Purpose of Soccer Shoes With Sock Liner

1. Introduction

Soccer has become a very popular game in the world. It is the most played, most watched and most revenue-generating sport. For players to be successful they need a high skill level in handling the ball during receiving, running with the ball and kicking. Quickness on the field with rapid accelerations and decelerations as well as during cutting movements has become increasingly important in the modern game of soccer. Footwear plays an important role in assisting the player to perform fast movements on the field, providing comfort and protecting the foot during kicking. Therefore, it is surprising how little research has been published in the field of soccer shoes. During the early days of soccer, English factory workers used their hard and long-laced leather work boots. Sometimes, players modified these boots by adding metal studs for better traction. In the late 1800s football boots replaced the work boots and six leather studs were added to the outsole for better traction. The hard leather soccer boots weighed more than 500 g and could go up to more than 1 kg in wet weather conditions. The lacing area still went over the ankle for better protection. During the world championship in 1954 Adi Dassler surprised the soccer community with shoes for the German National Team with a low weight of only 380 g. It was not before the 1960s that below the ankle football shoes were introduced. A continuous improvement in synthetic materials brings modern soccer shoes down to weights as low as 200 g without compromising traction and stability features. Sprinting speed, maximum ball velocity and even the kicking accuracy can be influenced by shoe design. Originating from game analyses and questionnaires about the desired properties of soccer shoes, a strategic research approach started in our biomechanics laboratory 10 years ago. A number of studies will be presented here, demonstrating how footwear design can enhance performance in soccer.

2. Game analyses

Soccer has become faster, more dynamic and players cover longer distances on the field. In 1954 Winterbottom reported running distances of only 3.2 km for soccer players during a game. Reilly and Thomas. (1976) found running distances of 8.7 km and Bangsbo et al. measured average distances of 10.8 km in 1991. Using satellite navigation (GPS) our laboratory determined the covered distances and speed profiles of different player types in professional and non-professional teams (Hennig and Briehle 2000). Seventy soccer players were analyzed in 14 different friendly games of different German soccer leagues. Five typical player personalities were identified in each team. These players were equipped with the GPS units (Garmin 12XL GPS). The five player positions found in most soccer formations are: classical one against one defenders, defense organizer (libero), playmaker, the wing players, and forwards. It was found that the playmaker and wing players showed the longest running distances of approximately 11 km during 90 min. The classical defender and defense organizer covered approximately 8% and the playmaker 5% less distance during a game. More interesting was the velocity profile of the players (Figure 1), showing how much distance was run at which speed.

The influence of soccer shoe design on playing performance: a series of biomechanical studies

Published online:

07 April 2010

Figure 1. Covered distances during a game by player position (movement speeds from 0 to 10 m/s).

Figure 1. Covered distances during a game by player position (movement speeds from 0 to 10 m/s).

Overall, the wing players had the highest physical demands in a game with the longest distances at the highest speeds. Between the first and the second half of the game players covered 4% more distance during the first half. The professional players (from five teams) covered on average 600 m more distance than the amateurs (nine teams). Using a computerized match analysis system, Di Salvo et al. (2007) studied 300 professional soccer players in 20 Spanish premier league and 10 champions league games during the 2002/2003 and 2003/2004 seasons. Compared to our GPS evaluation they reported only slightly higher average distances of 11.4 km across all positions. They also found the lowest distance for the central defenders, followed by the forward, and the largest covered distances for the central midfield (playmaker) and the wing players. They reported that the largest distances at high speeds were achieved by the wing players. These results are almost identical to our findings (Hennig and Briehle 2000).

An analysis of the women's against the men's game was performed by Althoff et al. (2010, this issue). Video analyses of the finals, semi-finals and quarterfinals of the world championship of the men in Korea/Japan (2002) and of the women in USA (2003) were conducted. Every action with the ball was characterized and localized on the playing field. It was found that women cover distances more by long passes rather than short range activities (dribbling, short passes). The women also use more headballs and try to get closer to the goal before trying to score. The authors concluded that the game strategy, as well as kicking techniques, are primarily determined by the difference in muscle strength between the genders, thus influencing movement speed and kicking power of the players.

3. Desirable soccer shoe properties

In spite of the world wide popularity of soccer, much less research has been published about soccer shoes when compared to running shoes. Nowadays, well established evaluation criteria for running shoes are available, mostly related to the prevention of overuse injuries rather than performance (Hennig 2008). Soccer shoes have to fulfill many more game-related demands and their design is more closely linked to performance.

A survey, looking at the most desirable features that players expect from their shoes, was sent out from our laboratory in 1998. Answers from 250 male soccer players showed us that there is primarily a demand for comfortable shoes, providing good traction and stability (Hennig 2006). From 11 shoe characteristics the players ranked their preferences from most desirable (1) to the least desirable (11) shoe feature. Shoe comfort was most important for our players, followed by traction and shoe stability. Ball sensing, often also referred to as touch or feel for the ball and low shoe weight are also shoe features of high interest to the players. Surprisingly, protection against injuries received a low ranking. It appears that players are much more concerned about performance aspects of the shoe rather than protection. Therefore, light weight and low cut shoes are the most favorable shoes for soccer players if comfort, traction and stability features are present. In 2006 the same questionnaire was sent out again and was answered by 73 male and 69 female soccer players. Figure 2 shows the priority list of the male soccer players and how the priorities did change from 1998 to 2006.

The influence of soccer shoe design on playing performance: a series of biomechanical studies

Published online:

07 April 2010

Figure 2. Priority ranking of most desirable soccer shoe properties from 1998 and 2006 (lowest value = best ranking).

Figure 2. Priority ranking of most desirable soccer shoe properties from 1998 and 2006 (lowest value = best ranking).

The most desirable features comfort, traction, and stability received even better rankings in 2006. Between 1998 and 2006 soccer became a more powerful and faster game. Good traction, stability and a low shoe weight support fast movements of the player on the field. Therefore, it is not surprising that these features received better rankings in 2006. The low priority values for kicking power and accuracy are not surprising because most players are not aware that a shoe could influence maximum ball speed or the precision of a kick. In the 2006 survey 69 female soccer players also ranked the most favorable shoe features. For the women comfort also had the highest priority and ball sensing as well as stability had similar values as rated by the men. However, traction features and low shoe weight were less important for the female players. Durability and injury protection were judged more important by the women but still belonged to the least important shoe features.

4. Evaluation of comfort

Fit and comfort are the most important properties that soccer players expect from their footwear. Using perception scale rating measures, it was shown that plantar pressure is the biomechanical load variable that subjects are best able to recognize and differentiate in running shoes (Hennig et al. 1996). Furthermore, plantar and dorsal pressures experienced by the foot were shown to be closely related to the perception of comfort (Jordan et al. 1997). Therefore, pressure distribution measurements are a good method to evaluate comfort in shoes. Using piezoceramic force transducers, we looked at the plantar pressures under the heel, midfoot, and forefoot in four different shoe constructions. Figure 3 shows the averaged peak plantar pressures of 18 subjects in these shoes. All subjects performed three repetitive trials for running, cutting movements and kicks on goal. The values from these three movements on the field were averaged and shown in Figure 3.

The influence of soccer shoe design on playing performance: a series of biomechanical studies

Published online:

07 April 2010

Figure 3. Peak pressure patterns in four different soccer shoe models (averaged across running, cutting and kicking).

Figure 3. Peak pressure patterns in four different soccer shoe models (averaged across running, cutting and kicking).

The results from shoe D demonstrate how well peak pressures can be reduced by modifying footwear design. The low pressures under the heel for shoe D were achieved by a curved heel bedding rather than a flat interface. A cupping of the heel distributes the acting force more evenly across a larger heel surface. Shoe geometry, placement of the cleats or studs, outsole construction and shoe plate stiffness influence the pressures under the foot. Pressure distribution measuring devices are helpful in the evaluation process for providing better comfort. In the same study we also determined the pressure patterns for seven different soccer specific movements. In Figure 4 the peak plantar pressure averages across our 18 subjects are shown for a cutting movement during a sudden change of direction.

The influence of soccer shoe design on playing performance: a series of biomechanical studies

Published online:

07 April 2010

Figure 4. Peak plantar pressures patterns during a cutting movement and under the support leg for kicking.

Figure 4. Peak plantar pressures patterns during a cutting movement and under the support leg for kicking.

High medial forefoot pressures can be observed under the first metatarsal head. These medial forefoot loads may lead to overuse injuries. Repetitive high impact loads on the foot are suspected to cause foot problems such as metatarsal stress fractures, metatarsalgia and interdigital neuroma (Hockenbury 1999). Nihal et al. (2009) identified a high incidence of first ray disorders for soccer players. Similar to our study, Eils et al. (2004) and Wong et al. (2007) measured the plantar pressures in soccer specific movements and both research groups concluded that the medial side of the plantar surface may be more prone to injuries in soccer. From a performance point of view, the knowledge about the loading pattern during cutting movements may also be used for designing soccer shoes with better traction. During a cutting movement traction is especially important for rapid changes in movement direction. Knowing that the medial forefoot exerts increased forces to the ground a larger penetration of the cleat or stud under this part of the foot will occur. Thus, the cleats under the medial forefoot are the most important outsole structures in providing the desired traction for better performance. The plantar foot surface of the support leg during kicking (Figure 4) experiences a completely different loading pattern. In this case the lateral fore- and midfoot areas experience the highest mechanical loads. Therefore, it is not a surprise that Sims et al. (2008) found a high incidence of fifth metatarsal stress fractures in soccer players. Again, the knowledge of the high lateral foot loads may help in improving the traction of the stance leg. Better stability of the stance leg through higher traction will improve kicking speed (Sterzing and Hennig 2008) and may also enhance kicking accuracy.

5. Traction and stability

Traction, after comfort, was ranked second among the most important soccer shoe features according to our players survey (Figure 2) on soccer shoe properties. Using mechanical devices for the measurement of soccer shoe traction properties is extremely difficult. In soccer we do not have uniform pressure distributions across the whole foot or even parts of the foot (Figure 4). Depending on the movement, time dependent pressure patterns will be present under the foot that cannot be reproduced or simulated by a mechanical device. Furthermore, cleat or stud shape and length as well as their arrangement across the outsole will modify the interaction of the shoe with the ground and produce different traction properties. Therefore, a functional traction test (FTC) was introduced in our lab in 1998 and was performed many times until today. The principle behind this functional traction test (FTC) is a very simple one. If subjects do not have the confidence in the traction properties of their shoes they will run slower on a given parcours. To avoid slipping they will run more cautiously. A FTC parcours should incorporate sections with multiple acceleration, deceleration, cutting and turning movements. From many FTC studies, carried out at our laboratory, we found significant differences in running times for stud type, stud geometry and stud length on the same parcours at a given weather condition. Sterzing et al. (2009) identified in a series of eight studies between 2002 and 2007 the effects of different footwear and surface conditions on running performance. Removing studs from the outsole resulted in as much as 26% slower running times. Stud type and stud geometry influenced running times on artificial surface by almost 3% and different surface conditions (ice and snow versus dry firm grass) resulted in running time differences of approximately 20%.

6. Maximum kicking speed

During maximum full instep kicking contact times of approximately 10 ms and peak forces of almost 3000 N were found using 5000 Hz high speed cinematography (Shinkai et al. 2009). Hennig and Zulbeck reported in 1999 that soccer shoe construction has an influence on maximum kicking speed during full instep kicks. Although the possible gain in maximum speed is only a few percent, it may still be the centimeters that the goal keeper would need, to reach the ball with his hands. Ball velocity is dependent on the impulse transfer from the leg to the ball. Assuming an impacting effective foot/leg mass of 3 kg and a foot speed of 80 km/h a resting ball (450 g) would be accelerated to more than 500 km/h if a full momentum transfer and no energy loss would occur. In real life, however, top soccer players may achieve maximum speeds of 130 km/h. Tsaousidis and Zatsiorsky (1996) pointed out that the foot to ball interaction cannot be modeled as a pure impact situation. It is also determined by a throwing-like movement, because the foot follows the ball after initial impact for more than 25 cm. The authors concluded that more than 50% of the ball's speed is determined without the contribution of the potential energy from ball deformation. Sterzing and Hennig (2008) performed a number of experiments to investigate soccer shoe properties on kicking speed. Better shoe traction for the stance leg improved kicking speed, whereas outsole stiffness and shoe weight did not have an influence. Amos and Morag (2002) found higher foot velocities during kicking in shoes with a lower mass. However, our group did not find a higher maximum ball velocity with lighter shoes. Shoe weight increases the impacting mass and thus apparently compensates for the lower velocities when kicking in shoes. Surprisingly, soccer players achieved higher maximum kicking velocities with their bare feet. The cinematographic analysis showed that during barefoot kicking the players have a higher degree of foot plantarflexion. This seems to allow a stronger mechanical coupling between the foot and the lower leg. As a consequence, the higher effective impact mass results in a larger impulse and increased kicking speed.

7. Kicking accuracy

Good precision in passing and kicking belongs to the most important skills in soccer. However, most players are not aware that a shoe can influence kicking accuracy. This is probably the reason why until recently (Hennig et al. 2009) there is no documentation of such research. Although it is well known from tennis that an increase in racket string tension will increase ball rebound accuracy, a similar principle was never applied to athletic footwear in ball games. It is common knowledge that inside kicks with a larger contact area between ball and shoe have a better precision than instep kicks. Why should the shape and the friction properties of the shoe upper not have an influence on kicking accuracy? We speculated that six shoe related factors could potentially influence kicking accuracy.

1. A more even pressure distribution across the ball will enhance kicking accuracy.

2. More friction between the shoe and the ball will prevent slipping during contact and thus cause better precision.

3. Spin production of the ball will cause a more stable path of flight in the air and thus be beneficial.

4. Better skin sensation increases the 'touch' of the ball and will enhance accuracy.

5. Stability of the body through better shoe traction of the stance leg will reduce movement variability and result in better accuracy.

6. Increased shoe mass on the kicking leg will cause a higher moment of inertia, stabilize the path of the foot, and thus enhance precision.

To test these hypotheses, we wanted to find out whether the effect of footwear is big enough to make a difference. We first looked at instrumentation to record precision in kicking. Finnoff et al. (2002) described an accuracy measuring method for testing players kicking skills and for training purposes. They applied Carbon paper on a plywood target and evaluated the marks, left by the ball during impact with the board. However, this is a laborious procedure, requiring much time and manpower for the evaluation. Therefore, we built a circular electronic target with a diameter of 120 cm. Thirty electrically conducting wires were fastened in a concentric pattern on a wooden board. During contact with the board electrostatic charges are transferred from the ball surface to the wires. Each of these wires is connected to a charge amplifier. The 30 amplifier outputs are sampled at a frequency of 2 kHz with a data acquisition system, and the center of the charge distribution across the wire arrangement was determined. In our first study we investigated the effect of five different shoe modifications and barefoot kicking on kicking precision (Hennig et al. 2009). During barefoot kicking socks were worn on the kicking leg to avoid skin pain as a consequence of friction between ball and skin. From a distance of 10 m the subjects had to perform best accuracy kicks to the center of the electronic target at a height of 115 cm above the ground. The mean accuracy from 20 repetitive kicks was determined in each of the six experimental conditions. The repeated measures ANOVA showed differences (P < 0.01) between the footwear conditions. Barefoot kicking was found to be least accurate against each of the five footwear conditions (Figure 5).

The influence of soccer shoe design on playing performance: a series of biomechanical studies

Published online:

07 April 2010

Figure 5. Kicking accuracy (in cm from the target center) and standard deviations (SD) in 6 different footwear conditions (**^,++ P < 0.01, *^,+ P < 0.05).

Figure 5. Kicking accuracy (in cm from the target center) and standard deviations (SD) in 6 different footwear conditions (**^,++ P < 0.01, *^,+ P < 0.05).

Therefore, good skin sensation for perceiving the touch of the ball does not seem to enhance accuracy. Uneven pressures across the ball to foot surface, caused by anatomical structures (bony prominences) could be one of the reasons for the lower kicking accuracy. The shoe upper material distributes the local pressure peaks above the bony prominences across a larger area and thus creates a more homogenous pressure distribution. Between the shoes, model C was significantly better in accuracy as compared to the four other footwear conditions. To follow up on the idea of homogenous pressures, we compared the dorsal pressures from shoe C against shoe model D. A Pedar (Novel Inc.) pressure distribution measuring insole was positioned on the upper of the shoes. Using an elastic rubber band, the insole was positioned and fastened to the medial mid- to forefoot of the shoe, where players hit the ball during instep kicks (Figure 6).

The influence of soccer shoe design on playing performance: a series of biomechanical studies

Published online:

07 April 2010

Figure 6. Attachment of the 'Pedar' pressure measuring insole to the upper of a soccer shoe.

Figure 6. Attachment of the 'Pedar' pressure measuring insole to the upper of a soccer shoe.

During instep kicks on the electronic target the pressure distribution between ball and shoe upper was measured for 20 subjects at a frequency of 571 Hz for both shoes. The peak pressure patterns across all subjects showed that shoe C showed on average lower pressure differences between adjacent transducers. From further studies on kicking accuracy we concluded that avoiding high pressure gradients across the foot during ball contacts is the main factor in achieving better kicking precision.

8. Conclusions

Soccer shoe research is still in its infancy. As compared to running shoes that were investigated thoroughly over the last 25 years, little is found in the literature about soccer footwear requirements and design. Soccer has become much more dynamic, and the players are much more athletic than in the past. Substantial differences exist between the women's as compared to the men's game, which should result in different footwear for female and male players. There are differences in foot anatomy and a much higher risk of knee injuries for the women. They also use different game strategies, primarily caused by their lower muscle strength and a less aggressive play. As compared to running shoes soccer footwear has to fulfill different demands. Traction and stability features of the shoes guarantee fast movements, cuts and turns for the players. But the shoe is also used for kicking. Touch of the ball and low shoe weight are on the wish list of soccer players. Most important for them, however is comfort and shoe fit. In-shoe pressure distribution measurements are well suited for assisting in the design of comfortable shoes. Traction and stability properties of soccer shoes can efficiently be evaluated with a functional traction test. Although most soccer players are not aware of it, kicking speed and accuracy can be influenced by footwear design. The challenge in soccer shoe design is to combine these performance-related properties with injury protection features.

Purpose of Soccer Shoes With Sock Liner

Source: https://www.tandfonline.com/doi/full/10.1080/19424281003691999

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