## 4 Discussion  
The protocol proposed in this paper supports the evaluation of a passive occupational exoskeleton for lumbar support, particularly during MMH at work. It collects parameters such as variations in the distribution of the pressure of the feet on the ground; physiological parameters like blood oxygen saturation, pulse rate, HRV, EDA, skin surface temperature, and postural variations; and perceptions of comfort and usability. A critical aspect of the protocol development is the execution of preliminary studies [47]. These studies test each component of the protocol, identify weaknesses, and correct them before starting the pilot or main study. The significance of preliminary studies is fundamental across all research fields and is emphasized by the US National Institutes of Health for its value in the research process [48]. Experiments evaluating exoskeletons are time-consuming due to the several factors that research studies consider. Such studies commonly involve repeated measures with and without the exoskeletons, including training periods for task execution and proper exoskeleton use [16]. Additionally, each instrument requires proper calibration time before use. For these reasons, conducting preliminary tests is even more crucial, as it prevents further time loss later. Also, in the data analysis phase, having an analysis mode already tested in preliminary studies ensures one can save time and resources in the final evaluation. Figure 11: Variation in the maximum pressure on the left foot (continuous line) and the right foot (dashed line) for each deposit level (L1, L2, L3, L4) (**a**); variation in the average pressure on the left foot (continuous line) and the right foot (dashed line) (**b**) for each deposit level (L1, L2, L3, L4). Figure 12: Pulse rate percentage variation concerning the rest condition after the test with the exoskeleton (black spots, continuous line) and without the exoskeleton (white spots, dashed line). The findings of the first preliminary study suggest that the exoskeleton produced some impact on the maximum pressure experienced on the feet of the workers (see Figure 8). However, these data do not explain how the forces were distributed during the tasks, and more research is necessary to investigate the causes of these variations. Moreover, the results in Figures 9 and 10 suggest that the use of the exoskeletons during manual lifting produced some impact on the pressure distribution on the distinct parts of workers' feet. Again, it is not possible to identify a cause of these variations; for better understanding of its nature, a more in-depth and extended analysis of a wider sample of users, together with a more rigorous and standardized definition of the picking and deposit procedure, are necessary steps [27]. The findings of the second preliminary study show differences between the pressures of the right and left foot on the ground (see Figure 11). The left foot presents higher pressure variation values on average for three out of four deposition levels regarding maximum pressure (Figure 11a) and across all four levels concerning average pressure (Figure 11b). As observed in the previous preliminary study, to better understand the pressure variations between the test with the exoskeleton and the test without the exoskeleton, and to determine whether the use of the device causes these variations, more extensive and standardized tests are necessary. These tests should involve lifting and storing loads with feet kept parallel and following the same picking and depositing sequence to ensure a consistent number of steps between tests. Also, the findings from the analysis of the physiological parameters revealed sharp variations in the values obtained from the tests with the exoskeleton and the tests without the exoskeleton. Figure 12 suggests that the exoskeleton might increase the pulse rate during use. Specifically, three users involved in the second preliminary study experienced significant increases in pulse rate with the exoskeleton.