## 4 Discussion
### New Approaches to the Use of FES in UMN Diseases  
For the upper extremities, a new system was investigated for the use of FES with biofeedback [43] for 21 post-stroke patients with severe upper extremity impairment, over five weeks, with movement improved with a FES device. However, in a group comparison for moderate upper extremity impairment, no significant difference was found during three weeks of FES and conventional therapy, respectively [27]. Whereas in the research carried out by [PERSON] et al. [38] regarding the use of FES for chronic post-stroke and moderate or severe SCI, while the ARAT score improved for both groups, there was a better outcome in the ARAT score for post-stroke patients than for SCI survivors. The Berg Balance Scale, Time Up and Go, Functional Ambulation Category, 6-Minute Walk Test, 10-Meter Walk Test, Fugl-Meyer Assessment, Motricity Index and Action Research Arm Test were reported for functional assessment. For clinical assessment, the Modified Barthel Index, Rivermead Mobility Index and Stroke Impact Scale were used. Four studies spread over six months, two investigated the effects of FES for one session, and the other eight were carried out for three to eight weeks. The outcomes of the analyzed papers were very heterogeneous, although gait speed was reported in 6 for the lower extremity stimulation (11 out of 14 papers). Further research should focus on the length of the research in time and the homogeneity of the reported outcomes and assessment scales [44]. For post-stroke FES users, the pulse duration was from 250 us to 475 us. Four studies used 40 Hz as the primary frequency, whereas one reported 20 Hz, and another, frequencies of 30 Hz and 35 Hz. The intensity used varied from 20 mA to visible contraction. Although FES orthotic devices should not allow skin irritations or injuries, skin erythema was reported in some cases. Nevertheless, we must emphasize that FES should not produce skin injuries if the electrodes are applied without error following the manufacturers' indications and if FES is performed by medical personnel trained and experienced in electrical stimulation. Previous systematic reviews and meta-analyses were performed on post-stroke, spinal cord injury or MS patients and suggested that FES was better than other methods of electrical stimulation (for instance, neuromuscular electrical stimulation and transcranial direct current stimulation) for improving motor function of the upper extremities and the abilities to perform ADL in post-stroke patients and spinal cord injuries [26; 45]. However, with post-stroke patients, FES combined with cycling needs further research [46]. Although much information regarding the use of FES in UMN disorders suggests patient improvements in ADL and walking, new technologies or strategies of combined therapies are needed. Recent product development research depicts that FES uses necessary adjustments, such as closed-loop operation and real-time feedback, but also emphasizes the ease of access to these devices for UMN-disabled subjects [47]. Among the papers analyzed, only [PERSON] et al. [36] approaches FES from the point of view of quality of life improvement and cost-benefit analysis for MS patients in a retrospective study; results suggests that although the cost is increased, efficiency and quality of life of MS patients improve compared to standard care. However, information on the costs of FES therapy is not presented in the other reviewed papers, and it represents a major gap in the existing literature and research. Therefore, future studies should also consider cost-benefit analysis in their research.