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Neuromuscular Electrical Stimulation

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.

Table 12 Neuromuscular Electrical Stimulation Interventions

Author Year

Country

Research Design

Score

Total Sample Size

MethodsOutcome
Needham-Shrophire et al., 1997

USA

RCT

PEDro=8

NInitial=43; NFinal=32

Population: Age: 18-45 yr; Gender: males=31, females=3; Level of injury: tetraplegia; Mean time since injury: 3 yr.

Intervention: Subjects randomly assigned to one of three groups: Group 1 – received 8 wk of neuromuscular stimulation (NMS) assisted arm ergometry exercise; Group 2 – received 4 wk of NMS assisted exercise, then 4 wk of voluntary arm crank exercise; Group 3 (control group) – voluntary exercise for 8 wk without the application on NMS.

Outcome Measures: Manual muscle test.

1.     No significant difference was found at the four-week evaluation between Groups 1 and 2 (p=0.22) or between Groups 2 and 3 (p=0.07).

2.     Subjects in Group 1 had a higher proportion of muscles improving one or more muscle grades after four weeks of NMS cycling compared with Group 3 (p<0.003).

3.     Following the second four weeks of training, a significant difference was found between Groups 1 and 3 (p<0.0005) and between Groups 2 and 3 (p<0.03).

4.     No statistical difference was found between Groups 1 and 2 (p=0.15).

Klose et al., 1993

USA

RCT

PEDro=5

NInitial=31; NFinal=28

Population: Age: 18-35 yr; Gender: males=24, females=4; Level of injury: C5-C7; Time since injury: ≥1 yr.

Intervention: Both groups received 45 min of aggressive exercise therapy three times per week for 12 weeks along with 30 min of neuromuscular stimulation (NMS) to assist with upper extremity muscle strength. Experimental group also received 12 wk of 30 min EMG biofeedback 3x/wk.

Outcome Measures: Manual muscle test, Functional activities score.

1.     Scores after training indicated no significant differences for the muscle test score and functional activities score between groups.

2.     Analysis of the repeated measures factor showed a significant change for the manual muscle test and functional activities score (p<0.05).

Effect Sizes: Forest plot of standardized mean differences (SMD±95%C.I.) as calculated from pre- and post-intervention data.

Cameron et al., 1998

USA

Case Series

N=11

Population: Age: 18-45 yr; Gender: males=10, females=1; Level of injury: C4-C7; Time since injury: >1 yr.

Intervention: Testing of hybrid device, eight weeks of Neuromuscular Stimulation (NMS) assisted exercise with training sessions three times per week.

Outcome Measures: Manual muscle test.

1.     All subjects showed improvement in one or more of their manual muscle scores with the most dramatic occurring in the tricep muscle group (average increase 1.1±0.2 for L triceps, 0.7±0.1 for R).

2.     Results show NMS in combination with resistive exercise can be used safely and assists in the strengthening of voluntary contractions.

Discussion

Two out of the three studies presented demonstrated significant improvements in upper limb strength following NEMS rehabilitation therapy. Needham-Shophire et al. (1997) and Cameron et al. (1998) found that NEMS alone or in combination with exercise was effective for strengthening the upper limb in subjects with chronic SCI. However, Klose et al. (1993) found that exercise therapy combined with NEMS was no more effective than exercise alone. Despite promising evidence that NEMS may be an effective therapy for SCI, further clinical trials are necessary to truly determine efficacy.

Conclusion

There is level 1b evidence (from one randomized controlled trial; Needham-Shrophire et al., 1997) that neuromuscular stimulation-assisted exercise improves muscle strength over conventional therapy.

There is level 2 evidence (from one randomized control trials; Klose et al., 1993) that the addition of NEMS does not improve patient scores in rehabilitation more than physical exercise alone.

There is level 4 evidence (from one case series study; Cameron et al., 1998) that neuromuscular stimulation-assisted ergometry alone and in conjunction with voluntary arm crank exercise was an effective strengthening intervention for chronically injured individuals.

There is mixed evidence about the efficacy of NMES to improve muscle strength.