Showing papers in "Ergonomics in 2000"

Activity theory as a framework for analyzing and redesigning work

Abstract: Cultural-historical activity theory is a new framework aimed at transcending the dichotomies of micro- and macro-, mental and material, observation and intervention in analysis and redesign of work. The approach distinguishes between short-lived goal-directed actions and durable, object-oriented activity systems. A historically evolving collective activity system, seen in its network relations to other activity systems, is taken as the prime unit of analysis against which scripted strings of goal-directed actions and automatic operations are interpreted. Activity systems are driven by communal motives that are often difficult to articulate for individual participants. Activity systems are in constant movement and internally contradictory. Their systemic contradictions, manifested in disturbances and mundane innovations, offer possibilities for expansive developmental transformations. Such transformations proceed through stepwise cycles of expansive learning which begin with actions of questioning the existing standard practice, then proceed to actions of analyzing its contradictions and modelling a vision for its zone of proximal development, then to actions of examining and implementing the new model in practice. New forms of work organization increasingly require negotiated 'knotworking' across boundaries. Correspondingly, expansive learning increasingly involves horizontal widening of collective expertise by means of debating, negotiating and hybridizing different perspectives and conceptualizations. Findings from a longitudinal intervention study of children's medical care illuminate the theoretical arguments.

Occupational low back disorder causation and control.

Abstract: Low back disorders (LBDs) continue to be the most common musculoskeletal problem in the workplace. It affects many workers, is associated with high costs to industry and the individual, and can negatively influence the quality of life for the workers. Currently there is significant controversy about the work-relatedness of LBD and the ability of ergonomics interventions to control the problem. This paper systematically examines the body of knowledge associated with LBDs and considers how information from different disciplines of study collectively might be used to assess the causality and control of LBD due to physical factors associated with work.

Training in virtual environments: transfer to real world tasks and equivalence to real task training.

Abstract: Virtual environments (VEs) are extensively used in training but there have been few rigorous scientific investigations of whether and how skills learned in a VE are transferred to the real world. This research aimed to measure and evaluate what is transferring from training a simple sensorimotor task in a VE to real world performance. In experiment 1, real world performances after virtual training, real training and no training were compared. Virtual and real training resulted in equivalent levels of post-training performance, both of which significantly exceeded task performance without training. Experiments 2 and 3 investigated whether virtual and real trained real world performances differed in their susceptibility to cognitive and motor interfering tasks (experiment 2) and in terms of spare attentional capacity to respond to stimuli and instructions which were not directly related to the task (experiment 3). The only significant difference found was that real task performance after training in a VE was less affected by concurrently performed interference tasks than was real task performance after training on the real task. This finding is discussed in terms of the cognitive load characteristics of virtual training. Virtual training therefore resulted in equivalent or even better real world performance than real training in this simple sensorimotor task, but this finding may not apply to other training tasks. Future research should be directed towards establishing a comprehensive knowledge of what is being transferred to real world performance in other tasks currently being trained in VEs and investigating the equivalence of virtual and real trained performances in these situations.

Teamwork in multi-person systems: a review and analysis.

Abstract: As the scope and complexity of modern task demands exceed the capability of individuals to perform, teams are emerging to shoulder the burgeoning requirements Accordingly, researchers have striven to understand and enhance human performance in team settings The purpose of this review is to summarize that research, from the theoretical underpinnings that drive it, to the identification of team-level elements of success, to the methodologies and instruments that capture and measure those characteristics Further specified are three important avenues to creating successful teams: team selection, task design and team training In other words, one can select the right people, provide them with a task engineered for superior performance and train them in the appropriate skills to accomplish that task Under task design, new technologies and automation are examined that both support and impede team functioning Finally, throughout are provided critical remarks about what is known about teamwork and what is needed to be known to move the science and practice of team performance forward The paper concludes with the identification of team issues that require further investigation

From human-machine interaction to human-machine cooperation

Abstract: Since the 1960s, the rapid growth of information systems has led to the wide development of research on human-computer interaction (HCI) that aims at the designing of human-computer interfaces presenting ergonomic properties, such as friendliness, usability, transparency, etc. Various work situations have been covered--clerical work, computer programming, design, etc. However, they were mainly static in the sense that the user fully controls the computer. More recently, public and private organizations have engaged themselves in the enterprise of managing more and more complex and coupled systems by the means of automation. Modern machines not only process information, but also act on dynamic situations as humans have done in the past, managing stock exchange, industrial plants, aircraft, etc. These dynamic situations are not fully controlled and are affected by uncertain factors. Hence, degrees of freedom must be maintained to allow the humans and the machine to adapt to unforeseen contingencies. A human-machine cooperation (HMC) approach is necessary to address the new stakes introduced by this trend. This paper describes the possible improvement of HCI by HMC, the need for a new conception of function allocation between humans and machines, and the main problems encountered within the new forms of human-machine relationship. It proposes a conceptual framework to study HMC from a cognitive point of view in highly dynamic situations like aircraft piloting or air-traffic control, and concludes on the design of 'cooperative' machines.

Designing automation for human use: empirical studies and quantitative models.

Abstract: An emerging knowledge base of human performance research can provide guidelines for designing automation that can be used effectively by human operators of complex systems. Which functions should be automated and to what extent in a given system? A model for types and levels of automation that provides a framework and an objective basis for making such choices is described. The human performance consequences of particular types and levels of automation constitute primary evaluative criteria for automation design when using the model. Four human performance areas are considered--mental workload, situation awareness, complacency and skill degradation. Secondary evaluative criteria include such factors as automation reliability, the risks of decision/action consequences and the ease of systems integration. In addition to this qualitative approach, quantitative models can inform design. Several computational and formal models of human interaction with automation that have been proposed by various researchers are reviewed. An important future research need is the integration of qualitative and quantitative approaches. Application of these models provides an objective basis for designing automation for effective human use.

A field study of supplementary rest breaks for data-entry operators.

Abstract: This study examined the effects of supplementary rest breaks on musculoskeletal discomfort, eyestrain, mood, and performance in data-entry workers. Two rest break schedules were compared in a within-subjects design. Workers alternated between a 'conventional' and a 'supplementary' schedule in 4-week intervals. The conventional schedule contained a 15-min break during the first half of the work shift and a 15-min break during the second half of the shift. The supplementary schedule contained the same two 15-min breaks, and a 5-min break during each hour which otherwise did not contain a break, for a total of 20 extra minutes of break time. Results are based on data from 42 workers. They indicated that discomfort in several areas of the body, and eyestrain, were significantly lower under the supplementary than under the conventional schedule. While symptoms increased from pre- to post-work periods under both schedules, the magnitude of the increases was significantly less under the supplementary schedule. In addition, increases in discomfort of the right forearm, wrist and hand over the course of the work week under the conventional schedule were eliminated under the supplementary schedule. These beneficial effects were obtained without reductions in data-entry performance.

Learning from errors in a driving simulation: effects on driving skill and self-confidence.

Abstract: Two experiments investigated the effect of making errors during training (error training) on a driving simulator versus learning from examples of errors (guided error training) on driving skill and confidence. Experiment 1 indicated that compared with errorless learning (where participants drove through a training run not designed to elicit errors), error training led to significantly better transfer to driving tests that were analogous to those situations encountered in training and more effective use of strategies for coping with a novel driving situation. Error training also reduced self-confidence in driving skill at the end of training relative to errorless learning. Experiment 2 provided weak evidence of the superiority of guided error training over errorless learning (where the driver in the video did not make any errors) on analogous tests, and no evidence of transfer to a novel test. Furthermore, guided error training did not influence self-confidence in driving skill. The potential value of driving simulators in providing active processing during driver training is discussed, along with the effects of passive and active exposure to errors on driver confidence.

Biomechanical and metabolic effects of varying backpack loading on simulated marching.

Abstract: Twelve healthy, male Army recruits performed three, 40-min treadmill marches at 6 km/h, under three load carriage conditions: 0%-body weight (BW) backpack load, 15%-BW load and 30%-BW load. Kinematic and kinetic data were obtained, immediately before and after each treadmill march, for computing ankle, knee and hip joint rotations and moments. Metabolic data (oxygen uptake (VO2), expired ventilation (VE), respiratory exchange ratio (RER)), heart rate (HR) and ratings of perceived exertion (RPE) were collected continuously during marching. Significant differences (p < or = 0.05) were observed between each load for VO2, HR and VE throughout the marches. At 40 min, relative energy costs for 0%-BW, 15%-BW and 30%-BW loads were 30, 36 and 41% VO2max, respectively. RPE responses during marching significantly differed for only the 30%-BW load and were greater than responses at 0%-BW and 15%-BW loads. During load carriage trials prior to treadmill marches (pre-march), peaks in internal, hip extension, knee extension and ankle plantar flexion moments increased with increasing backpack load. Relative to 0%-BW load, percentage increases in knee moments, due to 15%-BW and 30%-BW loads, pre-march, were substantially larger than the percentage increases for hip extension and plantar flexion moments, pre-march. Pre-march and post-march peaks in hip extension and ankle plantar flexion moments were similar with all loads, while notable pre-march to post-march declines were observed for knee extension moment peaks, at 15%-BW and 30%-BW load. Pre-march joint loading data suggests that the knee may be effecting substantial compensations during backpack loaded marching, perhaps to attenuate shock or reduce load elsewhere. Post-march kinetic data (particularly at 15%-BW and 30%-BW load), however, indicates that such knee mechanics were not sustained and suggests that excessive knee extensor fatigue may occur prior to march end, even though overall metabolic responses, at 15%-BW and 30%-BW load, remained within generally recommended limits to prevent fatigue during prolonged work.

Promoting children's physical activity in primary school: an intervention study using playground markings.

Abstract: The physical activity levels of 47, 5- to 7-year-old children were assessed before and after a school playground was painted with fluorescent markings. Children's physical activity was measured using heart rate telemetry during three playtimes before and after the markings were laid down. Children in the experimental and control groups spent 27 and 29 min, respectively, in moderate to vigorous physical activity (MVPA) before the intervention, increasing to 45 and 36 min, respectively, during the intervention period. MVPA, vigorous physical activity (VPA) and mean heart rate remained relatively stable in the control group compared to respective increases of 10 and 5% of playtime and 6 beats min(-1) in the experimental group during the intervention period. The ANCOVA analysis revealed significant interactions and main effects for the intervention for MVPA, VPA and mean heart rate. Conversely there were no main effect differences between groups. These results suggest that while playground markings had a significant and positive influence on children's physical activity, factors other than playground markings may also influence children's physically active play.

A case study of co-ordinative decision-making in disaster management

Abstract: A persistent problem in the management of response to disasters is the lack of co-ordination between the various agencies involved. This paper reports a case study of inter-agency co-ordination during the response to a railway accident in the UK. The case study examined two potential sources of difficulty for co-ordination: first, poorly shared mental models; and, second, a possible conflict between the requirements of distributed decision-making and the nature of individual decision-making. Interviews were conducted with six individuals from three response agencies. Analysis of reported events suggested that inter-agency co-ordination suffered through a widespread difficulty in constructing a reflexive shared mental model; that is, a shared mental representation of the distributed decision-making process itself, and its participants. This difficulty may be an inherent problem in the flexible development of temporary multi-agency organizations. The analysis focused on a distributed decision over how to transport casualties from an isolated location to hospital. This decision invoked a technique identified here as the progression of multiple options, which contrasts with both recognition-primed and analytical models of individual decision-making. The progression of multiple options appeared to be an effective technique for dealing with uncertainty, but was a further source of difficulty for inter-agency co-ordination.

The potential for social contextual and group biases in team decision making: Biases, conditions and psychological mechanisms

Abstract: This paper provides a critical review of social contextual and group biases that are relevant to team decision-making in command and control situations. Motivated by the insufficient level of attention this area has received, the purpose of the paper is to provide an insight into the potential that these types of biases have to affect the decision-making of such teams. The biases considered are: false consensus, groupthink, group polarization and group escalation of commitment. For each bias the following four questions are addressed. What is the descriptive nature of the bias? What factors induce the bias? What psychological mechanisms underlie the bias? What is the relevance of the bias to command and control teams? The analysis suggests that these biases have a strong potential to affect team decisions. Consistent with the nature of team decision-making in command and control situations, all of the biases considered tend to be associated with those decisions that are important or novel and are promoted by time pressure and high levels of uncertainty. A concept unifying these biases is that of the shared mental model, but whereas false consensus emanates from social projection tendencies, the rest emanate from social influence factors. The authors also discuss the 'tricky' distinction between teams and groups and propose a revised definition for command and control team. Finally, the authors emphasize the need for future empirical research in this area to pay additional attention to the social side of cognition and the potential that social biases have to affect team decision-making.

Behavioural implications of alarm mistrust as a function of task workload

Abstract: The research was conducted to investigate the effect of increasing primary task and alarm workload on alarm mistrust as reflected by alarm and primary task performances. A total of 126 undergraduate students performed a complex psychomotor task battery three times, with the number of concurrent tasks increasing each time. During their performance, the students were required to react to an alarm system (including visual and auditory components) of questionable reliability. Depending on the group to which participants were assigned, the alarm presentation rate constituted a low-, medium- or high-workload condition. Alarm response data (times, frequencies, accuracies) and primary task data (tracking error) were analyzed to assess performance differences as a function of primary and secondary task workload levels. Results generally supported the hypotheses: increasing primary task and alarm task workload degraded alarm response performance. Also, response frequencies supported earlier research suggesting that participants 'probability match' their response rates to alarm system reliability. The results are discussed with regard to the cry-wolf effect, attention theory and alarm system design.

Lumbar erector spinae oxygenation during prolonged contractions: implications for prolonged work

Abstract: Owing to the recent interest in torso stabilization exercises together with many questions regarding the duration of prolonged isometric holds in occupational settings, the authors attempted to assess the level of back muscle oxygenation during prolonged isometric contractions. Specifically, this study recorded relative oxygen saturation of haemoglobin/myoglobin using Near Infrared Spectroscopy (NIRS) in the L3 erector mass during prolonged isometric contractions at intensities from 2 to 30% of maximum voluntary contraction (MVC). It was hypothesized that available oxygen to these muscles is severely compromised even at moderate levels of activation observed in occupational work. Eight volunteers without a history of lower back pain or injury participated in this study. The exercise task involved isometric contraction of the lower erector spinae at five different levels of each subject's maximal voluntary contraction: 2, 5, 10, 20 and 30% MVC, presented in random order. Subjects were placed in a sitting position, with a curved plastic plate secured horizontally to the pelvis to minimize movement at the hip joint. During extensor exertions, they were restrained with a harness that was attached at chest level to a load cell. Each isometric contraction was performed for 30 s followed by 1 min of rest. All levels of contraction demonstrated reduction in oxygen. Given the concern for motion artefact on the NIRS signal, sham trials were conducted where the subjects went through the procedure of attaching the pulling cable but no active pull was performed. These trials showed no change in the NIRS signal. At this time NIRS appears to be the only non-invasive instrumentation available to indicate total available muscle oxygen during low level, prolonged work. Although the specific tissue volume sampled by NIRS cannot be positively identified, it appears that tissue oxygenation in the lumbar extensor musculature is reduced as a function of contraction intensity, even at levels as low as 2% of MVC. These data have implications for prolonged work where postures requiring isometric contractions are sometimes held for hours, and where musculoskeletal illness has been linked to prolonged contraction levels above 2%MVC--these data suggest a possible biological pathway.

Performance and human factors: considerations about cognition and attention for self-paced and externally-paced events

Abstract: The cognitive psychology school of thought has spawned models of sequential stages or phases of information processing associated with various tasks. It has encouraged the study of cognitions and attention as related to learning, performance and high levels of achievement in goal-directed complex activities in which movement is the medium of expression. Although more recently proposed dynamical systems models challenge the simplicity of this approach, there is little doubt that the ability to learn as well as to excel in performing movement skills depends to a great degree on the effective self-regulation of cognitive processes in a variety of situations. What to think about (or not think about) prior to, during and even after an event can have great consequences on present and subsequent performance. Relevant externally-provided and self-generated strategies should enable these processes to function at an optimal level, and are the subject of an increasing amount of research. For such purposes, it is convenient to categorize events as self-paced (closed) and externally-paced (open). Examples of both types of events exist in sport as well as in various occupations and recreational activities, with different information processing demands associated with each one. Any breakdown in a particular stage of processing will potentially lead to poorer performance. Special training techniques and strategies are evolving from the cognitive and psychophysiological research literature that might improve the level of functioning at each stage for either self-paced or externally-paced skills.

Culture, politics and ergonomics

Abstract: The beginning of a new century is an appropriate moment to consider the role of ergonomics in relation to the problems facing society. To help solve these serious global problems, ergonomics needs to be open to new disciplines, particularly those in the social sciences. Also, it may be difficult to generalize research on human-centred sociotechnical design without taking into account national characteristics, economics and political constraints. Currently there is more interest than ever in what ergonomics has to offer, but to deliver its promise requires a much broader approach than is usual. By adopting such new approaches one may help solve both the problems of the overdeveloped post-industrial societies and those of the societies of the Third World, where a new approach to work and economics may provide an improved chance for development given the recent changes in global economic policy.

Posture, discomfort and performance in a VDT task.

Abstract: Improvements in workplace, working posture, and discomfort need to be justified in terms of improvements in performance. Previously, a visual inspection task has been investigated. The objective of the current study was to demonstrate the interactions between workplace, work duration, discomfort, working posture, as well as performance in a 2-h typing task. Three levels of keyboard heights were used to change working posture (e.g. joint angles and postural shifts), and thus presumably discomfort (e.g. rating of perceived discomfort and body part discomfort), and performance (e.g. typing speed, error rate and error correction rate). The results indicated that the hypothesized posture-comfort-performance interrelationships were partially supported. Keyboard height had effects on working posture adopted. As in previous studies, the rate of postural shift was a good indication of discomfort in a VDT task. Discomfort and postural shift rate had adverse effects on performance (e.g. error rate). However, these effects on error rate may not be strong.

Usability testing in 2000 and beyond

Abstract: Usability testing is a widely used technique to evaluate user performance and acceptance of products and systems. It was introduced in the late 1980s and rose to popularity in the past decade. This paper provides a view of the current status of usability testing as a method and describes how it will be used in the 21st century. Although usability testing may not be the most efficient technique for discovery of usability problems, it is a reliable way to estimate quantitatively users' performance and subjective satisfaction with products. Four major trends in usability testing include: common reporting formats and methods for industry; Internet application and website testing; testing of mobile, handheld devices; and testing in more naturalistic environments such as simulated homes and classrooms. In the 21st century, 'quick and clean' usability testing methods are needed to provide valid and reliable data on how well people use products and systems, and how they like using them.

Team situation assessment and information distribution.

Abstract: Described is the cooperative work of constructing team situation awareness within two teams of a military command and control unit. Specifically discussed is how the distributed cognitive and cooperative work of decision-making of the two teams is structured. The situation enabled two different ways of distributing information within the team: one serial and one parallel. One team chose the parallel information transfer, the other the serial one. Discussed is the interaction patterns that emerge in the respective teams and their consequences for situation assessment and situation awareness. The differences are then discussed in terms of means of sharing information. Some hypotheses for future research are also offered.

The effect of glycogen depletion on the curvature constant parameter of the power-duration curve for cycle ergometry

Abstract: For high-intensity cycle ergometer exercise, the relation between power (P) and its tolerable duration (t) has been well characterized by the hyperbolic relationship: (P-thetaF) t = W', or P = W' (1/t)+thetaF, where thetaF may be termed the 'fatigue threshold'. The curvature constant (W') reflects a constant amount of work which is postulated to be equivalent to a finite energy store that relates to the oxygen-deficit: phosphagen pool, anaerobic glycolysis and oxygen stores. Compared to thetaF, the physiological nature of W' has received little consideration. The purpose of this study was therefore to establish the parameters of the power-duration curve (thetaF and W') for subjects in normal glycogen (NG) and glycogen depleted (GD) states. Seven healthy male subjects (aged 22 to 41 years) each performed four high-intensity square-wave exercise bouts on an electrically braked cycle ergometer under two different muscular glycogen content conditions, i.e. NG and GD states. Subjects performed the following exercise on the evening before the trial day to induce the GD state. Initially, they performed a 75-min cycling exercise at 60% of VO2max. After a 5-min rest period, they subsequently repeated a 1-min cycling bout at 115% of VO2max (separated by 1-min rest periods) until the subject could no longer maintain the prescribed pedal rate for the full minute. Subjects then reported to the laboratory after an overnight fast and performed a single high-intensity exercise bout. The GD procedure was repeated four times at 1-week intervals. In the GD state, the respiratory exchange ratio (RER) (VO2/VCO2) value during a recumbent control period prior to the trial was significantly lower than that in the NG state [GD: 0.84+/-0.02, NG: 0.94+/-0.04, mean +/- SD]. There was no significant difference for thetaF between GD and NG state [NG: 197.1+/-31.9 W, GD: 190.6+/-28.2 W]. W' in contrast was significantly reduced by the GD procedure [NG: 12.83+/-2.21 kJ, GD: 10.33+/-2.41 kJ]. The present results indicate that the muscular glycogen store seems to be an important determinant of the curvature constant (W') of the power-duration curve for cycle ergometry.

Prospective validation of a low-back disorder risk model and assessment of ergonomic interventions associated with manual materials handling tasks

Abstract: The evaluation of low-back disorder risk associated with materials handling tasks can be performed using a variety of assessment tools. Most of these tools vary greatly in their underlying logic, yet few have been assessed for their predictive ability. It is important to document how well an assessment tool realistically reflects the job's injury risk, since only valid and accurate tools can reliably determine whether a given ergonomic intervention will result in a future reduction in back injuries. The goal of this study was to evaluate how well a previously reported low-back disorder (LBD) risk assessment model (Marras et al. 1993) could predict changes in LBD injury rates as the physical conditions to which employees are exposed were changed. Thirty-six repetitive materials handling jobs from 16 different companies were included in this prospective cohort study. Of these 36 jobs, 32 underwent an ergonomic intervention during the observation period, and four jobs in which no intervention occurred served as a comparison group. The trunk motions and workplace features of 142 employees performing these jobs were observed both before and after workplace interventions were incorporated. In addition, the jobs' LBD rates were documented for these pre- and post-intervention periods. The results indicated that a statistically significant correlation existed between changes in the jobs' estimated LBD risk values and changes in their actual low-back incidence rates over the observation period. Linear and Poisson regression models also were developed to predict a change in a job's incidence rate and the number of LBD on ajob respectively, as a function of the job's risk change using this assessment model. Finally, this prospective study showed which ergonomic interventions consistently reduced the jobs' mean low-back incidence rates. These results support use of the LBD risk model to assess accurately a job's potential to lead to low-back injuries among its employees.

On-line driver workload estimation. Effects of road situation and age on secondary task measures

Abstract: In order to develop a driver-car interface that adapts the presentation of messages generated by in-vehicle information systems to driver workload, two experiments investigated potential determinants of driver visual and mental workload as indicated by performance on two secondary tasks. Experiment 1 suggested that road situation is a major determinant of visual and mental workload of the driver and that the processing resources of older drivers are somewhat more limited than those of younger and middle-aged drivers. Familiarity with the area of driving (when guided) and time of day (associated with traffic density) showed no secondary task effects. Experiment 2 showed that the categorization of road situations, proposed in Experiment 1, could underlie adaptation of visually loading messages to the workload incurred by driving. This was not found with respect to mentally loading messages.

Muscular rest and gap frequency as EMG measures of physical exposure: the impact of work tasks and individual related factors

Abstract: Owing to an orderly recruitment of motor units, low threshold type I fibres are presumed to be vulnerable in contractions of long duration. To study load on these fibres muscular rest was registered as the time fraction of electromyographic (EMG) activity below a threshold. Moreover, the frequency of periods with muscular rest, EMG gaps, was derived, since a low gap frequency has been shown to be a risk factor for musculoskeletal disorders. Trapezius EMG was registered in 24 female hospital cleaners, 21 female office workers and 13 male office workers during one working day. Cleaners have a high risk of neck/shoulder pain and had much less muscular rest than office workers measured as a percentage of total registered time (median value = 1.5%, range = 0.2-13% vs. median value = 12%, range = 0.0-32%, respectively). Gap frequency showed no difference between the two occupational groups. Both measures displayed a wide inter-individual variation. For the cleaners, some of the variance was explained by body mass index (BMI) and age, with lower values of muscular rest for older subjects with a high BMI. Among the office workers, low values of muscular rest and a high gap frequency were registered in subjects with a low subjective muscular tension tendency. Gender, strength, smoking, job strain, employment time and musculoskeletal symptoms had no impact on either EMG measure.

Development of physical selection procedures for the British Army. Phase 2: Relationship between physical performance tests and criterion tasks

Abstract: This paper is the second in a series of three to describe the development of physical selection standards for the British Army. The first paper defined criterion tasks (single lift, carry, repetitive lift and carry, and loaded march tasks) and set standards on the criterion tasks for all British Army trades. The principal objective was to determine which combination of physical performance tests could be best used to predict criterion task performance. Secondary objectives included developing so-called 'gender-free' and 'gender-unbiased' models. The objectives were met by analysing performance data on the criterion tasks and a large battery of physical performance tests collected from 379 trained soldiers (mean age 23.5 (SD 4.45) years, stature 1734 (SD 79.5) mm, body mass 71.4 (SD 10.58) kg). Objective 1 was met: the most predictive physical performance tests were identified for all criterion tasks. Both single lift tasks were successfully modelled using muscle strength and fat free mass scores. The carry model incorporated muscle endurance and body size data, but the errors of prediction were large. The repetitive lift models included measures of muscle strength and endurance, and body size, but errors of prediction were also large. The loaded march tasks were successfully modelled incorporating indices of aerobic fitness, supplemented by measures of strength, endurance or body size and composition. The secondary objectives were partially fulfilled, though limitations in the data hampered the process. Although only one model (a loaded march) was gender-free, three models were gender-related (i.e. contained 'gender' explicitly in the model). The remaining six were gender-specific (i.e. were appropriate for men or for women). Owing to both a lower accuracy of prediction in women's scores and a greater tendency for the women's scores to be distributed around the pass standards, a greater percentage of women than men were misclassified as passing or failing, resulting in indirect discrimination. A validation of the models in a separate sample of the user population of recruits is reported in the third paper in this series.

Effects of two types of intra-team feedback on developing a shared mental model in Command & Control teams

Abstract: In two studies, the effect of two types of intra-team feedback on developing a shared mental model in Command & Control teams was investigated. A distinction is made between performance monitoring and team self-correction. Performance monitoring is the ability of team members to monitor each other's task execution and give feedback during task execution. Team self-correction is the process in which team members engage in evaluating their performance and in determining their strategies after task execution. In two experiments the opportunity to engage in performance monitoring, respectively team self- correction, was varied systematically. Both performance monitoring as well as team self-correction appeared beneficial in the improvement of team performance. Teams that had the opportunity to engage in performance monitoring, however, performed better than teams that had the opportunity to engage in team self -correction.

Effects of load carriage on heart rate, blood pressure and energy expenditure in children.

Abstract: Fifteen male primary school children, aged 10 years, were selected to carry school bags of 10, 15 and 20% of their own body weights, where 0% body weight was used as a control. Maximum oxygen uptake (VO2max) tests were conducted on a motorized treadmill using a continuous incremental protocol. During the load carrying test, subjects walked on a treadmill at 1.1 m s(-1) for 20 min at each load condition. Blood pressures were measured before, immediately following, and at 3 and 5 min after every trial. Heart rate and expired VO2 were recorded before, during and 5 min after walking using a cardiopulmonary function system. The results showed a significant difference in oxygen uptake, energy expenditure and the recovery of blood pressure rise for between 10 and 20% body weight load conditions. The carrying weight of a school bag for children could be recommended as 10% of body weight because it was not significantly different from 0% load in the metabolic cost.

Pacing strategies during a cycling time trial with simulated headwinds and tailwinds.

Abstract: The aims of this study were to examine the effects of one self-selected and two enforced pacing strategies (constant and variable power output) on cycling performance during a time trial in which variable wind conditions were simulated. Seven male cyclists rode their own bicycles on a Computrainer cycle ergometer, which was programmed to simulate a 16.1 km time trial on a flat course with a 8.05 km h(-1) headwind in the first half of the race and a 8.05 km h(-1) tailwind in the second half of the race. Subjects rode an initial time trial (ITT) at a self-selected pace to the best of their ability. The mean power output from this trial was then used to calculate the pacing strategies in the subsequent two trials: Constant (C)--riders rode the whole time trial at this mean power output; and Variable (V)--riders rode the first headwind section at a power output 5% higher than the mean and then reduced the power output in the last 8.05 km so that the mean power output was the same as in the initial time trial and in trial C. Power output, heart rate and ratings of perceived exertion (RPE) were recorded every 1.61 km. Finish times, 8.05 km split times and blood lactate levels, pre- and post-exercise (to calculate delta lactate), were also recorded in each trial. In the ITT, riders chose a mean +/- SD power output of 267 +/- 56 W in the first 1.61 km which was 14% higher than the overall race mean +/- SD of 235 +/- 41 W. Power outputs then dropped to below the race mean after the first few kilometres. Mean +/- SD finish times in the C and V time trials were 1661 +/- 130 and 1659 +/- 135 s, respectively. These were significantly faster than the 1671 +/- 131 s recorded in the initial time trial (p = 0.009), even though overall mean power outputs were similar (234 - 235 W) between all trials (p = 0.26). Overall mean RPE and delta lactate were lowest in trial V (p < 0.05). Perceived exertion showed a pacing strategy by race split interaction (p < 0.0001), but it was not increased significantly during the first 8.05 km of the V condition when power outputs were 5% higher than in condition C. Heart rate showed no main effect of pacing strategy (p = 0.80) and the interaction between strategy and race split did not reach statistical significance (p = 0.07). These results suggest that in a 16.1 km time trial with equal 8.05 km headwind and tailwind sections, riders habitually set off too fast in the first few kilometres and will benefit (10 s improvement) from a constant pacing strategy and, to a slightly greater degree (12 s improvement), from a variable (5% +/- mean) pacing strategy in line with the variations in wind direction during the race. Riders should choose a constant power when external conditions are constant, but when there are hilly or variable wind sections in the race, a variable power strategy should be planned. This strategy would be best monitored with 'power-measuring devices' rather than heart rate or subjective feelings as the sensitivity of these variables to small but meaningful changes in power during a race is low.

Human factors in a dynamic information society: where are we heading?

Abstract: Society is becoming increasingly dynamic and integrated owing to the extensive use of information technology. This has several implications that pose new challenges to the human factors profession. In an integrated society, changes and disturbances propagate rapidly and widely and the increasing scale of operations requires also that rare events and circumstances are considered during systems design. In this situation, human factors contributions should be increasingly proactive, not only responding to observed problems, but also, they should be based on models of adaptive human behaviour in complex, dynamic systems. The paper suggests some methodological issues to consider for human factors analyses by designers, evaluators and teachers.

Designing safe job rotation schedules using optimization and heuristic search

Abstract: Job rotation is one method that is sometimes used to reduce exposure to strenuous materials handling; however, developing effective rotation schedules can be complex in even moderate sized facilities. The purpose of this research is to develop methods of incorporating safety criteria into scheduling algorithms to produce job rotation schedules that reduce the potential for injury. Integer programming and a genetic algorithm were used to construct job rotation schedules. Schedules were comprised of lifting tasks whose potential for causing injury was assessed with the Job Severity Index. Each method was used to design four job rotation schedules that met specified safety criteria in a working environment where the object weight, horizontal distance and repetition rate varied over time. Each rotation was assigned to a specific gender/lifting capacity group. Five versions of the integer programming search method were applied to this problem. Each version generated one job rotation schedule. The genetic algor...

Force direction and physical load in dynamic pushing and pulling.

Abstract: In pushing and pulling wheeled carts, the direction of force exertion may, beside the force magnitude, considerably affect musculoskeletal loading. This paper describes how force direction changes as handle height and force level change, and the effects this has on the loads on the shoulder and low back. Eight subjects pushed against or pulled on a stationary bar or movable cart at various handle heights and horizontal force levels while walking on a treadmill. The forces at the hands in the vertical and horizontal direction were measured by a force-transducer. The forces, body movements and anthropometric data were used to calculate the net joint torques in the sagittal plane in the shoulder and the lumbosacral joint. The magnitudes and directions of forces did not differ between the cart and the bar pushing and pulling. Force direction was affected by the horizontal force level and handle height. As handle height and horizontal force level increased, the pushing force direction changed from 45 degrees (SD 3.3 degrees) downward to near horizontal, while the pulling force direction changed from pulling upward by 14 degrees (SD 15.3 degrees) to near horizontal. As a result, it was found that across conditions the changes in force exertion were frequently reflected in changes in shoulder torque and low back torque although of a much smaller magnitude. Therefore, an accurate evaluation of musculoskeletal loads in pushing and pulling requires, besides a knowledge of the force magnitude, knowledge of the direction of force exertion with respect to the body.