Ergonomic evaluation of a wheelchair for transfer of disabled passengers at a large airport

Transferring disabled passengers to the aircraft, both arriving and departing, is one passenger service at a big airport. We use different ergonomic research methods (registration of heart rate, AET job analysis as well as a standardized questionnaire) to evaluate the present wheelchair design. Due to e.g. the high wheelchair backrest, the forces needed to handle the chair and other facts, the current wheelchair causes a strain bottleneck. The results of the AET analysis and the rating of the perceived exertion confirm this finding. A redesigned wheelchair based on ergonomic principles, which reduces stress on the employees and offers more comfort to disabled passengers, is presented.

Effects of vibration on arm and shoulder muscles in three body postures

The electromyographic responses of arm and shoulder muscles to vibrations were studied in three postures similar to the postures of drilling in a ceiling, drilling in a wall and drilling in a floor. This experiment was performed within the defined parameters of: vibrational frequency at 30 Hz, acceleration level 40 m.s-2 (rms), pushing force expressed as percentage maximal voluntary contraction, and gripping force which was set at 100 N. The exposure time for each test was 5 min. The general findings from these three body postures show that all the examined muscles were affected by exposure to vibration. The EMG index increased as follows: trapezius muscle 39% (p less than 0.05), lower-arm flexor muscles 23% (p less than 0.05), infraspinatus muscle 14% (p less than 0.05), lower-arm extensor muscles 14% (p less than 0.1) and biceps muscle 6% (p less than 0.1). The muscle most affected by vibration was found to be the trapezius muscle. It should be taken into consideration that vibration can be a contributing factor in neck/shoulder disorders among power handtool operators. The general conclusion from this study is that changes in working posture give different transmissions of vibration in the upper extremities. It seems as if the prime movers and muscles with an increased muscle length or increased degree of contraction are most affected by vibration.

Zur Objektivit�t, Validit�t und Reliabilit�t der Bestimmung von Erholungsdauern nach Ersch�pfungsversuchen bei schwerer dynamischer Muskelarbeit aus Zeitreihen der Herzschlagfrequenz

Records of heart rate after 152 experiments with exhaustion of three male subjects were rated by three experts to determine the end of the recovery phase. Inter-rater-reliability of recovery times vary between 0.87-0.97 according to the method of calculation. An algorithm for the identification of the end of recovery is developed by approximation of the expert-ratings. The corresponding rater-reliability of the algorithm is 0.9. A stepwise multiple regression shows, that most of the variance of recovery times is explained by heart rate at the end of the working phase (63.8%) and by the conditions of the rest phase (18.9%), whereas the stress conditions in the working phase, as type (10.6%), level (20%) and duration (0%) of stressors are concerned, have less explanatory value. These results differ from the literature. The differences are discussed with respect to different criteria for "fatigue" and "recovery".

[Tremor reaction to mental and emotional stress]

Reactions of tremor before and after stress were registered with a new method. Reactions with informatory-mental stress (adding tests with increasing time pressure) can only be interpreted by considering performance. Reactions with informatory-emotional stress (University examination; tasks in a central TV control room) are task specific when tremor is inter-individually normalized.

[Quantitative analysis of superposition of environmental task requirements]

Requirements for 1486 tasks have been registered with an Ergonomic Job Description Questionnaire (EJDQ). Frequencies of high and extremely high scaled environmental task requirements are analysed, related to branches, tasks and sex. The frequencies of superpositions are analysed for dominating requirements. Priorities for ergonomic research may be defined with the method presented.

Keyboard design through physiological strain measurements

The physiologically tolerable range of positions for the joints of the upper extremities have been investigated for typing tasks by recording the myoelectric activities of the involved muscles. For long-term typing tasks a split keyboard is recommended allocating a key field to each hand. The fields should be rotated against each other in the horizontal plane and inclined laterally.

[Development of demands with increasing technology in text processing]

Text-processing task demands are inquired about by means of an Ergonomic Job Description Questionnaire. The tasks are related to 5 steps of technologies and demands are documented for each of the technologies. With increasing technology demands on visual perception and work organisation dominate, while some demands on energetic work and environmental conditions decrease.

[An optimized filter band analyzer for quantification of localized muscle fatigue]

A filter bank analyzer is described which determines the central frequency of the electromyographic signal as a characteristic value and exhibits it continuously. In contrast with previous methods, this analyzer needs only a narrow frequency band and few filters to obtain exact quantitative results. The filter bank parameters are determined by adapting them to the amplitude spectra of electromyograms during fatiguing dynamic muscle work. Six parallel band-pass filters transmit the expected average spectral function, with minimized differences in the frequency range from 18 Hz to 140 Hz. The systematic error of the center frequency amounts to less than 0.5%, when using precision filters with high roll-off. An example compares the shift of center frequency method with the fatigue index of myoelectrical activity.

Ergonomics investigations of work-places in a police command-control centre equipped with TV displays

Ergonomics experiments were performed in a police command-control centre using computer controlled text processing systems with three alternative input devices: function keys, a light pen and a touch panel. A group of 14 operators was examined while using the alternative devices. Significant differences were found between the devices in terms of the following: sensory and motor activities, local muscular strain, transgressions of tolerance limits for 4-hour work sessions, and increases in heart rate. Suggestions for redesigning the control centre are given using anthropometric analysis. The paper also shows the relation between the sub-optimal design of a work system and the resulting strain.

[Ergonomic strain measurement in text processing]

Text processing task demands are analysed by using an Ergonomic Job Description Questionnaire. The tasks are classified by cluster analysis. Tasks out of each cluster are examined with respect to performance and physiological strain by 8-h measurements. These reactions are assessed in terms of tolerance limits and the distribution of demands is discussed for non-tolerable work conditions.

[Bioelectrode jellies for long-term monitoring (author's transl)]

The properties of 18 electrode jellies were investigated: electrical conductivity, ionic content, pH, skin irritation, and skin impedance reduction with different skin preparations, motion artifact, electrochemical noise with different electrode material, susceptibility to drying, ease of handling, and cost. There were significant differences of performance. Skin compatibility after 8 h ranged from "no irritation" to "severely irritating". A skin irritation most likely occurred with decornifying skin preparation. The specific skin impedance 24 min after the application ranged from 15 k omega . cm2 to 125 k omega . cm2. The motion artifacts differed up to 250%. All jellies produced negligible noise with Ag/AgCl and stainless steel electrodes. However, with gold and silver electrodes the noise amounted to 19 and 23 mu V. The NaCl content was correlated to the skin irritation and the impedance reduction. The impedance reduction correlated inversely to the skin compatibility and the motion artifact. Guidelines for the selection of an appropriate jelly in ergonomic long-term monitoring are given.

Occupational health studies on airport transport workers. II. Muscle strength of airport transport workers

Airport transport workers do manual work in loading and unloading the cargo space of passenger airplanes. In several types of airplanes the work has to be carried out in narrow spaces and in cramped positions. The present study describes the isometric strength of some muscle groups in 70 airport transport workers. Trunk extensors, trunk flexors, muscles involved in bimanual vertical lifting, elbow extensors, and elbow flexors were measured. A method with fixed positions and strictly isometric contractions was used. The strengths of the different muscle groups correlated with each other and with body weight; those of lifting, trunk flexors and biceps also with stature. The absolute strength of the muscle groups declined with advancing age at rates from 0.3% to 1.5% per year, the relative strength (N/kg body weight) by 0.9%-2.0% per year.

[Investigation of demands in data and text processing by an ergonomic job description questionnaire (DT-EIJDQ) (author's transl)]

A questionnaire for Ergonomic Job Description is developed for the area of text and data processing. The contents and structure of the method are described and its applicability is demonstrated in a field study. To interprete the data, methods of cluster, profile, and factor analyses are used. The jobs for which the data have been collected are classified according to their specific demands by the use of factor analysis. Further applications of the method are outlined.

[Methods for the unlimited measurement of the kinetics of power operated handles discussed by means of bicycle ergometer pedals (author's transl)]

For the unlimited measurement of the kinetics of symmetrical power operated handles a measuring device was installed on a bicycle ergometer. The two-dimensional deflection of the pedal cranks is measured and amplified by strain gauges, slip rings and operation-amplifiers. An analog voltage proportional to the position of the cranks is made by an angular potentiometer installed in the bottom chain. An exemplary course of the forces is given in function of the pedal angular.

[Job analysis applied to the disabled (author's transl)]

Job analysis data are helpful in solving a wide range of rehabilitation and ergonomic problems. The ergonomic job analysis procedure for the disabled is based on a universal procedure, called AET (Arbeitswissenschaftliches Erhebungsverfahren zur Tätigkeitsanalyse). To this basic procedure a supplement for the analysis of jobs for the disabled has been developed. The idea of supplementing a basic job analysis procedure for special purposes enables us not only to compare (cluster analysis) basic data of a wide range of jobs but also to analyse groups of jobs in more detail. This paper describes structure and contents of the supplement for the disabled. Examples for application are given.

[Evaluation of human strain during interrupted exposure to vibration (author's transl)]

The psychophysical reactions to stochastic vibrations transmitted in vertical direction to sitting man are investigated in simulated experiments under laboratory conditions. In the framework of an appropriate concept of assessment, indicators related to bottleneck situations in functional systems of the organism for activity and strain measurements allow the evaluation of the recreation efficiency of interruptions in exposure time. The special meaning of the distribution and thus the frequency rate of the interruptions can be illustrated particularly by the variance in time of the strain processes of selected muscles. Between the degree of muscle fatigue and the period of uninterrupted exposure time (expressed in "exposition-interruption-distribution") a significant correlation results so that numerous interruptions of vibration exposure should be considered as a profitable guideline for work design with respect to ergonomics.

Systematic selection of shift plans for continuous production with the aid of work-physiological criteria

Taking into account the numerous theoretically possible shift systems, we chose sensible shift systems with the aid of objective work-physiological criteria, eg, the duration of the daily working time, the positioning and duration of sleep and recreation time. With an agreed 40 h week shift, systems with a weekly working time of 42 h are more advantageous. If the shifts are equally attended over 24 h the following shift systems are recommended: when you have 8 h shifts the relation between the number of working days and the number of free days should be "3 n/n", whereby n must be larger than 1, within one shift rota. In the exceptional case of a 12 h shift the corresponding relation should be "2 n/n". Further unsuitable and recommended shift plan examples are demonstrated for these shift systems.

[Performance- and strain-compensation with informatory work]

With results from literature it is shown that eye-blinking-rate is negative significant correlated with physiologic performance ability. Experiments with an abstract tracking task presented in this paper confirm that eye-blinking-rate is an indicator for activation. Taking in the indicator for activation (blinking-rate), tracking performance and central-physiological strain, phases of performance- and strain-compensation (stability, effort, fatigue, performance break-down) are defined in an hierarchical concept of stability. The compensatory processes of the human operator are discussed on the background of a stress-strain-concept taking account of the principle of feed-back.

Ergonomics in the design and evaluation of a system for "postal video letter coding"

In co-operation with the German Central Post Office for Technological Development, the authors designed and investigated the task of and workplace for "Postal video-letter-coding". Experiments including measures of performance, errors, heart rate, arrhythmia, EMG's, and EOG's were used to experiment with variations in the design of displays, codes, keyboards, shifts and rest pauses. As a result of this work the following recommendations have been made by the authors and accepted by the authorities: An optimal display configuration has been developed with two vertically arranged tv displays. Coding-rules are to be simplified by modifications of the postcode. The usual flat keyboard has been replaced by an inclined and angular keyboard. Night-shifts must be avoided because of the tedious nature of the task. A work-rest-schedule of 50 min work and 10 min rest is proposed. In 1978 the complete work-system-design will be introduced in the standard postal service.

[Examination and assessment of time-variant human strain in motor car driving: real situation--simulation (author's transl)]

Time variant processes of activity, activation and strain of man are registrated during several hours of automobil driving (highway-autobahn) for different stress conditions and classified in terms of degrees of fatigue. By comparison with an assessment of strain in a simulated driving task with the same individuum and the same research-methods it is shown that the development of methods for measurement and assessment of time-variant human processes in laboratory experiments can be recommended, field-studies higher degrees of strain were found than under laboratory conditions.

Increasing awareness of ergonomics by in-company courses--a case study

There are some traditional ways for instruction and training in ergonomics, for example the academic method or the empirical way of self-taught practitioners. Because of a usually disinterested management, the last way is very often difficult to achieve. This report deals with experiences where a lucky chance happened and the idea of ergonomics arose from the management and became an inspiration of the whole plant.

[Examination of blinking-rate in a simulated four hour driving task]

In a driving simulation task performance and physiological measurement of strain was registered on 3 subjects in 9 experiments. The time-variant behaviour of blinking-rate was examined together with performance, self-rating and physiological strain. The correlating results make blinking-rate a possible indicator for activation of willingness to good performance. A multidimensional concept for assessment of the degree of individual fatigue is presented and validated in respect of working-time.

[Adaption of subjects in field studies of informatory working conditions (author's transl)]

Processes of adaption in measurements of performance - cycle-times, variance of cycle-times, informatory component of time and errors - and of physiological strain - electromyograms of musculus extensor digitorum and musculus rhomboideus, horizontal and vertical electrooculogram, heart rate and heart rate variability - are presented and described in type and frequency. Simultaneous reactions and successive reactions of measured variables in dependance of shift-time and of days are described. They are classified according to the causes "exercise" and "emotional habituation" and discussed in a model "experimenter - experimental situation".

Problems of determination of rest allowances Part 2: determining rest allowances in different human tasks

Within a task analysis related to strain on the individual, human tasks can be ordered into five steps differentiated by the various strains on human organs using different capabilities. For these five categories, examples of rest allowances based on laboratory as well as field study research using physiologically oriented methods are given. Different types of breaks are discussed and suitable measures for optimizing rest allowances are mentioned.

Problems in determining rest allowances Part 1: use of modern methods to evaluate stress and strain in static muscular work

After mentioning today's practice in handling the problem of setting rest allowances, definitions are given for the terms of fatigue, recovery and degree of fatigue. Discriminating between stress and strain leads to the possibilities in determining both. Measurable effects of fatigue in static muscular work are discussed. The procedure for determining optimal working rhythms by measuring stress and strain in static muscular work is explained.