Tom B. Leamon

Human-centred approaches in slipperiness measurement

A number of human—centred methodologies subjective, objective, and combined are used for slipperiness measurement. They comprise a variety of approaches from biomechanically-oriented experiments to psychophysical tests and subjective evaluations. The objective of this paper is to review some of the research done in the field, including such topics as awareness and perception of slipperiness, postural and balance control, rating scales for balance, adaptation to slippery conditions, measurement of unexpected movements, kinematics of slipping, and protective movements during falling. The role of human factors in slips and falls will be discussed. Strengths and weaknesses of human-centred approaches in relation to mechanical slip test methodologies are considered. Current friction-based criteria and thresholds for walking without slipping are reviewed for a number of work tasks. These include activities such as walking on a level or an inclined surface, running, stopping and jumping, as well as stair ascent and descent, manual exertion (pushing and pulling, load carrying, lifting) and particular concerns of the elderly and mobility disabled persons. Some future directions for slipperiness measurement and research in the field of slips and falls are outlined. Human-centred approaches for slipperiness measurement do have many applications. First, they are utilized to develop research hypotheses and models to predict workplace risks caused by slipping. Second, they are important alternatives to apparatus-based friction measurements and are used to validate such methodologies. Third, they are used as practical tools for evaluating and monitoring slip resistance properties of footwear, anti-skid devices and floor surfaces.

Measurement of slipperiness: fundamental concepts and definitions.

The main objective of this paper is to give an overview of basic concepts and definitions of terms related to the ‘measurement of slipperiness’ from the onset of a foot slide to a gradual loss of balance and a fall. Other unforeseen events prior to falls (e.g. tripping) are sparingly dealt with. The measurement of slipperiness may simply comprise an estimation of slipping hazard exposures that initiate the chain of events ultimately causing an injury. However, there is also a need to consider the human capacity to anticipate slipperiness and adapt to unsafe environments for avoiding a loss of balance and an injury. Biomechanical and human-centred measurements may be utilized for such an approach, including an evaluation of relevant safety criteria for slip/fall avoidance and procedures for validation of slip test devices. Mechanical slip testing approaches have been readily utilized to measure slipperiness in terms of friction or slip resistance but with conflicting outcomes. An improved understanding of the measurement of slipperiness paradigm seems to involve an integration of the methodologies used in several disciplines, among others, injury epidemiology, psychophysics, biomechanics, motor control, materials science and tribology.

Conceptual and definitional issues in occupational injury epidemiology

This paper presents several models that further define the concept of occupational injury. While traditional models have proved successful in isolating specific research questions and health phenomena, the conceptual model presented permits a broader view of all injury morbidity. This model is based on both the level and frequency of energy transfers. A process model of occupational injury is also presented to describe the basic pathophysiological relationships associated with tissue effects/damage and recovery/repair. Numerous tradeoffs exist in variable selection, and a third model explores some of these tradeoffs. Differences in terminology and fundamental principles can limit the progress of occupational injury research. Accordingly, an argument is made for consolidation and consensus of terms. Finally, considerations for research are suggested, with an emphasis on the severity of the injury, the risk ratio, and the population at risk.

Research to reality: a critical review of the validity of various criteria for the prevention of occupationally induced low back pain disability

Criteria have been suggested to reduce the incidence, or severity of low back pain disability. Five underlying theories for such criteria have been identified in the literature, and a critical review of the validity of these criteria has been carried out. Despite attributions elsewhere, peer-reviewed validation of the various criteria range from modest to nil. The need for a validation criterion for use in workplace design in order to reduce low back pain disability, or severity, is identified and the need for an international protocol to allow cross-study validation of present and future criteria is suggested.

Subjective assessment of floor slipperiness

Abstract Measured coefficients of friction of floor surfaces have not been shown to be consistent predictors of slipping and falling. However, human subjects appear to be able to perceive the slipperiness of a floor surface, and to modify their gait to mitigate the effects of slippery surfaces. This study investigated subjective rankings of floor surfaces (ceramic, steel, vinyl, plywood, and sandpaper) and the measured coefficients of friction. In addition, subjects reported a confidence rating on the occurence of a slip at “heel down”. The floor surfaces were selected a priori, to provide a range of slipperiness and subjects appeared to be able to reliably discriminate between those surfaces. Ceramic tile was the most frequently determined as the slippery floor with the high level of confidence ratings, CERTAIN and ALMOST CERTAIN. In other words, the confidence ratings were closely related to the subjective rankings. The higher the subjective rankings were, the higher the confidence ratings were. To prove subjective rankings by the quantitative measure, static coefficients of friction were measured and it appears that subjects were able to relate their sensations to a function of the static coefficient of friction.

Bending the tool and the effect on human performance: Further investigation of a simulated wire-twisting task

A previous experiment by the authors investigated the effect of the design of pliers on productivity. A simulated wire-twisting task performed at five heights between 10 inches above and 10 inches below elbow height formed the basis of the comparison. Pliers designed according to the American National Standard for long nose and long reach pliers were compared to bent-handled pliers designed at the Western Electric (WE) Co. The WE pliers, designed to reduce ulnar deviation during a wire-twisting task, resulted in productivity decrements between 1.4 and 17% across the five heights studied. The current experiment was a continuation of that study, adding orientation of the workplace in the sagittal plane as an independent variable. Wrist deviation in two planes were additional dependent measures, and the experiment was performed by female subjects with a mean age of 48.1 years. The results did not indicate a significant difference between productivity levels for the two pliers designs. Work height and work orientation, as well as their interaction, tended to have the strongest effects on productivity and wrist deviation. In general, productivity was inversely related to measures of discomfort and postural deviation.

An Investigation into the Effects of Knowledge of Results on Operator Performance

Abstract The effect of Knowledge of Results on the performance of female operators engaged on repetitive hand work in industry was investigated over a 40-day period. Significant changes in performance were observed. The relationship of these findings to earlier conflicting studies is discussed in terms of two mechanisms, the first utilizing information to alter and maintain the work pace and the second utilizing the feedback to motivate the subjects to alter their paces.

The effect of technique and shaft configuration in snow shoveling on physiologic, kinematic, kinetic and productivity variables.

A repeated measures 2 x 2 factorial design using a psychophysical experimental methodology was performed to quantify the effect of shaft design (straight and bent shaft) and shoveling technique (forward and backward progression) on heart rate, perceived exertion, productivity, trunk kinematics and load kinetics. Ten male subjects performed four 8-min trials of snow shoveling on a paved asphalt surface. The most notable finding was significantly less trunk flexion with the bent shaft (41.4 degrees ) than with the straight shaft design (49.2 degrees ). The study results led to a recommendation of a bent-shaft shovel for the purpose of reducing trunk flexion. In the absence of any strong positive evidence and due to poor subjective response to backward progression while shoveling, this technique was not recommended.

Bending the Tool and the Effect on Productivity: An Investigation of a Simulated Wire-Twisting Task

One facet of the ergonomics approach to the problem of cumulative trauma disorders (CTDs) in industry has been the design of hand tools aimed at reducing exposure to deviated wrist postures. Despite rising incidence rates, the wide dissemination of the Western Electric (WE) plier study, and several empirical investigations of bent-handled knives for the meat-packing industry, the demand for bent-handled tools is low. Most empirical investigations of such tools have focused on performance measures associated with discrete, well-defined motions rather than with performance in terms of output per unit time. It was hypothesized that the performance of operators using bent pliers might be significantly lower than that achieved with straight pliers. This hypothesis was confirmed through an experimental investigation of a simulated wire-twisting task comparing the WE pliers to standard needle-nose pliers. The performance decrement associated with the WE pliers, which depended on work height, ranged from 1.4% to ...

L5/S1: So who is counting?

Low back pain (LBP) is a major problem in the western world and criteria to control incidence rates of low back pain have been developed. The significance of predicted L5/S1 compression is examined in the context of its value as a criterion for reducing the incidence of LBP. A proposal is made to consider a broader, systems approach to LBP which is based on consideration of disability in light of the experimentally determined, significance of factors far removed from events at L5/S1. The potential benefits of considering the Low Back Pain Disability System (LBPDS) are identified.