title: Kinematics of the trunk in sitting posture: an analysis based on the instantaneous axis of rotation.
abstract: This paper presents a new approach for analysing trunk kinematics in sitting posture based on the characterisation of thorax and pelvis motion by means of ranges of motion and instantaneous axes of rotation (IAR). These variables are estimated from videophotogrammetric data. An experiment was carried out in order to analyse three motions associated with the flexion-extension movement: the absolute motions of the pelvis and thorax and the relative motion between the thorax and pelvis. The results obtained suggest a sequential activation of lumbar vertebrae in the flexion-extension motion. On the other hand, the location of the pelvis IAR shows that the movement of the pelvis on the seat is not just a rolling motion but a rolling with some level of sliding. Finally, the location of the IAR in the thorax-pelvis relative motion shows a mismatch between the trunk IAR and the backrest axis of rotation in several office chairs. The proposed technique provides a new approach for the kinematic analysis of sitting posture. The results can be applied to the improvement of biomechanical models of seated posture as well as to define some design criteria of work seats based on the fit between the trunk and backrest movements.
authors.affiliation: Departamento de Física Aplicada, Universidad Politécnica de Valencia, Valencia, Spain. afpage@ibv.upv.es
authors.forename: Alvaro
authors.initials: A
authors.lastname: Page
authors.forename: Helios
authors.initials: H
authors.lastname: de Rosario
authors.forename: Vicente
authors.initials: V
authors.lastname: Mata
authors.forename: Rosa
authors.initials: R
authors.lastname: Porcar
authors.forename: José
authors.initials: J
authors.lastname: Solaz
authors.forename: María José
authors.initials: MJ
authors.lastname: Such
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D006804:Ergonomics; D005260:Female; D006801:Humans; D008297:Male; D010388:Pelvis / Q000502:physiology*; D010780:Photogrammetry; D011187:Posture; D012399:Rotation; D013909:Thorax / Q000502:physiology*