Elements of an individuals occupational exposure, such as their posture can affect their comfort during work, and also their long term musculoskeletal health. Knowledge as to the extent of the influence of particular aspects of the exposures can help in providing guidance on risk evaluation, and direct future technical design focus. In many situations the exposures interact, and even if the effects of individual exposures are understood, the interactions are often less so. This is certainly the case with off-road driving exposures. Specific investigations have focussed on the effects of vibration exposure, resulting in the development of international standards and guidelines on measurement and evaluation of exposure. Consideration of the posture of the operator can be accomplished through postural assessment tools, although none of the currently available methods are developed specifically for use within a vehicle environment. The issues of both the posture of the operator and the seated vibration exposure are particularly apparent in off-road agricultural driving environments, where the driving task dictates that operator is often required to maintain specific postures whilst also exposed to whole-body vibration. In agriculture, many of the tasks require the operator to maintain axially rotated postures to complete the task effectively. The analysis of the combined effects of the axial rotation of the operator and the whole-body vibration exposure has been limited to a few studies within the literature, and is currently poorly understood. The overall aim of the thesis was to assess the influence of axial rotation and whole-body vibration on the musculoskeletal discomfort of the neck and trunk, in order that the true extent of the exposure risk may be evaluated. A field study was conducted to determine the common characteristics of some typical exposures, to provide a basis for the laboratory studies. A survey of expert opinion was conducted, examining the knowledge and experience of experts in assessing the relative influence of axial rotation and whole-body vibration on operators musculoskeletal health. The main investigations of the thesis are focussed in the laboratory, where the objective and subjective effects of axial rotation (static and dynamic) and whole-body vibration were investigated. Objective measures included the investigation of muscular fatigue in response to exposures. The tasks investigated in the field study indicated that the exposures often exceed the EU Physical Agents Exposure Limit Value, and that the axial rotation is a large component of the postures required. The survey of expert opinion concluded that combined exposure to axial rotation and whole-body vibration would increase the risks of lower back pain, and that acknowledgement of combined exposures should be included when assessing for risk. The results of the laboratory studies indicated that the greatest discomfort was present when subjects were exposed to axial rotation in the neck and shoulders. Out of the 8 muscles investigated, at most 6 of the 8 indicated fatigue during an experimental exposure. The muscle group which was affected most by the exposures was the m. trapezius pars decendens. Findings demonstrated that when subjects were exposed to axial rotation and whole-body vibration they indicated discomfort and their muscles fatigued. However, there was poor correlation between the sites of discomfort and the location of muscular fatigue. The discomfort findings suggest that there is an increased risk of discomfort from experiencing axial rotation together with whole-body vibration. Investigations of muscular fatigue do not substantiate this finding.

Une prédiction réaliste de la posture de conduite est requise tant pour la protection individualisée des conducteurs que pour la conception de véhicules, tout particulièrement lorsque des mannequins numériques (DHM) sont utilisés dans les premières phases de développement. Des plages étendues de réglage du volant et du siège sont disponibles dans les véhicules actuels, offrant aux conducteurs de nombreuses postures de conduite possibles. Ce travail de thèse vise à quantifier la variabilité intra- (i.e. la variabilité posturale pour un même conducteur) et inter-individu (i.e. la variabilité entre différents conducteurs), ainsi qu'à développer un modèle statistique de prédiction de posture de conduite. Les postures de conduite de 34 volontaires représentatifs de la population européenne ont été mesurées sur 5 véhicules différents. En faisant varier les ajustements initiaux du siège et du volant, une variabilité intra-individu de 22 ± 14 mm dans la direction longitudinale (x) et de 16 ± 12 mm dans la direction verticale (z) ont été observées pour la position du siège. En ce qui concerne la position du volant, une variabilité légèrement plus faible a été observée, 20 ± 15 mm en x et 13 ± 9 mm en z. La position du bassin dépend à la fois du type de véhicule et de l'anthropométrie du conducteur. Plus la hauteur d'assise du véhicule est basse, et plus le conducteur est grand, plus le siège est positionné bas et en arrière. Fait intéressant, l'angle du dossier par rapport à la verticale n'est affecté ni par l'anthropométrie du conducteur, ni par le type de véhicule. Un modèle statistique pour la prédiction de la posture de conduite basé sur les données expérimentales est proposé et comparé à d'autres modèles prédictifs existant. Les postures de conduite recueillies expérimentalement sont aussi comparées aux prédictions obtenues avec le mannequin numérique RAMSIS. Si l'on se base sur les valeurs de variabilité intra-individu pour la position des yeux et du bassin comme critère d'évaluation des prédictions de RAMSIS, seulement 16% et 30% des prédictions peuvent être considérées comme correctes. Différentes solutions pour améliorer les prédictions sont proposées / Realistic prediction of driving posture is required for both individualized protection and vehicle packaging especially when a digital human model (DHM) is used in early phase of a vehicle design. A large range of seat and steering wheel adjustments is available in today’s vehicles, offering many possibilities in driving position. The present PhD thesis aims at quantifying intra- (i.e. postural variability for a same driver) and inter-individual (i.e. variability between different drivers) variability and developing a statistical driving posture prediction model. Driving postures of 34 volunteers were recorded on 5 different vehicles, covering a large range of European drivers’ anthropometry and vehicle types. By varying initial adjustments and comparing road and laboratory conditions, we observed an intra-individual variation in the seat position, 22 ± 14 mm in longitudinal (x) direction and 16 ± 12 mm in vertical (z) direction on average. For steering wheel position, slightly smaller variations were also observed, 20 ± 15 mm in x and 13 ± 9 mm in z directions. As expected, hip position was strongly affected by both vehicle and driver’s anthropometry. Drivers sat lower and more backward for a taller driver and a higher seat. Interestingly, torso angle relative to the vertical direction was affected neither by vehicle nor by stature group. A statistical driving posture prediction model based on collected data is proposed and compared with other existing statistical models. Collected driving postures were also compared with the predictions by the digital human software modeling package RAMSIS. If we refer to the range of intra-individual variation in hip and eye locations for assessing RAMSIS predictions, only 30% and 18% of the predictions can be considered as good. Solutions for improving predictions are suggested

Prédire précisément la posture adoptée par un conducteur est primordial dans la conception d'un véhicule, surtout quand un mannequin numérique est utilisé. De plus, le marché automobile en Chine est en pleine expansion et devient le plus gros marché automobile. L'adaptation de la conception des véhicules aux spécificités de ce marché est un enjeu majeur pour de nombreux constructeurs automobiles. Le conducteur chinois se distingue du conducteur Européen par une anthropométrie différente, non seulement en taille mais aussi en proportion du corps. L'adaptation de la conception de la voiture au marché chinois devient un enjeu majeur pour de nombreux constructeurs automobiles. Cette thèse vise à (1) étudier l'effet des paramètres anthropométriques et des paramètres véhicule sur la posture de conduite, (2) développer un modèle statistique de prédiction de posture de conduite, (3) quantifier la variabilité intra- (i.e. la variabilité pour un même conducteur) et interindividus (variabilité entre différents conducteurs) des postures de conduite confortables. Les postures de conduite de soixante et un sujets ont été recueillies à l'aide de deux maquettes de véhicule multi-réglable sous quatre conditions d'essai en ajoutant progressivement le nombre de paramètres de contrôle (contraintes), de la configuration with "contraintes minimum" aux configurations proches des véhicules existants. En plus de la hauteur du siège, les effets des positions longitudinales de la pédale d'embrayage et du volant ainsi que l'angle de coussin de siège ont été étudiés. Les sujets ont été divisés en trois groupes de taille (petite, moyenne et grande). Un sous-échantillon (27 « nés française »et 21« nés Chinois») a été constitué avec une distribution de taille similaire et de ratios hauteur du buste / taille, longueur bras / taille et longueur jambe / taille différents / Accurate prediction of driving posture is essential for vehicle interior design, especially when a digital human model (DHM) is used. Meanwhile, the car market is booming in China. Chinese drivers are different from those of European in terms of anthropometry, not only in stature but also in body proportion. How to adapt car design to the Chinese market is becoming a major issue for many car manufacturers. The present PhD thesis aims at (1) studying the effects of key vehicle interior design dimensions and anthropometric variables on driving posture, (2) developing a statistical driving posture prediction model (3) quantifying intra-(i.e. variability of the same driver) and inter-individual (variability between different drivers) variability of comfortable driving postures. The driving postures of sixty-one subjects were collected using two multi-adjustable vehicle mock-ups under four test conditions by gradually adding the number of control parameters (constraints), from the “least constrained” driving condition to the configurations close to currently existing vehicles. In addition to seat height, the effects of the longitudinal positions of clutch pedal and steering wheel as well as seat cushion angle were investigated. The subjects were divided into three stature groups (short, average and tall). A sub-sample (27 ‘French-born’ and 21 ‘Chinese born’) was constituted with similar stature distribution and quite different in the sitting stature/stature, arm length/stature and thigh length/stature ratios

With more legislation being enforced to achieve a reduction in road transport CO2 emissions, automotive companies are having to research and develop technologies that deliver greener driving . Whilst emissions from passenger vehicles have dropped over recent years, there has been an increase in emissions from light commercial vehicles (LCVs). The nature of LCV delivery work is a routine of ingress/egress of the vehicle, changing from a standing to a seated posture repetitively throughout the day. One research focus is packaging occupants in to a smaller vehicle space, in order to reduce the amount of vehicle emissions over its lifecycle. For LCVs, benefits from space saving technology could be an increase in overall loading space (with the same vehicle length) or a reduction in the overall length/weight of the vehicle. Furthermore, an elevated seat posture could reduce the strain on drivers during ingress/egress, as it is closer than that of a conventional seat to a standing posture. Whilst space saving technology has obvious benefits, current driving conventions and standards are not inclusive of new and novel seated postures when packaging a driver in to a vehicle. The fundamental purpose of a vehicle driver s seat is to be comfortable and safe for the occupant and to facilitate driving. It has been shown that a seat needs both good static and dynamic factors to contribute to overall seat comfort. Additionally, comfortable body angles have been identified and ratified by studies investigating comfortable driving postures; however, this knowledge only applies to conventional driving postures. For an elevated posture , defined as having the driver s knee point below the hip point, there is little research or guidance. The overall aim of this thesis is to identify the ergonomic requirements of a wide anthropometric range of drivers in an elevated driving posture for LCVs, which was investigated using a series of laboratory based experiments. An iterative fitting trial was designed to identify key seat parameters for static comfort in an elevated posture seat. The results showed that in comparison with a conventional seat: Seat base length was preferred to be shorter (380mm compared with 460mm); Seat base width was preferred to be wider (560mm compared with 480mm); Backrest height was preferred to be longer (690mm compared with 650mm). These findings provided a basis for a seat design specification for an elevated posture concept seat, which was tested in two subsequent laboratory studies. A long-term discomfort evaluation was conducted, using a driving simulator and a motion platform replicating real road vibration. Discomfort scores were collected at 10-minute intervals (50-minutes overall) using a body map and rating scale combination. The results indicated that in comparison with the conventional posture, the elevated posture performed as well, or better (significantly lower discomfort for right shoulder and lower back; p<0.05, two-tailed), in terms of long-term discomfort. Furthermore, the onset of discomfort (i.e. the time taken for localised discomfort ratings to be significantly higher than the baseline ratings reported before the trial) occurred after as little as 10 minutes (conventional posture) and 20 minutes (elevated posture) respectively. A lateral stability evaluation was conducted using low-frequency lateral motion on a motion platform (platform left and right rolls of 14.5°). Stability scores were reported after each sequence of rolls, comparing scores on a newly developed lateral stability scale between three seats: Conventional posture seat; Elevated posture concept seat (EPS1); Elevated posture concept seat with modifications aimed at improving stability (EPS2). Participants reported being more unstable in EPS1, compared with the conventional posture seat (p<0.05, Wilcoxon). However, the EPS2 seat performed equally to the conventional posture seat. These findings suggest that the elevated posture seat developed in this research is a feasible and comfortable alternative to a conventional posture seat. Furthermore, the final elevated seating positions showed that real space saving can be achieved in this posture thus allowing for more compact and lighter vehicles and potentially reducing strain on drivers during ingress/egress.