Alwin Luttmann

Methodologies for evaluating electromyographic field data in ergonomics

Surface electromyography (SEMG) is an important tool for work load assessment in ergonomics. Several different approaches using amplitude as well as frequency parameters give fruitful information depending on question at issue in the laboratory as well as in field studies. One basic factor determining the choice of analysis method is whether the SEMG is interpreted as an indicator of forces/torques or pure muscular activation. Two methods for occupational SEMG data reduction representing two different approaches to SEMG applications in ergonomics, Exposure Variation Analysis (EVA), and Joint Analysis of EMG Spectrum and Amplitude (JASA), applied on the same SEMG recording from three muscles during urology surgeon work, have been compared. The EVA method categorised the three muscle recordings as too static with no EMG gaps while the JASA method identifies fatigue in two of the three recordings. The practical relevance of these findings is discussed.

Electromyographical indication of muscular fatigue in occupational field studies

Abstract Surface electromyography offers a valuable tool for the indication of muscular fatigue in occupational field studies. For this purpose, the time course of the electromyogram (EMG) has to be analysed, in order to detect typical fatigue-induced changes such as an increase in EMG amplitude or a shift in the spectral distribution towards lower frequencies. Such procedures need a detailed knowledge about the actual activity of the person and muscle under test for the total working time. This can be attained by encoding the activity of the person during the work and recording an electrical code signal together with the electrophysiological signals. For the indication of muscle fatigue, EMGs for situations connected with similar muscle load should only be compared, since the EMG amplitude as well as the spectrum do not only depend upon the fatigue state, but also upon the produced muscle force. This demand can be fulfilled by (i) interrupting the work and performing test contractions of known force in a predefined body posture or (ii) by comparing situations connected with a certain reference activity. (iii) In a recently developed approach for the joint analysis of EMG amplitude and spectrum (JASA) changes in the amplitude and the spectrum are considered simultaneously. This method permits the discrimination between fatigue-induced and force-related EMG changes. Using this procedure, changes in the EMG can be attributed to categories like fatigue or recovery as well as increase or decrease in the force production of the muscle under test. Applications from field studies during manual materials handling in a weaving mill, price recording at scanner checkouts in a supermarket and the performance of surgical work using endoscopic operation techniques in urology demonstrate the appropriateness of electromyography for fatigue indication in occupational physiology and ergonomics. Nevertheless, the commonly used measures of muscular fatigue such as increase in EMG amplitude and left shift in EMG spectrum are primarily related to the electrical activation and its propagation along the muscle fibres. Their connection to the fatigue-induced reduction in the force generating capacity of the muscle under test includes complex physiological implications. Therefore, the need for further development of fatigue indicators which are more directly related to muscular force is recognized. Relevance to industry In occupational health and ergonomics indication of muscular fatigue is needed, since activities inducing muscular fatigue can be performed for a limited time, only, and the quality of work can be influenced negatively. Electromyography offers valuable tools for the indication of fatigue and the appropriate assessment of ergonomic design measures.

Biomechanical analysis and assessment of lumbar stress during load lifting using a dynamic 19-segment human model

A dynamic biomechanical human model is presented which allows the quantification of mechanical parameters such as torque, compressive and shear forces, and pressure at the lumbar intervertebral discs. The human model comprises a total of 19 body segments. Various trunk flexions can be analysed due to the provision of 5 joints at the level of the 5 lumbar intervertebral discs. The influence of intraabdominal pressure on spinal load is considered. The inclusion of the influences of gravity and inertia permits the analysis of both static body postures and dynamic body movements. Since the model is 3-dimensional, the lumbar stress can be calculated during both symmetrical tasks in the median sagittal plane as well as during non-symmetrical ones. The influences on spinal stress of trunk inclination and the position of an external load relative to the body are quantified for various load weights up to 50 kg. The torque at the lumbo-sacral joint L5-S1 lies, dependent on posture and load lever-arm, within the range between 0 and 500 Nm; the compressive force on L5-S1 lies within the range between 0.4 and 10 kN, and the shear force at L5-S1 between 0.2 and 0.9 kN. The influences of lift velocity and jerky movement on lumbar stress are quantified. Simulated humpback and hollow-back postures are studied. The compressive forces at the 5 lumbar intervertebral discs are compared. The validity of the model is examined by comparing the model calculations with the intradiscal pressure measurements taken from the literature. Strength tests on lumbar intervertebral discs and vertebrae are collated from the literature in order to assess the lumbar stress during load lifting. The lumbar ultimate compression strength varies within a wide range. The mean value for a total of 307 lumbar segments amounts to 4.4 kN, the standard deviation to 1.9 kN. In conclusion, lumbar compressive force values during lifting fall within the same range as the strength values for the human lumbar spine.

Lumbar load during one-handed bricklaying

Abstract Lumbar load, as indicated by the moment of force and the force at the lumbosacral disc, was determined for one-handed bricklaying tasks using a dynamic 3-D model, ‘The Dortmunder’. The grasp height differed (90, 50, 10 cm). By contrast, the final postures were assumed almost upright in all cases. This resulted in considerable variance in the postures during the computer-simulated movements. The task duration varied (2.0, 1.5, 1.0 s). The lower the grasp height and the shorter the time, the higher the lumbar load (moment of force at L5-S1 up to 140 Nm, compressive force up to 6 kN), and the larger the differences between dynamic and static calculations. Increasing brick mass (0, 5, 10 kg) leads to an upward shift in the moment and compression curves (20 Nm or 1 kN per 5 kg). For the assessment of lumbar load during the analysed bricklaying tasks, the lumbosacral moment of force was first classified accoding to Tichauer (1978). Bricklaying involving a 50 cm grasp height requires ‘selection of labor, careful training and rest pauses’. Lower grasp heights of bricks of 10 kg should not occur throughout ‘the entire working day’. Lumbosacral force was then compared with lumbar strength values provided in the literature. These vary within a wide range (0.8–13 kN). Strength mean ± s . d . amounts to 5.0 ± 2.2 kN for the total sample ( n = 507), to 5.8 ± 2.6 kN for males ( n = 174) and to 4.0 ± 1.5 kN for females ( n = 132). Strength dependes primarily on age. Assuming linear regression models, strength (in kN) is 10.53-0.97/decade for males ( r 2 = 0.39) and 7.03-0.59/decade for females ( r 2 = 0.35). A strength prediction model considering 3 additional factors was developed ( r 2 = 0.62) in order to explain most of the remaining variance. Since average values may overestimate an individuals strength, the mean or regression model value should be reduced by the s . d . of the respective sample. This would result in a lumbar load limit of 5.5 kN for 25-year-old men and 2.6 kN for 55-year-old men. Corresponding values for women are 4.1 and 2.3 kN. If the brick-supply stack is 90 cm high, the lumbar load limits will not be exceeded for any person in these age groups. By contrast, all limits would be exceeded for a 10-kg 1-s brick transfer from a grasp height of 10 cm. In conclusion, to ensure that the predicted lumbar load during bricklaying remains below the limits, the brick-supply stack should be above 50 cm.

Cumulative occupational lumbar load and lumbar disc disease – results of a German multi-center case-control study (EPILIFT)

BackgroundThe to date evidence for a dose-response relationship between physical workload and the development of lumbar disc diseases is limited. We therefore investigated the possible etiologic relevance of cumulative occupational lumbar load to lumbar disc diseases in a multi-center case-control study.MethodsIn four study regions in Germany (Frankfurt/Main, Freiburg, Halle/Saale, Regensburg), patients seeking medical care for pain associated with clinically and radiologically verified lumbar disc herniation (286 males, 278 females) or symptomatic lumbar disc narrowing (145 males, 206 females) were prospectively recruited. Population control subjects (453 males and 448 females) were drawn from the regional population registers. Cases and control subjects were between 25 and 70 years of age. In a structured personal interview, a complete occupational history was elicited to identify subjects with certain minimum workloads. On the basis of job task-specific supplementary surveys performed by technical experts, the situational lumbar load represented by the compressive force at the lumbosacral disc was determined via biomechanical model calculations for any working situation with object handling and load-intensive postures during the total working life. For this analysis, all manual handling of objects of about 5 kilograms or more and postures with trunk inclination of 20 degrees or more are included in the calculation of cumulative lumbar load. Confounder selection was based on biologic plausibility and on the change-in-estimate criterion. Odds ratios (OR) and 95% confidence intervals (CI) were calculated separately for men and women using unconditional logistic regression analysis, adjusted for age, region, and unemployment as major life event (in males) or psychosocial strain at work (in females), respectively. To further elucidate the contribution of past physical workload to the development of lumbar disc diseases, we performed lag-time analyses.ResultsWe found a positive dose-response relationship between cumulative occupational lumbar load and lumbar disc herniation as well as lumbar disc narrowing among men and women. Even past lumbar load seems to contribute to the risk of lumbar disc disease.ConclusionAccording to our study, cumulative physical workload is related to lumbar disc diseases among men and women.

Evaluation and assessment of lumbar load during total shifts for occupational manual materials handling jobs within the Dortmund Lumbar Load Study – DOLLY

Abstract The load on the lumbar spine during occupational manual materials handling was previously investigated with respect to short activity sections or to specified load-handling types such as lifting or carrying. Within the so-called Dortmund Lumbar Load Study , analysis of the occupationally induced load on the lumbar spine during total working shifts in the field of surface construction, drop forge, industrial meat processing, and refuse collection was performed on the shop-floor. The body postures adopted, the action forces applied at the hands, and the resultant lumbar load for all load-handling tasks were analysed for 2 shifts in each field on the basis of video evaluations. Via a newly developed detailed classification procedure, the spatial position of the body segments as well as amplitude and direction of the action forces were described in a detailed manner. Consecutive biomechanical model calculations lead, for total shifts, to time courses of various measures for the load on the lumbar spine, such as flexion or torsional moments of force as well as compression and shear forces at the lumbosacral disc. In relation to recommended limits for the maximal disc compression provided in the literature, lumbar load is exceeded in numerous situations during a shift, in particular, with regard to persons of higher age. In a “dose model” applied in this study, the cumulative effect of single-task exposures was considered by superproportional weighting of the compressive force with respect to the corresponding duration of a working task. Relevance to industry A comprehensive evaluation of lumbar load for complete shifts is presented considering the real shop-floor conditions. Analyses for dustbin removal, surface construction and industrial meat processing have discovered numerous exceedings of lumbar-load limits. Such tasks should not be performed by older persons from the preventive point of view.

Zusammenhang zwischen manueller Lastenhandhabung und lumbaler Chondrose–Ergebnisse der Deutschen Wirbelsäulenstudie

ZusammenfassungIn einer multizentrischen populationsbezogenen Fall-Kontroll-Studie bei 351 Fällen mit lumbaler Chondrose mit Bandscheibenverschmälerung und 901 Kontrollprobanden wurde die Dosis-Wirkung-Beziehung zwischen be-ruflichen Wirbelsäulenbelastungen durch Lastenhandhabung und Rumpfbeugung sowie lumbaler Chondrose mit 10 unter-schiedlichen Dosismodellen einschließlich des Mainz-Dortmunder Dosismodell (MDD) untersucht.Die Studie zeigt eine positive Dosis-Wirkung-Beziehung zwischen der kumulativen beruflichen Wirbelsäulenbelastung durch Lastenhandhabung und Rumpfbeugung auf der einen Seite und der Entwicklung einer lumbalen Chondrose bei Männern und Frauen auf der anderen Seite. Die Dosismodelle mit der besten Modellanpassung zeichnen sich durch abgesenkte Schwellenwerte für die lumbale Bandscheibendruckkraft bei Lastenhandhabung und Rumpfvorneigung im Vergleich zum MDD, fehlende Tagesdosisschwelle, Berücksichtigung von zusätzlichen Formen der Lastenhandhabung wie Ziehen, Schieben, Werfen oder Fangen von Lasten und die Nutzung spezifischer biomechanischer Simulationsrechnungen für jede Belastungssituation aus.In der höchsten Dosisklasse fand sich eine signifikant um den Faktor 3,6 erhöhte Odds Ratio für lumbale Chondrose bei Männern und eine signifikant um den Faktor 1,9 erhöhte Odds Ratio für lumbale Chondrose bei Frauen. Das MDD gehört nicht zu den am besten anpassenden Dosismodellen hinsichtlich der Beschreibung einer Dosis-Wirkung-Beziehung.SummaryIn a population-based multi-centre case-control study on 351 cases with lumbar chondrosis with disc narrowing and 901 control subjects, the dose-response relationship was investigated between occupational exposure to manual load handling and/or working postures with trunk inclination with 10 different dose models including the Mainz-Dortmund Dose Model (MDD).The results of the study reveal a positive dose-response relationship between, on the one hand, cumulative lumbar dose caused by load handling and working postures with trunk inclination and, on the other hand, the development of lumbar chondrosis in men as well as in women. The dose models with the best goodness of fit are characterised by reduced thresholds for lumbar disc compression regarding load handling and working postures with trunk inclination in comparison to the MDD, a missing shift-dose threshold, the consideration of other types of load handling besides lifting and carrying such as pulling, pushing, catching or throwing and the application of specific biomechanical simulation calculations for the relevant loading activities.In the highest dose class a significantly increased odds ratio of 3.6 for lumbar chondrosis in men and 1.9 in women was found. The MDD does not belong to the most appropriate dose models for describing a dose-response relationship between occupational exposure and lumbar chondrosis.RésuméDans une étude cas-témoins multicentrée portant sur une population et réalisée auprès de 351 cas atteints d’une chondrose lombaire accompagnée d’un rétrécissement du disque intervertébral et de 901 sujets témoins, la relation de dose-effet entre les stress professionnels de la colonne vertébrale entraînés par la manipulation de charges et la flexion du tronc d’une part et la chondrose lombaire d’autre part a été examinée au moyen de 10 modèles de dose différents, y compris le modèle de dose Mainz-Dortmund (MDD).L’étude révèle une relation de dose-effet positive entre le stress professionnel cumulé de la colonne vertébrale dû à la manipulation de charges et à la flexion du tronc d’une part et l’apparition d’une chondrose lombaire chez les hommes et les femmes d’autre part. Les modèles de dose les mieux adaptés se distinguent par des valeurs seuils réduites pour la force de compression lombaire sur le disque intervertébral lors de la manipulation de charges et de l’inclinaison vers l’avant du tronc en comparaison avec le MDD, l’absence d’un seuil de dose quotidienne, la prise en compte d’autres formes de manipulation de charges (tirer, pousser, lancer ou attraper des charges) et l’utilisation de calculs de simulation biomécaniques spécifiques pour chaque activité stressante.Dans la catégorie de dose maximum, on a constaté un odds ratio significativement accru pour la chondrose lombaire de 3,6 chez les hommes et de 1,9 chez les femmes. Le MDD ne rentre pas dans la catégorie des modèles de dose les mieux adaptés pour décrire la relation de dose-effet entre l’exposition professionnelle et la chondrose lombaire.

Zusammenhang zwischen der kumulativen Wirbelsäulen-belastung durch Lastenhandhabungen und lumbalen Prolapserkrankungen — Ergebnisse der Deutschen Wirbelsäulenstudie

ZusammenfassungZiel der vorliegenden multizentrischen Fall-Kontroll-Studie ist die Untersuchung des Dosis-Wirkung-Zusammenhangs zwischen beruflichen Belastungen der Wirbelsäule und der Diagnose einer lumbalen Prolapserkrankung.286 Männer und 278 Frauen mit lumbaler Prolapserkrankung im Alter zwischen 25 und 70 Jahren wurden in vier Studien - regionen (Frankfurt am Main, Freiburg, Halle, Regensburg) prospektiv gewonnen. Bevölkerungsbezogene Kontrollpersonen (453 Männer und 448 Frauen) wurden über die regionalen Einwohnermeldeämter gewonnen. In einem strukturierten computergestützten persönlichen Interview wurde die gesamte Arbeitsanamnese unter Einschluss aller Berufsphasen mit mindestens einem halben Jahr Dauer erhoben. Auf der Grundlage einer zusätzlichen Expertenbefragung durch geschulte Technische Aufsichtspersonen der Unfallversicherungsträger wurde die Belastung der Lendenwirbelsäule in Form der Druckkraft auf die untere Lendenwirbelsäule für Lastenhandhabungsvorgänge und Arbeitssituationen mit Rumpfvorneigungen erhoben. Die kumulative Wirbelsäulenbelastung wurde mit 10 unterschiedlichen Dosismodellen abgeschätzt, die sich hinsichtlich der Druckkraftschwellen, hinsichtlich der Einführung eines schichtbezogenen Dosis-Schwellenwertes und hinsichtlich der Gewichtung der lumbalen Druckkraft gegenüber der Belastungsdauer unterschieden. Die Auswahl der Confounder basierte auf biologischer Plausibilität und auf dem Change-in-estimate-Kriterium1. Odds Ratios (OR) und 95%-Konfidenzintervalle (CI) wurden durch Hilfe der unkonditionalen logistischen Regressionsanalyse getrennt für Männer und Frauen berechnet, adjustiert für Alter, Region, Belastung durch Arbeitslosigkeit als bedeutsamem Lebensereignis (bei Männern) bzw. psychosozialer beruflicher Be -lastung (bei Frauen). Die Anpassungsgüte der einzelnen Dosismodelle wurde mit dem Akaike-Information-Kriterium bestimmt.Die vorliegende Fall-Kontroll-Studie zeigt einen statistisch signifikanten positiven Zusammenhang zwischen der kumulativen Wirbelsäulenbelastung durch berufliche Lastenhandhabungen oder Rumpfbeugehaltungen und der Diagnose einer Prolaps - erkrankung bei Männern wie bei Frauen. Bei Frauen findet sich eine monotone Dosis-Wirkung-Beziehung zwischen beruflicher Belastung und der Prolapserkrankung (OR für die höchste Expositionskategorie =2,5; 95%-Konfidenzintervall CI 1,6–3,8). Bei Männern findet sich ein Anstieg des Prolapsrisikos mit zunehmender kumulativer Belastung der Wirbelsäule (OR in der zweithöchsten Expositionskategorie=3,9; 95%-CI 2,6–6,0), allerdings fällt das Risiko in der höchsten Expositionskategorie wieder ab (OR=1,4; 95%-CI 0,6–3,2); dieses Ergebnis könnte sich mit dem Healthy-worker-Effekt erklären. Das Mainz-Dortmunder Dosismodell (MDD) gehört nicht zu den am besten anpassenden Dosismodellen zur Beschreibung des Dosis-Wirkung-Zusammenhanges; dies ist offensichtlich auf die hohen Schwellenwerte des MDD zurückzuführen. Überproportionale Gewichtung der Belastungshöhe gegenüber der Belastungsdauer führt nicht zu einer Verbesserung der Modellgüte bezüglich des Prolapsrisikos.Die vorliegende multizentrische Fall-Kontroll-Studie findet einen Zusammenhang zwischen der kumulativen Bandscheibenbelastung und einer lumbalen Prolapserkrankung bei Männern und Frauen. Auf der Grundlage der vorliegenden Studie findet sich auch unterhalb der MDD-Schwellenwerte (bezogen auf Druckkraft durch Lastenhandhabungen, Rumpfvorneigewinkel und Tagesdosis) ein erhöhtes Prolapsrisiko.SummaryThe aim of this multi-centre case-control study is to investigate the dose-response relationship between occupational load on the spine and diagnosis of a lumbar disc herniation.286 male and 278 female patients with lumbar disc herniation between 25 and 70 years of age were prospectively recruited in four study regions (Frankfurt am Main, Freiburg, Halle, Regensburg). Population control subjects (453 males and 448 females) were obtained from the regional population registers. In a structured computer-assisted personal interview, a complete occupational history was elicited, including every occupational period that lasted at least half a year. On the basis of job task-specific supplementary surveys performed by trained technical experts of the accident insurance institutions, the situational spinal load represented by the compression at the lower lumbar spine was assessed for materials handling and working situations with forward bending. The cumulative spinal load was calculated using 10 alternative dose models, varying the minimum exposure limits for disc compression and shift dose as well as the weighting of the lumbar disc compression in relation to the respective duration. Confounder selection was based on biologic plausibility and on the “change-in-estimate criterion“. Odds ratios (OR) and 95% confidence intervals (CI) were calculated separately for men and women using unconditional logistic regression analysis, adjusted for age, region, and unemployment as major life event (in males) and psychosocial strain at work (in females). The Akaike information criterion was used to measure the goodness of fit of the single dose models.The results of this case-control study reveal a statistically significant positive relationship between cumulative spinal load caused by occupational manual materials handling and working postures with forward bending and lumbar disc herniation in men as well as in women. In women, a positive doseresponse relationship between ccupational exposure and lumbar disc herniation (OR for the highest exposure category= 2.5; 95% confidence interval CI 1.6–3.8) was found. In men, prolapse risks increase in line with increasing cumulative spinal load (OR for the second-highest exposure category= 3.9; 95%-CI 2.6–6.0), but decrease in the highest exposure category (OR=1.4; 95%-CI 0.6–3.2); the latter result might be explained by healthy worker effect. The Mainz-Dortmund Dose Model (MDD) is not one of the most appropriate dose models for explaining the dose-response relationship, mainly because of the high threshold limits of the MDD. Overproportional weighting of workload intensity in relation to the respective duration does not improve the goodness of fit of the model regarding the risk of disc herniation.According to this multi-centre case-control study, cumulative load on the intervertebral discs is related to lumbar disc herniation in both men and in women. Based on the study shown here, there is also an increased risk of disc herniation below the MDD thresholds (regarding compression caused by materials handling, forward bending of the trunk and shift dose).RésuméL’objectif de la présente étude cas-témoins multicentrée est d’examiner la relation de dose-effet entre les stress professionnels de la colonne vertébrale et le diagnostic d’un prolapsus lombaire.286 hommes et 278 femmes entre 25 et 70 ans et atteints d’un prolapsus lombaire ont été recrutés prospectivement dans quatre régions d’étude (Francfort-sur-le-Main, Fribourg, Halle, Ratisbonne). Des sujets témoins prélevés dans la population (453 hommes et 448 femmes) ont été recrutés quant à eux par l’intermédiaire des bureaux régionaux de déclaration de résidence. Dans un interview personnel structuré et assisté par ordinateur, on a recueilli une anamnèse professionnelle complète incluant chaque période professionnelle ayant duré au moins six mois. Sur la base d’une enquête supplémentaire menée à bien par des experts techniques formés des organismes d’assurance accidents, la sollicitation de la colonne vertébrale représentée par la force de compression sur la colonne vertébrale lombaire inférieure a été évaluée pour la manipulation de charges et les situations professionnelles avec une inclinaison vers l’avant du tronc. Le stress cumulé de la colonne vertébrale a été apprécié au moyen de 10 modèles de dose différents qui divergent au point de vue des seuils de la force de compression, de l’introduction d’une valeur seuil de dose par roulement ainsi qu’au point de vue de la pondération de la force de compression lombaire par rapport à la durée respective de la sollicitation. Le choix des confondeurs s’est basé sur la plausibilité biologique et sur le critère change-in-estimate. Des odds ratios (OR) et des intervalles de confiance de 95% (CI) ont été calculés séparément pour les hommes et les femmes à l’aide de l’analyse de régression logistique non conditionnelle, puis ajustés selon l’âge, la région, le stress dû à la perte d’un emploi vécu comme un événement important (chez les hommes) voire le stress professionnel psychosocial (chez les femmes). La qualité d’adaptation de chacun des modèles de dose a été déterminée avec le critère d’information d’Akaike.La présente étude cas-témoins révèle un rapport positif statistiquement significatif entre le stress cumulé de la colonne vertébrale dû à la manipulation de charges dans le cadre du travail ou à l’inclinaison vers l’avant du tronc d’une part et le diagnostic d’un prolapsus chez les hommes ainsi que chez les femmes d’autre part. Les résultats obtenus révèlent chez les femmes une relation de dose-effet monotone entre le stress professionnel et le prolapsus (OR pour la catégorie d’exposition maximum=2,5 ; intervalle de confiance de 95% 1,6–3,8).-Chez les hommes, on constate une augmentation du risque de prolapsus lorsque le stress cumulé de la colonne vertébrale (OR dans la deuxième catégorie d’exposition=3,9 ; intervalle de confiance de 95% 2,6–6,0) s’accroît, mais ce risque diminue toutefois à nouveau dans la catégorie d’exposition maximum (OR=1,4 ; intervalle de confiance de 95% 0,6–3,2) ; ce résultat pourrait s’expliquer par l’effet healthy-worker. Le modèle de dose Mainz-Dortmund (MDD) ne rentre pas dans la catégorie des modèles de dose les mieux adaptés pour décrire la relation de dose-effet entre l’exposition professionnelle et le prolapsus ; cela est apparemment imputable aux valeurs seuils élevées du MDD. Une pondération surproportionnelle de l’import

Task analysis and electromyography for bricklaying at different wall heights

Abstract Work-sequence and posture analyses were performed in a field study on bricklaying. The study reveals that, for low walls, the bricklayers spend up to 75% of the total duration of the activity in an inclined posture, this percentage decreasing with wall height to between 20 and 25%. Where wall levels are below 100 cm, a load (brick) is held in one hand for approx. 30% and a load in both hands (brick, trowel and mortar) for 13% of the time. The percentages increase for higher walls to 45 and 30% respectively. The number of bricks laid per unit of time decreases with increasing wall height from about 2.7 bricks/min for a 20 cm wall to about 2.0 bricks/min for a 160 cm wall. The field study was supplemented by electromyographical laboratory investigations. These reveal that, with increasing wall height, the myoelectrical activity of the back musculature and of the left biceps muscle rises to a multiple of the activity for low walls. Workplace-design proposals were derived from the findings of the field and laboratory investigations under consideration of studies taken from the literature on the stress on the skeletal and cardiopulmonary systems. Accordingly, the scaffold should be frequently adapted to the wall height, thus excluding both low and high wall levels. In addition, the brick and mortar supplies should be arranged to allow the bricklayers to grasp them without bending down.

The load on the spine during the transport of dustbins

Situations causing high postural stress during the transport of dustbins were determined, and the load on the spine was estimated. Electromyographical analyses revealed workload situations with high muscular activities during the transport over edges. Thus the manipulation of large dustcontainers (1100 l) is rendered difficult by kerbstones. Because smaller dustbins (110 l-240 l) are often kept in basements or backyards, stairs must frequently be climed with a heavy load. To quantify the spinal stress, a biomechanical model was developed in order to calculate the torques and forces effective at the lumbosacral joint. In the computations several parameters and transport conditions, such as kerbstone height, were varied. That entails different working postures by the dustbins men. The influence on the load on the spine was estimated. The calculated results are compared with criteria taken from the literature. Special postures were devised to keep the torques and forces as small as possible, and thereby to decrease the health risk of the skeletal system when handling heavy weights like dustbins. In the case of a container transport, only two persons should manipulate and work in well-timed co-ordination and both in special postures. Finally, all dustbins should be positioned at places guaranteeing an easy transport over flat surfaces.