## 4 Discussion  
The aim of the present work is to analyze, in a group of chronically spinal cord injured children, the smoothness and efficiency metrics after receiving UE training using the Robic humanoid robot as support. All our participants completed all the training sessions and maintained a sufficient level of attention during each of them to properly follow the robot's instructions under the supervision of the therapist. We designed the training program based on some facts: (a) the hand is the main tool for manipulating the human environment, and to perform this function, it requires an efficient system of direction and transport provided by the shoulder, elbow and wrist [22]; (b) the central nervous system acts in a predictive fashion because it has \"internal models\", neural processes that can predict the effect of the interaction between different parts of the body and between the body and the environment [23]; (c) the central nervous system control muscles not one by one but in groups, in a task-specific way known as muscle synergy [24]. So, although our proposed robotic training program did not include specific exercises for the hands, nor did it include tasks aimed at improving their motor precision, we nevertheless expected, on the basis of the above concepts, to find some effect on hand movements related more to precision than to strength. And indeed, we found a tendency to shorten the hand trajectory with a reduction in the number of pikes, our most interesting findings, both related to the quality of upper limb motor control. We did not expect to find changes in arm muscle strength (UEMS), but we also found no variations in Box and Block test performance attributable to the robotic platform intervention. The most plausible explanation could be that the intervention was of short duration (10 sessions) and of too low an intensity to produce noticeable changes in the selected muscle groups during the training period. Previous studies with children and adolescents with disabilities show increased strength, improved mental well-being and better overall function following the timing of strength training programs, which were carried out in the participants' homes three times a week for 6 weeks (a total of 18 prescribed sessions) [25]. Therefore, the significant differences found in muscle strength and trajectory between the tetraplegic and paraplegic groups are directly attributable to the spinal cord injury itself, all the more so when the selected participants had chronic lesions of several years' evolution and established sensorimotor impairments. There is considerable evidence that voluntary exercise training improves the fitness of people with acute and chronic SCI, although the magnitude of the effect depends on the level and severity of SCI and the characteristics of the exercise program itself [26; 27; 28; 29]. However, the level of endurance and work capacity in tetraplegies does not approach that of their paraplegic counterparts, with the level of SCI being the key determinant of the magnitude of improvement. In our case, it was the children with cervical spinal cord injuries who had the clearest benefits, most likely because the training protocol was not intense enough for those with paraplegia, as the program does not reach the minimum recommended level of activity--at least 30 min of moderate-intensity activity on 5 or more days per week, or at least 20 min of vigorous-intensity activity on 3 or more days per week [30]. Our data also show that even \"suboptimal\" activity patterns have beneficial effects on more precision-related motor tasks, such as those of the hands. In this sense, the findings in the length of the movement trajectory are particularly interesting. The movement execution using longer and more curved trajectories have been described in patients who suffer from sensory deafferentation in addition to motor loss, as is the case of spinal cord-injured patients [23].