## 2 Materials and Methods  
### Test Subject and Research Procedure  
For this experiment, healthcare specialists were gathered, primarily consisting of nurses and rehabilitation specialists. In total, 44 participants (16 men and 28 women) were recruited for this research. The average age was 28 \(\pm\) 12 years, average height was 175.11 \(\pm\) 11.58 cm, and average weight was 75.30 \(\pm\) 12.58 kg. The sample size was calculated using GPower 3.1.9.7. for a statistical power of 0.95, an effect size of 0.475, and a significance level of 0.05, assuming a two-tailed data distribution. The calculation determined that 34 test subjects would suffice for single-tailed analysis. Each participant underwent 9 measurements, resulting in a total of 396 data measurements analyzed for this research. Additionally, test subjects were required to complete a form providing supplementary cross-sectional data. This form was used to evaluate test subjects' physical readiness based on sport activities they engage in and their frequency, together with other properties. This was a qualitative assessment granting scores from 1 to 10 to each of the test subjects. The goal was to study the possible correlation between fitness level and research results. Furthermore, test subjects were allocated to distinctive groups, which had been formed according to the results of their respective measurements. These data sets were used for comparison with the full research sample size. Groups were formed according to the following criteria: age, physical readiness, tenure, and gender. Age groups were divided into younger than 25 y.o. (\(n\) = 243), between 25 and 35 y.o. (\(n\) = 99), and older than 50 y.o. (\(n\) = 53). Test subject's physical readiness level was judged by score, with low score (\(n\) = 126) being below 6, mid score (\(n\) = 171) being 6 to 8, and high score (\(n\) = 99) being 9 to 10. Further criteria were tenure, first group having less than 1 year (\(n\) = 207), second group having 1 to 3 years (\(n\) = 99), and third group having more than 3 years of tenure (\(n\) = 90). Another group divided test subjects according to their gender, categorizing them as male (\(n\) = 144) and female (\(n\) = 252). The last group consisted of different lift scenarios, described in the next paragraph, each containing of same amount of measurements (\(n\) = 132). For this research, the motion of lifting a patient from a wheelchair to a bed was selected. This motion is based on techniques physiotherapists normally use in their work environments. The motion comprises three main phases: lifting, transferring, and putting down. The lifting and putting down are symmetrical motions, distinguishable by observing knee flexion/extension, as knees extend during lifting phase and flex during putting-down phase. Transferring phase involves trunk rotation and a shift in the center of gravity, increasing the complexity and potential risk of injury associated with this motion. This phase is identified as a gap between lift and put-down motions. Furthermore, three scenarios were chosen to evaluate possible technique and motion changes:  
1. The first scenario simulates a heavily physically disabled person, where patient does not assist the test subject in any way and remains relaxed. Patient's hands are down. 2. The second scenario simulates a patient with ability to move above the waist, where the assistance is provided by the patient placing their hands on the test subject's shoulders. The patient cannot stand on their own, and the assistance is minimal. 3. Similarly to the first scenario, in the third scenario, the patient does not assist at all, but in this case, test subject uses ergonomical belt during the lifting. Patient's hands are down, and body is relaxed. For consistency, the same person (180.10 cm height and 65.27 kg weight) participated as the patient in all the measurements to minimize the potential environmental variables. Main study procedure and sequence are shown in Figure 1. Test subject was equipped with the IMU marker system--Xsens Movella.