## 1 Introduction  
Upper limb impairment is defined by the International Classification of Functioning, Disability and Health model [1] as (1) impairments of body function, such as a significant deviation or loss in neuromuscularsuloskeletal and movement-related function related to joint mobility, muscle power, muscle tone, and/or involuntary movements, or (2) impairment of body structures, such as a significant deviation in structure of the nervous system or structures related to movement.  
Robot-mediated therapy after upper limb impairment, because of neurological or orthopedic diseases, is emerging in the rehabilitation field. A recent Cochrane review highlighted a potential benefit of the electromechanical and robot-assisted upper limb training in stroke patients [2]. In addition, robotic therapy can increase the efficiency of therapy, and therefore the accessibility to treatment [3]. In fact, in an era of increasing focus on healthcare resource utilization, a considerable interest is devoted toward reducing costs while preserving a high-quality level. From this perspective, economic evaluations of rehabilitation interventions using cost-effectiveness and/or cost-utility analysis are needed [4]. However, few studies have been conducted on the real costs of robotic and technological rehabilitation when compared to traditional rehabilitation. [PERSON] et al. [5] found that the costs of an additional upper limb treatment (robotic or conventional) in stroke patients can be recuperated because of lower general healthcare costs. Moreover, a recent systematic review, including five studies, found that robotic therapy produces a better economic outcome when compared to conventional therapy [6].  
In addition, [PERSON] et al. [7] suggested that the availability of a room equipped with more than one device can further increase the sustainability of the treatment, addressing an essential need of under-resourced healthcare systems [8]. In fact, although robotic devices are expensive, new organizational models where one physiotherapist supervises more than one patient could optimize the human resources. Some authors [9; 10; 11] suggested that this approach can be as effective as traditional therapy for stroke patients, presenting a more cost- and labor-efficient option. However, to the best of our knowledge, there have been no previous studies that analyzed either the rehabilitation dose provided to the patients or patient's satisfaction when different physiotherapist/patient ratios have been used. Moreover, the clinical characteristics of patients that could influence the proper physiotherapist/patient ratio remain uninvestigated.  
In April 2016, to implement the robotic rehabilitation in a sustainable way, a set of four technological and robotic devices for the upper limb was identified, and a robotic rehabilitation area was built and equipped with the set [12]. This allowed experimenting with a new organizational model where more than one patient is supervised by one physiotherapist, in order to increase the efficiency of the robotic treatment.  
Then, to critically evaluate the feasibility of this model, a study based on data related to the use of these devices in clinical practice was carried out.  
Specifically, the aim of this study was twofold: (1) to verify the feasibility, in terms of rehabilitation dose (as measured by the time of training) and patient satisfaction (as measured by the Visual Analogue Scale for Satisfaction), of a new organizational model in which one physiotherapist supervises up to four patients using a set of four robotic-technological devices; and (2) to identify the optimal number of patients that can be supervised by one physiotherapist, in accordance to the patients' upper limb impairment (measured by the Motricity Index), disability (measured by the Barthel Index), mobility (measured by the Deambulation Index), and comorbidity (measured by the Cumulative Illness Rating Scale).