## 4 Discussion  
There are several studies in the scientific literature that confirm the need to improve the comfort and ergonomic criteria of instruments for laparoscopic surgery. The instrument handle is an essential part  
Figure 8: Flexion-extension of the surgeons’ wrist during the laparoscopic tasks using the right and wrong size of instrument handle. The graph indicates the acceptable posture of the wrist according to RULA method. Figure 9: Results of the surgeons’ evaluation regarding the comfort of performing each task using the two types of instrument handles. of laparoscopic instruments, whose inappropriate design can have a detrimental effect on the surgeon's efficiency and wellbeing [33]. The rate of work-related musculoskeletal disorders in laparoscopy are from 73% to 100%, with poor instrument handle design being one of the main risk factors [34; 35]. In a survey by [PERSON] et al., they assessed the acceptance of different surgical instrument handle designs and they reported that conventional laparoscopic instrument handles such as the axial handle scored lowest in terms of comfort [36]. Other studies also indicated that axial handles require significantly more muscle activity than the other common types of instrument handle [37]. In this study, we have analyzed the relationship between the surgeons' ergonomics and performance and different sizes of a novel laparoscopic instrument handle design [11]. The results verify that the use of different instrument handle sizes has consequences on the surgeon's grip pressure and surgical skills. It seems that the use of an adequate size of instrument handle helps hand-eye coordination and bimanual dexterity in the development of laparoscopic tasks, reducing the execution time, as shown by the results of this study. [PERSON] et al. also presented an innovative laparoscopic handle design with a pistol grip attempting to address some of the ergonomic limitations in laparoscopic surgery [38]. Although the validation of this handle design was mainly subjective, they reported significantly shorter execution times in performing cutting and peg transfer tasks when compared to a conventional laparoscopic tool. However, execution time may not be a very meaningful assessment parameter in the case of the coordinated traction task. This task requires participants to exert a high degree of traction with the instruments and, therefore, to firmly the instrument handle. Due to the metal material of the rings, they sometimes slipped off the instrument tip, thus increasing the time required to complete the task, despite the surgeon's skills. Regarding the pressure exerted by the surgeon's fingers and palm using the instrument handle, the palm exerted the highest amount of pressure on the handle when compared to the rest of the anatomical sites analyzed. This result was also reported by [PERSON] et al. using a power grip configuration [39]. In the case of the fingers, the thumb and index finger applied a greater amount of pressure than the middle and ring fingers. This may be because of the primary use of the thumb to control the wheel to rotate the instrument tip and the index finger to operate the trigger that opens and closes it. It should be noted that the use of an inappropriate handle size, especially in more complex tasks such as the transfer task (labyrinth), led to a significant increase in the pressure on the palm. It seems that this substantial increase in palmar pressure was accompanied by a reduction in the pressure exerted by the thumb when controlling the instrument wheel. Therefore, instead of distributing the force exerted by the fingers and the palm in a more balanced way, in this case it was mainly focused on the surgeon's palmar area. In a power grip configuration, like the one we have in our design, the handle should be held by the partially bent fingers and the palm, exerting a counter pressure with the thumb lying near the plane of the palm.