Slip resistant properties of footwear on ice

The effect of tread patterns on slip resistance of footwear outsoles based on composite materials in icy conditions

INTRODUCTION

Falls on icy surfaces are the leading cause of injuries for outdoor workers. Footwear outsole material and geometrical design parameters are the most significant factors affecting slips-and-falls. Recently, composite materials have been incorporated into outsoles to improve traction, yet the best design parameters are not fully understood.

METHOD

In this effort, based on Taguchi orthogonal array design, 27 outsole prototypes were fabricated with different tread pattern features using our patented composites and tested in a simulated winter condition.

RESULTS

An analysis of variance (ANOVA) showed that surface area (p = 0.041, Contribution = 15.63%) was the only factor significantly affecting the slip-resistance of our prototypes. The best performance was observed for the maximized surface area covered by our composite material with circular and half circular plugs laid obliquely, mostly in the forefoot area.

PRACTICAL APPLICATIONS

These findings suggest that some tread design features of composite-based footwear have a great role in affecting slip-resistance properties of composite-based footwear.

Reducing fall risk for home care workers with slip resistant winter footwear

Falls on icy surfaces are the leading cause of occupational injuries for workers exposed to outdoor winter conditions. Slip resistant footwear has been shown to reduce the risk of falls for indoor workers but until recently, there was no accepted standard for evaluating the slip resistance of winter footwear on icy surfaces. Our team recently developed a lab-based testing protocol for measuring footwear slip resistance. This protocol, called the Maximum Achievable Angle (MAA) test, measures the steepest ice-covered slope that participants can walk up and down without experiencing a slip in a simulated winter environment. This lab-based protocol has found there is wide variability in the performance of commercially available winter footwear. In particular, we have found that a new generation of footwear that incorporates composite materials in the outsole, performs much better than most other footwear. The objective of this project was to investigate whether the footwear that performed well in our lab-based testing would reduce the risk of slips and/or falls in real-world winter conditions. One hundred and ten home healthcare workers from SE Health were recruited for this study and were asked to report their exposure to icy surfaces along with the numbers of slips and numbers of falls they experienced each week using online surveys over eight weeks in the winter. Fifty participants (the intervention group) were provided winter footwear that were among the best performing in the MAA test. The remaining sixty participants (the control group) wore their own footwear for the duration of the study. A total of 563 slips and 36 falls were reported over the eight-week data collection period. The intervention group consistently reported fewer slips (127 vs 436) and fewer falls (6 vs 30) compared to the control group. We found the slip rate in the intervention group was between 68.0% and 68.7% lower than the control group. Similarly, the fall rate was between 78.5% and 81.5% lower in the intervention group compared to the control group. These findings demonstrate that footwear that performs well in the MAA test can reduce the risk of both slips and falls in real-world winter conditions.

Standing balance on inclined surfaces with different friction

Working and walking environments often involve standing positions on different surfaces with inclination and different friction. In this study, standing balance of thirteen participants during sudden and irregular external perturbation to calf muscles was investigated. The aim of the study was to evaluate the combined effect of surface inclination and friction on standing balance. The main findings when eyes closed revealed that the standing utilised coefficient of friction (μ_SUCOF) increased when the surface was inclined for both high and low friction materials. The anterior-posterior torque increased more anteriorly when the surface was inclined toes down and when the surface friction was low. The results indicate that the anterior-posterior torque is a sensitive parameter when evaluating standing balance ability and slip risk. On inclined surface, particularly on the surface with lower friction, the potential slip and fall risk is higher due to the increase of standing utilised coefficient of friction and increased forward turning torque.

Slip resistance of winter footwear on snow and ice measured using maximum achievable incline

Protective footwear is necessary for preventing injurious slips and falls in winter conditions. Valid methods for assessing footwear slip resistance on winter surfaces are needed in order to evaluate footwear and outsole designs. The purpose of this study was to utilise a method of testing winter footwear that was ecologically valid in terms of involving actual human testers walking on realistic winter surfaces to produce objective measures of slip resistance. During the experiment, eight participants tested six styles of footwear on wet ice, on dry ice, and on dry ice after walking over soft snow. Slip resistance was measured by determining the maximum incline angles participants were able to walk up and down in each footwear-surface combination. The results indicated that testing on a variety of surfaces is necessary for establishing winter footwear performance and that standard mechanical bench tests for footwear slip resistance do not adequately reflect actual performance. Practitioner Summary: Existing standardised methods for measuring footwear slip resistance lack validation on winter surfaces. By determining the maximum inclines participants could walk up and down slopes of wet ice, dry ice, and ice with snow, in a range of footwear, an ecologically valid test for measuring winter footwear performance was established.

Evaluating Problems With Footwear in the Geriatric Population

Foot pathologies are common in nearly 80% of all elderly patients, and studies have indicated inappropriate footwear as one of the major underlying cause. It has been postulated that ill-fitting shoe wear affects plantar pressure, thus exacerbating weak balance. Complications arising from foot pathologies, which include difficulty in maintaining balance, have increased the risk of falls that can result in fractures and other serious injuries. The link between footwear and the onset or progression of certain foot pathologies has emphasized the need to explore and promote preventative measures to combat the issue. Wider and higher toe boxed shoes, along with sneakers, are examples of footwear documented to evenly distribute plantar pressure, increase comfort, and facilitate appropriate balance and gait. Ultimately, the use of appropriate footwear can help to better stabilize the foot, thus reducing the risk of sustaining debilitating physical injuries known to drastically decrease the quality of life among the geriatric population.

Assessing the performance of winter footwear using a new maximum achievable incline method

More informative tests of winter footwear performance are required in order to identify footwear that will prevent injurious slips and falls on icy conditions. In this study, eight participants tested four styles of winter boots on smooth wet ice. The surface was progressively tilted to create increasing longitudinal and cross-slopes until participants could no longer continue standing or walking. Maximum achievable incline angles provided consistent measures of footwear slip resistance and demonstrated better resolution than mechanical tests. One footwear outsole material and tread combination outperformed the others on wet ice allowing participants to successfully walk on steep longitudinal slopes of 17.5° ± 1.9° (mean ± SD). By further exploiting the methodology to include additional surfaces and contaminants, such tests could be used to optimize tread designs and materials that are ideal for reducing the risk of slips and falls.

Duration of slip-resistant shoe usage and the rate of slipping in limited-service restaurants: results from a prospective and crossover study

Several studies have indicated that slip-resistant shoes may have a positive effect on reducing the risk of slips and falls, a leading cause of injury at work. Few studies, however, have examined how duration of shoe usage affects their slip-resistance properties. This study examined the association between the duration of slip-resistant shoes usage and the self-reported rate of slipping in limited-service restaurant workers. A total of 475 workers from 36 limited-service restaurants in the USA were recruited to participate in a 12-week prospective study of workplace slipping. Of the 475 participants, 83 reported changing to a new pair of shoes at least once during the 12-week follow-up. The results show that slip-resistant shoes worn for less than six months were moderately more effective than those worn for more than six months. Changing to a new pair of shoes among those wearing slip-resistant shoes at baseline was associated with a 55% reduction in the rate of slipping (RR = 0.45, 95% CI = 0.23-0.89). Further research is needed to develop criteria for the replacement of slip-resistant shoes.

The influence of footwear sole hardness on slip characteristics and slip-induced falls in young adults

Theoretically, a shoe that provides less friction could result in a greater slip distance and foot slipping velocity, thereby increasing the likelihood of falling. The purpose of this study was to investigate the effects of sole hardness on the probability of slip-induced falls. Forty young adults were randomized into a hard or a soft sole shoe group, and tested under both nonslippery and slippery floor conditions using a motion analysis system. The proportions of fall events in the hard- and soft-soled shoe groups were not statistically different. No differences were observed between shoe groups for average slip distance, peak and average heel velocity, and center of mass slipping velocity. A strong association was found between slip distance and the fall probability. Our results demonstrate that the probability of a slip-induced fall was not influenced by shoe hardness. Once a slip is induced, slip distance was the primary predictor of a slip-induced fall.

Increased shoe sole hardness results in compensatory changes in the utilized coefficient of friction during walking

Based on mechanical testing, harder soled shoes have been shown to provide less available friction than soft soled shoes. Whether or not humans adjust their utilized coefficient of friction (COFu) and gait kinematics to accommodate the decrease in available friction while wearing hard soled shoes is not known. Fifty-six young adults participated in this study. Ground reaction forces, full body kinematics, stride characteristics and subjective perception of footwear slipperiness were recorded under both hard and soft soled shoe conditions. Paired t-tests were used to identify the differences between two shoes conditions. Results indicated that the peak COFu was significantly less when wearing the hard soled shoes compared to when wearing the soft soled shoes (0.23 vs. 0.26, P<0.001). The decrease in peak COFu was the result of a decrease in the resultant shear forces at the time of peak COFu as no difference in the vertical ground reaction forces was observed. When wearing hard soled shoes, subjects demonstrated decreased total body center of mass (COM) acceleration prior to and immediately following initial contact, decreased walking velocity, shortened stride length, and reduced ankle dorsiflexion angle at initial contact. Taken together, we believe that these gait modifications represent behavioral adaptations to wearing shoes that are perceived to be more slippery.

The effects of shoe traction and obstacle height on lower extremity coordination dynamics during walking

This study aims to investigate the effects of shoe traction and obstacle height on lower extremity relative phase dynamics (analysis of intralimb coordination) during walking to better understand the mechanisms employed to avoid slippage following obstacle clearance. Ten participants walked at a self-selected pace during eight conditions: four obstacle heights (0%, 10%, 20%, and 40% of limb length) while wearing two pairs of shoes (low and high traction). A coordination analysis was used and phasing relationships between lower extremity segments were examined. The results demonstrated that significant behavioral changes were elicited under varied obstacle heights and frictional conditions. Both decreasing shoe traction and increasing obstacle height resulted in a more in-phase relationship between the interacting lower limb segments. The higher the obstacle and the lower the shoe traction, the more unstable the system became. These changes in phasing relationship and variability are indicators of alterations in coordinative behavior, which if pushed further may have lead to falling.

Protection of feet in cold exposure

The paper summarizes the research on cold protection of feet. There exist several conflicting requirements for the choice of the best suited footwear for cold exposure. These conflicts are related to various environmental factors, protection needs and user comfort issues. In order to reduce such conflicts and simplify the choice of proper footwear the paper suggests dividing the cold into specific ranges that are related to properties and state of water and its possibility to penetrate into, evaporate from or condensate in footwear. The thermo-physiological background and reactions in foot are briefly explained, and main problems and risks related to cold injuries, mechanical injuries and slipping discussed. Footwear thermal insulation is the most important factor for protection against cold. The issues related to measuring the insulation and the practical use of measured values are described, but also the effect of socks, and footwear size. Other means for reducing heat losses, such as PCM and electrical heating are touched. The most important variable that affects footwear thermal insulation and foot comfort is moisture in footwear. In combination with motion they may reduce insulation and thus protection against cold by 45%. The paper includes recommendations for better foot comfort in cold.

Stepping over obstacles of different heights and varied shoe traction alter the kinetic strategies of the leading limb

This study aims to investigate the effects of shoe traction and obstacle height on friction during walking to better understand the mechanisms required to avoid slippage following obstacle clearance. Ten male subjects walked at a self-selected pace during eight different conditions: four obstacle heights (0%, 10%, 20% and 40% of limb length) while wearing two different pairs of shoes (low and high traction). Frictional forces were calculated from the ground reaction forces following obstacle clearance, which were sampled with a Kistler platform at 960 Hz. All frictional peaks increased with increases in obstacle height. Low traction shoes yielded smaller peaks than high traction shoes. The transition from braking to propulsion occurred sooner due to altered control strategies with increased obstacle height. Collectively, these results provided insights into kinetic strategies of leading limb when confronted with low traction and high obstacle environments. This study provides valuable information into the adaptations used to reduce the potential of slips/falls when confronted with environments characterised by low shoe-floor friction and obstacles. It also provides the necessary foundation to explore the combined effects of shoe traction and obstacle clearance in elderly people, more sensitive to slippage.

Slip, trip and fall injuries in potato, sugar beet and open field vegetable production in Finland

STF injuries are common in agriculture. The purposes of this study were to assess the magnitude of STF injuries, to identify contributing factors and to propose preventive actions to reduce injuries in potato, sugar beet and open field vegetable production in Finland. The material consisted of 1648 injury claim records and 22 interviews. The analysis showed 45% (n = 740) of the non-fatal injuries were STFs or jumps. Phrase analysis of injury descriptions provided further insight into the characteristics of STF injuries. The current findings suggest interventions should focus on making access paths (e.g. stairs, ladders, platforms) safer, minimising the need for mounting and dismounting equipment, decreasing manual material handling, improving contamination control and housekeeping in working areas and improving the safety of traffic areas and farmyards.