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Association between alternative cumulative lifetime vibration doses and low back outcomes
No full textPrevious analyses revealed that the daily compressive dose Sed based on internal lumbar forces might be a better predictor of low back pain (LBP) outcomes than daily doses based on acceleration (daily vibration exposure A(8), vibration dose value VDV) [1, 2]. The aim of the current study was to investigate whether acceleration-based (external) lifetime doses differ from force-based and compression-based (internal) lifetime doses for the prediction of LBP outcomes
Measures of internal lumbar load in professional drivers – dependence on posture, anthropometry, age, duration of exposure and type of machine
No full textIntroduction
In European and International Standards and Directives, external loads in terms of daily vibration exposure A(8) or vibration dose value VDV are used as predictors of adverse health effects. These values only partly reflect the internal load acting on the lumbar spine. Particularly for shock containing acceleration time histories, a method for the calculation of internal spinal forces on the basis of a Finite-Element-Model (FEM) was developed within the EU VIBRISKS project [1]. The model can be adapted to the anthropometry (ten categories) and the sitting posture (six categories) of the driver. The method has been proposed in a working draft of the Standardisation Committee ISO/TC 108/SC 4/WG 15 [2]. It has already been standardised in the German Standard DIN SPEC 45697 [3]. The risk assessment is based on the daily compressive dose Sed (MPa) and the risk factor R (non-dimensional). Both values are determined by the compressive internal forces, by the daily and lifetime exposure duration and by the age at the start of exposure. For a re-analysis of the Italian part of an epidemiological study performed within the VIBRISKS project, the internal forces, Sed and R were calculated for the 537 participants of the study.
Methods
Typical acceleration time histories for various machine types and working tasks were selected. Impacts due to sitting down or loosing the contact to the seat were eliminated. At the end, 19 checked time histories with a duration of 200 s were available. All signals were shock containing [4]. Beside the calculation of Sed and R factor, r.m.s., r.m.q. and standard deviation of the time histories of the internal forces were assessed in all three axes separately and as a vector sum. Therefore, a modification of the program published on the CD in DIN SPEC 45697 had to be used, because it was necessary to get the interim results of the calculations in terms of internal forces. In the horizontal axes, the daily doses were calculated without relation to the spinal endplate areas. The daily doses for the internal forces acting in anterior and posterior directions were separately computed. In total, 21 different variables were calculated.
Results
The values of the forces, Sed and R factor varied over the lumbar spine levels from T12/L1 to L5/S1. The shapes of the spine-level dependent curves were determined by the posture and the type of machine (example for posture group1 in Fig. 1).
The category of body mass and Body Mass Index (BMI) and the posture - in association with the covariates listed in Table 1 - significantly influenced the maximum R factor (statistical test: ANCOVA). The interaction between the body mass/BMI-category and the posture was not significant (F=1.3, p=0.11). When several machines in identical sitting posture were used, the type of machine showed a significant effect as well (Table 1, last three lines). In these cases, the effect of the yearly exposure duration was not longer calculated due to a lack of variability of the covariate. Instead of that, the last column of Table 1 contains the interaction between the body mass/BMI-category and the type of machine which was significant for all three postures. The p-value was p<0.001 in nearly all cases. The exceptions are indicated with (+) in Table 1.
Similar results were found for the forces and the Sed values.
Conclusions
The results of this study showed that the measures of internal lumbar load in a population of professional drivers according to ISO/WD 2631-5 were significantly influenced by numerous individual and work related factors: anthropometry, age, duration of exposure, posture and type of machine. Measures of internal lumbar load might be well suited as predictors of adverse health effects on the lumbar spine of an individual for a working lifetime.
References
[1] Hinz B, Seidel H, Blüthner R, Menzel G, Hofmann J, Gericke L, Schust M (2007) Whole-body vibration experimental work and biodynamic modelling, Annex 18 to the final report on Task 6.1: Whole-body vibration laboratory studies and biodynamic modelling. VIBRISKS (EC FP5 Project No. QLK4-2002-02650) www.vibrisks.soton.ac.uk
[2] ISO/WD 2631-5. Mechanical vibration and shock – Evaluation of human exposure to vibration – Part 5: Methods for evaluation of vibration containing multiple shocks. DIN, 2011. ISO/TC 108/SC 4/WG 15.
[3] DIN Deutsches Institut für Normung (2012) Mechanische Schwingungen und Stöße – Verfahren zur Bewertung stoßhaltiger Ganzkörper-Vibrationen; mit CD-ROM (Mechanical vibration and shock – Method for evaluation of impulsive whole-body vibration; with CD-ROM), German National Standard, DIN SPEC 45697.
[4] Schust M, Hinz B, Menzel G, Pinto I, Hofmann J, Bovenzi M (2012) Comparison of different methods for detecting multiple shocks in vibration time histories. Paper presented at the 47th United Kingdom Conference on Human Responses to Vibration, held at ISVR, University Southampton, 17 - 19 September 201
Relationships of low back outcomes to internal spinal load: a prospective cohort study of professional drivers
Full text linkPurpose – To investigate the relationships between low back symptoms and alternative measures of external dose and internal spinal dose in professional drivers exposed to whole body vibration (WBV).
Methods – The occurrence of low back symptoms were investigated in a cohort of 537 drivers over a two-year follow up period. Low back pain (LBP), individual characteristics, and work-related risk factors were investigated with a structured questionnaire. Exposure to WBV was evaluated by means of measures of external dose (daily vibration exposure in terms of either equivalent continuous acceleration over an eight-hour period (A(8)) or vibration dose value according to the EU Directive on mechanical vibration) and measures of internal lumbar load (daily compressive dose Sed and risk factor R according to ISO/CD 2631-5 2014).
Results – In the drivers’ cohort, the cumulative incidence of 12-month low back outcomes was 16.8% for LBP, 9.3% for chronic LBP, and 21.8% for sciatic pain. The measures of internal spinal load were better predictors of the occurrence of low back symptoms than the measures of daily vibration exposure. A two-fold increase in the risk estimates for low back outcomes was found in the upper quartile of the R factor (0.41-0.72 units) compared to the lower one (0.07-0.19 units).
Conclusions – In this prospective cohort study, measures of internal spinal dose performed better than measures of daily vibration exposure (external dose) for the prediction of low back outcomes in professional drivers. The ISO boundary values of the risk factor R for low and high probabilities of adverse health effects on the lumbar spine tend to underestimate the health risk in professional drivers
A cohort study of sciatic pain and measures of internal spinal load in professional drivers
No full textIn a prospective cohort study of 537 male professional drivers, the occurrence of sciatic pain showed stronger associations with measures of internal lumbar load expressed in terms of daily compressive dose Sed (MPa) and risk factor R (non-dimensional) according to ISO/WD 2631-5 (2013), than with measures of daily vibration exposure calculated as either 8-h energy-equivalent frequency-weighted acceleration (ms-2 r.m.s.) or Vibration Dose Value (ms-1.75) according to the EU Directive on mechanical vibration (2002). Herniated lumbar disc, previous lumbar trauma, and physical work load were also powerful predictors of the occurrence of sciatic pain over time. Psychosocial work environment was poorly associated with sciatic pain. The boundary values of risk factor R for low and high probabilities of adverse health effects on the lumbar spine, as proposed by international standard ISO/WD 2631-5 (2013), tend to underestimate the health risk in professional drivers
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Berechnung von Intra-spinalen Kräften und Risikomaßen bei Einwirkung von Ganzkörpervibrationen - Abhängigkeit von Körperhaltung, Körperstatur, Alter, Expositionsdauer und Expositionsmuster am Beispiel von 537 Teilnehmern einer epidemiologischen Studie
No full textMit Hilfe einer Re-Analyse der Daten von 537 Teilnehmern an einer epidemiologischen Studie im EU-Projekt VIBRISKS [1] sollte untersucht werden, inwieweit geschätzte Risiken, die auf mit Modellen vorhergesagten intra-spinalen Kräften beruhen [2], das Risiko für Beschwerden und Schmerzen in der Lendenwirbelsäule widerspiegeln. Sämtliche Vibrationsexpositionen waren nach unterschiedlichen Kriterien stoßhaltig [3].
Im vorliegenden Beitrag werden die Ergebnisse ausgewählter Berechnungen dargestellt. Die Verteilung des Risikos über die Lendenwirbelsäule wurde von der Sitzhaltung und von der Art des Fahrzeugs bestimmt. Die Körpermasse / BMI- Kategorie und die Körperhaltung hatten einen signifikanten Einfluss auf den maximalen Risikofaktor. Darüber hinaus war der Risikofaktor war umso höher, je länger die tägliche und die jährliche Expositionszeit und die Lebensexpositionszeit, und je höher das Lebensalter bei Beginn der Exposition waren. Für einige Haltungen und Fahrzeugtypen erreichten die dynamischen Anteile der intra-spinalen Kräfte in x-Richtung Werte, die mit denen in vertikaler Richtung (Kompressionskräfte) vergleichbar waren, obwohl der A(8)-Wert in x-Richtung nur einen Bruchteil desselben in z-Richtung betrug. Für die Entwicklung eines Schädigungsmodells für die Wirbelsäule auf Basis der horizontalen intra-spinalen Kräfte besteht auch international Forschungsbedarf. Die individuelle Abschätzung des Risikos mit Hilfe der DIN SPEC 45697 hat sich auch für größere Exponiertengruppen als praktikabel erwiesen
Measures of internal lumbar load in professional drivers – The use of a whole-body finite-element model for the evaluation of adverse health effects of multi-axis vibration
No full textThe present study aimed to (i) employ the method for evaluation of vibration containing multiple shocks according to ISO/CD 2631-5:2014 (Model 1) and DIN SPEC 45697:2012 in a cohort of 537 professional drivers, (ii) deliver the results for a re-analysis of epidemiological data obtained in the VIBRISKS study, (iii) clarify the extent to which vibration acceleration and individual variables influence risk values, such as the daily compressive dose Sed and the risk factor R, and (iv) compare the results with in vivo measurements and those obtained in previous studies with similar models. The risk factor R was influenced by the acceleration, lifetime exposure duration, sitting posture, age at the start of exposure and body mass/body mass index in order of decreasing effect. Age and annual and daily exposure duration had only a marginal effect. The daily compressive dose Sed and the risk factor R showed weak linear association with the daily vibration exposure A(8) and the vibration dose value VDV. The study revealed high shear forces in the lumbar spine
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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