Walter Rohmert

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

After mentioning todays 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.

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.

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.

A study stressing the need for a static postural force model for work analysis

The maximum endurance time (MET) in static force exertions was used as a parameter for the assessment of five working postures. By applying the methodology of Rohmert to the construction of a general model for static muscular work and evaluating the measured MET results, the need for a new static posture model has been shown. The aim of the present pilot study was to test MET in load situations that would indicate when the general model can be used or when a new static postural force model is needed. Subjects exerted static postural forces at different load levels until exhaustion. In the first two postures, the strain was concentrated on the upper limbs, where active forces (muscular) play a key-role and justify the use of the model. In the remaining postures, the strain affected mainly the back/trunk, where the mechanical equilibrium of the body is brought about by active (muscles) and passive (skeleton and ligaments) structures. During the tests electromyographic (EMG) measurements of selected muscles ...

Heart Rate Variability and Work-Load Measurement

Heart rate variability is a result of the superimposition of different sources of variation which are systemized. Three parameters are used to describe the phenomenon of heart rate variation. The range of variation of these parameters is discussed using examples from both laboratory and field investigations. Analyses demonstrate a correlation between heart rate and their variability. Discussion of of the variation of the chosen parameters suggests that, when heart rate variability is used as a measure of strain in field research, strain might be under-assessed.

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

SummaryThe 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<0.05), lower-arm flexor muscles 23% (p<0.05), infraspinatus muscle 14% (p<0.05), lower-arm extensor muscles 14% (p<0.1) and biceps muscle 6% (p<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.

AET—a new job-analysis method

The stress-relevant scaling of vocational activities by AET ascertains and compares job demands which are characterized by many different human activities. The AET results thus form a data bank which is suitable for various aims of ergonomic work evaluation and work design. The application of the specific supplement of H-AET in addition to AET itself allows detailed strain classification, especially in the field of demands of activity. If, by a stress-oriented taxonomy for work carried out in the range of vertical reach of the arms, anatomic-geometrical differentiations of vertical reach and biomechanical postural forces are coupled to the workplaces, it is possible to differentiate the scaled activities in a strain-relevant bottle-neck analysis. The characteristics of the scaled items allow the immediate determination of biomechanical risks of damage or the derivation of measures for workplace design.

Zur Theorie der Erholungspausen bei dynamischer Arbeit

ZusammenfassungAn einem Fahrradergometer wurden bei 60 Pedalumdrehungen pro Minute in Istündigen Versuchen Arbeiten teils pausenlos, teils mit eingeschobenen Pausen geleistet. Variiert wurden die effektive Leistung (Leistung während der Arbeitsabschnitte), die Dauer der Arbeitsabschnitte sowie die Dauer der Pausenabschnitte. Als Maß der Ermüdung durch die Arbeit wurden 3 Kriterien untersucht:1.EPS nach Versuchsende,2.Anstieg der mittleren minütliehen Pulsfrequenz während der Arbeit,3.Verhalten der Arbeitspulsfrequenz der letzten Minute der einzelnen Arbeitsabschnitte. Oberhalb der Dauerleistungsgrenze wächst die Ermüdung exponentiell sowohl mit der effektiven Leistung als auch mit der Dauer des Arbeitsabschnittes. Beide Einflußgrößen sind multiplikativ miteinander verknüpft.Aus den Versuchsergebnissen mit 6 bzw. 7 Versuchspersonen läßt sich der für Dauerarbeit notwendige Erholungszuschlag für Radfahrarbeit individuell unabhängig berechnen mit Hilfe der Gleichung:EZ = 1,9 (tarb)0.145 · (Neff/Ndlg−1)1.4 · 100% EZ = Erholungszuschlag in Prozent vontarb, tarb = Dauer eines Arbeitsabschnittes in Minuten, Neff = effektive Leistung während des Arbeitsabschnittes in mkp/sec, Ndlg = Dauerleistungsgrenzwert für pausenlose Arbeit in mkp/sec.

Untersuchungen über physiologische und biochemische indikatoren zur differenzierung zwischen mentaler und emotionaler beanspruchung bei psychischen leistungen

SummaryTo carry on earlier field experiments, the effects of mental or emotional loads were evaluated under laboratory conditions by means of physiological and biochemical indicators. Stress was produced by a method which allowed an exactly reproducible concentration performance to be obtained. The calculation task (a · b + c − d) was directed by means of an apparatus and the calculation speed could be varied from 1 to 30 calculations per minute. The calculations were presented either with constant or with continuously increasing frequency. The experiment was carried out to analyse and compare the effects of emotional and mental stress so that the used inventory of indicators could be validated for field experiments.On the basis of preliminary tests, the calculation with continuously increasing calculation speed with untrained subjects were chosen as emotional stress. Mental performance was given by calculations with constant calculation speed but on different levels; the tasks were relatively equal regarding the subjects individual maximum calculation capacity. As strain indicators, heart frequency and variability of the momentary heart frequency as well as the excretion of the catecholamines, adrenaline and noradrenaline, were used.Twenty-seven male students (aged from 18 to 26 years) took part in the experiments which consisted of 10 single sessions within 2 weeks with a daily calculation time of 55 min. For comparison after each session, either rest values or values according to 30% of the individual maximum Oz-uptake were taken.From the experiments, we could learn that heart frequency above all is suited for indicating short-term mental or combined mental and emotional strain, in contrast to the excretion of adrenaline which especially responds to longer lasting emotional strains. Finally, the excretion of noradrenaline reflects very clearly physical strain and points out involuntary muscle tensions and unintentional motor activities under emotional and combined emotionalmental strains, respectively. The variations of the momentary heart frequency are specific for each subject. Their direction can only be evaluated individually on the basis of preliminary tests, since the direction of the variations cannot be predicted.ZusammenfassungIn Fortführung früherer Feldstudien wurden unter Laborbedingungen die Effekte mentaler und emotionaler Belastungen mit Hilfe physiologischer und biochemischer Indikatoren studiert. Die Belastungen wurden über eine Versuchsanordnung erzeugt, mit welcher eine Konzentrationsleistung exakt reproduzierbar vorgegeben werden konnte. Es handelte sich um einen apparativ gesteuerten Rechenversuch (a · b + c − d), dessen Aufgabenvorschub zwischen 1 und 30 Aufgaben/min variiert werden konnte. Die Darbietung der Rechenaufgaben konnte konstant oder kontinuierlich steigend erfolgen. Ziel des Versuchs war es, die Wirkung emotionaler und mentaler Belastungen vergleichend zu untersuchen, um das benutzte Indikatoreninventar für Feldversuche zu eichen.Als emotionale Belastung wurde auf Grund von Vorversuchen das Rechnen mit kontinuierlich steigendem Aufgabenvorschub bei Ungeübten gewählt, als mentale Leistung das Rechnen mit konstantem Aufgabenvorschub auf verschiedenen Stufen, interindividuell relativ gleich zur maximalen Rechenkapazität. Als Beanspruchungsindikatoren standen die Herzfrequenz, die Variabilität der Momentanherzfrequenz sowie die Ausscheidung der Katecholamine Adrenalin and Noradrenalin mit dem Harn zur Verfügung.An den Versuchen nahmen 27 männliche Studenten (Alter 18 bis 26 Jahre) teil. Der Versuch mit einer täglichen Rechenzeit von 55 min bestand aus 10 Einzelversuchen innerhalb von 2 Wochen. Zu Vergleichszwecken wurden fur die gewählten Beanspruchungsindikatoren nach Versuchsende alternativ Ruhewerte oder Belastungswerte entsprechend 30% der individuellen maxi malen O2-Aufnahme gewonnen.In den Versuchen zeigte sich, daß die Herzfrequenz sich vornehmlich fur die Erfassung kurzfristiger mentaler bzw. kombinierter mentaler und emotionaler Beanspruchungen eignet, wdhrend die Adrenalinausscheidung vornehmlich auf longer dauernde emotionale Beanspruchungen reagiert. Die Noradrenalinausscheidung reflektiert schließlich besonders deutlich körperliche Beanspruchungen und weist bei emotionalen bzw. kombiniert emotionalmentalen Beanspruchungen auf unwillkürliche Muskelanspannungen und unbeabsichtigte motorische Aktivitdten hin. Die Variationen der Momentanherzfrequenz sind schließlich typenspezifisch. Ihre Richtung kann individuell nur auf Grund von Vorversuchen gedeutet werden, da vor allem unter großen mentalen Belastungen sonst die Richtung der Veränderungen nicht vorhergesagt werden kann.

Ergonomische Untersuchung von Teilzeit-Schichtsystemen und Pausen bei informatorischer Arbeit

SummaryParameters reflecting the stress to which shift workers are exposed (length of work cycle, mental relative to motor component of cycle, errors) and physiological strain (heart rate, variability of heart rate, horizontal and vertical electro-oculogram, electromyogram of m. extensor digitorum and m. rhomboideus) were measured in 16 female and 2 male subjects working five different shifts split up in three different ways by rest periods.Results: Repetitive mental work is tolerable in all day-time shifts. The optimum length of shift is 4 hrs. During the night shift this type of work is not tolerable with the rest periods allowed.Optimum performance is obtained with short rest periods, but this regimen imposes an incentive effect causing strain on physiological functions to be ignored so that they are taxed beyond the limits of endurance and high degrees of fatigue results.ZusammenfassungAn 16 Frauen und 2 MÄnnern wurden Messungen im Belastungsbereich (Cycluszeiten, deren motorische und informatorische Komponenten, Fehlleistungen) und Beanspruchungsbereich (Herzfrequenz, Arrhythmie, horizontales und vertikales Elektrooculogramm, Elektromyogramm des Musculus extensor digitorum und des Stamm-Muskels Musculus rhomboideus) zur Beurteilung von fünf unterschiedlichen, über den Tag verteilten Teilzeit-Schichten und drei verschiedenen Pausenregimes durchgeführt.Ergebnisse: Die untersuchte informatorische Arbeit ist in allen Tagschichten ertrÄglich. Die optimale Schicht-Arbeitsdauer ist 4 Std. In den Nachtschichten ist die Arbeit bei den verfügbaren Pausenzeiten unertrÄglich.Das untersuchte Kurzpausenregime ist vom Leistungsgesichtspunkt optimal, führt jedoch zu einem Antriebseffekt, der die Beanspruchung physiologischer Funktionen oberhalb der Dauerleistungsgrenze ignoriert und damit hohe Ermüdungsgrade hervorruft.