## 1 Introduction
Aimed to improve the order management process, [PERSON] and [PERSON] [25] proposed a conceptual framework, based on DT, of a decision support system, which is able to find the best solution through simulating several scenarios. Instead, [PERSON] et al. [26] combined DT and virtual reality in a co-simulation environment for assessing industrial workstations. They carried out a case study related to a human-robot collaborative workplace performing also ergonomic analysis. This research aims to fill the gap in the literature about the use of human DT to evaluate ergonomics by proposing a methodology that supports ergonomists/occupational physicians/line managers in mapping the ergonomics risk for all the workstations of manufacturing environment. There are two main motivations behind choosing a DT-based procedure for assessing the ergonomics. Firstly, it ensures that analyses are not affected by the ergonomist subjectivity, typical of the traditional (observational) techniques. Then, DT drastically reduces the computation times, thanks to algorithms able to quickly process data. So, since ergonomic analyses are significantly time consuming procedures, which could require hours for filling-in the spreadsheets, it is presumable saving a lot of time and then costs. This paper moves from a previous research [4], in which the authors proposed a novel methodological framework, based on the implementation of a DT, for carrying out near real time analyses about the performance of manufacturing production lines, in terms of working times and balancing. The core of the research in [4] was related to human motion data collection and transferring for reproducing the real production in a simulation scenario. Such model is able to supply output data useful to the evaluation of the desired line performances, besides representing a predictive model for the behavior of the line itself following possible modifications. Herein, the methodological framework has been modified and adapted in order to evaluate the worker's performance in terms of ergonomics, investigating the possible causes of risk of injury due to biomechanical overload: working postures, exerted forces, Material Manual Handling and repetitive actions. This procedure represents an innovation for the ergonomic screening of production lines that, currently, is still mainly performed by observational techniques and is a highly time consuming process. In fact, typically the ergonomist observes and records the work activity, estimates the index calculation parameters, fills in the checklists and evaluates the risk index. This process may require a significant amount of time, in the order of hours, to estimate the indexes of each workstation. In addition, the use of experimental data and DT allows an objective analysis as well as ensuring the repeatability of measurements. This approach contributes to the transformation towards the so-called smart factory, in agreement with the principles of Industry 4.0. A case study, aimed to demonstrate the effectiveness of the framework, has been set and performed at the Laboratory of Machine Design of the University of Campania [PERSON]. Data have been acquired by means of a wearable inertial motion tracking system [27] and the DT has been implemented in the Tecnomatix Process Simulate software by Siemens(r). The reminder of the paper is organized as follows. Section 2 describes the methodological framework, aimed to support the ergonomic assessment of the investigated working activity. Section 3 describes the case study that investigates an assembly activity reproduced in laboratory. Section 4 presents the results analysis and the discussions, while Section 5 concludes the paper.