Academic journal article Human Factors

Footwear Cushioning: Relating Objective and Subjective Measurements

Academic journal article Human Factors

Footwear Cushioning: Relating Objective and Subjective Measurements

Article excerpt

INTRODUCTION

Foot-ground interfaces exist in many different forms. Frequently the interface is a shoe or floor mat, and sometimes it is a carpet-like material, such as an Astroturf, providing specific biomechanical characteristics to help one perform effectively. Hence these interfaces can play an important role in improving functionality or performance, preventing injury, and reducing discomfort.

Human movement generally involves repeated loading at the foot-floor interface, resulting in force transmission through the human feet and toward the upper extremities. Proper cushioning attenuates these impact forces and protects the musculoskeletal system from potential injury (Schwellnus, Jordaan, & Noakes, 1990). The literature indicates that the term cushioning is used to describe only those aspects of the foot-floor interface that are concerned with reduction of the transmitted forces. As a result, the foot-floor interface literature is split into two distinct categories, related to injury and discomfort. In the biomechanics literature, injury has been linked to shock absorption, whereas the ergonomics literature primarily focuses on discomfort and has always made reference to the hardness or compression of materials, or both.

This paper is meant to develop a more unified approach to understanding cushioning. Aspects associated with cushioning - namely, injury, discomfort, and functionality - and their weaknesses will now be discussed.

Cushioning and Injury

Impact loads generated at the feet during activity have been implicated in a range of injury problems, such as stress fractures (Milgrom, Giladi, & Stein, 1985), Type 1 shin splints (Detmet, 1986), cartilage breakdown (Simon, Radin, Paul, & Rose, 1972), osteoarthritis (Radin, Paul, & Rose, 1972), knee injuries (Newell & Brainwell, 1984), and low back pain (Voloshin & Wosk, 1982). Hence, it is not surprising that a majority of consumers look for certain characteristics in footwear materials based on experience, prior injury, or marketing claims. As an example, the Japanese consider shoes' shockabsorbing properties to be the most important factor when used during sports activities (Hong Kong Trade Development Council, 1993). However, the definition of shock absorption and the range of its acceptable values are not clear.

In addition to the relationship between impact loads and injury, the literature also discusses footwear and injuries. For example, Gardner, Dziados, and Jones (1988) found that the running shoe age was a significant risk factor in the development of stress fractures. This finding has been attributed by Cook, Kester, and Brunet (1985) to the loss, with increased use, of either the mechanical-support or the shock-absorbing properties of the footwear midsole. Schwellnus et al. (1990) reported that neoprene insoles can significantly reduce the incidence of tibial stress syndrome through better shock absorption. Some have also found neoprene insoles to reduce transmitted forces better than viscoelastic insoles (Brodsky, Kourosh, & Stills, 1988). Note that the Nigg, Herzog, and Read (1988) study showed no reduction in vertical impact forces during running when viscoelastic insoles were compared with conventional running shoe insoles. In summary, even though the injuries experienced have been mostly repetitive strain injuries rather than acute injuries, the shock-absorption property has been identified as a primary factor in the prevention of injury. In the engineering literature, shock absorption is generally related to damping phenomena. However, the literature related to injury seems to imply that shock "absorption" is a reduction in impact force magnitude. Alternatively, it is meant to be a gradual increase in the load with slow deceleration (as opposed to an impact load, which is a rapid increase in load). Can the shock-absorption or deceleration property be perceived during running? …

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