A Swedish industrial research program 'Co-operative for Optimization of Industrial Production Systems Regarding Productivity and Ergonomics' (COPE).
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Accidents, Occupational↗
Biomedical subjects
J Winkel
Publications and source records attributed to J Winkel.
Sex differences and menstrual cycle effects in human spatial memory.
A typical test of spatial memory requires subjects to relocate a number of objects in their original, previously studied positions. It has been argued that this test includes multiple separate processing components (Postma, A., De Haan, E.H.F., 1996. Quarterly Journal of Experimental Psychology 48A (1), 178-199; Postma, A., Izendoorn, R., De Haan, E.H.F., 1998. Brain and Cognition 36, 334-345). One has to encode the precise positions occupied, assign the various objects to the correct (relative) locations, and achieve an integration of both types of spatial information. The present study examined the presence of sex differences and the role of hormonal factors for these selective components of spatial memory. A computerised, immediate (working) memory version of the test was used, comparing 23 males and 34 females on three experimental conditions: positions only, object-to-position-assignment, and the combined condition, requiring integration of the other two components. In line with previous research (Postma et al., 1998) males showed a selective advantage for fine-grained, metric positional reconstruction (i.e. positions-only). Interestingly, a within-subjects comparison in the females only revealed a menstrual cycle effect for exactly the same dimension of spatial memory. In the nonmenstrual phase, females were better than during menstruation. This clearly implies a role for sex hormones in spatial memory, even though a subsequent analysis of testosterone samples in saliva did not reveal a significant correlation with measures of spatial memory in both males and females.
Adolescent↗
Evaluation of questionnaire-based information on previous physical work loads. Stockholm MUSIC 1 Study Group. Musculoskeletal Intervention Center.
OBJECTIVES: The principal aim of the present study was to evaluate questionnaire-based information on past physical work loads (6-year recall). METHODS: Effects of memory difficulties on reproducibility were evaluated for 82 subjects by comparing previously reported results on current work loads (test-retest procedure) with the same items recalled 6 years later. Validity was assessed by comparing self-reports in 1995, regarding work loads in 1989, with worksite measurements performed in 1989. RESULTS: Six-year reproducibility, calculated as weighted kappa coefficients (k(w)), varied between 0.36 and 0.86, with the highest values for proportion of the workday spent sitting and for perceived general exertion and the lowest values for trunk and neck flexion. The six-year reproducibility results were similar to previously reported test-retest results for these items; this finding indicates that memory difficulties was a minor problem. The validity of the questionnaire responses, expressed as rank correlations (r(s)) between the questionnaire responses and workplace measurements, varied between -0.16 and 0.78. The highest values were obtained for the items sitting and repetitive work, and the lowest and "unacceptable" values were for head rotation and neck flexion. Misclassification of exposure did not appear to be differential with regard to musculoskeletal symptom status, as judged by the calculated risk estimates. CONCLUSIONS: The validity of some of these self-administered questionnaire items appears sufficient for a crude assessment of physical work loads in the past in epidemiologic studies of the general population with predominantly low levels of exposure.
Evaluation Studies as Topic↗
Significance of mat and shoe softness during prolonged work in upright position: based on measurements of low back muscle EMG, foot volume changes, discomfort and ground force reactions.
The aim of the investigation was to study the significance of mat and shoe softness during prolonged work in an upright position based on some physiological, biomechanical and comfort measurements related to the lower extremities and the low back. Eight healthy female volunteers performed 2 h of simulated standing and 2 h of standing/walking work tasks in the laboratory using four combinations of soft shoes, clogs, soft mat and concrete. Thus, each subject performed a total of eight 2 h work tests. The following parameters were measured pre-experimentally and one or more times during 2 h: total foot volume, vascular volume and interstitial volume of the left foot, EMG from the lumbar paraspinals, movement of centre of gravity (only during standing), biomechanical heel impact (only during standing/walking), perceived discomfort in lumbar back, legs and feet, whole body oxygen uptake, arterial blood pressure and heart rate. Using soft shoes rather than clogs during standing/walking work implies approximately a halving of the foot oedema formation and the heel impact. The effects due to the introduction of the soft mat are negligible. The local circulatory responses in the feet and the EMG-signs of paravertebral muscle fatigue are larger during standing compared to standing/walking work. The two investigated work types in this study differ regarding exposures as well as responses. Thus, it is recommended to shift between these postures and seated work during the working hours to improve job exposures.
Adult↗
Shoulder-arm muscle load and performance during control operation in forestry machines. Effects of changing to a new arm rest, lever and boom control system.
Three work station design studies in forestry machines were carried out with regard to shoulder/arm muscle load. (1) In an arm rest study, a movable (in the sagittal plane) arm rest was compared with a fixed one; (2) in a lever study, a mini lever with a small deflection was compared with an ordinary hand lever; (3) in a boom control study, a computer controlled boom system was compared with an ordinary boom system. In the arm rest study eight male subjects carried out lever operations in the laboratory. In the lever and boom studies, 15 male forestry students operated forwarders. Muscle load, cycle time, skill, perceived exertion, heart rate and preferred set up were recorded. The muscle loads on the upper trapezius, infraspinatus, extensor carpi ulnaris and flexor carpi radialis were recorded by electromyography. With mini lever and movable arm rest the upper trapezius load was reduced with preserved or decreased cycle time, although the grand mean of the 'static' load level was only about 2% of maximal voluntary contraction (MVC) and the effects of the new designs were small (about 0.7% MVC). The subjects preferred the lever/arm rest also giving the lowest muscle load. No differences between levers or arm rests were found in skill, perceived exertion or heart rate. It was not possible to draw any definitive conclusions regarding effects of the boom control system, due to technical problems. According to the literature, the duration of lever operation has increased considerably in forestry during recent years as part of a rationalization process. Partly due to this, it is suggested that the investigated work station improvements may not be sufficient to eliminate the risk for shoulder-neck disorders.
Arm↗
Physiological comparison of three interventions in light assembly work: reduced work pace, increased break allowance and shortened working days.
An industrial assembly task known to imply a high risk for shoulder-neck disorders was simulated in the laboratory. Eight females (aged 22-32 years) were trained to manage industrial work pace (120 according to the methods-time measurement system, MTM). They carried out seven work protocols at different days with different combinations of work pace (120 or 100 MTM), break allowance (20 min of active or passive breaks added every 2 h), and duration of the working day (2, 4 or 6 h). During 6 h of work at 120 MTM the electromyographic (EMG) amplitude from the upper trapezius muscle increased by about 11%, the EMG zero crossing rate decreased by about 2.5%, and perceived fatigue increased by about 4 CR10 scale units. When work pace was reduced to 100 MTM, the upper trapezius EMG amplitude decreased by 20% and became less variable. Heart rate decreased by about 10 bpm, perceived fatigue decreased by about 1 CR10 scale units, and shoulder tenderness was reduced by about 5%. However, the work task could still not be performed in a physiological steady state. Added breaks, whether active or passive, had no apparent effects on upper trapezius load during work or on physiological responses. Recovery of EMG, maximal strength, heart rate and blood pressure sensitivity, and tenderness was complete 4 h after work, independent of the preceding work conditions. These findings suggest that a limitation of the daily duration of assembly work may be more effective in limiting acute fatigue than reduced work pace or increased break allowance.
Adult↗
Reproducibility of a questionnaire for assessment of physical load during work and leisure time. Stockholm MUSIC I Study Group. MUSculoskeletal Intervention Center.
A self-administered questionnaire on physical load in lifetime occupational work, in present job, and in present leisure activities was tested for reproducibility with the test-retest method in 126 male and 217 female workers from 30 occupations. The questionnaire contained 92 questions and nine different response scales. The results indicated that questions concerning physical activity retrospectively and in the present job, vibrations in the present job, working postures involving the whole body, and questions concerning specific leisure activities (eg ball games, skiing, etc) seem to offer sufficient reproducibility to be worth testing for validity, at least at a 5-point ordinal level. Questions concerning working postures involving parts of the body, including awkward postures, and questions concerning manual materials handling seem to offer too poor reproducibility to be used in studies in which the aim is to quantify duration in proportions of a typical working day and frequencies in times per hour. Questions concerning level of physical activity and exertion in domestic work seem to offer too poor reproducibility to be used at a 5-point ordinal level. Gender, age, and musculoskeletal complaints did not influence the reproducibility to any great extent.
Adolescent↗
Can cardiovascular load in ergonomic epidemiology be estimated by self-report? Stockholm MUSIC 1 Study Group.
In ergonomic epidemiology exposure to local loads as well as cardiovascular load may contribute to general and local fatigue and musculoskeletal disease. Self-reported exposure is often the only feasible method in large population studies. The aim of this study was to evaluate retrospectively self-reported physical activity and perceived exertion as estimates of cardiovascular load during occupational work. The study population consisted of 39 men, representing 25 different occupations, and 58 women, representing 28 occupations. Ratings of physical exertion (RPE scale) and physical activity (Edholm scale transferred to multiples of the basal metabolic rate, METs) at the end of a work shift were correlated with the average heart rate during the same work shift. In the male population, both RPE ratings and METs correlated significantly (P < .01) with the average heart rate. No such correlation was observed in the female population.
Adult↗
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 defined 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.
Epidemiologic Methods↗
Validity of self-reported exposures to work postures and manual materials handling. Stockholm MUSIC I Study Group.
Exposure data from self-administered questionnaires on manual materials handling and work postures were validated in relation to direct measurements and systematic observations on 39 men and 58 women representing 45 different occupations. The agreement was tested at a dichotomous level and, when possible, with quantification of duration or frequency. At the dichotomous level the agreement was "acceptable" for nine variables concerning work postures and the handling of loads weighing > 5 kg. No variable showed "acceptable" agreement when the duration or the frequency was quantified in more detail (4- to 6-point scales). Musculoskeletal complaints seemed to introduce a differential bias for some lifting variables. Thus some variables for postures or the handling loads of > 5 kg may, under certain conditions, be acceptable for use in epidemiologic studies when the relative risks are high. However, self-reported exposure seems to be too crude if more-detailed information is required.
Female↗
Biochemical indicators of hazardous shoulder-neck loads in light industry.
Prolonged, repetitive handling of light material is known to increase the risk of shoulder-neck disorders. Biological risk indicators related to musculoskeletal exposure, applicable by the general practitioner in the workplace, could provide an instrument for early intervention and rehabilitation. Eight women were studied, all full-time workers performing assembly tasks associated with a high prevalence of shoulder-neck complaints. All subjects were more tender in the shoulder region than young women in low-risk occupations. Heart rate recordings indicated a low general metabolic load during work. Concentrations in antecubital venous blood of several markers for metabolic stress and cellular damage (lactate, ammonia, hypoxanthine, urate, malondialdehyde, potassium, creatine kinase) were normal for all subjects, and showed no increase during 3 consecutive working days. Thus, the blood markers did not reflect hazardous shoulder-neck exposure.
Adult↗
Can occupational guidelines for work-rest schedules be based on endurance time data?
Within the European Community, work is in progress to establish occupational guidelines for physical workload, including work-rest schedules. A model has been proposed which relies upon endurance time as a valid estimate of the short- and long-term physiological responses to continuous and intermittent exercise. On the basis of recent results from several Scandinavian research groups, the present paper questions the use of this model as a contribution to occupational guidelines. It is believed that the proposed model has a limited validity as a predictor of endurance time, as an indicator of short-term physiological responses, and as an estimator of risk for musculoskeletal disorders.
Adult↗
Significance of skin temperature changes in surface electromyography.
Differing results have been reported concerning the direction and quantity of the electromyogram (EMG) amplitude response to changes in tissue temperature. The EMG signals from the soleus muscle of six healthy human subjects were therefore recorded during dynamic exercise (concentric contractions) at ambient temperatures of 30 degrees C and 14 degrees C. The mean skin temperature (Tsk) above the muscle investigated was 32.9 degrees C and 21.7 degrees C, respectively. The core temperature, estimated by rectal temperature, was unchanged. The cooling of the superficial tissues caused approximately a doubling of the EMG amplitude. For the probability level 0.9 in the amplitude probability distribution function, the average signal level increased from 73 microV to 135 microV (P = 0.02). The average mean power frequency of the EMG signal was reduced from 142 Hz to 83 Hz (P = 0.004). The amplitude increase was not due to shivering but other possible explanations are presented. As the changes in Tsk investigated were within the range which may occur normally during the working hours, it was concluded that Tsk should be carefully controlled in vocational EMG studies.
Adult↗
Hand strength: the influence of grip span and grip type.
The maximal force from each of the fingers II-V (FF) and the resultant force between the jaws of the tool (RF), due to contribution from all fingers, were measured using a pair of modified pairs. The RF was measured at 21 handle separations and the FF was measured at seven handle separations for each finger. A traditional grip type was compared with a 'reversed' grip where the little finger was closest to the head of the tool. Sixteen subjects (8 females and 8 males) participated in the study. Both the RF and FF varied according to the distance between the handles. For both grip types, the highest RF was obtained at a handle separation of 50-60 mm for females and 55-65 mm for males. For wide handle separations, the RF was reduced by 10% (cm increase in handle separation). The force-producing ability of the hand was influenced by the grip type and the highest RF was obtained when using the traditional grip. An interaction was found between the fingers, i.e., the maximal force of one finger depended not only on its own grip span, but also on the grip spans of the other fingers. About 35% of the sex difference in hand strength was due to hand size differences.
Adult↗
Quantifying variation in physical load using exposure-vs-time data.
Variation has in recent years become an important concept in the analysis of loads on the locomotor system in occupational life. Studies of controlled variation in isometric exercise have concentrated on the effects of introducing pauses at regular intervals into an otherwise constant load. A complete description of the cyclic character of such regimens requires a set of three parameters. We suggest the use of the set mean load/cycle time/duty cycle. The design of laboratory studies should more often be based upon the activity patterns found in occupational life. In studies observing exposure, the variation concept introduces problems concerning how to define and how to quantify 'variation'. It is shown that present methods (APDF analysis and contraction frequency analysis) individually fail to pick up important aspects of variation. A new method for exposure variation analysis (EVA) is proposed. Examples are presented of EVA performed on vocational EMG registrations.
Ergonomics↗
Electromyographic activity in the shoulder-neck region according to arm position and glenohumeral torque.
The electromyographical (EMG) response to isometric ramp contractions of the right arm, the left arm, and both arms was studied using four pairs of surface electrodes above the right upper trapezius muscle (UT) of six men and six women. Contractions were made against gravity with the active arm(s) in eight positions, ranging from flexion to abduction. To describe arm positions, new, simple terminology was developed. Root mean square (rms)-converted EMG-signals were normalized (EMGnorm) with respect to a reference contraction. The EMGnorm corresponding to a 15 N.m torque in the right glenohumeral (GH) joint was strongly related to the position of the right arm (P less than 0.001). The shape of this relationship depended on the electrode position (P less than 0.001). The ratio between EMGnorm at 30 N.m and 15 N.m GH torques was related to arm position (P less than 0.001) and differed between electrodes (P less than 0.001). A left-side GH torque resulted in right-side (contralateral) EMG activity, typically corresponding to 20%-30% of that obtained during similar right-side GH torque. Bilateral GH torque implied 0%-50% increase in EMG activity as compared to that obtained with the right arm alone. The results have shown that signals from one pair of surface electrodes above UT cannot be taken as representative of the EMG activity from electrodes located elsewhere above UT. The EMG recordings reflected a complex pattern of muscular activation, significantly related to both outwardly visible factors (arm position, GH torque), and within-body servosystems (motor control reflexes).
Adult↗
[Why do musculo-skeletal stress injuries increase?].
The innovation of technologies in the industrial countries in recent decades has involved increased physical monotony and inactivity in working life. Parallel to this development the ergonomic quality of work station design has been improved. But the corresponding reduction in physical stress does not seem to diminish the frequency of symptoms from the locomotor system. On the basis of studies carried out in recent years, a U-shaped relationship between physical stress and symptoms is suggested, i.e. frequency of symptoms may increase not only when the physical stress is high but also when it becomes very low. It is concluded that further research on acceptable physical stress should comprise studies aimed not only at upper but also at lower limits, including minimal variation of the physical load.
Bone Diseases↗
Effects of leg activity and ambient barometric pressure on foot swelling and lower-limb skin temperature during 8 h of sitting.
Prolonged immobilization in an upright position often leads to discomfort and oedema in the feet of otherwise healthy subjects. To determine the significance of leg activity and ambient pressure on oedema formation, skin temperature (Tsk) and discomfort, 6 volunteers sat for 8 h with one leg immobilized and the other spontaneously active; one day at "sea level" (750 mmHg) and one day at reduced barometric pressure (540 mmHg). Foot swelling was measured by water plethysmography. Leg movements were continuously monitored by a Vitalog computer, and foot discomfort was estimated by analog-visual scales. The 8 hour swelling averaged 5.7% in the inactive foot, and 2.7% in the active foot (p less than 0.001). Tsk of the inactive foot levelled off towards ambient temperature (21 degrees C) within 4 h. For the active foot this fall was reduced by 2-3 degrees C (p less than 0.025). The increase in foot discomfort during the day was lowest in the active foot (p less than 0.005). High foot Tsk was associated with a high foot swelling rate. Reduced ambient barometric pressure had no effects on foot swelling or Tsk. It is concluded that modest leg activity during 8 h of sitting has several effects on the circulation in the feet: some effects promote and some prevent oedema formation. However, the net result is a reduction in foot swelling.
Adult↗