Table 2.

Functional electrical stimulation (FES) of denervated muscles in humans

Reference	Purpose	Subjects	Protocol/Parameters used	Results/Conclusion
Albertin et al., 2018	To investigate how the skin was affected by electrical stimulation	Three human subjects with complete conus and cauda equina lesion.	The FES protocol, for first few months- 4 s stimulation duration with impulses of 150 ms and 2 s stimulation pause with impulse pause of 500 ms. The parameters are modified with the progress. The home-based FES (hb-FES) conducted for 2 yr.	Skin biopsies from both left and right thighs before and after about 2 yr of FES were analyzed. Four out of six biopsies found statistically significant increase in the epidermis. On an average, there was a 28% increase in the epidermis biopsies post the hb-FES.
Gargiulo et al., 2011	Using finite element analysis to determine structural changes in bone, muscle and tendon during FES treatment	Two males with conus cauda syndrome	Parameters as used in the European Project RISE (Kern et al., 2009): 0–4 mon 2–6 mon 4–12 mon 8–24 mon	Muscle restoration in the FES group was visible through segmentation and Finite Element Analysis (increasing from 42% to 58%); decrease in fat from 8% to 2% was also observed.
Kern et al., 2010	To determine the effectiveness of home-based FES training	Twenty-five patients with complete conus/cauda equina lesions	At the beginning of the treatment, biphasic stimulation impulses of very long duration (120– 150 ms, 60–75 ms per phase at high intensity (up to 80 V and 250 mA). Parameters modified every 12 wk for 2 yr (depending on patient’s improvement).	Increase in muscle cross sectional area of the quadriceps muscle by an average of 35%. An increase in the size of muscle fiber was observed; especially in vastus lateralis by an average of 75% from 16.6 ± 14.3 to 29.1 ± 23.3 µm; recovery of tetanic contractility of muscles observed.
Kern et al., 1999	To discuss the effects of FES after denervation	Patients ranged from 1–30 yr of denervation; the degeneration rate varied widely	Performed using non-invasive surface electrodes with gel or wet sponge conducting layer; Parameters were very specific for each individual; Pulse duration was varied more than 150 ms in individuals with severe degeneration and regulated down to 40 ms with the training progress.	The study proved that the restoration and functional use of denervated muscle is possible using FES therapy. Seven patients could regain active standing up, although it took up to 2 yr of training for the first standing up; other patients achieved different levels of progress in their muscles.