Slip resistance of shoes in relation to walkway surfaces is of importance to forensic science. Pedestrians adapt to changes in shoe construction, walkway, and interface characteristics by altering patterns of movement. The instantaneous ratio of tangential to normal ground reaction forces (required coefficient of friction) is affected by such movement alterations. Slip probability depends on the ratio of required to available coefficient of friction (μr/μa). However, there are practical problems in application of this concept. Adequate assessments of the safety of footwear/walkway-surface interactions should take into account subject tests of μr in actual walking scenarios as well as material tests of μa and relevant footwear/walkway characteristics. Based on the literature, this paper discusses the relationship of μr to top-piece/outsole hardness and walking speed. A pilot experiment is described in which subjects walked across a force plate at a series of increasing speeds wearing shoes with the top-piece/outsoles replaced by various test materials. Correlations of μr versus top-piece/outsole hardness and walking speed are presented from data analysis of a single representative subject. The paper explores how biomechanical adaptations of the subject to his foot-wear may account for the fair-moderate correlations observed.
In recent years, alpine ski boots have increased in height and in lateral and medial stiffness. As a result of these changes, the forces experienced by the lower leg, and the resulting injury pattern, have changed. Fractures and sprains of the ankle and spiral fractures of the tibia have declined significantly. In order to understand more fully the nature of these forces, a normal ski boot was modified by the inclusion of twelve transducers. These transducers measured forces in various areas on the lower leg, as well as under the forward part of the foot and the heel. The knee angle and the ankle flexion angle in the sagittal plane were also recorded. The instrumentation required was completely portable and weighed approximately 6 kg. A test skier made a number of runs with the equipment in place. The results show that, as the skier drove his knee forward, the forces on the frontal area of the tibia increased. The forces on the heel and forward part of the foot also increased. In going through a turn, the heel thrust took place first, followed by an increase in force in the forward part of the foot. The slalom turns show a more inconsistent, or rapidly changing, pattern of force application than the giant slalom turns.
Pressure-induced pain is an important parameter in skiing safety. Pain is a complex phenomenon that includes not only the sensations evoked by tissue-damaging stimuli, but also the subject's response to those stimuli. Alpine skiers are willing to undergo “pain and discomfort” from their ski boots in order to improve their skiing performance. In this study, pressure-induced pain was applied to various areas of the foot and leg: the lateral and medial malleoli, the instep, the heads of the first and fifth metatarsals, the tibia, and the heel. The first six areas are regions of bony prominences, while the heel is an area that can undergo soft tissue damage from skiing in tight-fitting boots. Reliable and objective verbal descriptor pain scales have been developed that separate pain into two dimensions: the sensory and the affective. The sensory scale relates to the sensory discriminative aspects of pain, while the affective scale relates to the motivational and emotional aspects of pain. The pain-inducing pressure was applied with a hand-held plunger, in two testing sessions, one week apart. In one session the sensory scale was used, which contains such terms as weak and intense, and in the other session the affective scale was used, which uses such terms as unpleasant and excruciating. In each case, the subject determined the maximum value of force to be applied by indicating to the tester that the pain sensations were either “intense” or “excruciating.” At that time the force was removed and, later, random percentages (including a repeat application) of this subject-determined maximum force were applied to the same locations on the foot and leg of the same subject. Analysis of the data show this method to be a reliable technique for applying pressure-induced pain. A total of 15 subjects were used for the sensory testing session and 13 of those 15 for the affective testing. There were significant differences between locations of the foot and leg, with the tibia being the most sensitive and the heel the least sensitive.
Differences in slip resistance measurements under dry and wet conditions on the same smooth walkway surface may occur when testing with a Neolite®4-Test-Liner (NTL) test foot using the PIAST [Slip Test Mark II] and VIT [English XL] tribometers. To investigate the causes of these differences, two sets of NTL test feet (smooth and grooved) for each instrument were cut from the same piece of material. Slip-resistance measurements were made under both wet and dry conditions. The same operator was used for each tribometer, an observer monitored each test, and all testing was performed in the same room at the same time. The walkway surfaces were commercial floor materials. On dry surfaces, the measured slip resistance using the grooved test foot was the same or lower than the results using the smooth test feet. On wet surfaces, measured slip resistance using the grooved test feet increased slightly with the VIT and significantly using the PIAST. Averaged test results showed that the use of the grooved test feet on both instruments brought the readings these devices closer to each other; using the grooved test foot, the readings generated by the PIAST and VIT were not significantly different.
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