## 4 Discussion  
Robotic tools are emerging in the rehabilitation field, showing promising expectations for an intensive and personalized treatment. Nonetheless, these devices are expensive. Therefore, it is necessary to find the best organizational models to increase the number of patients who may have access to the technological rehabilitation, optimizing human resources. In this perspective, it is crucial to know if and how patient's disability, mobility, or comorbidity can influence an organizational model where a new, non-traditional ratio of physiotherapist/patient would be adopted. This study shows the feasibility, in terms of rehabilitation dose and patient's satisfaction, of an organizational model with one physiotherapist supervising more than one patient, using a set of four devices for a comprehensive upper limb rehabilitation. In a 45-min rehabilitation session, regardless of the physiotherapist/patient ratio, each patient performed about 30 min of training with an individual physiotherapist supervision of about 10 min. As expected, the time of training was significantly lower in the R4 group but with a gap of only 2 and 3 min compared to the R2 and R3 groups, respectively. Regarding the difference in the training time recorded between the R2/R3 and R4 groups, an increase of about 3 min of the rehabilitation session of the R4 group can be used to overcome this small gap. Therefore, our results showed that the physiotherapists in this study were able to supervise up to four patients, without a reduction of the treatment dose provided to the patient. This is a crucial point: in fact, several studies report an intensity-effect relation between the amount of therapy that individuals receive and the motor recovery [21; 22]; additionally, no ceiling effect for the intensity of the therapy has been observed [23; 24; 25]. Note that patient satisfaction was very high (8/10) without significant differences between groups, so patients were very satisfied even if treated together with one, two, or three other patients at the same time. Regarding the clinical characteristics of the patients, our data did not show differences when two or three patients were supervised by one physiotherapist. On the contrary, though as expected, the group in which four patients were supervised by one physiotherapist (R4) had a lower disability and comorbidity and higher mobility than the R2 and R3 groups. A remarkable result is that upper limb impairment did not influence the organizational model proposed, since the MI not significantly different between the groups (R2, R3, and R4). The multivariate analysis showed that only the BI can predict significantly the treatment group, meaning that the maximum number of patients supervised by one physiotherapist can be dependent on their level of autonomy. Therefore, the BI seems to be the most important variable that could influence the physiotherapist/patient ratio. Based on our results, a ratio of 1/4 could be used if the mean value BI of the group of patients is higher than 57. Note that patients with BI values lower than 60 are considered patients with a severe disability [14]. Our results showed a similar cut-off of disability, even if calculated as the mean of the group (BI mean score of group \(<\)57). The analysis of both clinical data and feasibility measures suggests that patients with a severe disability (BI mean score of the group \(<\)57) can be equally treated in groups of two or three patients, providing that they had the same dose. Instead, when a moderate disability is present, up to four patients can be supervised by one physiotherapist. This study also confirms the possibility of optimizing resources allocation. In fact, in our rehabilitation planning, a mean of 24 patients were treated each