International Journal of Health Sciences and Research Vol.13; Issue: 7; July 2023 Website: www.ijhsr.org Original Research Article ISSN: 2249-9571 International Journal of Health Sciences and Research (www.ijhsr.org) 290 Volume 13; Issue: 7; July 2023 A Predictive Model to Quantify Joint Torques and Support Reaction Forces When Using a Smartphone While Sitting with and Without Support: Toward a Risk Scale Proposition to Prevent Musculoskeletal Disorders JACQUIER-BRET Julien 1,2 , GORCE Philippe 1,2 , MERBAH Johan 3 1 International Institute of Biomechanics and Surgical Ergonomics, 2 Université de Toulon, CS60584, 83041 TOULON CEDEX 9, France 3 Association Er Bio-Connect – CS 10121, 83418 HYERES CEDEX, France Corresponding Author: Julien Jacquier-Bret, jacquier@univ-tln.fr DOI: https://doi.org/10.52403/ijhsr.20230741 ABSTRACT New portable technologies such as smartphones are developing in a very important way and their use rate is increasing every year. Faced with this growth, it is relevant to consider the risks of developing musculoskeletal disorders related to their increasing utilization. The objective of this study was twofold: 1) to propose a predictive model of the upper body joint angles, torques and reaction forces during smartphone interaction in seated position based on subject’s anthropometric data, environmental conditions and interaction strategies in the sagittal plane; 2) to propose risk scales for joint torques provided by the model and which could be integrated with information on posture as part of the musculoskeletal disorders prevention. One of the original aspects of the predictive model was to consider postural strategies between the trunk and the neck during smartphone interaction. The validation was carried out by comparing experimental data collected from 12 subjects who had to perform texting and web browsing task while sitting on a chair with or without support and the data simulated by the model under the same conditions. The results showed a satisfactory ability of the model to reproduce the subjects' posture. However, more marked differences were observed for reaction forces and for shoulder and elbow flexion when trunk flexion was significant. A validity domain for each parameter was computed for different seat and support heights according to the subjects' body mass index. From these data, joint torques risk scales have been constructed, to characterize the risks incurred by the users. Keywords: Predictive Model, Musculoskeletal disorders, Risk scale, Sitting, Posture, Torque/Force. INTRODUCTION Prevention of musculoskeletal disorders (MSDs) has an important research area for many years. The consequences on health operators induce a high rate of absenteeism with a significant additional cost which amounts to millions of hours of work stoppages. From a financial point of view, this translates into direct and indirect costs of several million euros for the health systems of the countries concerned (1). The international literature has studied this problem in depth through the understanding and analysis of work or leisure postures in order to assess the potential risks of (MSDs). Many parameters have been studied such as working positions/postures adopted (2), repetitiveness of the task (3, 4), duration (5, 6), load to be moved (7) and MSDs . The risk assessment is often done by ergonomic