Neuromuscular electrical stimulation (NMES) is a technique that utilizes electrical current to produce muscle contractions for the purpose of restoring motor function in individuals that have muscle weakness or paralysis (Knutson et al., 2019). In stroke patients, NMES has been shown to improve motor function recovery, especially when delivered in a way that assists patients in performing a task (e.g. walking or completing ADLs) (Howlett et al., 2015; Knutson et al., 2019). When combined with functional task practice, NMES is thought to improve recovery by promoting adaptive neuroplasticity (Kimberly et al., 2004; Rushton, 2003; Shin et al., 2008; Knutson et al., 2019). NMES generates muscle contraction by creating an electrical field near motor axons of peripheral nerves, which depolarizes the axonal membranes, consequently stimulating action potentials leading to muscle contractions (Knutson et al., 2019). Importantly, the strength of the muscle contractions can be modulated by changing the frequency, amplitude and duration of the current pulses. NMES can be applied transcutaneously with surface electrodes positioned over the target muscle(s), percutaneously with intramuscular electrodes that are connected to an external simulator, or subcutaneously with an implanted simulator (Knutson et al., 2019). Although NMES can be applied subcutaneously, most therapeutic applications are intended to be temporary and therefore non-invasive.
Despite the efficacy of NMES in stroke rehabilitation and potential application to SCI very few studies have investigated the effects of NMES in SCI rehabilitation. The methodological details and results from three studies are presented in Table 12.