In the early days football boots weighed approx. 500 grams when dry and twice as much when wet. Manufacturers when made aware player’s boots were only in contact with the ball for about 10% of the game developed less heavy boots. Lighter footwear meant players were less exhausted and subsequently the overall speed of play increased. This made for a more enjoyable spectator sport. By the early 50's the soccer boot was streamlined with the ankle hugging component reduced to below the malleoli (ankle bones).
Initially this met with some concerns about ankle injuries but proved ill founded. The traditional soccer boot was now a slipper or soccus. Leather soles were first replaced by molded rubber, then injection molded PVC, before nylon and plastic prevailed. The new synthetic materials were waterproof, cheap to produce and substantially lighter than leather. The upper of the slipper became thinner and improved treatment of leather with synthetic waterproof compounds contributed to the development of the new styles. Development of latex foam, meant the soccer shoe could be cushioned with no detriment to overall mass and new lightweight synthetics were stronger and harder wearing than traditional soles. By the 60s the overall weight of the new era of boots dropped significantly.
The physical properties of kangaroo skin were recognised very early in the 19th century and most quality sports footwear was made from marsupial's skin. This tradition has quietly continued in soccer shoes and now most quality shoes are made from medium brown, vintage kangaroo leather. This is a name given to the process of tannage (preparing the leather) and often the leather is dyed to popular colours. Kangaroo hide is the toughest and most durable available and been used to produce quality sports shoes for rugby, American football, baseball, basketball, tennis and cycling shoes for over a century. It is lightweight yet very strong and many times stronger than the same thickness of cowhide. Comfortable and supple it requires no break-in period and gives the player a tight fit with optimal feel for the ball. Suitably treated Kangaroo leather is favoured because of its high performance nature. Kangaroo leather has a naturally high strength-to-weight ratio. In the 80's, Australia's CSIRO undertook independent tests which confirmed these findings and determined that, when shaved to 20% of its original thickness, kangaroo leather retains between 30% and 60% of its original tensile strength, as compared to a retention rate of 1% -4% for calf and bovine leathers. In a further study by the CSIRO, it was found that kangaroo leather was at least 50% stronger than goatskin gloving leather in tear strength and puncture resistance. Microscopically the hide displays high uniform orientation of fibre bundles in parallel with the skin surface. The skin of the Kangaroo does not contain sweat glands or erector pili muscles, which would weaken the skin surface. The yellow elastic fibres (elastin) are evenly distributed throughout the skin thickness which gives the leather greater tenacity. These properties remain even when the leather is split. Tanning further enhances the leather's properties by unsticking the fibre bundles thereby allowing them to move independently.
From time to time animal rights activists have brought the use of kangaroo skin to the public's attention by condemning players like David Beckham, who initially endorsed their use. Reputable firms collect kangaroo hides during the Kangaroo Harvest and agencies such as Environment Australia - Wildlife Protection regulate and control the harvest and manufacture of all kangaroo leather. There are several tyoes of kangaroo and only non-endangered species can be used for the clothing industries. Public concern however encouraged development of the pleather industry and many top quality boots now incorporated plastic polymers as an alternative to animal leathers.
According to Grau (1997) the focus of boot research from the 70s was primarily directed at anti-pronatory control (preventing the foot from rolling over). This was combined by using cushioning mechanisms to damped shock to the foot. Later researchers looked at torsion and pressure distribution across the foot. Initially it was wrongly assumed overloading of the weightbearing foot was the primary cause of most injuries. This research led to shoe design thought to cope with the problems but the number of reported injuries did not decrease. Moreover it seemed, in retrospect, many reported injuries arose as a result of the injury preventing solutions in boot design. Many injuries are attributed to adverse physical conditions at the interface between the soccer shoe and the playing support surface. No shoe can ever guarantee full protection against serendipitous injury. The function of the soccer boot provides both a means of attachment to the playing surface whilst encasing the foot for protection. The maintenance of static balance for a player performing an individual skill demands a significant level of torque. Excess torque or twist passes proximally through the foot pedestal to damage the ankle or knee. During contact, a static foot anchored to the ground negates its ability to dampen down (shock absorb) external forces, such as caused by contact with another player. The ankle and knee then have to absorb the energy of impact; alternatively torque within the short bones of the foot may cause them to fracture. This type of incident was illustrated by injury to England's captain David Beckham during the FIFA World Cup Korea Japan 2002 game against Sweden in the opening round.
Grau S 1997 Quo vadis sport-shoes? Wish and reality of preventing injuries through sport shoes Third Symposium on Footwear Biomechanics, Tokyo 1997 International Society of Biomechanics.