## 2 Materials and Methods
### Data Processing  
The performance of workers during professional activities at the workstation was evaluated comprehensively using a range of criteria, including the measurement of mobility (angular displacements, linear velocities, and accelerations) of relevant body parts. Biomechanical and statistical analyses were conducted to identify the most pertinent variables that were both interpretable and aligned with the research objectives. The derived formulas adhered to the principles of classical mechanics and biomechanical standards for reporting human movement. Additionally, the selected variables conformed to established standards for assessing risks associated with repetitive tasks, working postures, and force limits during machinery operations. A thorough review of signal processing techniques for biomedical data was conducted, and advanced system-build fusion algorithms were utilised. Signals were processed using Kalman filtering, incorporating a digital bandpass Finite Impulse Response filter with a recommended default value of 79 points. This method facilitated direct access to processed IMU sensor data for a subsequent analysis, ensuring accuracy and reliability in the evaluation. The production cycles of each participant were analysed according to the number of cycles and the cycle time in seconds. The start of the cycle was defined as the time when the worker reached for the part. The mobility of employees at machining or assembly workstations was assessed by separately characterising angular displacements (angles) and angular velocities (the rate of change of angular displacement over time) of the primary body parts engaged during work. Specific focus was placed on the movements of the pelvis, lower back (lumbar region), upper trunk (thorax), shoulder complex (connecting the upper arm to the axial skeleton at the thorax), upper arms, and forearms linked by the elbow joints. Following the International Society of Biomechanics recommendations for the reporting of human joint motion [42; 43], the following angles (measured in degrees) were chosen for left and right sides and sampled every 0.01 per cent of cycle time, in particular, the following:  
* For the pelvis--Pelvic tilt: Forward (positive) or backward (negative) movement of the pelvis in the sagittal plane relative to the global coordinate system. Pelvic obliquity: Upward (positive) or downward (negative) movement of the pelvis in the frontal plane. Pelvic rotation: Internal (positive) or external (negative) rotation of the pelvis in the transversal plane. * For the lower trunk (lumbar region)-- Lumbar flexion-extension: Anterior (positive) or posterior (negative) movement of the lumbar region in the sagittal plane. Lumbar lateral flexion: Movement of the lumbar region to the left (positive) or right (negative)in the frontal plane. Lumbar internal-external rotation: Internal (positive) or external (negative) rotation of the lumbar region in the transversal plane. * For the upper trunk (thorax)--Thoracic flexion-extension: Anterior (positive) or posterior (negative) movement of the thorax in the sagittal plane. Thoracic lateral flexion: Movement of the thorax to the left (positive) or right (negative) in the frontal plane. Thoracic internal-external rotation: Internal (positive) or external (negative) rotation of the thorax relative to the global coordinate system in the transversal plane. * For the shoulders--Shoulder flexion-extension: Anterior (positive) or posterior (negative) movement of the humerus relative to the thorax in the sagittal plane. Shoulder abduction-adduction: Abduction (positive) or adduction (negative) movement of the humerus relative to the thorax in the frontal plane. Shoulder internal-external rotation: Internal (positive) or external (negative) rotation of the humerus in the transversal plane. * For the elbows--Elbow flexion-extension: Positive (flexion) or negative (hyperextension) movement of the forearm relative to the humerus along the transversal axis.