Modelling the response of the spinal system to whole-body vibration and repeated shock Helmut Seidel a, * , Michael J. Grin b a Department for Occupational Health, Federal Institute for Occupational Safety and Health FIOSH), Noeldnerstr. 40-42, 10317 Berlin, Germany b Human Factors Research Unit, Institute of Sound and Vibration Research, University of Southampton, Southampton SO17 1BJ, UK Abstract Back problems are very common and contribute to discomfort and days o work. Some back disorders are attributed to in- appropriateloadingofthespinethatcanbecombinedwithotherin¯uentialfactorssuchabodyposture,whole-bodyvibrationand shock. Many models have been developed to predict the forces in the spine associated with vibration and shock. However, the problem is complex due to the incompletely understood dynamic responses of the body, the in¯uence of many variables and the eect of muscle forces. Thispapersummarisesthecurrentstateofknowledgerelevanttothepredictionofforcesinthespineassociatedwithwhole-body vibration and shock. The paper also introduces presentations at a workshop on the modelling of spinal loads associated with vi- bration and shock held in Berlin in October 1999. Relevance Biodynamic models may be used to estimate risks of injury or disease and optimise environments so as to minimise risks. However,thedevelopmentofusefulmodelsrequiresanunderstandingofthecomplexinteractionbetweenmechanicalforcesandthe livingbody.Theapplicationofmodelsrequiresknowledgeoftheiraccuracyandlimitations. Ó 2001ElsevierScienceLtd.Allrights reserved. Keywords: Biodynamic models; Vibration; Mechanical shock; Spinal loading; Validation 1. Introduction Modellingtheresponseofthespinalsystemtowhole- body vibration and repeated shock provides the possi- bility of predicting the forces acting on the disks and endplates of vertebrae. These forces may be used to es- timatetheriskstohealthfromvibrationandshock.Due to the complex structure of the human body, complex dynamicmodelsbasedonhumananatomyarerequired toadequatelyre¯ectthedynamicpropertiesofthespine andadjacentpartsofthebody.Othertypesofmodelare less suitable: i) static models do not re¯ect suciently the dynamic properties of the body, including the lum- bar spine, ii) some simple models reproduce input± output relations without considering anatomical struc- turesorthemechanismsinvolvedinbodymovementor the causation of injury. Comprehensive reviews of dynamic models of seated humanscanbefoundelsewheree.g.,[1±5]).Intheideal case, the veri®cation of a model would rely on forces measured in vivo within the spine. However, few such data are available. Therefore, non-invasive biodynamic measurements are used. They oer the possibility to comparepredictionsfrommodelswithreality.Although conformity with appropriate measurements is a prereq- uisite for a model, it does not provide conclusive evi- dence of the veracity of predicted forces in the spine. This brief review summarises existing dynamic mod- elsofsittinghumansandsuggestsbiodynamicdatathat canbeusedforthevalidationofmodels.Theaimofthe reviewistoprovideabriefcriticaloverviewofavailable sources as a basis for the consideration of other con- tributionstotheworkshop.Thereviewdoesnotseekto repeattheknowledgepresentedinthepublicationslisted as references. 2. Dynamic models of sitting man The interest is restricted to models closely related to human anatomy. Consequently, some other models Clinical Biomechanics 16 Supplement No. 1 2001) S3±S7 www.elsevier.com/locate/clinbiomech * Corresponding author. E-mail address: h-seidel@gmx.de H. Seidel). 0268-0033/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII:S0268-003300)00095-4