The reliability of the Extra Load Index as a measure of relative load carriage economy

Abstract

The aim of this study was to measure the reliability of the extra load index (ELI) as a method for assessing relative load carriage economy. Seventeen volunteers (12 males, 5 females) performed walking trials at 3 km·h^?1, 6 km·h^?1 and a self-selected speed. Trial conditions were repeated 7 days later to assess test–retest reliability. Trials involved four 4-minute periods of walking, each separated by 5 min of rest. The initial stage was performed unloaded followed in a randomised order by a second unloaded period and walking with backpacks of 7 and 20 kg. Results show ELI values did not differ significantly between trials for any of the speeds (p = 0.46) with either of the additional loads (p = 0.297). The systematic bias, limits of agreement and coefficients of variation were small in all trial conditions. We conclude the ELI appears to be a reliable measure of relative load carriage economy.

Practitioner Summary: This paper demonstrates that the ELI is a reliable measure of load carriage economy at a range of walking speeds with both a light and heavy load. The ELI, therefore, represents a useful tool for comparing the relative economy associated with different load carriage systems.     

The Extra Load Index as a method for comparing the relative economy of load carriage systems

The Extra Load Index (ELI) has been proposed as a suitable method of assessing the relative economy of load carriage systems. The purpose of this study was to determine, based on empirical evidence, that the ELI can accommodate variations in both body composition and added load. In total, 30 women walked carrying loads of up to 70% body mass at self-selected walking speeds whilst expired air was collected. In addition, each of the women had body composition assessed via dual energy X-ray absorptiometry. Results show that the ELI is independent of body composition variables, the magnitude of additional loads and the speed of progression. Consequently, it is suggested that it represents an appropriate method of comparing load carriage systems in both scientific and commercial arenas. STATEMENT OF RELEVANCE: This paper demonstrates that ELI is independent of body composition, added load and speed and is therefore an appropriate method to generalise comparisons of load carriage systems. It has the advantage of being easily understood by manufacturers and consumers whilst retaining appropriate scientific precision.     

A survey of anthropometry and physical accommodation in ergonomics curricula

The size and shape of users are an important consideration for many products and environments. Designers and engineers in many disciplines must often accommodate these attributes to meet objectives such as fit and safety. When practitioners have academic training in addressing these issues, it is typically through courses in Human Factors/Ergonomics (HF/E). This paper investigates education related to physical accommodation and offers suggestions for improvement. A survey was conducted wherein 21 instructors at 18 universities in the United States provided syllabi for 29 courses, which were analysed to determine topics related to anthropometry and resources used for the courses. The results show that within the US, anthropometry is covered in the majority of courses discussing physical ergonomics, but important related concepts were often omitted (e.g. digital human modelling, multivariate accommodation and variability across global populations). Curricula could be improved by incorporating more accurate anthropometry, multivariate problems and interactive online tools.

Practitioner Summary: This paper describes a study investigating collegiate ergonomics courses within the US in the area of physical accommodation. Course schedules and texts were studied for their treatment of several topics related to accommodating the spatial requirements (anthropometry) of users. Recommendations are made for improving course curricula.     

Ergonomics in the development and implementation of organisational strategy for sustainability

This is the first phase of an ergonomics study of sustainability in a rail organisation, particularly environmental sustainability. The main emphasis has been on the use of a qualitative approach to carry out in-depth consultation with those in influential and policy setting roles in the organisation, collecting and analysing perceptions on sustainability policy and related business processes. The study identified factors affecting implementation of policy on sustainability and these have been developed to produce a list of requirements for implementing the policy. The findings are valuable in understanding the range of attitudes, aspirations and perceived constraints, from the perspective of those in senior roles in the company, and development of a sustainability strategy for a rail infrastructure owner. There is need for wider consultation, both within the organisation and externally, to validate and refine the understanding of barriers to the implementation of the policy. The role of ergonomics in supporting the work on sustainability is discussed.

Practitioner Summary: The study collects in-depth views from senior managers on the challenges of implementing a policy on sustainability in a rail organisation. Outputs include a list of factors affecting implementation of policy and requirements for better implementation of policy in this area. Potential contributions of ergonomics to sustainability in organisational contexts are discussed.     

Systems scenarios: a tool for facilitating the socio-technical design of work systems

Abstract

The socio-technical systems approach to design is well documented. Recognising the benefits of this approach, organisations are increasingly trying to work with systems, rather than their component parts. However, few tools attempt to analyse the complexity inherent in such systems, in ways that generate useful, practical outputs. In this paper, we outline the ‘System Scenarios Tool’ (SST), which is a novel, applied methodology that can be used by designers, end-users, consultants or researchers to help design or re-design work systems. The paper introduces the SST using examples of its application, and describes the potential benefits of its use, before reflecting on its limitations. Finally, we discuss potential opportunities for the tool, and describe sets of circumstances in which it might be used.

Practitioner Summary: The paper presents a novel, applied methodological tool, named the ‘Systems Scenarios Tool’. We believe this tool can be used as a point of reference by designers, end-users, consultants or researchers, to help design or re-design work systems. Included in the paper are two worked examples, demonstrating the tool’s application.     

The predictive validity of the RSI QuickScan questionnaire with respect to arm,shoulder and neck symptoms in computer workers

The aim of this study was to determine whether results from the RSI QuickScan questionnaire on risk factors for arm, shoulder and neck symptoms can predict future arm, neck and shoulder symptoms in a population of computer workers. For this prospective cohort study, with a follow-up of 24 months, 3383 workers who regularly worked with a computer were approached. Generalised estimating equations (GEE) with 6, 12, 18 and 24 months time lags were used to determine whether high exposure was related to symptoms at follow-up. The results showed that high scores on 9 out of 13 scales, including previous symptoms, were significantly related to arm, shoulder and neck symptoms at follow-up. These results provide support for the predictive validity of the RSI QuickScan questionnaire.

Practitioner Summary: The results showed that high scores on 9 out of 13 scales, including previous symptoms, were significantly related to arm, shoulder and neck symptoms at follow-up. The RSI QuickScan questionnaire may be recommended as a tool in the identification of computer workers who should be targeted with interventions aimed at prevention of future symptoms.     

Designing sustainable work systems: The need for a systems approach

There is a growing discussion concerning sustainability. While this discussion was at first mainly focused on a society level – and sometimes regarding especially environmental problems, one can now see that this topic is of increasing relevance for companies worldwide and even the social dimension of this three pillar approach is gaining more and more importance. This leads to some questions: Is sustainability already a part of human factors thinking or do we have to further develop our discipline? How can we define sustainable work systems? What are the topics we have to consider? Do we need a new systems ergonomics perspective regarding whole value creation chains and a life-cycle perspective concerning products (and work systems)? How can we deal with potential contradictions about social, ecological, and economic goals?     

On the paradoxical decrease of self-reported cognitive failures with age

The science of Human Factors and Ergonomics (HF/E) often relies on self-report. This is a cause for concern because subjective methods are inherently susceptible to bias. Here, we present, examine and discuss a puzzling association between age and self-reported cognitive failures as assessed with Broadbent's Cognitive Failures Questionnaire (CFQ). Despite many well-established age-associated forms of cognitive decline, older persons actually report almost equivalent, or even less, cognitive failures on the CFQ than younger persons. Our present analysis indicates that this paradox may be resolved through the fact that people show age-related learning/adaptation/compensation and by the observation that the CFQ measures peoples' beliefs with respect to an individually idiosyncratic reference. Yet, at the heart of the paradox may be the idea that people cannot remember their own cognitive failures, pointing to even greater concerns with all forms of subjective self-report and its use in HF/E.     

Characterisation of regional skin temperatures in recreational surfers wearing a 2-mm wetsuit

The purpose of this study was to investigate skin temperatures across surfers’ bodies while wearing a wetsuit during recreational surfing. Forty-six male recreational surfers participated in this study. Participants were instrumented with eight wireless iButton thermal sensors for the measurement of skin temperature, a Polar RCX5 heart rate monitor and a 2-mm full wetsuit. Following instrumentation, participants were instructed to engage in recreational surfing activities as normal. Significant differences (p < 0.001) in skin temperature (T_sk) were found across the body while wearing a wetsuit during recreational surfing. In addition, regional skin temperature changed across the session for several regions of the body (p < 0.001), and the magnitude of these changes varied significantly between regions. We show for the first time that significant differences exist in skin temperature across the body while wearing a wetsuit during a typical recreational surfing session. These findings may have implications for future wetsuit design.

Practitioner Summary: This study investigated the impact of wearing a wetsuit during recreational surfing on regional skin temperatures. Results from this study suggest that skin temperatures differ significantly across the body while wearing a 2-mm wetsuit during recreational surfing. These findings may have implications for future wetsuit design.     

A proposed index of usability: a method for comparing the relative usability of different software systems

. Usability is becoming a more and more important software criterion, but the present usability measurement methods are either difficult to apply, or overly dependent upon evaluators' expertise. Based on human information processing theory, this study identified eight human factors considerations which are relevant to software usability. These considerations as well as the three stages of human information processing theory formed the framework from which our Purdue Usability Testing Questionnaire (PUTQ) is derived. An experiment was conducted to test the validity of PUTQ. The experiment result showed high correlation between PUTQ and the Questionnaire for User Interaction Satisfaction (QUIS version 5.5). In addition, PUTQ detected the differences in user performance between two experimental interface systems, but QUIS failed to do so.     

The aesthetic and the ethic dimensions of human factors and design

This article discusses the relationship between aesthetics, ethics, and the traditional research issues in human factors, and argues that it is important and beneficial both to the human society and to the human factors profession that we incorporate the aesthetic and the ethic dimensions explicitly and consciously in human factors research and practice. These two dimensions can help us put the current human factors research in a larger context. We can see more clearly the limitations of current research and the needs and challenges for research in new areas. The two dimensions also offer some new perspectives from which we can examine the current work systems and products, explain the demise of old work systems and products, and predict the possible emergence of new work systems and products.     

Nanomaterials in the field of design ergonomics: present status

Application of nanotechnology and nanomaterials is not new in the field of design, but a recent trend of extensive use of nanomaterials in product and/or workplace design is drawing attention of design researchers all over the world. In the present paper, an attempt has been made to describe the diverse use of nanomaterials in product and workplace design with special emphasis on ergonomics (occupational health and safety; thermo-regulation and work efficiency, cognitive interface design; maintenance of workplace, etc.) to popularise the new discipline ‘nanoergonomics’ among designers, design users and design researchers. Nanoergonomics for sustainable product and workplace design by minimising occupational health risks has been felt by the authors to be an emerging research area in coming years.

Practitioner Summary: Use of nanomaterials in the field of design ergonomics is less explored till date. In the present review, an attempt has been made to extend general awareness among ergonomists/designers about applications of nanomaterials/nanotechnology in the field of design ergonomics and about health implications of nanomaterials during their use.     

The effect of load distribution within military load carriage systems on the kinetics of human gait

Military personnel carry their equipment in load carriage systems (LCS) which consists of webbing and a Bergen (aka backpack). In scientific terms it is most efficient to carry load as close to the body's centre of mass (CoM) as possible, this has been shown extensively with physiological studies. However, less is known regarding the kinetic effects of load distribution. Twelve experienced load carriers carried four different loads (8, 16, 24 and 32 kg) in three LCS (backpack, standard and AirMesh). The three LCS represented a gradual shift to a more even load distribution around the CoM. Results from the study suggest that shifting the CoM posteriorly by carrying load solely in a backpack significantly reduced the force produced at toe-off, whilst also decreasing stance time at the heavier loads. Conversely, distributing load evenly on the trunk significantly decreased the maximum braking force by 10%. No other interactions between LCS and kinetic parameters were observed. Despite this important findings were established, in particular the effect of heavy load carriage on maximum braking force. Although the total load carried is the major cause of changes to gait patterns, the scientific testing of, and development of, future LCS can modify these risks.     

The Revised Strain Index: an improved upper extremity exposure assessment model

Abstract

The Revised Strain Index (RSI) is a distal upper extremity (DUE) physical exposure assessment model based on: intensity of exertion, frequency of exertion, duration per exertion, hand/wrist posture and duration of task per day. The RSI improves upon the 1995 Strain Index (SI) by using continuous rather than categorical multipliers, and replacing duty cycle with duration per exertion. In a simulation of 13,944 tasks, the RSI and 1995 SI showed good agreement in risk predictions for 1995 SI scores ≤3 (safe) and >13.5 (hazardous). For tasks with 1995 SI scores of >3 and ≤13.5, the two models showed marked disagreement, with the RSI providing much greater discriminations between ‘safe’ and ‘hazardous’ tasks for various combinations of force, repetition and duty cycle. We believe the RSI is a substantially improved model that will be useful for DUE task analysis, intervention and design.

Practitioner Summary: RSI is a substantial improvement over the 1995 SI. It should be a valuable tool for designing and analysing tasks to determine risk of musculoskeletal injuries. RSI is applicable to a wide variety of tasks including very low force and very high repetition tasks such as keyboard use.     

Task exposures in an office environment: a comparison of methods

Task-related factors such as frequency and duration are associated with musculoskeletal disorders in office settings. The primary objective was to compare various task recording methods as measures of exposure in an office workplace. A total of 41 workers from different jobs were recruited from a large urban newspaper (71% female, mean age 41 years SD 9.6). Questionnaire, task diaries, direct observation and video methods were used to record tasks. A common set of task codes was used across methods. Different estimates of task duration, number of tasks and task transitions arose from the different methods. Self-report methods did not consistently result in longer task duration estimates. Methodological issues could explain some of the differences in estimates seen between methods observed. It was concluded that different task recording methods result in different estimates of exposure likely due to different exposure constructs. This work addresses issues of exposure measurement in office environments. It is of relevance to ergonomists/researchers interested in how to best assess the risk of injury among office workers. The paper discusses the trade-offs between precision, accuracy and burden in the collection of computer task-based exposure measures and different underlying constructs captures in each method.     

A proposed index of usability: A method for comparing the relative usability of different software systems

Abstract

Usability is becoming a more and more important software criterion, but the present usability measurement methods are either difficult to apply, or overly dependent upon evaluators' expertise. Based on human information processing theory, this study identified eight human factors considerations which are relevant to software usability. These considerations as well as the three stages of human information processing theory formed the framework from which our Purdue Usability Testing Questionnaire (PUTQ) is derived. An experiment was conducted to test the validity of PUTQ. The experiment result showed high correlation between PUTQ and the Questionnaire for User Interaction Satisfaction (QUIS version 5.5). In addition, PUTQ detected the differences in user performance between two experimental interface systems, but QUIS failed to do so.     

Elite handcycling: a qualitative analysis of recumbent handbike configuration for optimal sports performance

Our understanding of handbike configuration is limited, yet it can be a key determinant of performance in handcycling. This study explored how 14 handcycling experts (elite handcyclists, coaches, support staff, and manufacturers) perceived aspects of recumbent handbike configuration to impact upon endurance performance via semi-structured interviews. Optimising the handbike for comfort, stability, and power production was identified as key themes. Comfort and stability were identified to be the foundations of endurance performance and were primarily influenced by the seat, backrest, headrest, and their associated padding. Power production was determined by the relationship between the athletes’ shoulder and abdomen and the trajectories of the handgrips, which were determined by the crank axis position, crank arm length, and handgrip width. Future studies should focus on quantifying the configuration of recumbent handbikes before determining the effects that crank arm length, handgrip width, and crank position have on endurance performance.

Practitioner Summary: To gain a greater understanding of the impact of handbike configurations on endurance performance, the perceptions of expert handcyclists were explored qualitatively. Optimising the handbike for comfort and stability, primarily via backrest padding and power production, the position of the shoulders relative to handgrips and crank axis, were critical.     

The role of anthropometry in designing for sustainability

An understanding of human factors and ergonomics facilitates the design of artefacts, tasks and environments that fulfil their users’ physical and cognitive requirements. Research in these fields furthers the goal of efficiently accommodating the desired percentage of user populations through enhanced awareness and modelling of human variability. Design for sustainability (DfS) allows for these concepts to be leveraged in the broader context of designing to minimise negative impacts on the environment. This paper focuses on anthropometry and proposes three ways in which its consideration is relevant to DfS: reducing raw material consumption, increasing usage lifetimes and ethical human resource considerations. This is demonstrated through the application of anthropometry synthesis, virtual fitting, and sizing and adjustability allocation methods in the design of an industrial workstation seat for use in five distinct global populations. This work highlights the importance of and opportunities for using ergonomic design principles in DfS efforts.

Practitioner Summary: This research demonstrates the relevance of some anthropometry-based ergonomics concepts to the field of design for sustainability. A global design case study leverages human variability considerations in furthering three sustainable design goals: reducing raw material consumption, increasing usage lifetimes and incorporating ethical human resource considerations in design.     

The use of systems development methodologies in practice: a field study

This paper discusses the findings of a field study of experienced systems developers which investigated the use of systems development methodologies (SDMs) in practice. Among the main findings to emerge are the following. There is a wide difference between the formalized sequence of steps and stages prescribed by a methodology and the methodology-in-action uniquely enacted for each development project. Also, there is much evidence which suggests that developers omit certain aspects of methodologies not from a position of ignorance, but from the more pragmatic basis that certain aspects are not relevant to the development environment they face. Thus, methodologies are tailored to the needs of the prevailing development environment and, being documented in a single manual often, are framed at a higher level of granularity that specifies broad activities and objectives, rather than specifying in a very detailed fashion the exact manner in which development should take place. Additionally, the findings clarify the apparently contradictory position in the literature as to whether developer experience is positively or negatively correlated with methodology use. The study would suggest that experienced developers are likely to use methodologies, albeit ones which have been heavily customized to the exigencies of the particular situation.     

A method for using legacy data for metamodel-based design of large-scale systems

Despite a steady increase in computing power, the complexity of engineering analyses seems to advance at the same rate. Traditional parametric design analysis is inadequate for the analysis of large-scale engineering systems because of its computational inefficiency; therefore, a departure from the traditional parametric design approach is required. In addition, the existence of legacy data for complex, large-scale systems is commonplace. Approximation techniques may be applied to build computationally inexpensive surrogate models for large-scale systems to replace expensive-to-run computer analysis codes or to develop a model for a set of nonuniform legacy data. Response-surface models are frequently utilized to construct surrogate approximations; however, they may be inefficient for systems having with a large number of design variables. Kriging, an alternative method for creating surrogate models, is applied in this work to construct approximations of legacy data for a large-scale system. Comparisons between response surfaces and kriging are made using the legacy data from the High Speed Civil Transport (HSCT) approximation challenge. Since the analysis points already exist, a modified design-of-experiments technique is needed to select the appropriate sample points. In this paper, a method to handle this problem is presented, and the results are compared against previous work.