict ankle flexion. Proprioceptor straps are popular. Some players prefer low-cut uppers for better ankle flexibility, but the incidence of ankle injuries may increase with use of these shoes[7] ( Fig. 26-11 ).

 
 

Figure 26-11  Basketball shoes.

 

 

The emphasis of recent design research in basketball shoes has been the reduction of inversion injuries to the ankle. Shoes with increasing amounts of ankle restriction in the upper significantly reduce ankle joint inversion.[8] However, with increasing amounts of ankle restriction, movements not only are restricted in the sagittal plane but also in the frontal plane, leading to reduced agility. Therefore a design compromise must be met between performance and protection of the athlete from injury.

Barrett et al.[9] studied 622 college basketball players to see whether shoe type and height had an effect on the incidence of ankle sprains. In a prospective, randomized study, the player was given a pair of high-top, high-top with inflatable air chambers, or low-top basketball shoes to wear during all games during the season. There was no significant difference noted among the three groups in this study, and there was no significant relationship between shoe type and incidence of ankle sprains.

Volleyball

Volleyball requires quick movements, sudden stops, jumping, and side-to-side motion. The indoor sport usually is played on wood surfaces. The shoe should provide lateral support, be lightweight, provide a flat-herringbone or deep-ripple rubber sole, good cushioning, ventilation, firm heel counter, and toe-drag protection.

 

Field Sport Shoes

Field sports combine many types of movement and a variable degree of body contact. Running is basic to all these sports. Spike and stud formations vary from sport to sport but almost all have replaceable or detachable cleats, studs, or spikes affixed into nylon soles. Generally, smaller studs in a denser formation help to prevent ankle and knee injuries secondary to less penetration of the cleat into the playing field. In addition, weight distribution is better in multistudded designs.

Soccer

Soccer involves mainly running, kicking, jumping, sliding, stretching, and multidirectional movements. The playing surfaces are natural grass and artificial turf. Soccer is played almost entirely by the feet, with the ball being kicked off the medial, lateral, and dorsal aspects of the foot. Soccer shoe lasts tend to be snug fitting, often using European lasts, which are somewhat narrower than American lasts. Thinner soft leathers are preferred for the upper because players like to feel the ball, but the tongue should be well padded to reduce lace pressure and to cushion the dorsal kicking area of the foot. Some players use the tongue and lace area to produce spin and control the ball ( Fig. 26-12 ). Soles should be flexible at the metatarsophalangeal joints for running and have torsional stability.

 
 

Figure 26-12  Soccer shoes.

 

 

Football

Running is the primary motion in football, along with quick lateral movements and the production of great forces secondary to blocking and hitting. Studies have shown that injuries may be caused from wearing fewer, longer cleats, which produce excessive pressure beneath the cleats from increased foot fixation.[1] More specifically, the excessive resistance to rotation causes knee injuries during the twisting motions of football. The maximal diameter of a cleat tip should be seven sixteenths of an inch, and the maximal overall length is one-half inch. A seven-stud pattern is preferred on natural grass. Nylon soles are preferred because they shed dirt easily and prevent caking of mud between the studs. Multistudded rubber soles are common on natural grass.

Shoewear exists for linemen, backs, and kickers. Uppers for linemen must provide support and protection. High-cut or semi-high-cut boot designs are preferred. A sturdy toe box and firm heel counter are recommended. Astroturf linesmen's shoes are multistudded for grass and have shorter, more numerous studs for traction and stability.

The uppers used for backs are similar as for linemen. For added mobility, a low-cut design usually is preferred. Lightweight Astroturf shoes with nylon or cotton mesh uppers reinforced with suede are popular. These shoes usually have a rubber outsole with a waffle design that wraps up at the toe and front quarter for better lateral support.

For placekickers, a shoe with a square toe box usually is hand made for the kicking foot and conventional for the nonkicking foot. The shoe usually is custom made for the individual kicker at the professional level. A soccer shoe usually is preferred for kickers who kick from the side of the foot. For punting, either a soccer or a back's shoe is used. Some players kick in a traditional football back's shoe ( Fig. 26-13 ).



 

Figure 26-13  Football shoes.

 

 

Heidt et al.[10] evaluated the shoe-surface interaction in anterior translation and rotation of 15 football shoes produced by three manufacturers. The shoes evaluated in this study included traditional cleated football shoes, court shoes, molded-cleat shoes, and turf shoes. No overall differences among shoes on grass versus Astroturf were reported. There were significant differences noted for cleated and turf shoes. Shoes tested in conditions for which they were not designed were found to have excessive or extreme minimal friction characteristics that could be unsafe.

Torg et al.[11] found that an increase in ambient temperature could affect shoe-surface interface friction and potentially place the knee and ankle at increased risk of injury. They tested artificial turf football shoes, a natural grass soccer-style shoe, and a basketball-style turf shoe. Only the basketball-style shoe could be called “safe” or “probably safe” at all five temperatures studied.

Lambston et al.[12] reported on a study of football cleat design. The four major football shoe styles in the study included edge (longer irregular cleats placed at the periphery of the sole and smaller pointed cleats placed at the interior), flat (cleats in the forefoot area are the same height, shape, and diameter, similar to a soccer shoe), screw-in (seven screw-in cleats 0.5 inches in height and diameter), and pivot disk (10-cm circular edge on the sole of the forefoot with one 0.5-inch cleat in the center) type shoes. The edge design was found to produce a higher torsional resistance than the other three designs combined. This higher torsional resistance was associated with a significantly higher rate of anterior cruciate ligament injuries.[12]

Baseball

The sport of baseball requires sprinting, throwing, and complex batting movements. The playing surface usually is natural but may be artificial turf with dirt or clay on infield base paths. A traditional baseball shoe has a U-throat, and a conventional lacing system is the ultimate design. Lasts are similar to those used for a football shoe. On natural turf, steel cleats with a design of three in the front and two in the heel are used extensively. Removable cleats are available in steel, PU, and nylon. For pitchers, a pitching toe often is added for toe-drag reinforcement.

Rugby

The movements in rugby are similar to those of a football lineman or back. A drop kick is used, but the ball must touch the ground before it is kicked. The surface is natural grass. The rugby boot is similar in design to a soccer shoe with four front cleats and two heel cleats. A semicut or three-quarter cut style commonly is used for ankle protection. For linemen and some wing quarterbacks, a hard, square toe box is used. Multistudded versions of rugby boot models also are made for firm playing surfaces.

 

Winter Sports

Skating

Skating mechanics are similar for all skating events, although footwear and blades are specialized. Ankle movement and support are essential to skating performance. However, the subtalar joint must be free to allow positioning of the blade on the ice.

The traditional leather boot and the injection-molded model are the two main types of boots available. A leather boot should have good ankle support and a firm heel counter with elongation of the medial side. Uppers are made from thick-grade leather or split leather, with a leather or textile lining that gives the foot and ankle stability but allows some flexibility. Metal eyelets are used in the lower portion of the throat, and metal hooks above the ankle.

Ice hockey skates were the first to use injection-molded models. A viscous plastic is injected under pressure into molds to form the lower and upper parts of the boot. The two parts are placed together, completing a hinged outer shell. A soft foam liner then is added.

The hinged, two-piece design gives the boot some of the lateral flexibility needed in ice skating. Leather boots tend to become more flexible with age.

Figure skating

Figure skating requires the athlete to jump, skate, balance, spin, dance, and lift. The performing surface is the ice on artificial or natural rinks. The upper is either full- or top-grain cowhides. Good-quality boots are lined with lightweight, top-grain leather or suede. A firm heel counter, usually elongated on the medial side for added arch support, is important. Soles are PVC or PU molded units with a shank for added support. Screw-in blades often are used so that the position of the blades may be changed. The lasts used in figure skating are semipointed, with a narrow shank and heel to contain the foot and maintain position.

The quality of the blades helps to determine the quality of the skate. Blades commonly are made of tubular steel or plastic frame with high-tempered steel that is hollow ground to give two skating edges to the blade. The blades can be nickel- or chrome plated. Figure skating and free-style blades have a front to back curvature called a radius or rocker. The placement of the blades usually is slightly medial to the midline of the sole. For jumps or spins, a toe rake or pick is used. With forward motion, the picks also can help to prevent the blade from sliding sideways. For figures, a pair of skates without a pick and with less sharply ground blades often is preferred.

Ice hockey

Ice hockey requires skating, quick stops, quick turns, and balance on the ice of artificial and natural rinks. A high-cut model of leather or ballistic nylon with leather reinforcement is available. A good skating boot requires a firm, protective, leather toe box of polyethylene or firm fiber and comfortable ankle padding, with a high cut over the Achilles tendon for protection. A molded boot with a hinged upper can provide additional protection and durability. High-grade boots have a leather lining.

The goalie wears a specially designed molded or leather boot with a protective casing. The boots have a low-cut design at the ankle, which allows increased flexibility and also accommodates goalie pads. The blades are thick and reinforced, with increased surface area in contact with the ice to block shots at the goal.

Speed skating

Speed skating requires balanced skating with a low center of gravity in the lunge position. Skaters often compete with bare feet in skates. The skating surface is ice on artificial or natural ice tracks. The uppers have a deep-cut U-throat with a full lacing pattern to the toes. A three-quarter ankle boot is the preferred design, with a firm heel counter elongated on the medial side.

Thin (one-sixteenth inch), straight blades of either tubular steel or plastic frames are used. The blade is long (30 to 45cm) and is placed distal to the skating boot via a high-profile frame to allow a lean of low angle between the skate and the track. Higher-quality blades are chrome plated.

Alpine skiing

Alpine skiing requires ankle and knee flexion, forward lean, and balance on snow-covered surfaces. Ski boots provide a high-cut upper of a hinged or one-piece, injection-molded plastic, outer shell to support the lower leg. The boot should provide rigid support for the foot and ankle and allow forward ankle flexion. Adjustable buckles, dial closure devices, or straps are used for instep support and a comfortable, snug fit. More recently, rear-entry and midentry boots have eliminated buckles and overlaps on the vamp, instep, and ankle regions to reduce pressure. Inner liners can contain a foot bed, a variety of wedges, or adjustable canting devices. To relieve pressure, conforming foam or pressure-flow bags can be used ( Fig. 26-14 ).

 
 

Figure 26-14  Ski boots.

 

 

Ski boots are one of the last categories of athletic footwear to accommodate the female athlete. Important design differences include an elevated heel for a shorter female Achilles tendon, easier forward flexion, and a more flared ankle cuff.

Cross-country skiing

Cross-country skiing requires fast walking movements, running, jogging, downhill skiing, and balance on snow-covered terrain. Boot and bindings act together as a hinge between the foot and the ski and must be compatible. Boots are made of leather, Gore-Tex, nylon, or poromeric materials that allow air to circulate and transpire. Boots should be waterproof, as seam free as possible, with rigid heel counters. Good forefoot flexion is essential. Rubber soles are preferred for use on snow and ice.

 

Other Sports

Aerobic dancing

Aerobic dancing requires stationary running, skipping, jumping, stretching, dancing, and stair climbing. The dance surface is on carpet or covered surfaces. The shoe requirements are a combination of a lightweight, shock-absorbing running shoe and a modified indoor court shoe. Medial and lateral support is needed, as well as a wrap-up toe and heel protection. The forefoot requires stabilization and good shock absorption. EVA and PU combinations, air systems, and gel are used in shock-absorbing forefoot pads. Flexibility in the forepart is important.

Bicycling

Bicycling involves use of the gluteus, quadriceps, hamstrings, and calf muscles to generate the power necessary to perform upward and downward thrusts through the forefoot. The foot often is placed into a valgus or varus position on the pedal, causing pressure to develop on the lateral or medial sides of the foot. Cleat and pedal placement can be changed to prevent this canting.

A cycle racing shoe has a last similar to that used for a sprinting shoe, with a wide girth, semipointed toe, narrow waist, and narrow heel. A high toe box is required for toe movement. Uppers usually are made of smooth calf or kid leather with perforations for ventilation. Racing shoes usually are unlined and tend to stretch. Rigid soles are made of reinforced steel, nylon, or PU and can protect the foot from pedal pressure. Depending on the system, shoes are affixed to pedals by cleats, which improve cycling efficiency by locking the foot to the pedal for upward and downward thrust. Most shoes have adjustable cleats, permitting angular and fore and aft adjustments ( Fig. 26-15 ). Clips hold the foot to the pedal, but clipless systems are available.

 
 

Figure 26-15  Cycle racing shoes.

 

 

 

Injuries Related to Athletic Footwear

A properly designed and constructed athletic shoe can help to protect athletes from both external and internal forces that may lead to injury.

Toes

Ingrown and black toenails (subungual hematoma) are common problems seen in athletes and usually are the result of tight-fitting shoes or shear forces that cause the toes to abut the end of the toe box. An adequate high and wide toe box and proper shoe fit should reduce the incidence of this injury.

Corns result from pressure on the toes from the toe box. If the athlete has hammertoes, then the proximal interphalangeal joint is more prominent, and a corn can result in this location. A high toe box and proper shoe fit usually eliminate this problem. The use of various pads, splints, and lambs wool can be helpful.

Forefoot

Blisters

Blisters are caused by friction of the skin's rubbing against a shoe, sock, or other material. Applying a piece of moleskin or paper tape can be helpful. A cushioned liner such as Spenco (Spenco Medical Products, Waco, TX) may help to cut down on shearing and sliding inside the shoe.

Calluses

Similar to corns, calluses are hyperkeratoses caused by friction and pressure that may or may not be painful. Calluses may occur over the ball of the foot at sites of pressure on the skin from underlying bone. A cushioned shock liner can help to equalize the weight load. Calluses may be pared, and pads made from adhesive felt or foam rubber may be placed proximal to the callus. A Spenco insole, contoured anatomic foot bed, or other shock-absorbing and friction-reducing materials are used in many athletic shoes to prevent calluses. Following proper lacing techniques will help to improve foot stability and reduce shear forces between the foot and the shoe.

Metatarsalgia

Metatarsalgia is a nonspecific diagnosis that describes pain in and about the head of the metatarsal, metatarsophalangeal joint, and adjacent soft-tissue structures. Metatarsalgia can result from atrophic fat pad, basic anatomy of the metatarsals, increased pressure on the metatarsal heads, neurologic dysfunction, postsurgical changes, metabolic disorders, and inflammation. A well- cushioned liner and midsole material in addition to a rocker sole, which allows the athlete to roll off the painful forefoot, can be useful.

Sesamoiditis

The sesamoid bones are prone to injury because of their location under each big toe joint. Cavus feet, equinus of the first metatarsal, or rigid foot can cause excessive pressure to be placed on the sesamoids. A shoe with a good, shock-absorbing, midsole material extending out into the forefoot must be worn to protect the area. A rocker sole can be helpful. Orthotics that incorporate a sesamoid pad placed just proximal to the injured sesamoid to float the painful area is a useful way to treat this problem.

Interdigital neuroma

The most common location for an interdigital neuroma is in the third webspace. Excessive pressure on the ball of the foot or a shoe that does not fit well in the girth may contribute to this problem. A shoe with excellent shock-absorbing properties that extend out into the forefoot must be worn to protect the area. A rocker sole can be helpful. Orthotics incorporating a metatarsal pad placed just proximal to the involved webspace to help spread the metatarsal heads can take pressure off of the inflamed nerve.

Nerve entrapment

Cutaneous nerves, including the sural, saphenous, deep peroneal, and superficial peroneal nerves, can lie under pressure areas of an athletic shoe and result in a painful nerve irritation. Their location makes them vulnerable to compression. Nerve compression is a direct result of wearing irritating or tight-fitting shoes. Ski boots and ice skates are the two major types of athletic footwear that produce this problem. To avoid this problem, shoes should be padded, lacing techniques modified, and careful shoe fit followed.

Heel

Plantar Fasciitis

To prevent this common injury, a shoe must have excellent shock-absorbing abilities in the heel. A varus heel pad or wedge also can be indicated to decrease forces on the medial aspect of the heel. Once the problem develops, heel cups, foam pads with a cutout, or orthotics with a well-cushioned heel and a well to float the painful area can be indicated. A shoe with a firm medial heel counter can decrease pronation and stress on the plantar fascia.

Bursitis

The retrocalcaneal and pre-Achilles bursa can be irritated during sports. This disorder can result from poor shoe fit, an ill-padded heel counter, or excessive heel motion. The athlete should be advised to buy a shoe with well-padded heel counter, an Achilles notch that accommodates the Achilles tendon in plantarflexion, and an adequate heel height of at least 15mm.

Achilles Tendon

Low heel elevation in an athletic shoe often is a factor in the development of Achilles tendinitis. To prevent irritation of the tendon, a shoe with a well-padded Achilles tendon pad or notch should be worn. Heel lifts can be worn to elevate the foot in the shoe and reduce tension on the tendon. A firm heel counter can reduce the side-to-side motion of the heel and the Achilles tendon, thus reducing irritation of the tendon.

Ankle

Sports involving walking, running, or jumping often can result in inversion injuries to the ankle. If an athlete has a tendency to inversion injuries of the ankle, a shoe should be worn that has a firm heel counter, a moderately flared heel for a runner, and the stability of a high-cut model rather than a low-cut model for field or court sports. Hockey skates and alpine ski boots should provide good ankle support. Taping, various shoe wedges, braces, and orthoses all are used in the treatment and prevention of ankle sprains.

 

Conclusions

Each year athletic shoes tend to get better. In the last 10 years, motion control has improved, shock absorption has followed a pendulum and found its middle ground, and the trend is toward lighter materials. Although maximal foot speed may increase slightly in a lighter shoe, protection of the foot must not be compromised. Footwear should be designed to enhance athletic performance and prevent overuse.

 

References

  1. Torg JS, Quendenfeld T: Effect of shoe type and cleat length on incidence of severity of knee injuries among high school football players.  Res Q1971; 42:203.
  2. Valiant GA: The effect of outsole pattern on basketball shoe traction.   In: Terauds J, Gowitzke BA, Hole LE, ed. Biomechanics in sports III & IV,  Del Mar, CA: Academic Publishers; 1986.
  3. Milgrom C, et al: The effect of shoe sole composition on in vivo tibial strains during walking.  Foot Ankle Int2001; 22:598.
  4. Clarke TE, et al: The effects of shoe design parameters on rear foot control in running.  Med Sci Sports Exerc1983; 15:376.
  5. Alexander RM: How elastic is a running shoe?.  New Sci1989; 123:45.
  6. Kerr RF, et al: The spring in the arch of the human foot.  Nature1987; 325:147.
  7. Garrick JG, Requ RK: Role of external support in the prevention of ankle sprain.  Med Sci Sports Exerc1973; 5:200.
  8. Robinson JR, Frederick EC, Cooper LB: Systematic ankle stabilization and the effect on performance.  Med Sci Sports Exerc1986; 18:625.
  9. Barrett JR, et al: High versus low-top shoes for the prevention of ankle sprains in basketball players. A prospective randomized study.  Am J Sports Med1993; 21:582.
  10. Heidt RS, et al: Differences in friction and torsional resistance in athletic shoe-turf surface interfaces.  Am J Sports Med1996; 24:834.
  11. Torg JS, Stilwell G, Rogers K: The effect of ambient temperature on the shoe-surface interface release coefficient.  Am J Sports Med1996; 24:79.
  12. Lambston RB, Barnhill BS, Higgins RW: Football cleat design and its effect on anterior cruciate ligament injuries. A three-year prospective study.  Am J Sports Med1996; 24:155.