## 4 Discussion
We assume that the data from the stimulating device acting on the biofeedback rule motivated the subjects to obtain regular and continuous therapy, which was an important factor contributing to therapy effectiveness. Few studies on the degeneration of motor fibers in the upper and lower extremities as a secondary change in the peripheral nervous system to spinal cord injury were reported. They provided evidence for abnormalities of the axonal type comparable to our study [7,10]. [PERSON] et al. showed, similar to our research, evidence for the inhibition of degenerative changes in axons [15]. However, their analysis was performed for the short-term observation period following high-frequency (100 Hz), stimulation with 0.4 ms stimulation pulses and 5 times 30-min sessions for one week. They did not provide the results of long-term observations. We used low-frequency stimulation, 39 Hz on average, and 17.5 ms pulses 5 times a week for 17 min sessions applied for 10 months, which, based on the methodological principles, seems safer because they were designed based on the current physiological and clinical status of the patients. We used a similar algorithm of electrostimulation to that recommended by [PERSON] et al., who achieved positive effects after chronic stimulation at frequencies of about 30 Hz and percentages of effective stimulation time below 50% were considered as safe [6]. Nevertheless, they claimed that more precise data drawn from large databases are necessary. Study participants were recruited between 4 and 12 months after injury. It is a well-known fact that, particularly in people with motor iSCI, substantial spontaneous neurological recovery occurs during this time [23]. The effectiveness of evidence-based motor rehabilitation methods, such as the presented electrotherapy, which support functional recovery in this period, should be further investigated and developed. One of our study's limitations is that the mechanisms underlying stimulus-induced recovery are not well understood, which makes future research focused on the topic an essential source of data. Another is the heterogeneity of the spinal cord damage in iSCI patients assessed with the ASIA scale, although we attempted to recruit subjects with rigorous enrolment rules. The improvements found in the neurophysiological parameters in the cohort under investigation cannot be associated exclusively with the applied therapy. Different severities of incomplete spinal cord injuries, individual responses to treatment, a different spontaneous regeneration course, and the other unknown factors may affect the final result. Perhaps needle electromyography studies might provide convincing data on the motor neuron degeneration stage; however, this diagnostic method is invasive. In some cases, our patients with severe atrophic changes would further lose punctured myocytes. Thus, we decided also to use the non-invasive sEMG having in mind our patients' comfort and their well-being. In our study, we attempted to position the stimulating electrodes for electrotherapeutic purposes directly over the anatomical passage of peroneal and tibial nerves, considering the location of stimulating electrodes in electroneuographical tests prior to stimulation. We believe that thanks to such an approach, we avoided stimulation of surrounding excitable structures. We are aware that having a non-treated identical control group (ideally submitted to a placebo-like intervention) in our study would broaden the scope of the functional regeneration mechanism from the view of basic neuroscience. On the other hand, it would be difficult for iSCI patients, who look for any improvement of their health status following applied electrostimulation, to understand the importance of the placebo approach in the project of which he or she should be informed in advance. Ethical and clinical responsibility does not allow for such a proposal for iSCI patients to verify our proposed therapeutic procedure with reference to the standard and the still limited available treatment methods.