Relationship between maximum acceptable work time and physical workload

For safe job design, it is necessary to know the maximum acceptable work time (MAWT) for a given workload. The aim was to establish the relationship between MAWT and physical workload. Cycling tests at six different work rates relative to personal maximum working capacity were performed by 12 young adults in the laboratory. The oxygen uptake (VO(2)) in the per cent maximum aerobic capacity (%VO(2max)), relative heart rate (RHR) and relative oxygen uptake (RVO(2)) were collected throughout the test. MAWT was determined by observing the heart rate data during the test. The results showed that MAWT was negatively correlated with %VO(2max), RHR and RVO(2) (p < 0.01). Three exponential regression models were obtained and all their R(2) > 0.80. These models suggest that long-hour shifts (> 10 h) should assign a lower work intensity than for an 8-h workday. It is also logical that the workload limit for a 4-h work shift could be set at about 10% VO(2max) higher than the suggested limit for an 8-h workday.     

Physiological strain during kitchen work in relation to maximal and task-specific peak values

Six female and three male subjects from a hospital kitchen volunteered for the study. The subjects were working on a conveyor belt collecting and sorting dirty plates, glasses and cutlery for cleaning. In the study, a medical examination, a maximal clinical exercise test with a 12-lead electrocardiogram (ECG) and a maximal arm cranking test were performed in the laboratory. Further, each subject was studied for 30 min during a normal work shift in the kitchen. Oxygen uptake (VO₂) and heart rate (HR) were continuously registered. During the work period, a rating of perceived exertion (RPE) was asked at the 5th, 15th and 30th minute. Physiological responses were measured by a portable system (K4) both in the laboratory and in the field. VO₂ and HR measured in the field were proportioned to corresponding maximal values during cycling and to peak values during arm-cranking. The mean VO₂ for the male and the female subjects during kitchen work was 0.65±0.16 l min^-1. This corresponded to 24% of VO_2max and to 41% of VO_2peak during arm-cranking. The difference was significant (p<0.001). Owing to a magnetic field at the conveyor belt, reliable HR values were obtained only from the female subjects. The mean HR during work among the female subjects was 101 beats min^-1. It corresponded to 55% of HRmax and 67% of HR during arm-cranking (p<0.05). The present study shows that the peak relative work intensity is markedly higher when it is expressed relative to the corresponding muscle group's VO_2peak instead of the VO_2max. Similar difference was also seen in the HR response. More task-specific testing of physical capacity may provide improved evaluation of physical strain in a job.     

A 16-year follow-up study of physical capacity in relation to perceived workload among ageing employees

The main purpose of this study was to ascertain musculoskeletal and cardiovascular capacity among ageing employees in relation to workload over a period of 16 years. The data were obtained by physical capacity tests and ratings of perceived exertion (RPE) during working day. The study group consisted of 89 subjects, who were all employed in the municipal branch and were on average 51.9 years old at the beginning of the follow-up period in 1981 and 67.3 years in 1997, when the most of the subjects had retired (with only two subjects still working). During the 16-year follow-up period, age-related decline in physical capacity was observed. Nevertheless the improvement in flexibility of spine and in isometric trunk muscle strength compared with the same age subjects was more common among the subjects with high workload than among the subjects with low workload. However, among the subjects with high workload, physical capacity was poorer than among the subjects with low workload, especially among the women. The results suggest the conclusion that there are differences in workers' physical capacity in relation to their perceived workload during working life. These differences remained when the subjects had retired. Interestingly, those who had high workload had lower muscle strength than those who had low workload. This may indicate that high physical workload does not have any training effect on the muscle strength of ageing workers.     

Life-time occupational exposure to heavy work and individual physical capacity

The aim of the present study was to retrospectively analyze the effect of occupational physical activity on maximal isometric hand grip strength and maximal oxygen consumption among males and females between 19 and 64 years of age in different occupations. A life-time occupational physical activity index was formed from questions in a questionnaire. The maximal isometric hand grip strength was measured with a dynamometer and maximal oxygen consumption was estimated from a submaximal bicycle ergometer test. The results showed a negative correlation between physical activity and estimated maximal oxygen consumption among males but no other statistically significant associations between life-time physical activity and the present physical capacity was found. The present results suggest that a high level of occupational physical activity does not maintain individual physical capacity.     

The physical demands upon (Dutch) fire-fighters in relation to the maximum acceptable energetic workload

The aim of this study was to assess the tasks and activities that make physical demands on Dutch fire-fighters and to compare them with a guideline related to the development of excessive fatigue. The occupational physical demands on Dutch fire-fighters were assessed by conducting a task analysis during 85 24-h shifts. While workplace observations on the duration and frequency of physical tasks and activities were recorded, the heart rate was measured. This was then used to calculate the heart rate reserve percentage (%HRR) for predefined working periods, tasks and activities during 24-h shifts. The findings indicate that actual fire-fighting during 24-h shifts is characterised by a low frequency of incidents, a short ‘turn-out’ time, short tasks, and activities with a moderate to occasionally high energetic workload. Two tasks which sometimes occur in actual fire-fighting exceeded the guideline on energetic workload. The conclusion was that, though the number of incidents and the occupational demands are low during 24-h shifts, the peak loads for these two tasks are energetically high and could lead to excessive fatigue. Consequently, attention may need to be paid to health surveillance for persons exposed to such energetic peak loads, the development of physical and medical selection procedures, training, and workplace adjustments.     

Quantitative relationship model between workload and time pressure under different flight operation tasks

The goal of this study was to establish a quantitative relationship model between workload and task demand under different tasks, when time pressure was set as the main influential factor to the task demand, with three workload measurement parameters. The workload “redline” was also analyzed and determined with the relationship models between the workload measurement parameters and time pressure. The experiment was designed with three different tasks under different time pressures. Three workload measurement parameters (subjective evaluation workload, accuracy and pupil diameter) and the subjective feeling threshold of time pressure were measured experimentally and then used in a comprehensive analysis for the relationship model. The data analysis result showed significant differences in workload under different time pressures, but workload was not affected by the task type. With a time pressure of 0.8, participants felt a sense of time urgency and the accuracy decreased by approximately 85%. The results demonstrate that the subjective evaluation workload, accuracy and pupil diameter can be used as the measurement parameters for the workload under different time pressures and for different tasks. Thus, for a time pressure of 0.8, an accuracy of 80%–85% was determined as the workload “redline”. Linear relationships were found between subjective evaluation workload, and pupil diameter and time pressure, and a quadratic curve relationship was found between accuracy and time pressure. Workload prediction can thus be performed using these relationship models between workload and time pressure.     

Effects of different physical workload parameters on mental workload and performance

The design and evaluation of an occupational task should include an assessment of mental workload, since excessive levels of mental workload can cause errors or delayed information processing. Physically demanding work that is performed concurrently with a cognitive task may impact mental workload by impairing mental processing or decreasing performance. The primary objective of this study was to determine whether there is a differential effect of various types of physical activity on both mental workload and cognitive performance. Objective and subjective assessment tools (heart rate variability and visual analog scale) were used as indicators of mental workload, while correct responses during an arithmetic task reflected levels of performance. Thirty participants (ages 18-24 years) performed a combination of tasks inducing both physical and mental workload. Type of physical effort, frequency of movement, and force exertion level were manipulated to alter the workload associated with the physical activity. Changes in subjective ratings generally corresponded to changes in both performance on the arithmetic task and objective mental workload assessment. Some discrepancies occurred at the highest physical force exertion level as participants perceived an increase in effort to maintain the same level of performance. Further research is needed to determine the force exertion threshold, beyond which the physical effort required interferes with mental workload and/or cognitive performance.

Relevance to industry

Technological advancements have increased the requirement for many workers to execute cognitive tasks concurrently with physical activity. When designing and evaluating such situations it is important to determine the interactive effects of these activities. A simple, uni-dimensional tool is suggested as a screening tool to identify situations requiring excessive or increased mental workload that many degrade performance or place additional stress on the individual.     

Distribution and determinants of maximal physical work capacity of Korean male metal workers

The distribution of maximal physical work capacity (MPWC) can be used to establish an upper limit for energy expenditure during work (EEwork). If physically demanding work has wearing effects, there will be a negative relationship between MPWC and workload. This study was conducted to investigate the distribution of MPWC among Korean metal workers and to examine the relationship between workload and MPWC. MPWC was estimated with a bicycle ergometer using a submaximal test. Energy expenditure was estimated by measuring heart rates during work. The study subjects were 507 male employees from several metal industries in Korea. They had a lower absolute VO_2max than the Caucasian populations described in previous studies. The older workers had a lower physical capacity and a greater overload at work. A negative relationship was found between MPWC and workload across all age groups. Upper limits for EEwork for all age groups and for older age groups are recommended based on the 5th percentile value of MPWC.     

Comprehensive maximum acceptable weight of lift database for regular 8-hour work shifts

Abstract

This paper presents comprehensive maximum acceptable weight of lift data for male and female industrial workers for 8-hour shifts. The experimental data collected in this study, for 8 hours, were compared with previous studies of Snook (1978) and Ayoub et al. (1978). Since data from all three studies compared favourably, they were integrated to develop comprehensive databases.     

Workload and physical capacity among ageing municipal employees—a 16-year follow-up study

The main purpose of this study was to ascertain musculoskeletal and cardiovascular capacity among ageing employees in relation to workload over a period of 16 years. As the more specific aims were to find out firstly if the physical capacity was different among subjects who had high workload compared with subjects who had low workload and secondly if the changes in physical capacity during the follow-up period were different between subjects with high workload than among subjects with low workload

The data were obtained by physical capacity tests and field measurements (assessments of musculoskeletal and cardiovascular load). The study group consisted of 95 middle-aged subjects who were on average 51.9 years old at the beginning of the follow-up in 1981 and they were all employed. In 1997 they were 67.3 years and 93 of the subjects had retired. The sample represented workers who were employed in municipal occupations in different regions of Finland.

During the 16-year follow-up period age-related decline in physical capacity was observed. In general the subjects with low workload had better physical capacity than the subjects with high workload, especially among women. The improvements in physical capacity were more common than declines among subjects with low physical workload over the follow-up period. Among subjects with high physical workload the situation was mostly vice versa. However, the declines in isometric trunk extension strength and in aerobic capacity were more common among subjects with physically low workload than among subjects with high workload. The differences between high and low workload groups in physical capacity were larger among women than among men. It was concluded that physical workload seems to have more wearing effects than training effects on ageing workers.

Relevance to industry

Physically heavy work may have no training effect on physical capacity among aged workers. The physically heavy work has to be individually adjusted to correspond to a worker's physical capacity, bearing in mind age-related decline of physical capacity, and thereby preventing the overload of the worker.     

Self-similarity: Behind workload reshaping and prediction

Energy efficiency has become one of the most important challenges in designing future computing systems. Workload reshaping and prediction have a significant impact on the energy conservation of computer components. In this paper, by using three HTTP traffic traces, we perform various evaluations to explore the possible reasons and indications which impact the workload reshaping and prediction. The experimental results indicate that the principles of reshaping workload to improve prediction quality are constructing or improving the self-similarity of the reshaped workloads.     

The physical and physiological workload of refuse collectors

In order to secure a safer and healthy work situation, the heavy physical loads imposed on 23 refuse collectors (aged 26-54) working in the city of Haarlem, in The Netherlands, were studied in a series of three experiments between 1984 and 1987. The aims were respectively (1) to study the load for workers collecting dustbins or polythene bags; (2) to introduce changes to reduce the load to avoid exceeding the overload criteria by individual refuse collectors; and (3) to investigate the effects of interventions to improve the efficiency of refuse collecting. The maximal isometric lifting force (F_max) and the maximal aerobic power( [Vdot]O_2max of 23 refuse collectors were measured in the laboratory. F_max was measured with an isometric dynamometer pulling with one arm from the floor; the mean value was 912 (± 127)N. VO_2max was measured running on a treadmill; the mean value was 43-3 (±0-8) ml O₂ per kg body mass per min. The physical load on the oxygen transport system was measured through work analysis and by a continuous registration of the heart rate over three working days. Criteria for overload were set at a mean external load of 20% Fm? and a mean energy expenditure of 30% VO_2max and an energy expenditure of 50% VO_2max or more for a maximum of 60 min per day. Replacement of dustbins by polythene bags resulted in a 70% increase in the total amount of refuse collected, an increase in throwing frequency, but a lower mean load per throw, and no significant differences in the mean heart rate over the working day. When polythene bags were used the mean values did not exceed the overload criteria, but 39% of the individual collectors did have a workload that was too high with respect to one of the criteria. In the last experiment the collectors were advised to reduce their work load by (a) lifting no more than two bags at a time; (b) reducing their walking pace; and (c) taking more breaks. Although compliance with the recommendations was good, and the weight lifted and the walking speed decreased, the physiological load remained the same. This may have been caused by a 15% increase in the total amount of refuse that had to be collected at that time.     

Effect of block weight on work demands and physical workload during masonry work

The effect of block weight on work demands and physical workload was determined for masons who laid sandstone building blocks over the course of a full work day. Three groups of five sandstone block masons participated. Each group worked with a different block weight: 11 kg, 14 kg or 16 kg. Productivity and durations of tasks and activities were assessed through real time observations at the work site. Energetic workload was also assessed through monitoring the heart rate and oxygen consumption at the work site. Spinal load of the low back was estimated by calculating the cumulated elastic energy stored in the lumbar spine using durations of activities and previous data on corresponding compression forces. Block weight had no effect on productivity, duration or frequency of tasks and activities, energetic workload or cumulative spinal load. Working with any of the block weights exceeded exposure guidelines for work demands and physical workload. This implies that, regardless of block weight in the range of 11 to 16 kg, mechanical lifting equipment or devices to adjust work height should be implemented to substantially lower the risk of low back injuries.     

Job rotation as a factor in reducing physical workload at a refuse collecting department

The effect of job rotation on the physical workload was investigated for male employees working at a refuse collecting department. Before the introduction of job rotation, an employee worked as a street sweeper, as a refuse collector or as a driver. After the introduction of job rotation, every employee was allowed to alternate between two of the three possible jobs during the day, i.e. refuse collecting/street sweeping, refuse collecting/driving or street sweeping/driving. Two non-rotation groups (i.e. refuse collectors and street sweepers) and two rotation groups (i.e. refuse collectors/street sweepers and street sweepers/drivers) were mutually compared. The physical workload was determined by measuring the perceived load, energetic load and postural load during a full working day. Job rotation resulted in a significant decrease of the perceived load and energetic load and a slight decrease of the postural load. The results indicate that the total amount of work performed by means of job rotation resulted in an overall reduced physical workload of the employees of the refuse collecting department.     

The investigation and evaluation of work and workplaces

Most workplaces and jobs demonstrate a mis-match in relation to the workers involved with them. To assess this we must measure the work loads, the workplace characteristics, the work performance, the interactions of these with the workers and the consequences for them. Changes are devised as a result of these measures, and insofar as the measures fall short of the comprehensive list above, then the modifications may be sub-optimal as important aspects are not taken into account. The results of the changes, too, need a similar comprehensive assessment.

The paper will follow through the process of investigating industrial workplaces. It will briefly introduce techniques developed for assessing a range of aspects and how they lead to the development of changes. The view of the worker as a total person will be supported by proposals for the combined evaluation of the task, the workplace etc and the state and effects of the social environment, with suggestions for their economic evaluation.     

Work hours, workload, sleep and fatigue in Australian Rail Industry employees

Research suggests that less than 5 h sleep in the 24 h prior to work and/or more than 16 h of wakefulness can significantly increase the likelihood of fatigue-related impairment and error at work. Studies have also shown exponential safety declines with time on shift, with roughly double the likelihood of accident or injury after 10 h relative to the first 8 h. While it is acknowledged that reduced sleep, increased wakefulness and longer work hours produce work-related fatigue, few studies have examined the impact of workload on this relationship. Studies in the rail industry have focused on drivers. This study investigated fatigue in a large sample of Australian Rail Industry Employees. Participants were from four companies (n = 90: 85m, 5f; mean age 40.2 ± 8.6 y). Data was analysed for a total of 713 shifts. Subjects wore wrist actigraphs and completed sleep and work diaries for 14-days. They also completed the Samn–Perelli Fatigue Scale at the beginning and end of shifts, and the NASA-TLX workload scale at least twice during each shift. Average (±SD) sleep length (7.2 ± 2.6 h), prior wake at shift end (12.0 ± 4.7 h), shift duration (8.0 ± 1.3) and fatigue (4.1 ± 1.3, “a little tired, less than fresh”) were within limits generally considered acceptable from a fatigue perspective. However, participants received 5 h or less sleep in the prior 24 h on 13%, were awake for at least 16 h at the end of 16% and worked at least 10 h on 7% of shifts. Subjects reported that they felt “extremely tired, very difficult to concentrate,” or “completely exhausted, unable to function effectively” on 13% of shifts. Sleep length (OR = 0.88, p < 0.01), shift duration (OR = 1.18, p < 0.05), night shift (REF = morning shift, OR = 2.12, p < 0.05) and workload ratings (OR = 1.2, p < 0.05) were significant predictors of ratings of extreme tiredness/exhaustion (yes/no). While on average, sleep loss, extended wakefulness, longer work hours and work-related fatigue do not appear problematic in this sample, there is still a notable percentage of shifts that are likely to be associated with high levels of work-related fatigue. Given the size of the Australian Rail Industry, with thousands of shifts occurring each day, this is potentially of operational concern. Further, results indicate that, in addition to sleep length, wakefulness and work hours, workload significantly influences fatigue. This has possible implications for bio-mathematical predictions of fatigue and for fatigue management more generally.     

The relationship between physical workload and quality within line-based assembly

Reducing costs and improvement of product quality are considered important to ensure productivity within a company. Quality deviations during production processes and ergonomics have previously shown to be associated. This study explored the relationship between physical workload and real (found during production processes) and potential (need of extra time and assistance to complete tasks) quality deviations in a line-based assembly plant. The physical workload on and the work rotation between 52 workstations were assessed. As the outcome, real and potential quality deviations were studied during 10 weeks. Results show that workstations with higher physical workload had significantly more real deviations compared to lower workload stations. Static work posture had significantly more potential deviations. Rotation between high and low workload was related to fewer quality deviations compared to rotation between only high workload stations. In conclusion, physical ergonomics seems to be related to real and potential quality deviation within line-based assembly.

Practitioner Summary: To ensure good productivity in manufacturing industries, it is important to reduce costs and improve product quality. This study shows that high physical workload is associated with quality deviations and need of extra time and assistance to complete tasks within line-based assembly, which can be financially expensive for a company.     

Evaluation of the effect of a paver’s trolley on productivity, task demands, workload and local discomfort

The objective of this study was to determine the differences in the number of paving stones laid (productivity), task demands, energetic workload, body region discomfort and preference when laying paving stones with or without use of a paver’s trolley (n = 8) in a within-subject controlled study of pavers. The number of paving stones laid and the task demands were measured by means of systematic observations at the workplace. The energetic workload was determined using the percentage of heart rate reserve (%HRR). Body region discomfort was measured using visual analog scales, and the workers’ preference was ascertained via interview. The use of a paver’s trolley had no effect on productivity, %HRR or body region discomfort compared to working without a paver’s trolley. The duration of knee-straining activities did not differ between working with (141 min) and without (146 min) the paver’s trolley. However, six of the eight pavers indicated that, given suitable circumstances, they wanted to use the paver’s trolley.

Relevance to industry

To reduce the chance of work-related low back and knee complaints among pavers, the duration, frequency and intensity of lower back and knee-straining activities should be limited by means of technical measures such as mechanical paving. The paver’s trolley does not appear to reduce knee-straining activities and therefore does not appear useful in reducing the risk of knee complaints and disorders.     

Measurements of team workload: A time pressure and scenario complexity study for maritime operation tasks

Workload is a critical factor influencing team performance in complex systems. There remains no consensus on the selection of team workload measures. Through an experiment based on simulated maritime operation tasks, team workload was manipulated by time pressure and scenario complexity to investigate the responses of three categories (subjective, performance-based, and physiological) of potential team workload measurements. The results show that time pressure had significant effects on all the three categories of measurements, especially on subjective indicators, miss rate, completion rate, operation accuracy, and eye movements. Significant main effects of scenario complexity on subjective team workload and the selected team performance measurements were also found, such as response latent time, miss rate, completion rate, and operation accuracy. Physiological measurements may not be sensitive for measuring team workload when scenario complexity serves as a major influencing factor of team workload.     

Microgravity simulation: physical and psychological workload evaluation tests in an underwater environment

As weightlessness is not completely reproducible on Earth, usability evaluation of space systems is often simulated through tests in an aquatic environment. A Neutral Buoyancy Facility test programme was organized in a special pool to simulate Extra-Vehicular Activities on the Columbus module of the future International Space Station with the aim of assessing various aspects of crew interface design.This study was designed to evaluate workload using visibility, accessibility and operability tests. Diving workload was determined through basic physiological measurements, such as pulmonary ventilation and heart rate during underwater operations.As anxiety can influence physiological processes, and consequently also the workload evaluation determined through these parameters, we developed an evaluation methodology to investigate the anxiety level based on a specific questionnaire submitted to all subjects before and after the dives.Heart rate increased in underwater work to a value approximately 50% larger than the value obtained in the resting condition while sitting outside the pool. This increase in heart rate was accompanied by an increase in pulmonary ventilation of 200% larger than the value recorded in the rest condition while sitting outside the water. The extent of these increases was notable in all the test subjects, who varied in age and stature.Recorded values of workload, heart rate and pulmonary ventilation were evaluated on the basis of Christensen's (Arbeitsphysiol. 14 (1950) 251) and Wells’ (J. Appl. Physiol. 10 (1957) 51) classifications. Through this analysis it was possible to determine that the workload, indicated by performance on our neutral buoyancy tests, corresponds to moderate physiological work.For test subjects, anxiety related to underwater performance was light. Among the causes of anxiety all the subjects indicated the lack of confidence with neutral buoyancy tests and a feeling of lack of safety, typical of aquatic environments.We can conclude that context did not produce considerable psychological effects, and consequently that the psychological load did not influence heart rate and pulmonary ventilation values that can therefore be directly related to task workload.