REQUIRED COEFFICIENT OF FRICTION ANALYSES IN RUNNING

The purpose of this study was to analyze the possible alterations in the required coefficient of friction (RCOF) in running under the following conditions: a) barefoot against shod; b) self-selected velocity and cadence versus imposed cadence and c) along three running phases (initial contact, mid-stance and propulsion). Two Kistler force plates were used to measure the horizontal and vertical components of ground reaction forces in order to calculate the RCOF. Statistical differences were found for cadence and phase factors. Barefoot-Shod conditions did not present statistical differences. An interaction between velocity and phase of cycle was found. At propulsion phase, an increased RCOF were revealed, especially with the interaction of an imposed cadence. In conclusion, the present study supports the relevance of RCOF as a variable affecting and being affected during running to be taken into consideration at many experimental conditions

The influence of gait cadence on the ground reaction forces and plantar pressures during load carriage of young adults

Biomechanical gait parameters ground reaction forces (GRFs) and plantar pressures during load carriage of young adults were compared at a low gait cadence and a high gait cadence. Differences between load carriage and normal walking during both gait cadences were also assessed. A force plate and an in-shoe plantar pressure system were used to assess 60 adults while they were walking either normally (unloaded condition) or wearing a backpack (loaded condition) at low (70 steps per minute) and high gait cadences (120 steps per minute). GRF and plantar pressure peaks were scaled to body weight (or body weight plus backpack weight). With medium to high effect sizes we found greater anterior-posterior and vertical GRFs and greater plantar pressure peaks in the rearfoot, forefoot and hallux when the participants walked carrying a backpack at high gait cadences compared to walking at low gait cadences. Differences between loaded and unloaded conditions in both gait cadences were also observed.info:eu-repo/semantics/acceptedVersio

Gait Posture

Background:Adequate footwear is an important factor for reducing the risk of slipping; as shoe outsoles wear down, friction decreases, and slip and fall risk increases. Wear theory suggests that gait kinetics may influence rate of tread wear.Research question:Do the kinetics of walking (i.e., the shoe-floor force interactions) affect wear rate?Methods:Fourteen participants completed dry walking trials during which ground reaction forces were recorded across different types of shoes. The peak normal force, shear force, and required coefficient of friction (RCOF) were calculated. Participants then wore alternating pairs of shoes in the workplace each month for up to 24 months. A pedometer was used to track the distance each pair of shoes was worn and tread loss was measured. The wear rate was calculated as the volumetric tread loss divided by the distance walked in the shoes. Three, mixed linear regression models were used to assess the impact of peak normal force, shear force, and RCOF on wear rate.Results:Wear rate was positively associated with peak RCOF and with peak shear force, but was not significantly related to peak normal forces.Significance:The finding that shear forces and particularly the peak RCOF are related to wear suggests that a person\u2019s gait characteristics can influence wear. Therefore, individual gait kinetics may be used to predict wear rate based on the fatigue failure shoe wear mechanism.R01 OH010940/OH/NIOSH CDC HHSUnited States/R43 AR064111/AR/NIAMS NIH HHSUnited States/2022-05-01T00:00:00Z33735824PMC816792711292vault:3710

Appl Ergon

Available coefficient of friction (ACOF) is a common metric of footwear traction performance. ACOF is the ratio of friction to normal force, often averaged over a time-interval. The time-interval needed to achieve repeatable and valid ACOF is unknown. A post-hoc analysis was performed on nine shoe-floor-contaminant combinations to assess the repeatability and bias of data averaged across 4 time-intervals (2\u202fms, 50\u202fms, 100\u202fms, 200\u202fms) after the target normal force was reached. The ability to predict human slips was assessed for ACOF across these intervals. Differences in repeatability and validity across the four intervals were small. However, statistically significant differences were observed for the shortest compared with the longest interval (lower repeatability yet modestly improved predictive ability). Given the limited impact of time-interval on the results, a shorter interval of 50\u202fms is recommended to enable testing of smaller floor samples.R44 AG059258/AG/NIA NIH HHS/United StatesR01 OH010940/OH/NIOSH CDC HHS/United StatesS10 RR027102/RR/NCRR NIH HHS/United StatesR01 OH007592/OH/NIOSH CDC HHS/United StatesR01 OH008986/OH/NIOSH CDC HHS/United States2021-01-01T00:00:00Z31568960PMC69223068874vault:3427

Footwear Sci

Worn shoes contribute to injuries caused by slip-and-fall accidents. The peak required coefficient of friction (RCOF) has been associated with tread wear rate. However, the temporal relationship between RCOF and shoe wear is unknown. The purpose of this study was to determine whether the contact region at the time of peak RCOF is consistent with the region of shoe wear. The shoe contact region at peak RCOF was imaged by frustrated total internal reflection. Images of worn tread after months of use were captured. The worn tread region was more posterior than the contact region at RCOF and did not correlate with the contact region at the time of RCOF. The contact regions observed during earlier stance (within 83 ms of heel contact) were more consistent with the worn region, suggesting that RCOF may not directly cause tread wear. These results serve to motivate future studies to identify early-stance gait parameters associated with tread wear development.R01 OH010940/OH/NIOSH CDC HHSUnited States/S10 RR027102/RR/NCRR NIH HHSUnited States

J Biomech

This paper quantified the heel kinematics and kinetics during human slips with the goal of guiding available coefficient of friction (ACOF) testing methods for footwear and flooring. These values were then compared to the testing parameters recommended for measuring shoe-floor ACOF. Kinematic and kinetic data of thirty-nine subjects who experienced a slip incident were pooled from four similar human slipping studies for this secondary analysis. Vertical ground reaction force (VGRF), center of pressure (COP), shoe-floor angle, side-slip angle, sliding speed and contact time were quantified at slip start (SS) and at the time of peak sliding speed (PSS). Statistical comparisons were used to test if any discrepancies exist between the state of slipping foot and current ACOF testing parameters. The main findings were that the VGRF (26.7 %BW, 179.4\u202fN), shoe-floor angle (22.1\ub0) and contact time (0.02\u202fs) at SS were significantly different from the recommended ACOF testing parameters. Instead, the testing parameters are mostly consistent with the state of the shoe at PSS. We argue that changing the footwear testing parameters to conditions at SS is more appropriate for relating ACOF to conditions of actual slips, including lower vertical forces, larger shoe-floor angles and shorter contact duration.R01 OH007592/OH/NIOSH CDC HHS/United StatesR01 OH008986/OH/NIOSH CDC HHS/United StatesR44 AG059258/AG/NIA NIH HHS/United StatesS10 RR027102/RR/NCRR NIH HHS/United States2019-06-06T00:00:00Z29759653PMC59877606337vault:3026

Gait Posture

Background:A plurality of fatal falls to lower levels involve ladders. After a slip/misstep on a ladder, climbers use their upper and lower limbs to reestablish contact with the ladder.Research question:This study investigates the impact of upper body strength, hand placement and foot placement on fall severity after a ladder climbing perturbation.Methods:Participants performed upper body strength tests (breakaway and grip strength) and climbed a vertical, fixed ladder while a misstep perturbation was applied under the foot. After the perturbation, three hand placement and two foot placement responses were generally observed. Common hand placement responses included the hand moving two rungs, one rung, or did not move to a different rung. Foot placement responses included at least one foot or no feet reestablished contact with the ladder rung(s). Fall severity was quantified by the peak harness force observed after the perturbation.Results:Increased strength, reestablishing at least one foot on the ladder, and ascending (compared with descending) the ladder was associated with a reduction in fall severity. An interaction effect indicated that the impact of hand placement was altered by climbing direction. Moving the hand one rung during ascent and moving the hand two rungs during descent was associated with an increased fall severity. Cases where the hand decoupled from the ladder was associated with higher fall severity. Upper body strength assessed using a portable grip dynamometer was sufficient to predict fall severity.Discussion:This study confirms the multifactor role of upper body strength, hand placement and foot placement in preventing falls from ladders. Furthermore, a portable dynamometer shows potential to screen for high-risk individuals. Results of this investigation may guide targeted interventions to prevent falls from ladders.20182020-02-01T00:00:00ZP20 GM109040/GM/NIGMS NIH HHS/United StatesR21 OH010038/OH/NIOSH CDC HHS/United States30439684PMC6380680717

Shoe–Floor Interactions in Human Walking With Slips: Modeling and Experiments

Shoe–floor interactions play a crucial role in determining the possibility of potential slip and fall during human walking. Biomechanical and tribological parameters influence the friction characteristics between the shoe sole and the floor and the existing work mainly focus on experimental studies. In this paper, we present modeling, analysis, and experiments to understand slip and force distributions between the shoe sole and floor surface during human walking. We present results for both soft and hard sole material. The computational approaches for slip and friction force distributions are presented using a spring-beam networks model. The model predictions match the experimentally observed sole deformations with large soft sole deformation at the beginning and the end stages of the stance, which indicates the increased risk for slip. The experiments confirm that both the previously reported required coefficient of friction (RCOF) and the deformation measurements in this study can be used to predict slip occurrence. Moreover, the deformation and force distribution results reported in this study provide further understanding and knowledge of slip initiation and termination under various biomechanical conditions

J Biomech

Shoe outsole tread wear has been shown to increase slip risk by reducing the tread's ability to channel fluid away from the shoe-floor interface. This study establishes a connection between geometric features of the worn region size and slipping. A mechanistic pathway that describes the relationship between the worn region size and slip risk is assessed. Specifically, it is hypothesized that an increased worn region size leads to an increase in under-shoe fluid pressure, which reduces friction, and subsequently increases slipping. The worn region size, fluid pressure, and slip outcome were recorded for 57 participants, who were exposed to an unexpected slip condition. Shoes were collected from each participant and the available coefficient of friction (ACOF) was measured using a tribometer. A greater shoe worn region size was associated with increased slip occurrence. Specifically, a 1\ua0mm increase in the characteristic length of the worn region (geometric mean of its width and length) was associated with an increase in slip risk of ~10%. Fluid pressure and ACOF results supported the mechanistic model: an increase in worn region size correlated with an increase in peak fluid pressure; peak fluid pressures negatively correlated with ACOF; and increased ACOF correlated with decreased slip risk. This finding supports the use of worn region size as a metric to assess the risk of slipping.20202021-05-22T00:00:00ZR01 OH010940/OH/NIOSH CDC HHS/United StatesS10 RR027102/RR/NCRR NIH HHS/United States32423543PMC7362878799

Ergonomics

Assessing footwear slip-resistance is critical to preventing slip and fall accidents. The STM 603 (SATRA Technology) is commonly used to assess footwear friction but its ability to predict human slips while walking is unclear. This study assessed this apparatus' ability to predict slips across footwear designs and to determine if modifying the test parameters alters predictions. The available coefficient of friction (ACOF) was measured with the device for nine different footwear designs using 12 testing conditions with varying vertical force, speed and shoe angle. The occurrence of slipping and the required coefficient of friction was quantified from human gait data including 124 exposures to liquid contaminants. ACOF values varied across the test conditions leading to different slip prediction models. Generally, a steeper shoe angle (13\ub0) and higher vertical forces (400 or 500|N) modestly improved predictions of slipping. This study can potentially guide improvements in predictive test conditions for this device. |: Frictional measures by the STM603 (SATRA Technology) were able to predict human slips under liquid contaminant conditions. Test parameters did have an influence on the measurements. An increased shoe-floor testing angle resulted in better slip predictions than test methods specified in the ASTM F2913 standard.R44 AG059258/AG/NIA NIH HHS/United StatesR01 OH010940/OH/NIOSH CDC HHS/United StatesS10 RR027102/RR/NCRR NIH HHS/United StatesR43 AR064111/AR/NIAMS NIH HHS/United StatesR01 OH007592/OH/NIOSH CDC HHS/United StatesR01 OH008986/OH/NIOSH CDC HHS/United States2020-07-16T00:00:00Z30638144PMC73655918780vault:3574