Elsevier

Gait & Posture

Volume 15, Issue 2, April 2002, Pages 159-171
Gait & Posture

Changes in gait when anticipating slippery floors

https://doi.org/10.1016/S0966-6362(01)00150-3Get rights and content

Abstract

Falls precipitated by slipping are listed among the leading causes of injuries. The biomechanical analysis of such events is a necessary component of the slips/falls prevention research. One of the challenges of biomechanical studies is reproducing the unexpected nature of real-life slipping accidents. Thus, the goal of this study was to quantify changes in gait biomechanics when subjects anticipate slippery environments. Foot ground reaction forces and body dynamics of 16 subjects were recorded during level walking and descending ramps of varying frictional properties and inclination. Gait biomechanics were compared among three types of dry trials: (1) baseline (subjects knew the floor was dry); (2) anticipation (subjects were uncertain of the contaminant condition, dry, water, soap or oil); and (3) recovery trials recorded after a contaminated trial (subjects again knew the floor was dry). Subjects were asked to walk as naturally as possible throughout testing. Anticipation trials produced peak required coefficient of friction (RCOFpeak) values that were on average 16–33% significantly lower than those collected during baseline trials, thus reducing slip potential. During recovery trials, RCOFpeak values did not return to baseline characteristics (5–12% lower). Postural and temporal gait adaptations, which affected ground reaction forces, were used to achieve RCOFpeak reductions. Statistically significant gait adaptations included reductions in stance duration (SD) and loading speed on the supporting foot, shorter normalized stride length (NSL), reduced foot-ramp angle and slower angular foot velocity at heel contact. As a result of these adaptations, anticipation of slippery surfaces led to significant changes in lower extremity joint moments, a reflection of overall muscle reactions. Thus, this study suggests that significant gait changes are made when there is a potential risk of slipping even though subjects were asked to walk as naturally as possible. Insights are also gained into the adaptations that are used to reduce the potential of slips/falls.

Introduction

Falls are a major cause of serious injuries and even deaths. More than 20% of injury-related emergency department visits have been attributed to falls, the single largest cause of such visits [1]. The US economic cost of falling accidents ranks second in the USA [2]. The cost of falling injuries is also substantial among occupational populations for a number of reasons including the advancing age of the labor force [3] but also the severity of the injuries, with more than 25% of the workers sustaining falling injuries missing 31 days or more at work [4]. In a comparative study on analysis of injury mortality data across industrial countries, Fingerhut et al. frequently listed falling among the three leading generators of fatalities [5]. The loss of balance leading to falls is often the result of slipping events [6]. The US National Health Interview Survey questionnaire of 1997 revealed a clear majority (64%) of the work-related falls attributed to slipping, tripping or stumbling. The 1992–1998 occupational same level fatal falls records providing narrative description of the incident indicated that slipping was the most common triggering event (43% of the cases). In 1998, slips, trips and falls accounted for 16.8% of all nonfatal occupational injuries involving days away from work and 11.9% of job-related deaths [4]. The incidence of slip accidents varies with geographical location and external environmental conditions. For example, it is particularly high among occupational populations (e.g. miners and mail deliverers) working outside during cold winter months [7], [8]. In Sweden, Björnstig et al. found the cost of medical care inflicted by slipping accidents on ice and snow comparable with the cost of all traffic injuries in that same area [9].

Findings of biomechanical gait experiments have been used in an effort to understand human factors that cause slips/falls accidents and their complex interaction with environmental factors [10], [11], [12], [13], [14]. Gait biomechanics and the health of the sensory and neuromuscular systems are included in human factors. Among the most important environmental factors are the frictional and material properties of the shoes and floors. One important example of the interaction between human and environmental factors is the increased risk of slipping as the frictional requirements of the task performed (walking, load carrying, pushing/pulling) exceed the available frictional capabilities of the shoe/floor interface, i.e. the measured coefficient of friction [12]. Thus, the frictional requirements of a particular task measured in slips/falls experiments are useful in setting thresholds of minimal friction needed to avoid a slip and determining whether an environment is ‘slip-safe’. In addition, relevant gait variables generated from biomechanical slips/falls studies have been employed in the development of a new generation of slip resistance testers that measure the frictional properties of the shoe/floor interface by simulating foot movements during locomotion [15], [16], [17].

The use of biomechanical gait studies in slips/falls prevention research goes beyond measuring slip resistance and setting frictional thresholds to achieve slip-safe environments. Gait biomechanics partially determine the outcome of walking onto a contaminated floor and are reflection of the ability of the human neuromotor system to: (1) decrease slip potential in possibly dangerous environments (before a slip occurs); and (2) recover from a slip event by generating corrective reactions in an attempt to avoid a fall. The success of the human neuromotor system in achieving those goals will be affected by various factors such as anthropometry, strength, age, task (physical constraints) and cognitive/behavioral factors (mental stress, reaction time, attention, fear of falling). Thus, biomechanical studies are a valuable clinical tool to investigate the impact of each of those factors on the ability to decrease slip potential and recover balance after a slip event.

A challenge in slip/fall biomechanical studies has been to reproduce the unexpected nature of real-life slipping accidents in laboratory settings. The effect of anticipating potentially slippery surfaces on gait biomechanics has not been investigated. Andres et al. [18] have compared the kinematic characteristics of steps prior to and onto a targeted known slippery area. However, the subjects knew the surface was slippery. Examining possible gait adaptations arising from anticipation effects will have implications on the findings of slip/fall experiments and provide insights on ‘control mechanisms’ used to reduce slip and fall potentials.

The goal of this study was to investigate whether subjects change gait biomechanics (on both level and inclined surfaces) when there is a possibility of a slippery environment. Specific changes in walking patterns (if any) adopted were quantified. The findings reported here (dry surfaces) are part of a larger study that investigated gait biomechanics on different surfaces of varying inclination and slipperiness (dry, wet, soap, oil).

Section snippets

Subjects

Sixteen healthy subjects (eight male, eight female) participated in this study with informed consent approved by the Institutional Review Board of the University of Pittsburgh. Their ages ranged from 19 to 30 years (mean 23 years, S.D. 4 years), mean weight from 62.6 to 82.4 kg (mean 68.7 kg, S.D. 6.8 kg) and height from 1.63 to 1.85 m (mean 1.73 m, S.D. 0.07 m). Exclusionary criteria included a history of neurological or orthopedic disease and any difficulties impeding normal locomotion.

Experimental set-up

A

Baseline data and ramp angle effect

In order to investigate the anticipation effect of slippery surfaces on gait biomechanics, baseline normative values on horizontal and inclined vinyl surfaces were first recorded. As anticipated, the kinetics of locomotion in these baseline trials were affected by ramp angle [11]. More specifically, increases in the ramp angle were associated with increases in ground reaction forces and RCOFs (Fig. 1). For level walking, the typical biphasic shear force reached a maximum of 1.8 N/kg and

Discussion

The main finding of this study was that human adaptations to ‘potentially’ slippery surfaces (anticipation trials) resulted in significant differences in gait biomechanics when compared with characteristics of baseline trials, during which subjects walked onto a known dry surface. The overall effect of these adaptations was a reduction in the peak RCOF, thus decreasing slip and fall potentials [10], [11], [12], [13], [16], [19], [20]. In addition, these adaptations led to significant reductions

Acknowledgements

Supported by NIOSH (5 R03 OH03621).

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