Thursday, February 12, 2009

Sports Shoes. Protective aspect of sports shoes & current concepts: part III

1. The protective function of sports shoes.
The shoe can be thought of as a powerful tool for controlling human movement. A well-designed shoe can assist in reducing the number of lower limb injuries arising from sport and training activities (9).
Barnes RA et al reviewed the types of injury acquired by sportsmen in both training and playing is then followed by a discussion of aspects of footwear design and their role in both contributing to and preventing lower limb injury. Finally, the paper considers support and shock absorption techniques in the context of footwear design (9).
Working on hip injuries Paluska recommends; coaches, trainers and medical personal who care for runners should advocate running regimens, surfaces, shoes, technique and individualised conditioning programmes that minimise the risk of initial or recurrent hip injuries (5). Running shoes are designed specifically for different foot types in order to reduce injuries. Running in the correct footwear matched for foot type may have a greater influence on mechanics when runners become exerted (4).
Butler RJ et al evaluated changes in kinematics and kinetics over the course of a prolonged run when low (LA) and high (HA) arched runners wear motion control and cushioning shoes. They found, in LA runners, MC shoes decreased tibial internal rotation compared to CT shoes over the course of a prolonged run. In HA runners, running in the CT shoes reduced tibial shock compared to the MC shoes (4).
A study by Larsen et al shows that it may be possible to prevent certain musculoskeletal problems in the back or lower extremities among military conscripts by using custom-made biomechanic shoe orthoses (6).
According to Thecker et al the most encouraging evidence for effective prevention of shin splints involves the use of shock-absorbing insoles (7).
van der Putten EP et basing on a biomechanical analysis, came up with a different approach to shoe design specifically for mountain climbing. They recommended
1. Regional thinning of the sole, which allows easy flexion and extension of the toes.
2. That the form of the shoe should conform to the natural form of the foot & the shoe closure should provide a close fit for feet with width differences of up to 20 mm. Further they developed a shoe-sizing system.
After testing the prototypes they concluded that the new shoe design can contribute to the prevention of foot injuries and deformations in sport climbing (8).
Lake MJ reviewed the typical biomechanical approaches used to identify protection offered by sports footwear during dynamic activities
Lake MJ recommended
1. Subject tests should be used in combination with standard mechanical techniques to evaluate footwear protection.
2. Impact attenuation characteristics of footwear during sporting activities were most distinguished by analysis of tibial shock signals in the frequency and joint time-frequency domains.
3. Lateral stability and traction properties of footwear are better assessed using game-like manoeuvres of subjects on the actual sporting surface.
Advances in tools allowing measurement of dynamic foot function inside the shoe also aid our assessment of shoe protective performance. In combination, these newer approaches should provide more information for the design of safer sports footwear (1).

Current issues in the design of running and court shoes:
2. a. Energy aspects:
Sport shoes can have an influence on the energetics of human movement. The two main aspects where sport shoes can play a role are in maximizing the energy which is returned to the athlete and minimizing the energy which is lost by the athlete. Maximum values of energy storage in a shoe sole are on the order of 10 J. However, not all of this energy is returned to the athlete as shoe midsoles lose approximately 30% of the energy input (2).
Strategy to minimize energy loss include (1) reducing the mass of the shoe, (2) using appropriate midsole materials which dissipate unwanted vibrations, (3) implementing constructions which improve the stability of the ankle joint and (4) increasing the bending stiffness of shoe midsoles which reduces the energy lost at the metatarso-phalangeal joint (2).
b. Performance aspects:
Depending on the movement, energy return form the sports shoe sometimes occurs at the wrong time, frequency, location and in the wrong direction which compromises the ultimate influence on improving performance. As a result, the actual influence that energy return has on performance is probably minimal (2).
Energy that has not been lost for tasks not directly related to the actual performance may be applied to the movement and may result in an increase of athletic performance. Stefanyshyn DJ et al have proposed that athletic footwear can have a much larger influence on performance by minimizing the energy which is lost as opposed to maximizing the energy which is returned.
3. Current concepts of sports shoe design:
Three most important functional design factors for sport shoes: injury prevention, performance and comfort. For running shoes, pronation control and cushioning are still considered to be the key concepts for injury prevention despite the fact that conclusive clinical and epidemiological evidence is missing to show the efficacy of these design strategies. Several design features have been proposed to be effective in controlling the amount of pronation. However, the kinematic effects of such features seem to be subject-specific and rather small especially when looking at the actual skeletal motion.
Recent running shoe research suggests that cushioning may not or only marginally be related to injuries and that cushioning during the impact phase of running may be more related to aspects such as comfort, muscle tuning or fatigue.
For court shoes, lateral stability, torsional flexibility, cushioning and traction control appear to be important design strategies to decrease the risk of injury. For court shoes, optimal traction seems to be the key factor for performance. Research in the area of shoe comfort is still sparse.
With respect to running performance, the shoe concepts of weight reduction, efficiency and energy return are important (as discussed above). The concept of energy return does not seem to be a feasible concept whereas concepts which aim to minimize energy loss appear to be more promising and successful, e.g. weight reduction, reduction of muscle energy required for stabilization.
Cushioning, fitting and climate concepts appear to improve the comfort of both running and court shoes.
References:
1. Lake MJ; Ergonomics. 2000 Oct;43(10):1610-21.
2. Stefanyshyn DJ et al; Sportverletz Sportschaden. 2000 Sep;14(3):82-9.
3. Reinschmidt C; Sportverletz Sportschaden. 2000 Sep;14(3):71-81.
4. Butler RJ; Gait Posture. 2007 Jul;26(2):219-25. Epub 2006 Oct 20.
5. Paluska SA; Sports Med. 2005;35(11):991-1014.
6. Larsen K; J Manipulative Physiol Ther. 2002 Jun;25(5):326-31.
7. Thecker SB; Med Sci Sports Exerc. 2002 Jan;34(1):32-40.
8. van der Putten EP et al; Appl Ergon. 2001 Aug;32(4):379-87.
9. Barnes RA; J Sports Sci. 1994 Aug;12(4):341-53.

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