## 4 Discussion  
This study provides evidence of the positive effects of the application of functional electrical stimulation (FES) to nerves, with personalized and safe algorithm parameters based on the results of clinical neurophysiology tests in patients after iSCI. In general, the effect of peripheral axonal degeneration of motor fibers was significantly inhibited, which prevented degeneration of neuromuscular synapses at motor units of distal lower extremity muscles. Our findings also support the hypothesis that stimulation of peripheral nerves can modulate lumbar spinal cord excitability. The approach of stimulation of nerve fibers rather than muscle fibers seems to be more effective considering [PERSON]'s theory of neuromodulation (\"cells that fire together, wire together\") [20]. Such stimulation evokes long-term effects on the spinal locomotor centers, creating central pattern generators and supporting motor recovery in iSCI patients [21]. [PERSON]'s theory has been proven both in animal and human trials, which found that descending volleys and stimulation of afferent and efferent fibers peripherally induced the synaptic plasticity at the motor centers [22]. In our study, the stimulation of motor (in an orthodromic way) and sensory (in an antidromic way) nerve fibers was expected to evoke convergence and facilitation of sensory influences relayed from afferent fibers and increase the excitability of motoneurons transmitting impulses to effectors through a biofeedback mechanism. As a result, we recorded the increase in the amplitudes during sEMG recordings in T1, which expressed the improvement of muscle contractile properties in lower extremities; it possibly also correlated with the reinnervation of new muscles fibers. Moreover, the increase in the amplitude parameters in ENG recordings after stimulation of more peroneal than tibial nerves reflected the improvement of the transmission of the neural impulses. Many investigators have reported the beneficial effects of nerve stimulations in iSCI patients. However, in these studies, the best approach, timing, duration, and intensity of electotherapy parameters were not sufficiently described to repeat the tests. Electrostimulation protocols were not systematically documented, which limits meta-analyses and makes it impossible to replicate therapies with similar procedures [13]. Research that provided valuable evidence of the effectiveness of electrostimulation after injuries in animal trials [13; 16], in clinical conditions is still considered ineffective in humans [3; 6; 11]. Moreover, disputes about using the specific electrostimulation algorithm are mostly caused by the lack of individual adjustment of parameters to the current functional state of muscles activity and nerve impulse transmission in iSCI patients. In most cases, standard, fixed programs with pre-determined parameters are delivered with electrostimulation equipment. However, most of them do not consider the objective results from precise, sensor-based neurophysiological tests performed prior to and after treatment, such as in the presented study. With the description of the standardized list of parameters necessary to define the algorithm of electrostimulation, such an approach would be promising due to the possible optimization of the parameters' safety. It would also allow the results to be compared, not only before and after treatment, but also between different studies. According to our research methodology and the results, the principles of electrotherapy algorithms were based on physiological premises, and software-supervised, personalized electrostimulation within nerve motor fibers enabled effective therapy for iSCI patients. Thus, it also helps to maintain nerve impulse transmission function in the period during which spontaneous repair phenomena are occurring at the level of the damaged spinal cord.