## 2 Materials and Methods
### Test Subject and Research Procedure
This system was chosen because it offers great flexibility working with larger measurement sample sizes and small number of errors that would require repeating the measurement. A standard systems marker set was used, consisting of 17 markers in total. Data were captured at 60 Hz. The system was calibrated while standing and walking. Afterward, three different scenarios were performed with three repetitions each. In total, nine measurements were taken for each test subject. After each measurement, a visual inspection was conducted to ensure data consistency and quality. The measurement was repeated if any issues were detected with the data. Once all data were collected, batch HD processing was performed to smooth out, recenter, and improve the data. HD smoothing was carried out in Movella Xsens MVN 2023.2 software package. Processed position data of 17 markers were exported in.xlsx format. This file was directly plugged into a model created in Rhino Grasshopper 7 SR34 software package. Test subjects' individual anthropometric data were captured before conducting the measurement. For data that could not be directly measured, such as segment weights and center of gravity distances, calculations were based on the [PERSON], and [PERSON] methods, as these are widely utilized [15; 16; 17]. Individualization in the model involves scaling limb marker positions according to the specific measurements of each subject. The same individualized scaling was applied in the mathematical moment calculation. The patient load force profile was integrated into model, parametrizing it based on the duration of each measurement. After completing the calculations in the model, the data were normalized by patient height and time. However, normalization was applied only to the joint moment and motion amplitude data, while the accumulated moment was excluded from normalization. This approach was taken because the duration of motion significantly influences the accumulation of load. In the final steps, the data were grouped based on different test subject parameters. Statistical calculations were then performed on these grouped data sets, presented, and evaluated. The lifting procedure scheme is presented in Figure 2A. Both surfaces are adjusted to an exact height of 0.6 m. The wheelchair is positioned at an angle near the bed, with its brakes engaged. The test subject approaches the patient, and the motion analysis begins when he/she starts bending. The end position of the motion is defined when the test subject stands up, straightens their back, and positions their head in a neutral or semi-neutral position. The experimental scheme to determine the patient load profile is presented in Figure 2B. Due to the motion's complexity, the need for additional equipment, and the large sample size, real-time measurement of patient's loads proves challenging. Consequently, it was decided to conduct an experiment that would allow the determination of load profile of a patient, leveraging the consistency of using the same patient across all measurements. For this experiment, a BTS P-6000 force plate was employed, initially recoding at 250 Hz. A total of ten measurements were conducted. The experiment consists of two independent measurements:  
1. The patient begins by sitting on the chair without touching the force plate, with legs lifted. The measurement commences when the patient stands on the force plate,  
Figure 1: Flow chart of study procedure. remains standing for a few seconds, and then returns to a seated position on the chair. This is presented in Figure 2B(1) scenario. 2. The second measurement begins with the patient sitting on the chair with their legs touching the force plate. The patient is lifted by the test subject between two surfaces, replicating the main research scenario. Throughout the lift, the patient keeps their legs on the force plate, allowing measurement of the remaining force. This setup enables continuous measurement of the force exerted while the patient's legs remain in contact with the force plate throughout the lifting motion.