## 6 Conclusions and Future Work  
This study implemented two game modes for hand rehabilitation. Both game modes were controlled using the following hand movements: wrist extension, wrist flexion, ulnar and radial deviations, and fist. The game difficulty was randomly adjusted in the non-tailored game mode, whereas the game difficulty was dynamically adjusted using a fuzzy logic system in the tailored game mode based on the participants' ROMs. Additionally, participants' engagement was computed using EEG signals collected via a Unicorn sensor and a Bitalino sensor. Moreover, questionnaires were applied to participants after finishing playing both game modes to gather their opinions on their favorite game mode, the game mode that is the easiest to play, the game mode that is the least frustrating to play, the game mode that is the least boring to play, the game mode that is the most entertaining to play, and the game mode that has the fastest game response time. The non-tailored game mode reported the highest mean engagement index (mean = 6.297, standard deviation = 11.274) when the EEG signal was collected via a Unicorn sensor, whereas the tailored game mode achieved the highest mean engagement index (mean = 3.619, standard deviation = 0.551) when the EEG signal was collected via the Bitalino sensor. Nevertheless, Wilcoxon-Signed-Rank test revealed that there was only a significant difference in the engagement index between game modes when the EEG signal was collected via the Unicorn sensor (\(p\) value = 0.04054). Regarding the players' opinions, [PERSON]'s exact tests revealed significant associations between the game modes (non-tailored, tailored) and only the following players' variables: ease of play when the Unicorn sensor was used to collect the EEG (\(p\) value = 0.009341); and frustration when the Unicorn sensor was used to collect the EEG (\(p\) value = 0.0466). As mentioned earlier, future research could focus on (i) employing other biosignals (e.g., respiration, electrocardiogram, and electrodermal activity) to compute the participants' engagement; (ii) conducting further experiments with participants with hand injuries and those past their twenties; (iii) implementing other membership functions and defuzzification methods to perform DDA; (iv) implementing other artificial intelligence methods (e.g., Q-learning, neural networks) to perform DDA; (v) using other participants' features as inputs to adjust the game difficulty (e.g., the participants' muscle effort and the participants' engagement); and (vi) using other non-player-characters' features (e.g., color, shape, and speed) to perform DDA. Conceptualization, R.D.G.-R. and E.J.R.-R.; methodology, [PERSON]-R., E.J.R.-R. and L.M.A.-V.; software, R.D.G.-R.; validation, R.D.G.-R., E.J.R.-R. and L.M.A.-V.; formal analysis, [PERSON]-R., E.J.R.-R., L.M.A.-V. and A.M.-H.; investigation, R.D.G.-R. and E.J.R.-R.; data curation, R.D.G.-R.; writing--original draft preparation, [PERSON]-R., E.J.R.-R., L.M.A.-V. and A.M.-H.; writing--review and editing, [PERSON]-R., [PERSON], [PERSON] and [PERSON]; visualization, [PERSON]-R., [PERSON], [PERSON] and [PERSON]; supervision, [PERSON], [PERSON] and [PERSON]. All authors have read and agreed to the published version of the manuscript. This research received no external funding and The APC was funded by Universidad Veracruzana. The study was conducted in accordance with the Declaration of Helsinki, and approved by the Ethical Committee of the School of Engineering and Science at Tecnologico de Monterrey (protocol code CA-EIC-2403-01, 15 April 2024). Informed Consent Statement: Informed consent was obtained from all subjects involved in the study. The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy concerns. [PERSON] thanks Mexican National Council of Humanities, Science and Technology Conahcyt (Consejo Nacional de Humanidades, Ciencias y Tecnologias) for funding his MPhil studies (CVU number: 1221049, scholarship number: 821654).