Industrial seating and spinal loading

Little information is available in the literature concerning an ergonomic systems view of industrial seats. This study has been aimed at expanding knowledge of industrial seat design. For this purpose, a model for evaluating industrial seats has been proposed, listing demands and restrictions from the task and the workplace. It also includes responses and effects on the sitter, and methods of measurement for evaluating industrial work seats. The appropriateness of work seat design has been assessed in laboratory and field studies, using methods to measure body loads, their effects and responses. These have been body height shrinkage, biomechanical methods, subjective assessment, and posture assessment. The shrinkage method, including equipment and procedures, has been developed in this project. It assesses the effect of loads on the spine in vivo by using body height changes as a measure of disc creep. The results are well correlated with spinal loads. The method is sensitive enough to differentiate between spinal loads of 100 N difference. The results are also related to the perception of discomfort. Biomechanical methods have been developed for calculating compressive, shear, and momental loads on the spine. Ratings of discomfort, body mapping, interviews, video recordings, and prototype equipment for the recording of head posture have also been used. The methods have been shown to be appropriate for seat evaluation. Work seats have been evaluated in different tasks, incorporating back-rests of different height, width and shape, conventional seat pans and sit-stand seats. It has been shown that advantageous chair features could be referred to each particular task. The tasks evaluated included forward force exertion (high backrests advantageous), vision to the side (low backrests advantageous), work with restricted knee-room (seats allowing increased trunk-thigh angle advantageous), grinding (high, narrow backrests advantageous), punch press work (increased seat height advantageous), and fork lift truck driving (medium height backrest advantageous). The work task has been shown to be a major influence on seat design, and must therefore always be thoroughly considered

Industrial seating and spinal loading

Little information is available in the literature concerning an ergonomic systems view of industrial seats. This study has been aimed at expanding knowledge of industrial seat design. For this purpose, a model for evaluating industrial seats has been proposed, listing demands and restrictions from the task and the workplace. It also includes responses and effects on the sitter, and methods of measurement for evaluating industrial work seats. The appropriateness of work seat design has been assessed in laboratory and field studies, using methods to measure body loads, their effects and responses. These have been body height shrinkage, biomechanical methods, subjective assessment, and posture assessment. The shrinkage method, including equipment and procedures, has been developed in this project. It assesses the effect of loads on the spine in vivo by using body height changes as a measure of disc creep. The results are well correlated with spinal loads. The method is sensitive enough to differentiate between spinal loads of 100 N difference. The results are also related to the perception of discomfort. Biomechanical methods have been developed for calculating compressive, shear, and momental loads on the spine. Ratings of discomfort, body mapping, interviews, video recordings, and prototype equipment for the recording of head posture have also been used. The methods have been shown to be appropriate for seat evaluation. Work seats have been evaluated in different tasks, incorporating back-rests of different height, width and shape, conventional seat pans and sit-stand seats. It has been shown that advantageous chair features could be referred to each particular task. The tasks evaluated included forward force exertion (high backrests advantageous), vision to the side (low backrests advantageous), work with restricted knee-room (seats allowing increased trunk-thigh angle advantageous), grinding (high, narrow backrests advantageous), punch press work (increased seat height advantageous), and fork lift truck driving (medium height backrest advantageous). The work task has been shown to be a major influence on seat design, and must therefore always be thoroughly considered

IISE Trans Occup Ergon Hum Factors

Background:Low back pain is a significant problem and one of the primary musculoskeletal conditions affecting active duty service members. There is a need to comprehensively assess the effects of repetitive deadlifts as a physical training modality on lumbar spine loads and the potential mechanisms involved in lumbosacral injuries among soldiers.Purpose:The purpose of this narrative review is to summarize studies of low back biomechanics during repetitive deadlifts as used in training programs to improve lifting capacity.Methods:PubMed and Google Scholar were searched for studies of lifting that met our inclusion and exclusion criteria. Only full text articles in English were included, and their reference lists were further searched.Results:Heavy deadlifts can result in large compressive and shearing spinal loads that range from 5 \u2013 18 kN, and 1.3 \u2013 3.2 kN, respectively. No studies of lower back biomechanics during repetitive deadlifts were found. However, findings of studies that investigated lower back biomechanics during other types of repetitive lifting suggest a high likelihood for adverse changes in lower back biomechanics that can increase risk of lower back injury.Conclusion:Repetitive deadlifting is increasingly implemented as a training modality to develop maximal lifting capacities required in military occupations. Further research is needed to understand the effects of such a training modality on lower back biomechanics and risk of injury.KL2 TR001996/TR/NCATS NIH HHSUnited States/T42 OH008455/OH/NIOSH CDC HHSUnited States

Effets de la posture de travail sur les patrons musculaires de la région lombaire lors d’une tâche répétitive

En Amérique du Nord, la posture debout prolongée est largement utilisée dans les entreprises, alors que dans d'autres régions du monde, le travail s'effectue plutôt à partir de la position assise. Le travail en station debout prolongée a déjà été associé à divers symptômes comme la douleur lombaire et la fatigue généralisée. Des études récentes ont démontré une association entre la douleur lombaire en posture debout prolongée et des patrons de coactivation (activation coordonnée de paires de muscles) des muscles de la région lombo-pelvienne. Cependant, ces patrons n'ont jamais été mesurés pour d'autres postures de travail, ou lorsque la posture debout était accompagnée de gestes répétitifs des membres supérieurs. L'objectif principal de ce projet était d'évaluer l'effet de différentes posture de travail (debout, assise, assis-debout) sur les patrons de coactivation musculaire lombo-pelvienne lors d'une tâche manuelle répétitive réalisée dans deux environnements distincts (laboratoire, milieu de travail). Un objectif secondaire consistait à mesurer, pour chacune des postures, l'association entre les patrons musculaires et les symptômes d'inconfort. L'hypothèse de travail était qu'il y aurait un lien entre les mesures de coactivation et la manifestation des symptômes d'inconfort, comme déjà démontré pour la posture statique debout. La seconde hypothèse formulée prévoyait que comparativement aux données de la littérature démontrant une augmentation de la coactivation lombo-pelvienne lors d'une tâche de posture debout sans mouvements des bras, la présence de ces mouvements dans notre étude contribuerait à atténuer l'augmentation de coactivation lombaire normalement observée avec le temps. Finalement, une troisième hypothèse avançait que les changements de posture influenceraient les patrons de coactivation musculaire lombo-pelvienne de l'ensemble des participants, mais de façon moins marquée chez les travailleurs expérimentés que chez les novices évalués en laboratoire. Un groupe de 11 travailleurs dont les tâches incluent le travail en station debout avec gestes manuels répétitifs a suivi le protocole de recherche directement en milieu de travail (5 hommes, 6 femmes, âge moyen : 43.2 ± 8.8/ années d'ancienneté : 11.6 ± 9.3). Un groupe de 18 personnes sans expérience, apparié selon le sexe et l'âge, a suivi le protocole de recherche en laboratoire (10 hommes, 8 femmes, âge moyen : 32.4 ± 8.2). Lors de trois séances expérimentales (présentées dans un ordre aléatoire), les participants des deux groupes ont effectué une tâche manuelle répétitive pendant une demi-heure en position debout, assise ou assis-debout. Le siège utilisé pour le travail assis et le banc servant à la posture assis-debout ont été ajustés selon les normes ergonomiques. Les patrons bilatéraux d'activation des muscles de la région lombo-pelvienne (érecteurs du rachis, obliques externes, droits de l'abdomen, moyens glutéaux) ont été enregistrés à l'aide d'électrodes de surface, et les scores d'inconfort à l'aide de schémas corporels et d'échelles durant la tâche manuelle et aussi durant des intervalles de posture statique. Des mesures de coactivation ont été effectuées selon deux méthodes décrites dans la littérature : la méthode de corrélations croisées et la méthode de calcul de l'information mutuelle. Des analyses de variances entre les variables Temps et Posture ont été appliquées sur les indices d'inconfort, et les mesures de coactivation ont été réalisées à l'aide de deux modèles statistiques (un modèle pour les données de laboratoire, un modèle pour les données du travail). L'analyse des données enregistrées en milieu de travail a démontré peu d'effets de posture; cependant, une plus grande coactivation bilatérale entre les muscles moyens glutéaux lors du travail debout confirme les résultats publiés précédemment pour les tâches effectuées en posture statique debout. Il n'y a aucun changement significatif dans le temps des indices de coactivation, et peu de travailleurs ont rapporté de l'inconfort lors du travail réalisé dans chacune des trois postures. Cependant, contrairement à ce qui était attendu, les résultats de laboratoire ont révélé que plusieurs indices de coactivation ainsi que le nombre de participants ayant rapporté de l'inconfort étaient plus élevés lors de la tâche en posture assise. De plus, une augmentation dans le temps des deux indices de coactivation a pu être observée. Il est possible que les différences d'expertise mais aussi dans la façon de faire les gestes avec les bras expliquent les discordances de résultats entre les volets milieu de travail et laboratoire. Les résultats présentés dans ce rapport ainsi que d'autres résultats récents de notre laboratoire mettent en lumière l'impact de la posture de travail, de l'expérience/expertise, et des gestes des bras sur les indicateurs de coactivation lombaire, et pourraient ainsi avoir un impact sur les facteurs pronostiques de l'apparition de symptômes en lien avec le travail manuel en posture prolongée

Der Einfluss des Sitzens nach lumbalen Bandscheibenoperationen auf den Verlauf der postoperativen Beschwerden und die berufliche Wiedereingliederung

Das Nachsorgekonzept nach lumbalen Bandscheiben-Operationen beruht auf biomechanischen Untersuchungen von Nachemson, die bereits 1966 publiziert worden sind. Seine Studien zeigten, dass sich das Sitzen nach Bandscheiben- Operationen und bei Rückenschmerzpatienten ohne Operation ungünstig auf den Rehabilitationsprozess auswirkt. Aufgrund dieser Befunde wurde das Verbot des Sitzens in das Rehabilitationskonzept aufgenommen und ist noch immer weit verbreitet. Häufig entstehen dabei aus einer ängstlichen Vermeidungshaltung muskuläre Dysbalancen. Es habituiert sich ein erhöhter Tonus der Erector trunci-Muskulatur. So können myotendinotische Sekundärbeschwerden auftreten, die zu einer verzögerten beruflichen und sozialen Wiedereingliederung beitragen. Dabei ist vor allem die verzögerte berufliche Reintegration volkswirtschaftlich von großer Relevanz. Neue Untersuchungen, insbesondere von Wilke et al., Rohlmann et al. und Althoff et al., konnten die von Nachemson im Sitzen erhobenen Daten nicht bestätigen. Aufgrund dieser Ergebnisse lässt sich die Arbeitshypothese aufstellen, dass die bisher übliche Empfehlung, das Sitzen zu vermeiden, für Patienten nach lumbalen Bandscheiben-Operationen obsolet ist. Es kann vielmehr davon ausgegangen werden, dass eine Lockerung dieser Richtlinie die Rehabilitation und die berufliche Wiedereingliederung nach lumbalen Bandscheiben-Operationen erleichtern und beschleunigen kann. Weiterhin kann davon ausgegangen werden, dass der Heilungsprozess, durch eine Be- und Entlastung und damit durch eine verbesserte Diffusion beschleunigt werden kann, wenn in der postoperativen Phase ein liberales Regime bezüglich der Körperhaltung eingeführt und die Wahl der Position dem Patienten weitgehend selbst überlassen wird. Der Patient sollte selbst die Körperhaltung wählen, die er als bequem empfindet. Ängste werden reduziert und die myotendinotischen Sekundärbeschwerden dürften abnehmen. Zu diesem Zweck wurde eine klinische Untersuchung durchgeführt, die insgesamt 50 Patienten in zwei Gruppen randomisiert. Eine Gruppe, als liberal bezeichnet, erhielt eine Sitzerlaubnis, die andere, als konventionell definiert, weiterhin Sitzverbot. Anhand von drei klinischen Nachuntersuchung, zwei von den Patienten selbst auszufüllenden Fragebögen (Oswestry -Schmerskala und Allgemeinen Depressionsskala), einem Sitz- und Schmerztagebuch und zum Abschluss eine MRT- Untersuchung der LWS vor und nach Kontrastmittelgabe, sollten die beiden Gruppen miteinander verglichen und die o. g. Hypothesen verifiziert oder falsifiziert werden. Der Vergleich der beiden Gruppen anhand der klinischen Untersuchungen ergab statistisch keinen signifikantern Unterschied im Hinblick auf den postoperativen Verlauf, insbesondere der postoperativen Schmerzen und Beschwerden, bzw. Behinderungen wie z. B. Lähmungen oder Sensibilitätsstörungen. Ebenso verhält es sich bei der Auswertung der Oswestry- Schmerzskala und der ADS- L. Auch hier ergaben alle Befragungen keine signifikanten Unterschiede zwischen den beiden Gruppen, so dass nicht von einer erhöhten Einschränkung der Patienten der liberalen Gruppe im Alltag ausgegangen werden kann. Das Sitz- und Schmerztagebuch zeigt ebenfalls keine signifikanten Unterschiede innerhalb der ersten 28 postoperativen Tage. Deutlich war zu erkennen, dass eine tägliche Steigerung der Sitzdauer nicht mit einer Erhöhung der Schmerzintensität oder einem vergrößerten Beschwerdebild einherging. Auch die Ergebnisse der MRT- Untersuchung der LWS wiesen keine nennenswerten Unterschiede zwischen den beiden Gruppen auf, die möglicherweise gegen eine Sitzerlaubnis gesprochen hätten. Die Erkenntnisse, die aus diesen Resultaten gewonnen werden können, bestätigten die o.g. Vermutungen, dass die Erlaubnis des Sitzens während der postoperativen Phase nicht zu einem verlängerten oder erschwerten Verlauf der Genesung führt oder sich schädlich auf diesen auswirkt. Das Sitzverbot kann als veraltet angesehen werden und, wenn weitere Untersuchungen die Beobachtungen bestätigen, sogar aus dem Therapieregime genommen werden. Eine frühere berufliche Wiedereingliederung erscheint mit einem liberalen postoperativen Regime erreichbar.The concept of rehabilitation after lumbar disc surgery is based on biomechanical studies by Nachemson, which were published in 1966. He found out that, after lumbar disc surgery, the intravertebral pressure is greater in a sitting position then in a standing or lying posture. As a result of these findings, avoiding the sitting position was included in the rehabilitation concept for patients who had undergone lumbar surgery or suffered from low back pain syndrome. Muscular imbalances with secondary discomfort often arise, resulting in a prolonged social or employment reintegration, together with the corresponding economic damage. New investigations, particularly by Wilke et al., Rohlmann et al. and Althoff et al., show a lower pressure on the lumbar spine and the intravertebral pressure in the sitting position as contrasted with other body positions. The data collected by Nachemson could not be confirmed. A working hypothesis was created that the standard procedures which called for avoiding the sitting position after a lumbar intravertebral disc surgery are obsolete. Instead, the restriction should be relaxed in order to facilitate and accelerate the social and professional reintegration of the patient. Additionally, it could be that a liberal regime whereby the patients choose the position they like and in which they feel comfortable accelerates the healing process. The position changes result in a better diffusion in the intravertebral disc. Patient fears are mitigated and the secondary myotendinotics symptoms decrease. For this purpose, as documented in the present study, we carried out a clinical examination. A total of 50 patients were randomized into two groups. One group, known as the “liberal” group was given permission to sit. The other group, defined as the “conventional” was asked to avoid sitting. To test our hypothesis we compared the two groups using three clinical follow-ups; two questionnaires to be completed by the patients, Oswestry Pain Scale and the General Depression Scale; a sitting and pain diary; and finally, an MRI scan of the lumbar spine with and without contrast agent. On the basis of the clinical examination, the comparison of the two groups showed no statistically significant difference regarding the postoperative course, especially postoperative pain and discomfort, or disability such as paralysis or sensory disturbances. The same was found for the evaluation of the Oswestry Pain Scale and the ADS-L. Again the significant differences between the two groups were apparent. Importantly, the Oswestry pain scale showed no increased restrictions for the patients in the liberal group in everyday life. The sitting and pain diary also showed no significant differences between the two groups that might have spoken against permitting recovering patients to sit. The insights gained from these results confirmed the above hypothesis. Permitting sitting during the postoperative period did not result in a prolonged or complicated recovery nor were there any harmful effects. If further investigations confirm these observations, the restriction on sitting could be considered obsolete and removed from the rehabilitation programs. This could facilitate the earlier return to work

Low back pain and everyday activities : the influence of axial rotation on low back pain

Low back pain (LBP) is a major problem in the industrialized world. The aetiology of LBP is multicausal: heavy physical workload, sedentary work, whole body vibration, smoking, as well as minimal influence over work conditions, poor social relations and psychological factors all play a dominant role (Thorbjornsson et al. 2000). Heavy physical workload is often cited as a primary factor, and is mostly related to an overload and high intradiscal pressure of the intervertebral discs. After Nachemson measured intervertebral disc pressure in vivo in 1964 and found higher disc pressure in sitting, lifting and bending than in standing and lying down, most physicians concluded that high intradiscal pressure, e.g. from heavy workload, should be avoided. Because of low intradiscal pressure during lying down, bed rest was the first choice in case of LBP, and recommendations for activities were restrictive. It is now evident that bed rest for longer than two days is ineffective in case of LBP (Deyo et al. 1986) and even leads to chronicity and disuse (Waddell 1993; Bortz 1984); there is now worldwide consensus about the value of maintaining or resuming normal activities and doing exercises of any kind (Koes et al. 2001). However, even today, it is common in routine medical practice, that physicians still tend to restrict rather than encourage physical activity and work for patients with LBP (Rainville et al. 2000). It is also remarkable that in daily practice it is not the extent of spinal load that may be most painful, but the lack of spinal motion. Most LBP patients say that: "I can easily do sports, cycling and walking, but sauntering, sitting and even lying down is painful". The controversy between the "spinal load" axiom and this clinical information from patients was the main incentive for the work presented in this thesis

TIME VARYING GENDER AND PASSIVE TISSUE RESPONSES TO PROLONGED DRIVING

Background: Prolonged sitting in an automobile seat may alter the passive tissue stiffness of the lumbar spine differentially in males and females. Gender specific ergonomic interventions may be indicated for the automobile seat design. Purpose: To compare time-varying passive lumbar spine stiffness in response to a two hour simulated driving trial with time-varying lumbar spine and pelvic postures during sitting in an automobile seat. A secondary purpose was to investigate gender differences in lumbar spine stiffness, seat/occupant pressure profile, discomfort rating and posture. Methods: Twenty (10 males, 10 females) subjects with no recent history of back pain were recruited from a university population. Participants completed a simulated driving task for two hours. Passive lumbar range of motion was measured on a customized frictionless jig before, halfway through and at the end of the two-hour driving trial. Changes in the passive moment-angle curves were quantified using the transition zone slopes, breakpoints and maximum lumbar flexion angles. Lumbar spine and pelvic postures were monitored continuously during the simulated driving trial with average and maximum lumbar flexion angles as well as pelvic tilt angles being calculated. Results: Both men and women initially demonstrated an increase in transitional zone stiffness after 1 hour of sitting. After 2 hours of sitting, transitional zone stiffness was found to increase in males and decrease in females. During sitting, women were found to sit with significantly greater lumbar flexion than males and to significantly change the amount of lumbar flexion over the 2 hour period of simulated driving. Conclusions: Postural differences during simulated driving were demonstrated between genders in this study. In order to prevent injury to the passive elements of the spine during prolonged driving, gender specific ergonomic interventions, such as improved lumbar support, are indicated for the automobile seat