## 1 Introduction  
The incidence rate of pediatric-onset spinal cord injury (SCI) was estimated to be 3.3 and 6.2 cases per million per year for traumatic and non-traumatic SCI, respectively, in Europe [1]. Among other sequelae, SCI impairs the function of the upper extremity (UE), affecting the patient's level of independence and influencing the performance of activities of daily living and social participation.  
After an injury, rehabilitation treatment is approached from different areas and perspectives. Moreover, in the case of the pediatric population, aspects such as adherence and attention during therapeutic sessions are fundamental when analyzing the results of treatment. To increase engagement and quality of life in this population, therapeutic interventions need to address all factors, including the underlying psychosocial aspects, instead of task and environment modification alone [2].  
Advances in Rehabilitation Robotics have introduced new and reliable technologies into the therapeutic process [3]. Clinical experimentation demonstrates that a patient's motivation is a key aspect of the successful implementation of neural rehabilitation therapies with robotic devices [4] and directly correlates to how fully a patient is engaged in the treatment. Another line of research attempts to integrate the motivation factor, including the \"social\" aspect, into robotic-based rehabilitation therapies [5]. An example would be the Inroboics Rehab Clinic solution, in which Robic (NAO robot, Aldebaran Robotics) provides guided training and social interaction with the patient. NAO robot has been successfully applied in cardiac rehabilitation in a pilot study [6], and the Inroboics Rehab Clinic platform has been previously applied to children with infantile cerebral palsy (CP) and obstetric brachial plexus palsy [7].  
However, although all these experiences have been positive, there is no evidence to date of studies that have attempted to quantify the possible improvements in the movement patterns of the UE due to robotic treatment. Movement patterns can be analyzed according to different biomechanical aspects and characteristics of motor control, with the smoothness of movement being one of the most interesting since this is a quality that is highly altered in the presence of neurological pathology [8; 9]. Smooth movement is defined as movement towards a target without deviations from its ideal trajectory [8]. Also, the analysis of the efficiency metric is of special interest from the pattern of the executed UE movement based on the evaluation of the trajectory length [10]. Both metrics of UE movement quality, smoothness and efficiency are computed from kinematic data from the hand and are known to be affected in the adult SCI population [9; 10] but have not been addressed in children.  
The present study is proposed in a pediatric population with SCI and is based on the initial hypothesis that the behavior in these metrics should be different depending on whether the patient suffers from paraplegia or tetraplegia. Therefore, the aim is to analyze the behavior of the smoothness and efficiency metrics after a treatment received with the Robic humanoid robot that proposes the UE training specifically designed in this research for the pediatric population.  
The rest of the paper is organized as follows:  
* Section 2 describes the methodology in relation to the design and implementation of the UE training by means of the Inroboics Rehab Clinic platform; the characteristics of the participants; the experimental protocol and the content of each experimental session; and the variables analyzed;
* Section 3 presents the results in relation to the variables described at baseline and at ending the UE training;
* Sections 4 and 5 included the discussion and conclusions of the study, respectively.