The nature and measurement of stress

This paper considers why asking what physiological measures of stress there are is not a sensible question. In so doing, it examines the nature of stress as described by contemporary theories and explores their implications for measurement. It concludes that there cannot be direct physiological measures of stress, only physiological correlates. The measurement of stress must focus on the individual' s psychological state, as related to their perception of the environment and emotional reaction to it ( mood). In discussing the question of measurement, the paper introduces the issues of reliability, validity and fairness, and emphasizes that they should be raised in relation to all types of measure, not just those that are subjective     

Evaluation of metabolism from heart rate in industrial work

Oxygen consumption ([Vdot]O₂) and heart rate (HR) were measured in 40 men performing different types of industrial work in eight factories

A [Vdot]O₂-HR relationship was established for each subject using an exercise test on a bicycle ergometer. HR measured during the industrial work was entered in the [Vdot]O₂-HR function, and [Vdot]O₂ thus calculated. A systematic comparison of the calculated [Vdot]O₂ (c[Vdot]O₂) with the actual measured [Vdot]O₂ (m[Vdot]O₂), showed that c[Vdot]O₂ significantly overestimated the [Vdot]O₂ during industrial work. The degree of overestimation was related to the type of work performed. The static muscular activity and the non-steady-state characteristics of the work were responsible for most of the overestimation

A more reliable technique for estimating metabolic rate is to make simultaneous measurements of [Vdot]O₂ and HR at different times during the work day and then from these recordings establish a function: [Vdot]O₂=f(HR). Continuous HR recordings can then be used to calculate a more accurate estimate of the metabolic rate.     

Bicycle messengers: energy expenditure and exposure to air pollution

The purpose of the study was to determine the level of energy expenditure and exposure to air pollution for bicycle messengers. Relationships between heart rate (HR) and oxygen uptake, and between HR and pulmonary ventilation (VE) for each participant were established in laboratory tests. Air pollution and HR were measured during one working day. The total oxygen uptake was then described as the total energy expenditure in Joule (J) and in multiples of the energy expenditure at rest (MET). The mean energy expenditure during a working day (8 h) was 12 MJ, (4.8 MET). The level of air pollution exposure when cycling seemed to be comparable with the levels of exposure when sitting inside a vehicle. The VE during cycling was four times higher than resting value. Increased VE led to increased exposure to air pollution.     

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.     

Comparing the physiological and perceptual responses of construction workers (bar benders and bar fixers) in a hot environment

This study aimed to (1) quantify the respective physical workloads of bar bending and fixing; and (2) compare the physiological and perceptual responses between bar benders and bar fixers. Field studies were conducted during the summer in Hong Kong from July 2011 to August 2011 over six construction sites. Synchronized physiological, perceptual, and environmental parameters were measured from construction rebar workers. The average duration of the 39 field measurements was 151.1 ± 22.4 min under hot environment (WBGT = 31.4 ± 2.2 °C), during which physiological, perceptual and environmental parameters were synchronized. Energy expenditure of overall rebar work, bar bending, and bar fixing were 2.57, 2.26 and 2.67 Kcal/min (179, 158 and 186 W), respectively. Bar fixing induced significantly higher physiological responses in heart rate (113.6 vs. 102.3 beat/min, p < 0.05), oxygen consumption (9.53 vs. 7.14 ml/min/kg, p < 0.05), and energy expenditure (2.67 vs. 2.26 Kcal/min, p < 0.05) (186 vs. 158 W, p < 0.05) as compared to bar bending. Perceptual response was higher in bar fixing but such difference was not statistically significant. Findings of this study enable the calculation of daily energy expenditure of rebar work.     

On physiological demands and sustainability in meat cutting

Meat cutters' work has been investigated by several researchers. However, knowledge about the physiological demands of meat cutting is almost lacking. The aim of this explorative study was to assess physiological demands in meat cutting, to compare them with International Labour Organization (ILO) recommendations for acceptable workload and to discuss the findings in relation to individual and work-related factors. In accordance with the ILO recommendations, work was categorised as sustainable or non-sustainable based on critical relative aerobic strain (RAS) levels. Twenty-one beef and pork cutters participated in the study, which included workload measurements, assessment of workplace and individual factors. Thirteen meat cutters were categorised as having non-sustainable and eight as having sustainable work. Results suggest that the workload is higher in beef cutting than in pork cutting, and that longer work experience is related to lower RAS. Other factors contributing to the physical workload are discussed.

Practitioner Summary: Meat-cutting work may exceed recommended physical workload levels. Beef cutting is physically more demanding than pork cutting. Furthermore, factors such as years in the profession, knife sharpness, work pace, wage system, working technique, maximum oxygen uptake level and muscular strength should be considered when planning actions regarding the workload for meat cutters.     

The utility of heart rate and minute ventilation as predictors of whole-body metabolic rate during occupational simulations involving load carriage

The utility of cardiac and ventilatory predictors of metabolic rate derived under temperate and heated laboratory conditions was evaluated during three fire-fighting simulations (70-mm hose drag, Hazmat recovery, bushfire hose drag; N = 16 per simulation). The limits of agreement for cardiac (temperate: ? 0.54 to 1.77; heated: ? 1.39 to 0.80 l min^? 1) and ventilatory surrogates (temperate: ? 0.19 to 1.27; heated: ? 0.26 to 1.16 l min^? 1) revealed an over-estimation of oxygen consumption that exceeded the acceptable limits required by occupational physiologists (N = 25; ± 0.24 l min^? 1). Although ventilatory predictions offered superior precision during low-intensity work (P < 0.05), a cardiac prediction was superior during more demanding work (P < 0.05). Deriving those equations under heated conditions failed to improve precision, with the exception of the cardiac surrogate during low-intensity work (P < 0.05). These observations imply that individualised prediction curves are necessary for valid estimations of metabolic demand in the field.     

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.     

Efficacy of adjusting working height and mechanizing of transport on physical work demands and local discomfort in construction work

The efficacy of ergonomics measures to reduce physical work demands in a real working situation is often assumed, but seldom studied. In this study, the effect of adjusting working height and mechanization of transport on physical work demands and local discomfort of bricklayers' work was evaluated during a field experiment in the construction industry. In a within-subjects controlled experiment, 10 bricklayers and 10 bricklayers' assistants worked in two different conditions. Working height of bricks and mortar, and transport of materials were manipulated. The physical work demands were assessed through real time observations at the work site. Local discomfort of the lower back and of the shoulder region was measured by means of a visual analogue scale. Working with a scaffolding console to adjust the working height of the storage of materials resulted in a significant reduction of the frequency and duration of trunk flexion (?>?60°) by 79% and 52% respectively, compared with bricks set out on the ground floor. Mechanization of transport of materials resulted in a significant reduction of the frequency and duration of trunk flexion (?>?60°) by 94% and 92% respectively, compared with the condition of manual handling. The frequency of handling objects (?>?4?kg) reduced significantly by 86%. Local discomfort of the lower back was significantly less in the ergonomic conditions, while no significant difference was found for local discomfort of the shoulder between both conditions in bricklayers' assistants.     

Evaluation of three methodologies to estimate the VO2max in people of different ages

Aging and gender are factors that affect the variation of physical work capacity. The present paper highlights the importance of the metabolism used by ergonomics to establish the appropriate limits of loads at work. This study compares the aerobic capacity of people from 20 to 71 years old split in 5 different groups. The laboratory experiment tested 33 volunteers (19 women and 14 men). A submaximal step test was used to measure the VO₂ using a portable breath by breath metabolic system and a telemetric heart rate monitor. Three methods to estimate the VO_2max were compared: 1) a direct measurement of VO₂, 2) estimation by heart rate, and 3) a step test method using predetermined charts. Significant difference was encountered among the estimation methods as well as among the age ranges (F_2,92 = 6.43, p < 0.05 y F_4,92 = 7.18, p < 0.05 respectively). The method of direct measurement and the method of predetermined charts were different for the estimation of the VO_2max with a confidence level of 95%. The method of predetermined charts is better adapted for males and people younger than 30 years. The estimation through non invasive heart rate apparatus was a good appraiser of the maximal oxygen consumption considering both genders and all the age groups.     

Determination of worker physiological cost in workspace reach envelopes

Oxygen uptake (VO₂), heart rate (HR) and myoelectric activity (EMG) were measured while performing a repetitive task in the normal, maximum and extreme workspace reach envelopes. The VO₂ and HR increased significantly from the normal to the maximum to the extreme workspace reach envelope. The average increases in VO₂ when compared to the normal workspace were 19 and 52%, respectively. The corresponding average increases in HR were 6 and 14%, respectively. The increase in EMG for anterior deltoid, upper trapezious and erector spinae showed a significant increase from normal to maximum and from maximum to extreme workspaces. The average increases in EMG for anterior deltoid, upper trapezious and erector spinae, compared to the normal workspace were 96, 37 and 48% respectively for the maximum workspace and 193, 95 and 106% for the extreme workspace, respectively. The research indicated for the first time that during task performance, worker physiological cost would increase significantly with the increase in workspace reach levels.     

The effects of a passive exoskeleton on muscle activity and metabolic cost of energy

ABSTRACT

Nowadays, low back pain has a high incidence during the crowd who work under a long time and repeated stoop condition. Exoskeletons may form a new strategy to reduce the risk of developing low back pain in stressful jobs. A passive exoskeleton device was introduced in this article to apply to the static maintenance of forward bending work, so as to reduce the load of back muscles when wearers work, which plays the role of prevention and subsequent rehabilitation of low back pain. The hypothesis is that these systems would decrease the severity and number of work-related back injuries, while enhancing workers’ safety. Through a preliminary analysis and a substantial number of experiments, we have demonstrated the feasibility of our approach to substantially decrease the forces and muscle activities at the L5/S1 location during bending. In the static holding experiment, we find lower muscle activity (by 35%～61%) and lower metabolic cost of energy (by 22%) when wearing the exoskeleton. The results demonstrate good potential of this passive exoskeleton to reduce muscle activities at the L5/S1 location and metabolic cost of energy.     

The Ergonomics Research Society THE SOCIETY'S LECTURE, 1974* The Borderland of Anatomy and Ergonomics

A survey of The status of ergonomics in Poland was conducted over a three week period during July 1978 under the sponsorship of the National Academy of Sciences scientific exchange programme. Ergonomic activities were reviewed in Warsaw and Cracow by means of a series of visits to academic and research institutions. Among the organizations contacted were: the Institute of Industrial Design, the Polish Psychological Association, the Institute of Psychology at the University of Warsaw, the Academy of Fine Arts in Cracow and The Institute of Psychology associated with the Jagiellonian University. Based on interviews with prominent scientists in the forefront of ergonomic activities, the report provides a review of the historical development of ergonomics, the composition of the ergonomics community, current research interests and applications, and anticipated future trends. The Poles claim credit for having coined the term Ergonomics in 1857. They are proud to have formed the first Ergonomics Society in the Eastern European bloc of nations. Its current membership totals over 400 and they look forward to hosting the 1979 International Ergonomics Association meeting in Warsaw. There are only about 100 engineering psychologists in Poland. Engineers and physiologists or physicians tend to dominate the ergonomics field. There appears to be strong support for this emerging discipline from the State and industrial enterprises and ergonomics can be expected to become increasingly more important in Poland.     

The evaluation of smaller plasterboards on productivity, work demands and workload in construction workers

Manual handling of plasterboards in order to construct interior building walls is a risk factor for musculoskeletal complaints. Unfortunately, mechanical lifting aids to reduce the physical workload are impractical for this task. Therefore, the effect of smaller plasterboards on productivity, work demands and workload was evaluated in an exploratory study among experienced construction workers (n=4-8) at the worksite. The dimensions and weight of the conventional and smaller plasterboards (PB) were: PB120 (2440 x 1200 x 15 mm; 33 kg) and PB90 (2440 x 900 x 12.5 mm; 20 kg), respectively. Productivity was defined as meters of plasterboard mounted. Work demands were assessed by means of real time observations of tasks and activities. Workload was determined using continuous heart rate monitoring and subjective judgments of perceived workload. Productivity and total work time per working day did not differ between PB120 and PB90. Duration of mounting (29% increase) and anchoring (26% increase) were longer for PB90 than PB120. Duration of lifting, carrying and turning over plasterboards, and percentage of heart rate reserve showed no difference between PB120 and PB90. A majority of the workers preferred PB90. For the last two reasons and because PB90 weighs approximately 40% less than PB120, PB90 seems preferable. The workload in both conditions, however, was considered high.     

Comparative analysis of methods for determining the metabolic rate in order to provide a balance between man and the environment

The incorrect determination of metabolic rate can be linked to discrepancies between the model of the PMV (Predicted Mean Vote) and real thermal sensation collected in field studies. Aiming to improve the correlation of the PMV model and the real thermal sensation, this work established new values for the metabolic rate: one way being called “calculated” using Newton's Method and the other called "measured" using a metabolic analyzer. Welder's activities were evaluated, through the measurements of environmental and personal variables. New values of metabolic rate were determined for this activity. The values found for the calculated form and the measured one were, respectively, 178.63 and 145.46 W/m², different from the range provided by the table of ISO 8996 (2004) for this activity (75–125 W/m²). In order to verify which of the values of the metabolic rate was closer to the real thermal sensation of PMV, a linear regression was made between the PMV and the real thermal sensation in three ways: S × PMV_tabulated (R² = 0.1749), S × PMV_calculated (R ² = 0.7481) and S × PMV_measured (R² = 0.7854). It was found that the values measured by the instrument gave a higher coefficient of determination which was chosen for the correction of the table. The correction of the table provides a value of M_predicted, that is a value of metabolic rate that corrects the values provided by the tables of ISO 8996 (2004), by means of a correction coefficient. For the welder's activities in a metal-mechanics industry, tabulated values can be multiplied by the correction coefficient 1.4648 in order to minimize inaccuracies. The PMV_predicted, obtained through the M_predicted, when related to the actual thermal sensation, provides a coefficient of determination of 0.7511, thereby improving the model of the PMV.     

On-site observations of physical work demands of train conductors and service electricians in the Netherlands

The objective of the present study was to assess the exposure to physical work demands of train conductors and service electricians at a railway company in the Netherlands. On-site observations were performed using the Task Recording and Analysis on Computer observation system to identify the mean duration and frequency of tasks, activities and body postures. In total, 36 train conductors and 41 service electricians were observed for a net working day of 7 h. Results showed that train conductors and service electricians climbed a flight of stairs on average 249 and 258 times, respectively, and that service electricians worked above shoulder height for 65 min on average. In both jobs, guidelines were exceeded, e.g. duration of standing, the number of times climbing a flight of stairs, kneeling and squatting or working in awkward postures, which are risk factors for developing musculoskeletal complaints. Suggestions are made concerning how to reduce these risk factors.

Statement of Relevance: Understanding physical work demands is essential for recognising risk factors for musculoskeletal disorders. Since train conductors and service electricians in the Netherlands reported work-related complaints, on-site observations were performed to determine the duration and frequency of physical work demands. Risk factors were identified in both professions, providing insights concerning preventative measures.     

Assessment of physical demands and comparison of multiple exposure definitions in a repetitive sawmill job: board edger operator

The primary objectives of the study were to 1) describe the physical exposures in a sawmill job with a high incidence of upper extremity musculoskeletal injuries in terms of multiple measures of posture, exertion and frequency (with varying definitions) and 2) to examine the comparability of those definitions. Surface electromyography and electrogoniometry were used to quantify the muscle demands and joint motions. Fourteen board edger operators from two sawmill facilities participated. All exposure assessments, with the exception of surface EMG measurements, were performed on the production lines. EMG measurements were performed within the facility in a location removed from the production line. The measurements showed that, on average, ranges of motions of 59, 102 and 84 degrees respectively in the planes of wrist radial/ulnar deviation, flexion/extension and pronation/supination were required to perform the job. Significant differences (p < .001) were observed between ranges of motion defined by peak postures and those due to peak postures required to perform the primary task only. Performance of the primary task required an average of 32% of maximum voluntary contraction from the forearm muscles assessed. Repetitions per day ranged, on average, from 2,015 to 9,365. Incidence of reported upper extremity musculoskeletal injuries in the two facilities assessed was found to be higher with the greater total exposure. However, examination of the trend with a standardized measure of injury incidence was not possible.     

Simultaneous metabolic labeling of cells with multiple amino acids: Localization and dynamics of histone acetylation and methylation

Simultaneous metabolic labeling of cells with multiple amino acids combined with acetic acid urea-PAGE and MS was used to characterize histones in Kasumi-1 cells treated with the histone deacetylase inhibitor depsipeptide (DDP). The approach allowed for rapid targeting, identification, and subsequent characterization of peptides containing sites of acetylation or methylation. Multiple methylation sites were determined for histone H3 including: di- and tri-methylation of K9 and K27; mono- and di-methylation of K36 and K79; and mono-methylation of K37. The acetylation patterns for histones H4 and H3 were established. Quantitative analysis of the modification change after treatment with DDP was also performed and the dynamics of H4 acetylation determined. Functional analysis by RT-PCR showed that DDP unregulated p21 expression with a maximum after 18-h exposure. Chromatin immunoprecipitation experiments indicated that DDP treatment caused an accumulation of hyperacetylated histone H4 and H3 isoforms and a decrease in K9 di-methylation of H3 on the p21 promoter.     

Assessment of physical work load in epidemiologic studies: concepts,issues and operational considerations

Ergonomic epidemiology is a rapidly increasing field of research providing data on the occurrence of musculoskeletal disorders and possible risk factors. The present paper states, on the basis of a literature overview, that physical work load (mechanical exposure) is poorly denned and measured in most studies on ergonomic epidemiology. On this background the paper: (1) suggests adjustments of mechanical exposure concepts and terminology; (2) concludes that invalid exposure assessment may, to a large extent, explain the lack of quantitative data on relationships between mechanical exposures and musculoskeletal disorders; and (3) suggests some guidelines for future quantitative assessments of mechanical exposure in large populations.