Load on knee joint and knee muscular activity during machine milking

Abstract

Ten professional milkers simulated 20 different standardized machine-milking work postures. Various differences in level between milkers and cow, and various postures at each level, were studied. Knee muscular activity was recorded electromyographically. In the milking procedure when attaching the teat cups to the udder the body position was photographed and the loading moment of force about the bilateral knee axis was calculated by means of a biomechanical model. Working with straight knees resulted in comparatively high moments tending to extend the knee (with the highest mean of 56 N m). This moment was for some subjects close to their maximum strength capacity. A 65° knee angle in the standing postures with small level-difference between cow and milker gave the least knee loading moment (i.e. around zero) independently of body weight. The horizontal distance between operator and cow showed high importance for the amplitude of the knee load. The model for determining knee load can generally be applied to other similar activities when standing bent forwards.     

Ankle joint load and leg muscle activity in various working postures during machine milking

Abstract

Ten professional milkers simulated 20 different standardized machine-milking work postures. The loading moment of force about the bilateral ankle axis was calculated using a computerized biomechanical sagittal plane model. Leg muscular activity was recorded with time-averaged, full-wave rectified electromyography which was normalized. The muscular activity level was generally low. The calculated loading moment was always dorsifiexing and did not exceed 50 N m. This is not above 50% of the maximum strength capacity and is lower than the load during many daily activities. Straight knee working postures induced lower ankle load compared with flexed knee postures. The model for determining ankle load can be used to investigate similar activities.     

Comparison of biomechanical loading during use of conventional stud welding equipment and an alternate system

We investigated the effect of an alternative welding system designed to reduce exposure to extreme trunk flexion on measures of trunk inclination and muscle activity. Among 10 participants, data were collected while using conventional stud welding equipment and while using the alternate system. Paired t-tests were used to compare results between the two welding systems. Mean trunk inclination angle was reduced with the alternate system (34.4° versus 9.7°, p < 0.01). Percent time with trunk inclination angles greater than 60° was also reduced (40.0% versus 4.7%, p < 0.01). In general, the alternate system resulted in less desirable upper trapezius muscle activity levels. The alternate system appears to be effective in reducing exposure to extreme trunk flexion among stud welders. Continued development of the system should explore features designed to reduce shoulder forces and improve productivity.     

Posture evaluations of tethering and loose-housing systems in dairy farms

The purpose of this study was to evaluate the most common simultaneous and individual segment postures in terms of body and finger posture classifications. Observations were made at three dairy farms. One employed a tethering system and the other two used loose-housing systems. The evaluations of the tethering system were performed through six processes that were subdivided into 11 operations, whereas only one process of ‘milking’ was investigated in loose-housing systems. Generally, farmers who worked in both systems bent and/or twisted their upper-body segments and continuously used a power grasp to wrap an object with all five fingers. Posture analyses of the tethering system revealed that ‘moving corn’ seemed less stressful, whereas ‘cleaning udders,’ ‘attaching the machine,’ ‘washing the machine,’ and ‘sweeping the floor’ were more stressful than other operations. Postural workloads on the trunk and head were greater in the tethering system than in the loose-housing systems due to differences in implements, the working height, and the working distance.     

Reducing the physical work load and strain of personal helpers through clothing redesign

This study assessed the effects of redesigning clients’ clothing on the physical work load and strain of personal helpers. Five women, aged 18–54 years, who helped persons with physical disabilities were measured at their worksites before and after development of the clothes worn by clients. The physical work load and strain of the helpers’ dressing/undressing of clients were determined from their hand and back movements, work time, muscular activity, heart rate (HR), percentage of heart rate range (%HRR), and rating of perceived exertion (RPE). The muscular activity of the right (p=0.05) and left (p=0.02) trapezius muscles, HR (p=0.03), and %HRR (p=0.03) of the helpers were lower when the new outerwear was used in place of traditional outerwear. Four helpers reported lower perceived exertion, and three had shorter work time with the new outerwear. This study showed that redesigning clients’ clothing can help reduce the physical work load and strain of personal helpers.     

Validity of self-reported duration of work postures obtained by interview

The aim of the study was to validate interview data concerning the duration of four work postures (1) sitting, (2) standing/walking with hands above shoulder level, (3) standing/walking with hands between shoulder and knuckle level, and (4) standing/walking with hands below knuckle level. The self-reported time spent in each posture was tested in relation to observations and technical measurements in 20 subjects during two full working days. The linear relationships between self-reports and observations were strong for the three postures; sitting (r²=0.55), hands above shoulder level (r²=0.58) and hands below knuckle level (r²=0.69). Thus, using this interview technique, self-reports concerning time spent in (1) sitting, (2) standing/walking with hands above shoulder level and, (3) standing/walking with hands below knuckle level may be accurate enough for studying these work postures in epidemiological studies.     

A computerised system for analysing working postures in agriculture

This paper aims to show a computerised program for analysing work postures in agriculture. The system contains two types of routines for studies of observation, Working Posture Analysing Sytem (WOPALAS) and a simple Video film technique for Registration and Analysis of working postures and movements (VIRA). Furthermore the system consists of programs for moment calculations and routines for registration of problems in the locomotive organs. The computerised system provides several advantages compared with traditional manual systems. For the operator, it is a less demanding work and the analyses are more accurate. The system rapidly provides the results of an analysis.     

Repetitive work in perspective

Abstract

A view of the evolution of repetitive work is presented. The need to re-evaluate its meaning, significance and value is expressed in a social and production technology context. The implication for ergonomists is outlined.     

Fatigue and human reliability revisited in the light of ergonomics and work psychopathology

In the process control human-beings are actually information processors, solving many problems, especially covariance-problems which involve various interconnected and interactive factors.

The purpose of this experiment was to investigate the types of cognitive strategy and information-processing procedure used in solving covariance-problems, and to evaluate and determine the best strategy.

Fifty-five subjects participated in the experiment to solve two-factor covariance-problems. Verbal protocols and structural analysis were used to record and analyse the cognitive processes of covariance-problem solving. Verbal protocols were coded and analysed to differentiate the basic operators and thence explore the various strategies.

The results indicated that under two-factor covariant conditions, there were nine kinds of cognitive strategy. The 'biconvex-lens’ strategy was the most effective. All nine strategies can be classified into three categories, trial-and-error, analytic and intuitive.

This experiment research was the first study on cognitive strategies in solving covariance-problems. New topics for further study are put forward.     

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.     

Perceived competence in computer use as a moderator of musculoskeletal strain in VDU work: An ergonomics intervention case

Musculoskeletal strain and other symptoms are common in visual display unit (VDU) work. Psychosocial factors are closely related to the outcome and experience of musculoskeletal strain. The user – computer relationship from the viewpoint of the quality of perceived competence in computer use was assessed as a psychosocial stress indicator. It was assumed that the perceived competence in computer use moderates the experience of musculoskeletal strain and the success of the ergonomics intervention. The participants (n = 124, female 58%, male 42%) worked with VDU for more than 4 h per week. They took part in an ergonomics intervention and were allocated into three groups: intensive; education; and reference group. Musculoskeletal strain, the level of ergonomics of the workstation assessed by the experts in ergonomics and amount of VDU work were estimated at the baseline and at the 10-month follow-up. Age, gender and the perceived competence in computer use were assessed at the baseline. The perceived competence in computer use predicted strain in the upper and the lower part of the body at the follow-up. The interaction effect shows that the intensive ergonomics intervention procedure was the most effective among participants with high perceived competence. The interpretation of the results was that an anxiety-provoking and stressful user – computer relationship prevented the participants from being motivated and from learning in the ergonomics intervention. In the intervention it is important to increase the computer competence along with the improvements of physical workstation and work organization.     

A privacy-preserving and unobtrusive sitting posture recognition system via pressure array sensor and infrared array sensor for office workers

Sitting posture recognition is essential in preventing work-related musculoskeletal disorders (WMSDs). WMSDs are of huge concern for office workers whose working process is averagely 81.8% sedentary. Prevailing studies have utilized cameras, wearables, and pressure sensors to recognize sitting postures. The cameras and wearables can achieve accurate recognition results, while personal privacy concerns and inconvenience for long-term use impede their adoption. Meanwhile, the pressure sensors are privacy-preserving and convenient. However, they cannot accurately recognize the sitting posture with different states of the trunk, head, upper extremity, and lower extremity. Considering the pros and cons of those approaches, this study proposes a novel privacy-preserving and unobtrusive sitting posture recognition system, which combines a pressure array sensor with another privacy-preserving sensing technology, i.e., an infrared array (IRA) sensor. Moreover, a deep learning-based sitting posture recognition algorithm is developed, which adopts a feature-level fusion strategy and does not require a complex handcrafted feature extraction process. Based on the ergonomics studies, ten daily sitting postures with the states of different body parts are selected. This system achieved an overall 90.6% accuracy using the leave-subject-out validation approach based on the self-collected dataset from 21 subjects. It has a great potential for privacy-preserving and unobtrusive related applications for sitting posture management.     

Trends in approaches to night and shiftwork and new international standards

This paper examines whether improving physical ergonomics working conditions affects worker productivity in a call centre with computer-intensive work. A field study was conducted at a catalogue retail service organization to explore the impact of ergonomics improvements on worker production. There were three levels of ergonomics interventions, each adding incrementally to the previous one. The first level was ergonomics training for all computer users accompanied by workstation ergonomics analysis leading to specific customized adjustments to better fit each worker (Group C). The second level added specific workstation accessories to improve the worker fit if the ergonomics analysis indicated a need for them (Group B). The third level met Group B requirements plus an improved chair (Group A). Productivity data was gathered from 72 volunteer participants who received ergonomics improvements to their workstations and 370 control subjects working in the same departments. Daily company records of production outputs for each worker were taken before ergonomics intervention (baseline) and 12 months after ergonomics intervention. Productivity improvement from baseline to 12 months post-intervention was examined across all ergonomics conditions combined, and also compared to the control group. The findings showed that worker performance increased for 50% of the ergonomics improvement participants and decreased for 50%. Overall, there was a 4.87% output increase for the ergonomics improvement group as compared to a 3.46% output decrease for the control group. The level of productivity increase varied by the type of the ergonomics improvements with Group C showing the best improvement (9.43%). Even though the average production improved, caution must be used in interpreting the findings since the ergonomics interventions were not successful for one-half of the participants.     

Effect of sampling interval on the reliability of ergonomic analysis using the Ovako working posture analysing system (OWAS)

In industry, the Ovako working posture analysing system (OWAS) is applied using different sampling intervals. However, it has not yet been established what influence the sampling interval has on the reliability of the data collection. For this purpose, the sampling interval of an existing ergonomic analysis of working postures using OWAS with 20,601 observations was varied between 2 and 90 s to investigate the effects of deviation from the original sampling interval of 1 s. Based on these comprehensive industrial data, which was statistically analyzed with regression analyses, it can be concluded that in the ergonomic analysis of working postures using OWAS, direct observations should have a sampling interval of 20 s, and video-based observations should have a sampling interval of 10 s or less.Relevance to industryThe Ovako working posture analysing system (OWAS) is a practical and frequently selected method for the ergonomic analysis and evaluation of working postures. However, the selection of a suitable method is as least as important as the definition of a sampling strategy providing reliable values obtained through observation. For this reason we investigated the effect of the sampling interval and recommend using 20 s for direct observations and 10 s or less for video-based observations.     

Cooperation in professional support—the human sciences in industry

This paper deals with the ‘state of the art” in the basic philosophy relating to the balance between man and work in a large electronics company in the Netherlands. One of the main topics of industrial management is the optimum fit between the work (content, conditions, environment, organization and human relations) and the ambitions, needs, capacities, limitations, health, well-being, and performance of the worker. To achieve an optimum fit between man and work, close cooperation, preferably even integration, is needed between all the experts in the human sciences in the company: medical doctors, psychologists, social workers, safety engineers, and so on. There is no single problem concerning the balance between man and work which is confined to only one discipline; from the viewpoint of the questions to be answered and the problems to be solved the distinctions between the human science disciplines are purely artificial. Even more important, perhaps, is the integration of the human sciences into engineering, which in practice means close cooperation between the above-mentioned professionals and engineers of all kinds in their role as 'designers of work'. This is the background to the origin of certain multidisiplinary activities such as occupational hygiene, ergonomics or human engineering, work structuring and organization renewal, all professional fields involving human scientists and engineers alike. This common basic philosophy, which must be clear and simple, calls for a mutual understanding and acceptance of the underlying goals of the different disciplines (health, individual care, safety, efficiency, profit, and so on); but above all it requires a common goal for the company as a whole in which human and commercial interests coincide.     

Doing ‘organizational work’: Expanding the conception of professional practice in ergonomics

Literature on ergonomic practice contains many discussions of how ergonomists should work but far less attention has been paid to how they do work and the factors that influence their practice. In an effort to improve our understanding of ergonomic practice as it occurs and how it is conditioned by broader contexts, we conducted an interview study with 21 ergonomists in Canada. We were particularly interested to understand the different kinds of activities study participants engaged in during the course of their work, the challenges they faced and the strategies they employed for facing these challenges. Findings indicate that in the course of their professional practice ergonomists engage in a variety of types of activities. This includes consulting on risk factors as well as a proactive role of fostering the application of ergonomics in organizations. The process of advocating for ergonomics brought study participants into a variety of interactions and collaborations with workplace parties in a type of activity we have called “organizational work”. In the course of doing organizational work, ergonomists utilize different strategies, including “political manoeuvring”, tailoring data collection and report presentations to clients’ concerns and ‘goal hooking’ in order to make the case for implementing ergonomics in workplaces. The article concludes with a list of “tips” for practicing ergonomists that are suggested by the analysis.     

Modular data logger system for physical workload measurements

Direct technical measurements of physical workload have advantages in studies of work-related musculoskeletal disorders. A data logger has been developed, based on 20 and 40 Mbyte PCMCIA (Personal Computer Memory Card International Association) flash memory cards, for electromyography (EMG), inclinometry and goniometry. They are provided with an input for marking of events that can be used for synchronization with other loggers and with video recordings. To make the data easier to access by the preceeding analysis software, application software has also been developed that reorganizes the data. The loggers are easy to operate and enable whole-day ambulatory field recordings without any need for reduction or compression of the data.     

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.     

A method for measuring work interference in surgical teams

To enhance surgical systems we need to manage the performance of the teams that comprise them. To do this we must measure the properties and processes of teams and account for the demands and conditions of their work. Recent research shows that observation is a potentially valuable method of measurement, but its potential application in surgery remains unclear. In this study of laparoscopic cholecystectomy, an observer applied observational measures of teamwork in the operating theatre and recorded intra-operative interference from observed distraction and interruption. Results showed that it was feasible to observe a broad scope of teamwork and to reveal the frequency and source of work interference. However, the measures were necessarily selective and so limited in their analysis of the conditions and events that might interfere with the collective work in surgery. Such measures may however prove useful when applied in conjunction with other methods of measurement and utilised as performance feedback data.     

Reliable exposure assessment strategies for physical ergonomics stressors in construction and other non-routinized work

The objective of this research was to provide guidelines for the reliable assessment of ergonomics exposures in non-routinized work. Using a discrete-interval observational sampling approach, two or three observers collected a total of 5852 observations on tasks performed by three construction trades (iron workers, carpenters and labourers) for periods of several weeks. For each observation, nine exposure variables associated with awkward body postures, tool use and load handling were recorded. The frequency of exposure to each variable was calculated for each worker during each of the tasks on each of the days. ANOVA was used to assess the importance of task in explaining between-worker and within-worker variability in exposures across days. A statistical re-sampling method (bootstrap) was used to evaluate the reliability of exposure estimates for groups of workers performing the same task for different sampling periods. Most exposures were found to vary significantly across construction tasks within trade, and between-worker exposure variability was generally smaller than within-worker exposure variability within task. Bootstrapping showed that the reliability of the group estimates exposure for the most variable exposures within task tended to improve as the assessment periods approached 5 – 6 d, with marginal improvements for longer assessment periods. Reliable group estimates of exposure for the least variable exposures within task were obtained with 1 or 2 d of observation. The results of this study demonstrate that an initial estimate of the important environmental or task sources of exposure variability can be used to develop an efficient sampling strategy that provides reliable estimates of ergonomics exposures during non-routinized work.