## 4 Conclusions  
In this article, we provided a comprehensive overview of the currently available end effector-based devices for gait and balance rehabilitation. In addition, we proposed a classification of the existing different lower-limb devices that are suitable for the rehabilitation of gait and balance functions. In this classification, the difference between direct and indirect balance rehabilitation was highlighted, since we found that most of the studies considered balance rehabilitation a side effect of gait training devices, and thus there was a need to provide a classification that considers this small, although important, nuance.  
Regarding the reviewed end effectors, most of them are prototypes and have not been clinically tested. Moreover, there exists a disproportion in the number of end effector-based prototypes for gait training and those for direct balance rehabilitation, being more for gait rehabilitation. Only two end effectors out of 55 are designed to provide gait and direct balance rehabilitation independently and simultaneously. By analyzing the different driving mechanisms, we realized that due to their attractive features, PKMs are extensively used in end effector-based devices to generate rehabilitation trajectories. However, the use of lower-mobility PKMs is still limited, and most of the designs tend to use full-mobility Stewart platforms.  
We conclude the article by suggesting some directions for future research, among which three are of particular interest to the rehabilitation field. On the one hand, we believe that the existing prototypes should be further improved to transfer them from research to a clinical setting. This would supply the health system with new and more effective tools for the rehabilitation process. On the other hand, future research should focus on the use of lower-mobility PKMs as the driving mechanisms for the end effectors, since their compelling features make the prototypes suitable for gait and balance rehabilitation while the number of actuators and the cost is reduced. Finally, efforts should be invested in the development of new end effectors capable of providing gait and direct balance rehabilitation independently and simultaneously. These double-purpose end effectors, in combination with assessment tools, can meet most research and clinical needs in a cost-effective way.  
All authors contributed to the conceptualization and methodology; writing--original draft preparation, P.D.; writing--review and editing, S.H. and E.M.; visualization, P.D., S.H., and E.M.; supervision, J.C., M.D., F.J.C., and C.P.; project administration, F.J.C. and C.P.; funding acquisition, F.J.C. and C.P. All authors have read and agreed to the published version of the manuscript.  
This research received financial support for the project PID2019-105262 RB-I00 funded by MCIN/ AEI/10.13039/501100011033 and for the project PDC2022-133787-I00 funded by MCIN/ AEI/ 10.13039/501100011033 and by the European Union Next Generation EU/PRTR. This research was also funded by the Basque Government for the project 2018222013 and PhD grant PRE_2023\(2\)0168.  
Not applicable.  
The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.