Showing papers in "Ergonomics in 1987"

Some effects of jet-lag and their alleviation by melatonin

Abstract: Seventeen healthy volunteers (10 women and 7 men, aged 29-68) were flown from London to San Francisco between 20 November 1985 and 25 January 1986 and remained there for 14 days prior to flight home. Subjects took melatonin (N = 8, 5 women, 3 men) or placebo in a double-blind design, at 18.00h local time for three days before the return flight and at bedtime (22.00-24.00h) in Great Britain for four days. For three days before departure and on days 1-7,14,15, 21 and 22 after their return subjects collected 6-hourly sequential urine samples and kept a daily sleep log. They recorded mood and oral temperature 2 hourly and performed logical reasoning and letter cancellation tests 4 hourly from 08.00h (or wake up time) to 24.00h (or bedtime) whichever was the earlier. Urine was also collected for 48 h prior to departure from the U.S.A‥ On day 7 after their return subjects rated ‘jet lag’ (10 cm visual analogue scale—VAS) from 0 (insignificant) to 100 (very bad). Melatonin significantly improved ‘jet la...

Work technique and its consequences for musculoskeletal disorders.

Abstract: Work in the manufacturing industry is associated with a high prevalence of cervicobrachial disorders. The outcome in individual cases varies; some go without symptoms for many years, others have to be relocated because of serious disorders after only a few years. Since the gross characteristics of the work tasks do not show a large variation, powerful individual factors must exert their influence, either protecting the individual or increasing vulnerability. A prospective study was conducted to identify such factors. The aim was to relate the outcome in terms of disorders in the neck-shoulder-arm region to such factors as individual variations in working technique, physical capacity, and medical and work history. In order to investigate individual differences in working technique two subgroups of women were studied. The results show that the number of changes in posture, as well as the percentage of work cycle time spent with the upper arm in different angular sectors, varied to a large extent among worke...

Information integration and the object display An interaction of task demands and display superiority

Abstract: Two tasks, varying in their demands to integrate multiple information sources, were used in a comparison of two graphical display formats. One display technique, an ‘object display’, utilized different dimensions of a single perceptual object to display task-relevant information. A contrasting graphical technique, a ‘bar graph’, used the same dimension of several separate objects to present identical information. In one experiment, 24 subjects used both displays to perform a simulated process control task in which integration of information from several time-varying sources was required. In a second experiment, 20 additional subjects used both displays in a non-integration task that required monitoring for particular values of six independent system outputs. Results of the integration experiment revealed that performance was superior when the object display was used. However, when the non-integration task was studied, the bar graphs provided more efficient performance. Thus, the requirement to integrate i...

Lorry driver's time habits in work and their involvement in traffic accidents

Abstract: Using representative samples of drivers operating in freight transportation, the sociological features of lorry drivers, the process of formation of this group, and their work conditions are described. In many ways they are similar to other blue collar workers. The analysis of career evolution shows the existence of social processes of selection, whereby some people leave this sort of work, while others stay in it but try to improve their working conditions by migrating to firms offering better salaries and/or easier conditions. As ‘normal’ durations and rhythms of work are known, it was possible to calculate the risk exposure to road accident involvement (according to the time at which the drivers are at the wheel and in relation to the amount of work already carried out) and to compare it, using a representative sample of the drivers involved, to the time features of the driver's activities prior to the accident. This demonstrated that the risk of involvement in an accident increases with the n...

Noise, unattended speech and short-term memory

Abstract: Studies of ‘noise pollution’ have typically used unpatterned white noise. The present study compares the effect of noise with that of unattended speech. Three experiments required the immediate serial recall of sequences of nine visually presented digits accompanied by silence, noise or unattended speech in an unfamiliar language. Experiments 1 and 2 showed a clear effect of unattended speech at both 75dB(A) and 95dB(A), while unattended noise had no effect in either study. Experiment 3 used a separate groups design combining 95 dB(A) noise and quiet with instructions either to remain silent or to rehearse overtly. Overt rehearsal enhanced recall, while unattended noise again had no effect. It is suggested that noise does not interfere with short-term memory but that unattended speech does impair performance by disrupting the articulatory loop component of working memory. Implications for studies of ‘noise pollution’ are discussed.

Generation of muscle tension additional to postural muscle load.

Abstract: This paper presents methods and the first results of experiments designed to test the hypothesis that individuals in many situations generate muscle loads in excess of those necessary to maintain postural stability. Excess muscle loads of this kind are demonstrated in experiments where specific movements are performed under various constraints and where VDU-based psychophysical tests are performed with a high level of arousal. Most recordings from the psychophysical tests showed a near identical tension pattern for all muscles tested, with very low variability apart from sudden or slow changes in mean load. There were considerable inter-individual differences in tension patterns, and some implications of these findings in terms of health effects in real-life work situations are discussed.

Sex difference in muscular strength in equally-trained men and women

Abstract: Although the magnitude of the sex difference in muscular strength is well documented, the extent to which it reflects long-term behavioural differences in physical activity compared to innate biological differences in muscle mass or neuromuscular function is unclear. The purposes of this study were to determine: (1) the magnitude of the sex difference in upper- and lower-body strength in groups of men and women with similar backgrounds of physical activity and (2) the extent to which the difference in strength could be explained by indices of muscle size. Maximum curl, bench press, handgrip, leg press and leg extension strengths; fat-free weight (FFW); and upper-arm, forearm and thigh fat-free cross-sectional areas (FFCSA) were measured on 24 male and 25 female swimmers and 23 male and 25 female non-athletes, 15-28 years of age. Sex differences in absolute strength for both groups were typically smaller than those previously reported. Sex differences in absolute strength were generally smaller for the swi...

Reassessment of the role of intra-abdominal pressure in spinal compression

Abstract: Biomechanical models used to estimate loads on the lumbar spine often predict internal low back forces for heavy lifts that exceed known tissue tolerances, yet the particular lift caused no apparent damage to the lifter. To deal with this paradox, many researchers have incorporated some form of spinal compression alleviation from intra-abdominal pressure (IAP). The purpose of this work was to re-examine some of the issues involved in the feasibility of IAP to reduce spinal loads during stressful lifts. Questions remain over the trade-off between the beneficial tensile force on the spine, exerted via the diaphragm and pelvic floor when IAP is produced, and the undesirable compressive effects of abdominal muscular force required to maintain the pressure within the abdomen. Various strategies of modelling IAP and its effects on low back loading were employed, Three major differences between this and most previous models of IAP effects were the attempt to quantify the size of abdominal muscle forces and the u...

Trunk loading and expectation

Abstract: Much of the epidemiological literature has reported that there is a link between sudden unexpected load handling and the risk of a low back injury. However, few biomechanical studies have investigated the effect of this type of loading on trunk muscular response. An experiment was performed to test the hypothesis that sudden unexpected loads would create excessive forces upon the trunk due to the overcompensation of the trunk muscles, and to quantify the degree of overcompensation. Twelve male subjects were asked to hold a box in a static lift position while weights ranging from 2-27 to 907kg were dropped into the box from a constant height. Under some conditions (expected) the subjects were permitted to observe the weight drop while under other conditions (unexpected) the subjects were deprived of visual and auditory cues during the weight drop. Several components of the trunk response were observed. Mean muscle forces for the unexpected condition exceeded those in the expected condition by nearly two-an...

Trunk extensor endurance: determination and relation to low-back trouble

Abstract: The strength and endurance of the trunk extensors were studied in relation to the extent of earlier low-back trouble (LBT) in a homogeneous, and occupationally active group consisting of 53 male postmen (occupational seniority > 2 years). The isometric endurance was measured (1) prone with the unsupported trunk in a horizontal position and the legs and hips fixated to a couch (couch method) and (2) standing, at 60% MVC (pulling test). The participants were divided into three groups according to the extent of previous LBT Group I, LBT to a degree that made work impossible; Group II, LBT experienced but not to the degree that work was hindered, and Group HI, LBT never experienced. The main findings were that isometric endurance time of the trunk extensors was shorter in Group I than in Groups II and III, while the strength of the trunk extensors was independent of the person's earlier low-back episodes The two methods for the determination of trunk extensor endurance were compared. It was shown that Method ...

The prevalence and causation of tennis elbow (lateral humeral epicondylitis) in a population of workers in an engineering industry

Abstract: Lateral humeral epicondylitis (tennis elbow) is often considered to be work related but the incidence and prevalence among industrial workers has not previously been studied In this study the prevalence of this condition and its relationship to some work factors was investigated in 540 workers in a modern engineering industry The prevalence was 7-4% (40/540). Work was found to be the probable cause in 35%, tennis in 8% and other leisure activities in 27% of the patients. No cause was found in the remaining 30%. There was no correlation with sex, while a significant correlation was found with age, the incidence increasing with advancing age On the basis of job classification according to their elbow stress, it was found that these workers with work-related epicondylitis had higher elbow stress jobs compared to other sufferers and to the workforce as a whole.

The effects of load placement on the EMG activity of the low back muscles during load carrying by men and women

Abstract: An electromyographic (EMG) study of the lumbar paraspinal muscles during load carrying was undertaken in a group of 24 healthy subjects, 12 male and 12 female. Two different magnitude loads (10% and 20% of the subject's body weight) and four different carrying positions were compared with walking without an external load. Results indicated changes in back muscle activity showing a significant interaction between load magnitude and carrying position. Compared to walking without an external load, lumbar paraspinal EMG activity showed slight decreases when loads were carried in a backpack position or in the hand ipsilateral to the muscle. EMG activity contralateral to the hand carrying the load was significantly increased. Significant increases occurred when loads were carried anterior to the chest with the arms and a significant difference was found between male and female subjects for this carrying position. These findings have implications for the selection of carrying methods.

Power hand tool vibration effects on grip exertions

Abstract: Operation of vibrating power hand tools can result in excessive grip force, which may increase the risk of cumulative trauma disorders in the upper extremities. An experiment was performed to study grip force exerted by 14 subjects operating a simulated hand tool vibrating at 9.8 m/s2 and 49 m/s2 acceleration magnitudes, at 40 Hz and 160 Hz frequencies, with vibration delivered in three orthogonal directions, and with 1.5kg and 3.0kg load weights. Average grip force increased from 25.3 N without vibration to 32.1 N (27%) for vibration at 40 Hz, and to 27.1N (7%) for vibration at 160 Hz. Average grip force also increased from 27.4 N at 9.8 m/s2 acceleration to 31.8 N (16%) at 49m/s2. Significant interactions between acceleration x frequency, and frequency x direction were also found. The largest average grip force increase was from 25.3N without vibration to 35.8N (42%) for 40 Hz and 49 m/s2 vibration. The magnitude of this increase was of the same order as for a two-fold increase in load weight, where ave...

Postural adjustments while standing with two types of loaded backpack

Abstract: Two types of frame backpack, the internal-frame pack and the external-frame pack, are commonly used by hikers to carry heavy loads. The centre of volume of the internal-frame pack is lower and closer to the body than that of the external-frame type. This study examined how carrying each pack type changed the body posture compared with the typical standing posture as a control. The packs were loaded with 19 kg loads for the men and 14 kg loads for the women. The positions of the knees, hips, shoulders and ears were recorded photographically; the whole-body centre of gravity and the partial centres of gravity above the knee and hip were calculated. The nine female and seven male subjects were experienced in carrying packs. Both types of packs caused the subjects to lean forward; the bend was greatest above the hips but the knees and hips were also forward of the control position. The internal-frame pack caused a greater displacement and also a greater uncompensated torque at the hips: The female subjects ov...

Effects of moderate cold on performance of psychomotor and cognitive tasks.

Abstract: Two experiments were performed to study the effects of exposure to moderate cold ( + 5°C) on psychomotor and cognitive tasks requiring sustained attention. Twelve male and 12 female subjects partic...

The use of a non-motorized treadmill for analysing sprint performance

Abstract: The measurement of human power output and anaerobic capacity in high-intensity exercise has traditionally been made using cycle ergometers. The assessment of power output during running has proved difficult because previous approaches have limited themselves to using motorized treadmills. In the present study the problems associated with motorized treadmills were overcome by using a non-motorized treadmill which was instrumented so as to allow the measurement of power output during sprint running. A non-motorized treadmill (Woodway model AB) was used because it allows rapid changes in running velocity normally found in sprinting to be monitored. In order to calculate the horizontal component of the applied power the instantaneous values of both the horizontal component of applied force and the treadmill belt speed were measured, and their product determined. A harness, attached to a force transducer, was passed around the waist securing the subject to the crossbar without restricting the movement of the l...

A method for estimating physical working capacity at the fatigue threshold (PWCFT)

Abstract: Presently available tests of physical working capacity (PWC) such as [Vdot]O2max and critical power may not be appropriate for unfit subjects because they require maximal or supramaximal workloads. Therefore, the purpose of this study was to evaluate a submaximal discontinuous incremental bicycle ergometer test (PWCFT) with an end point (fatigue threshold) determined by recording electromyographic (EMG) fatigue curves in the quadriceps muscle. The fatigue threshold was defined as the lowest workload producing a slope of the EMG voltage-time relation that was significantly different from zero slope at p<0.05 (single tail). The test-re-test reproducibility of PWCFT (n=17 subjects) was found to be r = 0.947, with no significant difference between trials. Thirty-two healthy male subjects aged 18-29 (mean 23-4 ± 31 years) whose fitness levels ranged from highly trained to untrained sedentary level were tested for PWCFT, lactate threshold (OBLA), percentage heart rate range at PWCFT (%HRR), and heart rate-workl...

The clarity and comfort of printed text

Abstract: The successive lines of printed text form a pattern of ‘stripes’. The spatial characteristics of this pattern have been measured and found to be similar to those of patterns that induce discomfort, anomalous visual effects and even seizures. It is argued that reading provokes ‘eye-strain’ and seizures because of the striped properties of text, and that it is for this reason that headaches and seizures are reduced by covering the lines of text above and below those being read. In studies in which subjects are asked to judge the clarity of text it is shown that judgements of clarity are affected by the spatial characteristics of the pattern, in particular, the spacing between the lines. The average area of the page occupied by a letter (i.e. the product of the separation between the lines and the mean horizontal spacing between the centres of letters) accounts for less variance than does the separation between the lines of text. Within the constraints of conventional typography, the clarity of text could pe...

Workplace injuries in the developing countries

Abstract: Transfer of technology and industrial development without consideration for the characteristics of the local users and the environmental conditions of the recipient countries has proved to be not only socially destructive but economically expensive in terms of human suffering and material losses Most developing countries (DC) are paying an unacceptably high price in terms of suffering, sickness and also loss of production due to work-related accidents Poor working conditions and non-existence of an effective injury prevention programme in many DCs has resulted in a very high sickness and accident rate. In such circumstances, the salary and social benefits of the worker are low, because productivity is well below its capacity. This vicious cycle also results in the worker's malnutrition and low working capacity, resulting in turn in greater vulnerability to disease and job-related accidents A greater awareness is needed among employers and the workforce of such common problems as increased health hazards, ...

Lumbo-sacral loads and selected muscle activity while turning patients in bed

Abstract: Handling patients in bed using a pique (a waterproof padded sheet placed under the patient) is associated with a high incidence of risks for the spine with, in particular, the activity of pulling and turning the patient with the pique representing the highest risk. Fifteen female nursing aides were evaluated for compression and shear forces at the L5/S1 joint and for selected muscular activities in the trunk and shoulders. Films, force platforms and EMG recordings supplied the data; dynamic segmental analyses were performed to calculate reaction forces at L5/S1, and a planar single-muscle equivalent was used to estimate internal loads. Different execution parameters were examined including execution velocity, height of bed, direction of effort, leg position and knee support. A ‘free’ task, and a manual task not involving the pique, were also investigated. Recommendations are made for reducing spinal loading. The results also suggest that a change of direction in the trunk motion may present some risks whe...

Physiological responses of fire fighters to workload and thermal stress

Abstract: The physical work performance of eight fit fire fighters wearing fire brigade uniforms and wearing breathing apparatus was assessed. They were tested in a climatic chamber set at temperatures of 15 and 45°C respectively. The test was performed with and without fire fighting equipment. The subjects walked on a treadmill at a speed of 3.5km/h, which produce a workload equivalent of 20% of the subjects' maximal oxygen uptake without equipment, and 30% with equipment. The test lasted for 60 min. Heart rate, oxygen uptake, skin and deep body temperatures were measured during the test. The subjects estimated perceived physical exertion and perceived temperature. Wearing fire fighting equipment increased the oxygen uptake by 0.4 1min-1. Heart rate at the end of the experiments reached near-maximum levels when the temperature was 45°C with equipment, and deep body temperature increased to an average of 38.7°C. The subjects' ratings of perceived exertion were highly correlated to heart rate. The loading induced by...

Experimental investigation of psychophysiological stress-reactions induced by different system response times in human-computer interaction∗

Abstract: In human-computer interaction, system response times are considered to have important effects on operator performance and stress response. To evaluate the effects of short (2s) and long (8s), as well as constant and variable, system response times, a laboratory study was conducted with 68 subjects in four independent groups working at a simulated computer workplace. Subjects had to perform a simple detection and correction task at a visual display terminal in six trials of 20min each, the first being a training trial with identical conditions for all subjects. Performance and physiological measures (heart rate, electrodermal activity, and blood pressure) were taken during the trials, and subjective measures of mood and physical state as well as physiological measures were done in the resting periods iiftcr the trials. In addition to a general adaptation effect over the trials, experimental effects were shown mainly for the duration factor: subjects under conditions of long, as compared to those under shor...

The immediate effects of strenuous exercise on free-recall memory.

Abstract: A free-recall memory task was used to assess the after-effects of strenuous exercise on the cognitive functioning of young adults. In a first study, 24 college-age subjects performed tests of memory immediately following a treadmill run to voluntary exhaustion. The number of words recalled following exercise did not differ from the number of words recalled by 24 subjects in a non-exercise control group. Further, there were no differences in the serial position effect between the two groups. In a second study, 12 highly fit subjects were compared with 12 subjects of average fitness. No differences were found.

Exposure to ergonomic stressors in the garment industry: application and critique of job-site work analysis methods.

Abstract: Recently developed work analysis techniques permit the quantitative description of job demands such as force and non-neutral postures on a continuous basis. Such characterization of workplace exposures facilitates the identification of highly stressful work elements. It is also a necessary tool for the epidemiologic study of occupational musculoskeletal disorders and their risk factors. The methods were applied to the analysis of 14 garment assembly jobs, employing 151 women, among whom an elevated prevalence of upper limb musculoskeletal disorders had previously been found. The goals of the job analyses were to document the biomechanical features of the jobs and to evaluate the work analysis methods for the characterization of ergonomic exposures in an epidemiologic study. The cycle lengths of the 14 jobs ranged from 9·5 seconds to 3·4 minutes. Wrist and hand postures that were used frequently included finger pinches, wrist extension and ulnar deviation. The methods were extremely time and labour-intensi...

The adaptation of night nurses to different work schedules.

Abstract: Twenty-nine full-time permanent night nurses, 94 part-time permanent night nurses, and 44 nurses working in a weekly rotating two-shift system but doing some night work from time to time answered questionnaires on morningness, rigidity of sleeping habits, aspects and effects of night work, subjective health, etc. For one month they also carefully registered their sleeping times. The full-time nurses displayed a tendency to be evening people and were more vigorous and less rigid in their sleeping habits than the rotating nurses. The latter mentioned more subjective health complaints. The most striking difference between the permanent night nurses and the rotating nurses was found in their evaluation of aspects and effects of shift work. The permanent flight nurses always gave a more favourable evaluation. There was not much difference between the sleep of the three groups, except that the permanent nights nurses slept on average less than the rotating nurses. The differences found can be explained...

A reanalysis of spinal motion during vibration.

Abstract: Calibrated film of the motion of the lumbar spine during vibration was reanalysed, making use of a number of computer based techniques to improve accuracy and reduce measurement noise. The results demonstrated resonant behaviour at about 4 Hz and indicated that at vibration levels of the order of 1 m/s2 there exists bending of the order of 1° (peak to peak) between adjacent vertebrae in the lumbar spine. The bending is complex and involves phase differences along the spine and possibly a rocking motion of the pelvis.

Effects of different types of physical activity on the performance of perceptual tasks in peripheral and central vision and coincident timing.

Abstract: The aim of this study was to analyse the effects of different types of metabolic fatigue, induced by anaerobic alaciacid, anaerobic lactacid, sub-maximal aerobic, and maximal aerobic efforts, on the performance of a sensory task (peripheral threshold detection), a sensory-motor task (coincidence-anticipation), and a cognitive task (recall in central vision) Each of three experimental groups performed one of the above mentioned tasks under all types of fatigue Running bouts on a treadmill were used to induce the different types of fatigue Results show that performance in peripheral vision improves with all types of effort For coincidence-anticipation, only constant error is affected by anaerobic alactacid and maximal aerobic efforts; the former producing a change in behaviour from lateness to anticipation, whereas the latter significantly reduces lateness Finally, performance in the cognitive task is significantly disturbed by the maximal aerobic exercise It is suggested that, while sensory and adapt

Work organization and Low back pain in nursing personnel

Abstract: Nursing personnel are at a high risk from occupational low back injury. Work organization has been suggested as one factor playing a part in the aetiology of occupational low back pain. Baseline data for a prospective epidemiology study were gathered by means of a questionnaire. One part of the questionnaire elicited characteristics of work organization, perceived autonomy, the relationship with head nurse and satisfaction in the relationship with co-workers. Information on history of musculoskeletal problems, reported frequency of lifting and personal characteristics was also gathered. Of 787 nursing staff at two acute care hospitals, 154 (19-6%) reported troublesome low back pain occurring within the previous 6 months. From univariate analyses, such characteristics of work organization as shift, type of schedule and primary versus functional nursing were not associated with low back pain. The relationship with head nurse and perceived autonomy of the job also were not related to recent back pain. Recent...

A worksite method for shoulder muscle fatigue measurements using EMG, test contractions and zero crossing technique

Abstract: Local muscular fatigue is an important aspect of ergonomic studies. Spectral analysis of electromyographic (EMG) signals may be applied to provide a quantitative measure of the extent of muscular fatigue. The present study was aimed at methodological development of practical and reliable field studies for the shoulder region, EMG signals were recorded during short test contractions performed at regular intervals during work and at rest. Signal analysis was performed using the zero-crossing method. The results show that the zero-crossing method gives results which are as relevant as the MPF-method. The test contraction concept in conjunction with the zero-crossing technique is called Frequency Analysis of Test Contractions (FTC). An evaluation experiment on ten subjects at rest yielded the intrinsic standard deviation of the method and also revealed lateral covariation of the trapezius and infraspinatus muscles.

Patterns of differences between the maximum weights of lift acceptable to experienced and inexperienced materials handlers.

Abstract: Maximum acceptable weight of lift (MAL) data were collected on 74 inexperienced students and compared with data previously collected for 74 experienced (industrial) materials handlers under identical experimental conditions to determine the patterns of differences in the MAL of the two groups. The results revealed that while students and industrial workers did not differ significantly in their physique and isometric strength exertion capabilities, there were statistically significant differences in the weights the two groups were willing to lift for regular 8 h shifts. Male students, on the average accepted 11% less weight than industrial males; female students accepted 6% less weight than industrial females. For 12 h shifts, the MAL differences between the two groups narrowed down to within 2%. The reductions in MAL with lifting frequency, box size, and lifting height for inexperienced and experienced workers were found to be similar. When the psychophysical methodology is used, inexperienced students te...