## 2 Materials and Methods
### Measurement Set-Up  
We employed the myoMuscle Master Edition system (myoMOTION(tm), Noraxon, Scottsdale, AZ, USA) equipped with Master Research 3.0 (MR3) software to record pertinent parameters. This system has 16 inertial motion units (IMUs), utilising inertial sensor technology. The IMUs, incorporating a triad of sensors--a 3D accelerometer, gyroscope, and magnetometer--utilise fusion algorithms to transform sensor data into three-dimensional rotation angles (yaw-pitch-roll or navigation angles) in absolute space. The inertial motion capture system comprising sensors was affixed to the body of the participant (Figure 1), as per the established myoMOTION protocol delineated in the instruction manual. This setup was tasked with recording body accelerations. The scientific validity and high precision of the Inertial Measurement Unit (IMU) system in determining angles have been previously affirmed, exhibiting a maximum error margin of \(\pm\)0.4 degrees for static assessments and \(\pm\)1.2 degrees for dynamic evaluations [34; 39].  
Figure 1: An experimental setup involving a computer workstation and the positioning of IMU sensors on an employee’s body. The image shows the locations of IMU sensors on the body, providing a visual example of the model used in the study. The computer workstation was equipped with MR3 software for data collection and analysis, and the body is positioned frontally to facilitate accurate motion tracking during calibration.  
The current study systematically examined a series of standardised machining tasks. These tasks comprised the following steps: (1) lifting four components simultaneously--three with one hand and one with the other--from a metal container; (2) clearing metal chips from the clamping base; (3) securing components onto the clamping device; (4) performing the deburring process; (5) transferring the components to an engraving machine to initiate the marking cycle; (6) conducting a visual inspection to ensure task accuracy; and (7) placing the components onto a danger. The manipulation processes were primarily unilateral, with the left limb performing active manipulative actions, while the right limb played a stabilising and supportive role. Each component weighed approximately 520 g before the operation and 380 g after processing. These standardised tasks facilitated accurate motion capture using inertial sensors, allowing for a detailed analysis of angular displacements, velocities, and asymmetries in the thoracic and lumbar regions. The experimental setup also included a series of standardised assembly tasks, specifically focusing on constructing the spring-piston unit. The task sequence consisted of the following steps: (1) retrieving the spring with the left hand from its designated container; (2) picking up the piston with the right hand from the corresponding piston box; (3) positioning the spring pack vertically within the centring sleeve; (4) placing the piston on top of the spring pack; (5) performing a visual inspection to verify the accuracy of the operation; and (6) transferring the completed spring-piston unit to the next assembly point. The weights of the components used in this process ranged between 100 and 400 g.  
The measurements were subjected to a pre-processing procedure. This involved a thorough review of the collected data, leading to the elimination of any records that were incorrectly logged. Initially, there was one such case. Following this, each remaining record underwent a meticulous verification process against the workstation manual to ensure its accuracy and reliability.