Gait parameters as predictors of slip severity in younger and older adults

This study investigated the association between slip severity and pre-slip gait characteristics of younger and older subjects. Sixteen younger and eleven older healthy adults walked onto an unexpectedly slippery surface. Slip severity was categorized as either hazardous or non-hazardous using a 1.0 ms peak slip velocity threshold. The results showed that hazardous slips were associated with greater step lengths (normalized by leg length) (SLR), larger and more rapidly changing foot - floor angles (FFA) at heel strike, and increased cadence across the two subject groups. Older subjects were found to walk with shorter SLR and with smaller and more slowly changing FFA at heel strike compared to younger subjects. However, both younger and older subjects experienced hazardous slips at the same rate. A logistic regression model relating SLR and cadence to slip severity predicted that increased SLR and decreased cadence would result in increased probability of hazardous slip (R2 = 0.45, chi2 = 15.30, p<0.01). A second logistic regression model relating FFA with slip severity predicted that increased FFA would result in increased probability of hazardous slip (R2 = 0.53, chi2 = 16.55, p<0.01). These results suggest that gait characteristics prior to foot contact play an important role in the severity of an ensuing slip. The finding that older adults experienced hazardous slips at the same rate as young adults even though their SLR and FFA are smaller suggests that age is also playing a role in other aspects of postural control that impact slip severity.     

Heel contact dynamics in alternative footwear during slip events

IntroductionSlips, trips and an induced loss of balance have been identified as the major causative factor for workplace injuries involving falls. Moreover, alternative footwear such has crocs and flip flops have been used in and around work places, especially with the usage of crocs in slip prone hospital settings.PurposeThe purpose of the study is to analyze the effects of alternative footwear [crocs (CC), flip-flops (FF)] and industry standard slip resistant shoes (LT) on heel dynamics during slip events.MethodsEighteen healthy male participants following a repeated measures design for each footwear condition, were tested for heel kinematics during normal dry surface gait (NG); unexpected slip (US), alert slip (AS) and expected slip (ES). A 3 × 4 repeated measures ANOVA was used to analyze the dependent slip parameters (heel slip distance-HSD & mean heel slip velocity-MHSV) at p = 0.05.ResultsSignificant interactions between footwear and gait trials were found for HSD & MHSV, with significantly greater slip parameters exhibited by CC & FF compared to LT during US.ConclusionAlternative footwear (CC & FF) demonstrated greater slips, but were limited to slip events that were unexpected. With the knowledge and anticipation of slippery flooring conditions, participants were able to lower the slip parameters by kinematically modifying heel contact dynamics. The LT had significantly lower slip parameters and maintained a normal gait pattern for all slip trials, and demonstrates to be the choice of footwear for maneuvering slippery flooring conditions; while alternative footwear combined with unexpected slip events contributed to potentially hazardous and hazardous slips.Relevance to IndustryAlternative footwear such as crocs are widely used in hospitals which are slip prone environments. This study provides evidence that these alternative footwear may predispose to hazardous slips and recommends the use of slip resistant footwear or slip resistant modifications to alternative footwear under known or unknown slippery conditions.     

Effects of foot placement,hand positioning,age and climbing biodynamics on ladder slip outcomes

Ladder falls frequently cause severe injuries; yet the factors that influence ladder slips/falls are not well understood. This study aimed to quantify (1) the effects of restricted foot placement, hand positioning, climbing direction and age on slip outcomes, and (2) differences in climbing styles leading to slips versus styles leading to non-slips. Thirty-two occupational ladder users from three age groups (18–24, 25–44 and 45–64 years) were unexpectedly slipped climbing a vertical ladder, while being assigned to different foot placement conditions (unrestricted vs. restricted toe clearance) and different hand positions (rails vs. rungs). Constraining foot placement increased the climber's likelihood of slipping (p < 0.01), while younger and older participants slipped more than the middle-aged group (p < 0.01). Longer double stance time, dissimilar and more variable foot and body positioning were found in styles leading to a slip. Maintaining sufficient toe clearance and targeting ladder safety training to younger and older workers may reduce ladder falls.

Practitioner Summary: Ladder falls frequently cause severe occupational fall injuries. This study aims to identify safer ladder climbing techniques and individuals at risk of falling. The results suggest that ladders with unrestricted toe clearance and ladder climbing training programmes, particularly for younger and older workers, may reduce ladder slipping risk.     

Age-related changes to wheelchair efficiency and sprint power output in novice able-bodied males

This study examined the effect of age on sub-maximal wheelchair propulsion efficiency and sprint power output (SPO) in inexperienced able-bodied males. Two age groups were used for this study: a younger adult group (N = 10; mean age 24.8 ± 3.0 years) and an older adult group (N = 8; mean age 70.9 ± 5.2 years). No one had prior manual wheelchair experience. The primary outcome measures were gross mechanical efficiency (GME), mechanical effectiveness (ME) during sub-maximal treadmill wheeling and SPO during a max sprint test. There were no significant differences in GME; however, there was a significant difference in ME [0.74 ± 0.12 and 0.62 ± 0.08 (p = 0.007)] and sprint test [SPO = 224.66 ± 79.25 and 125.98 ± 53.02 (W) (p = 0.008)], for younger and older adults, respectively. Healthy, active older individuals can have a physiological capacity similar to younger populations to wheel sub-maximally, but their ME and lower SPO reduce the ability to propel manual wheelchairs during maximal wheeling.     

Visual effects of the luminance surrounding a computer display

The luminance surrounding a computer display can potentially reduce visibility of the display (disability glare), result in sensations of discomfort (discomfort glare) and result in transient adaptation effects from fixating back and forth between the two luminance levels. The study objective was to measure the effects of surround luminance levels upon these functions in younger and older adults to determine recommended surround luminance levels. The younger age group comprised 20 subjects (mean age 27.9 years, range 23 – 39) and the older group 17 subjects (mean age 55.5 years, range 47 – 63). The central task was presented with luminance of 91 cd/M², tested surround luminance levels were 1.4, 2.4, 8.9, 25.5, 50, 91, 175, 317, and 600 cd/M². Disability glare was tested with low contrast (20%) visual acuity charts, transient adaptation was tested with a task that required regular fixation between the two luminance levels, discomfort was measured with a questionnaire after reading stories with different surround luminance levels, and preferred luminance was measured by method of adjustment. The surround luminance significantly affected transient adaptation (p < 0.0001), optimal performance occurred at 50 cd/M² and above for the young group and at 91 cd/M² and above for the older group. Neither low contrast acuity (disability glare) nor symptoms when reading were significantly affected by surround luminance. There was wide variation in preferred surround luminance; however, average preferred surround luminance was 86.9 cd/M² for the young group and 62.2 cd/M² for the older group, slightly below the central luminance of 91 cd/M². The effects of the surround luminance within the tested range are not large; however, the data show that the lowest surround luminance levels should be avoided and that surround luminance levels at or slightly below that of the central task are preferred.     

The anatomy of a slip: Kinetic and kinematic characteristics of slip and non-slip matched trials

To improve understanding of slip propagation mechanisms, one could compare features of early stance phase during slips and non-slips. This study investigated the similarities and differences in kinematics and utilized COF of paired trials, defined as a matched pair of slip and non-slip trials produced by the same participant walking on the same floor condition at the same walking speed condition. Twenty-two participants produced 47 matched trial pairs while walking at 1.5, 1.8 and 2.1 m/s, over a forceplate with an available COF ranging from 0.12 to 0.21. Heel displacement was captured with an infrared motion tracking system and utilized COF was derived from ground reaction forces. ANOVA revealed no significant differences between the slip and non-slip groups in horizontal heel velocity just prior to heel strike or for heel velocity or slip distance during the 20 ms period following heel strike. Significant differences were found between the groups in utilized COF and horizontal heel velocity at 25 and 30 ms following heel strike. Differences in heel kinematics and kinetics during early stance phase between the slip and non-slip trials are discussed. The results differ from several previous studies, likely due to methodological differences, as the present study was conducted on marginally slippery surfaces, as opposed to very low COF conditions with thick contaminant layers.     

Rearward movement of the heel at heel strike

This paper describes the observation of rearward movement (RM) of the heel following heel strike occurring during normal gait. Thirty-one participants recruited as part of a larger study on slip kinematics walked the length of an 8-m runway at a speed of 1.5 m/s. Several floor surfaces, presented dry and with contaminant, were used for the purpose of eliciting a wide range of small slip distances. The normal force applied to a forceplate mounted in the runway was used to identify heel strike, as well as to calculate the utilized coefficient of friction during early stance phase. A motion analysis system tracked the displacement of two heel-mounted markers, and the data were used to derive kinematic variables related to the heel strike event. Results showed that RMs occurred in 18.1% of 494 trials, with a mean rearward displacement of 5.02 (+/-3.68) mm. When present, RMs occurred in close temporal proximity to heel strike, typically completing RM within 40 ms of the heel strike event. When divided into groups by age, older participants (>40 years) were more than twice as likely to have RMs as younger participants. When grouped by height or weight, differences in the proportion of trials with RMs were small. In trials where RMs were observed, forward slip distances were significantly less than for trials with no RMs, 2.17 (+/-3.87) mm vs. 12.58 (+/-10.71) mm, respectively. The time until the heel stopped moving during the post-heel strike period was not significantly different between RM and non-RM trials. Further investigation of this gait feature may improve understanding of normal gait patterns and may have implications for future slipmeter development.     

Coseismic lateral offsets of surface rupture zone produced by the 2001 Mw 7.8 Kunlun earthquake,Tibet from the IKONOS and QuickBird imagery

Analyses and interpretations of 1m‐resolution IKONOS, and 61cm‐resolution QuickBird images reveal that the distribution of strike‐slip offsets and ground deformation characteristics of the coseismic surface rupture produced by the 2001 M _w 7.8 Kunlun earthquake occurred in the western segment of the strike‐slip Kunlun fault, northern Tibet. The 2001 coseismic strike‐slip offsets measured from IKONOS images range from 2 m up to 16.7 m, generally 3–8 m, which are generally consistent with those measured immediately in the field after the earthquake. The coseismic surface ruptures along which offsets were observed are mainly composed of a numerous of en echelon shear faults and cracks which are concentrated on a rupture zone ranging from a few meters up to ～500 m in width. The offsets measured along individual shear faults or crack are typically 2–7 m, but up to >10 m in several locations. Our results show that high resolution remote sensing imagery provides a powerful tool for measuring coseismic strike‐slip offsets and detecting the ground deformation produced by a large earthquake in the remote and high mountain Tibet region.     

Prediction of slips: an evaluation of utilized coefficient of friction and available slip resistance

The purpose of this study was to investigate the relationship between measures of floor surface slip resistance and an individual's peak utilized coefficient of friction (COF_U) on the probability of a slip occurring during level walking. Video, kinematic and ground reaction force data were recorded simultaneously as subjects walked at a self-selected speed during conditions of normal and reduced floor surface slip resistance. Peak COF_U during weight acceptance was calculated and the available floor surface slip resistance was measured using the variable incidence tribometer (VIT). Separate logistic regression analyses identified that knowledge of the available slip resistance (as measured by the VIT) in combination with an individual's peak COF_U allowed for greater accuracy in classifying slip outcomes (89.5%; p = 0.004), while knowledge of only the available slip resistance reduced the accuracy of categorization to 78.9% (p = 0.021).     

Navigating the Online World: Gaze,Fixations, and Performance Differences between Younger and Older Users

ABSTRACT

The world’s populations and workforces are aging and older adults are now the fastest growing group of internet users. Unfortunately, age-related declines may prevent older adults from performing web-based tasks with the same ease as their younger counterparts. Recent studies have suggested that peripheral navigation may exacerbate age-related online performance gaps as older adults fail to adequately search peripheral elements. Such studies have however relied on the use of preexisting websites with no control for layout, complexity, or prior familiarity. This study tested whether age-related differences in online performance and search behavior exist across various navigational layouts. Participants (N = 47) completed four online tasks with purpose-built websites of equivalent difficulty, length, and content type, yet with varying navigational layouts (center; left-periphery; top-periphery; inconsistent). Participants’ performance (i.e., accuracy/efficiency), search behavior (i.e., eye gaze/fixation), and satisfaction were examined. Identifiable differences between age-groups and navigational layouts were found, with top-peripheral navigation proving most detrimental to the online performance and satisfaction of both younger and older adults. The results inform design principles that aim to increase older adults’ online functionality, and provide an extensive platform for further research.     

Can an off-the-rack orthotic stiletto alter pressure and comfort scores in the forefoot,arch and heel?

The study sought to investigate whether an orthotic stiletto could modulate the pressure and comfort under the forefoot, arch and heel that stiletto wearers experience. Twenty-two women participated. We measured the peak pressure and pressure-time integral for orthotic stilettos with built-in metatarsal pad, heel cup and arch support; standard stilettos without inlays; and trainers. Comfort was recorded during 3 × 3 working days. The orthotic stiletto exhibited lower metatarsal head1 (MTH) and MTH2+3 and heel pressures than the standard stiletto (p < .01), and a long second metatarsal increased MTH2+3 pressure (p < .01). The comfort in the forefoot and heel was higher in the orthotic stiletto than in the standard one (p < .01), and comfort in the forefoot was correlated to the pressure-time integral of MTH2+3 (p = .03) and not peak pressure. Off-the-rack orthotic stilettos can notably reduce plantar pressures and improve forefoot and heel comfort during everyday use.

Practitioner Summary: Off-the-rack orthotic stilettos with built-in metatarsal pad, arch support and heel caps can lower the pressure under the heel and forefoot in comparison with a standard stiletto and can improve comfort during everyday use. Having a long second metatarsal is a risk factor for increased forefoot pressure.     

Increasing surfboard volume reduces energy expenditure during paddling

Abstract

The purpose of this study was to investigate how altering surfboard volume (BV) affects energy expenditure during paddling. Twenty surfers paddled in a swim flume on five surfboards in random order twice. All surfboards varied only in thickness and ranged in BV from 28.4 to 37.4 L. Measurements of heart rate (HR), oxygen consumption (VO₂), pitch angle, roll angle and paddling cadence were measured. VO₂ and HR significantly decreased on thicker boards [VO₂: r = ?0.984, p = 0.003; HR: r = ?0.972, p = 0.006]. There was also a significant decrease in pitch and roll angles on thicker boards [Pitch: r = ?0.995, p < 0.001; Roll: r = ?0.911, p = 0.031]. Results from this study suggest that increasing BV reduces the metabolic cost of paddling as a result of lower pitch and roll angles, thus providing mechanical evidence for increased paddling efficiency on surfboards with more volume.

Practioner Summary: This study investigated the impact of surfboard volume on energy expenditure during paddling. Results from this study suggest that increasing surfboard volume reduces the metabolic cost of paddling as a result of lower pitch and roll angles, thus providing mechanical evidence for increased paddling efficiency on surfboards with more volume.     

Impact of joint torques on heel acceleration at heel contact, a contributor to slips and falls

Slips/falls are a health burden in the workplace. Previous research has implied a relationship between foot dynamics at heel contact and slips/falls; however, heel acceleration has received little attention. Heel acceleration as the heel contacts the ground is the result of the combined effort of the leg joint torques to control motion of the foot. This study aims to examine the association of heel acceleration with fall risk, and explore the main joint torque determinant of heel acceleration at contact. Sixteen young and eleven older adults walked on known dry floors and in slippery environments expected to be dry. Heel acceleration at heel contact in the direction of motion, i.e. anterior/posterior, was compared between slip-recovery and slip-fall outcomes. Results showed that subjects that recovered contacted the floor with a greater heel deceleration (p < 0.05) than fall subjects. Knee torque alone explained 76% of the heel acceleration variability (p < 0.01). These data suggest that walking with reduced knee flexion torque at heel contact results in a reduced heel deceleration, a potential risk factor for slip-initiated falls.     

Preliminary observations on parameters of human location

Abstract

A preliminary experimental field investigation was conducted on seventeen normal male adults to study the important observable parameters of human locomotion and the interrelationship existing among them. New generalized terms such as specific speed (statures s^?1), specific energy consumption (kJ kg^?1 min^?1), percentage increase of peak heart rate and a non-dimensionalized term, relative step length, have been introduced. Superiority of cadence and specific speed over speed and specific energy consumption over energy consumption has been observed and a single linear relationship connecting specific speed and specific energy consumption up to a speed of 6·7 m s^?1 (24 km h^?1) has been seen. Stair climbing and Baithaki exercises have been included as two other rhythmic activities for the sake of comparison with locomotion. Use of cadence as a relatively more important observable gait parameter for walking or running activity as well as for other rhythmic activities has been suggested. These findings have potential for application in the field of work study and industrial engineering.     

Effects of aging on the biomechanics of slips and falls

Although much has been learned in recent decades about the deterioration of muscular strength, gait adaptations, and sensory degradation among older adults, little is known about how these intrinsic changes affect biomechanical parameters associated with slip-induced fall accidents. In general, the objective of this laboratory study was to investigate the process of initiation, detection, and recovery of inadvertent slips and falls. We examined the initiation of and recovery from foot slips among three age groups utilizing biomechanical parameters, muscle strength, and sensory measurements. Forty-two young, middle-age, and older participants walked around a walking track at a comfortable pace. Slippery floor surfaces were placed on the track over force platforms at random intervals without the participants' awareness. Results indicated that younger participants slipped as often as the older participants, suggesting that the likelihood of slip initiation is similar across all age groups; however, older individuals' recovery process was much slower and less effective. The ability to successfully recover from a slip (thus preventing a fall) is believed to be affected by lower extremity muscle strength and sensory degradation among older individuals. Results from this research can help pinpoint possible intervention strategies for improving dynamic equilibrium among older adults.     

The effect of age on in-vivo spine stiffness,postures and discomfort responses during prolonged sitting exposures

Many industrialised working populations are ageing and prolonged sitting exposures are prevalent across occupational sectors. The purpose of this work was to determine the effect of age and sex on passive spine stiffness, postures and discomfort in response to seated work. A total of 34 participants were recruited, with 17 older adults with an average age of (standard deviation) 63.7 (±3.9) years and 17 younger adults aged 23.8 (±5.0) years. Participants were asked to sit continuously for 90?min while typing. Baseline passive spine stiffness was higher in older adults at 40% flexion compared to younger adults (p?=?.0233). Older adults sat in less normalised flexion, at 33.4% (±16.4) compared to 60.9% (±20.2) in the younger group (p?=?.0003). Discomfort was higher among older adults in the neck, right shoulder and middle back regions (p?<?.0086). An understanding of age-specific responses to workplace exposures is essential to determine whether age-specific interventions are warranted.

 

Practitioner summary: Older adults had higher passive spine stiffness and sat with less flexion during prolonged sitting. Discomfort was higher among older adults and occurred earlier in the simulation compared to younger participants, indicating that interventions, such as walking breaks may need to be implemented earlier during sitting for aged workers.     

Estimating post‐fire organic soil depth in the Alaskan boreal forest using the Normalized Burn Ratio

As part of a long‐term moose browse/fire severity study, we used the Normalized Burn Ratio (NBR) with historic Landsat Thematic Mapper (TM) imagery to estimate fire severity from a 1983 wildfire in interior Alaska. Fire severity was estimated in the field by measuring the depth of the organic soil at 57 sites during the summer of 2006. Sites were selected for field sampling from five fire severity classes based on threshold NBR values. The linear relationship between post‐fire NBR and organic soil depth among sites within the burn was weak (r ² = 0.26), and improved substantially (r ² = 0.66) when restricted to non‐wetland black spruce sites. The relationship between NBR and aspen/willow counts was non‐linear. Sites with high densities of aspen stems consistently occurred in the high fire severity classes, and sites with high willow stem densities consistently occurred in the moderate fire severity class. However, NBR varied substantially from sites with low aspen or willow reproduction and therefore predicting aspen or willow regeneration based on post‐fire NBR values would be difficult.     

Association of subjective ratings of slipperiness to heel displacement following contact with the floor

Falls precipitated by slipping are listed among the leading causes of occupational injuries. Several factors may influence the risk of slips and falls, including perception of surface conditions. The current research examined the relationship between perceptions of slipperiness and slip distance at heel strike. The investigation compared objective and subjective measures for 31 participants ranging in age from 19 to 67 years old. Subjective slipperiness ratings for several floor surface and walking velocity conditions were obtained. Small slips were not generally perceived, but a uniform slip distance threshold could not be identified due to the large variability in ratings. The Pearson correlation coefficient between slip distance and subjective ratings for slides (30-100mm) was r=-0.17. Results indicate that subjective ratings should be used cautiously as a measure of slipperiness, partially due to possible underestimation of slipperiness and the variability in perceptions.     

Effect of different handgrip angles on work distribution during hand cycling at submaximal power levels

The effect of different handle angles on work distribution during hand cycling was determined. Able-bodied subjects performed hand cycling at 20% of maximum power level (mean (SD) power level: 90.0 (25.8) W) at a cadence of 70 rpm using handle angles of ±30°, ±15° and 0°. The handle angle had a significant effect on work during the pull down (p < 0.001) and lift up (p = 0.005) sector, whereby the highest work was performed with handle angles of +30° and ?15° respectively. The cycle sector had a significant effect on work (p < 0.001) and significantly (p = 0.002) higher work was performed in the pull down sector (25% higher than mean work over one cycle) as compared to the lift up sector (30% lower than mean work over one cycle). Therefore, a fixed handle angle of +30° is suggested to be optimal for power generation. The results of this study help to optimise the handbike–user interface. A more pronated handle angle compared to the one conventionally used was found to improve the performance of hand cycling and thereby the mobility of disabled people.     

Workplace slip,trip and fall injuries and obesity

The objective of this study was to examine the relationship between slip, trip and fall injuries and obesity in a population of workers at the Idaho National Laboratory (INL) in Idaho Falls, Idaho. INL is an applied engineering facility dedicated to supporting the US Department of Energy's mission. An analysis was performed on injuries reported to the INL Medical Clinic to determine whether obesity was related to an increase in slip, trip and fall injuries. Records were analysed that spanned a 6-year period (2005–2010), and included 8581 employees (mean age, 47 ± 11 years and body mass index [BMI], 29 ± 5 kg/m²; 34% obesity rate). Of the 189 people who reported slip, trip and fall injuries (mean age, 48 ± 11 years), 51% were obese (P < 0.001 compared with uninjured employees), and their mean BMI was 31 ± 6 kg/m² (P < 0.001). Obesity in this population was associated with a greater rate of slip, trip and fall injuries.