Effects of Neuromuscular Electrical Stimulation on Muscle Weakness Among Older Populations with Non-neurological and Non-orthopedic Pathologies: A Systematic Review

Objective(s): Our primary objective was to compile evidence on the effects of neuromuscular electrical stimulation (NMES) or functional electrical stimulation (FES), or both, on parameters of muscle strength among middle age and older adults with or without systemic pathologies. Secondly, we aimed to determine commonly used NMES/FES stimulation parameters.

Data Sources: Electronic databases, including PubMed, Cochrane Library and Scopus were searched from year 2017 to 2023.

Study Selection: Studies were included if they 1) included middle-age or older adults (>45 years); 2) were randomized controlled trials (RCTs); 3) used NMES or FES as a training tool; 4) examined at least one outcome of muscle strength; 5) reported at least one NMES/FES stimulation parameter (frequency or duration or amplitude). Studies were excluded if they: 1) were not in English; 2) included adults with neurologic or orthopedic conditions.

Data Extraction: Two reviewers extracted the study design, demographics, intervention/control conditions, outcomes, and results. The quality of RCTs (risk of bias) was assessed using the PEDro scale.

Data Synthesis: 9 RCTs (PEDRo scores 5-9, fair-good) with a pooled sample of 335 participants aged 45-70 years were included. 2 out of 9 studies included adults undergoing hemodialysis, 3 studies included healthy older adults, others included adults with liver transplant, obstructive pulmonary disease, cancer, post-COVID-19. 4 studies compared the effect NMES/FES with standard care (e.g., resistance training), 4 studies compared different stimulation parameters of NMES/FES (e.g., frequency or muscle group), whereas 1 study compared with sham NMES/FES. 5 studies delivered NMES/FES for 12 weeks, others delivered for 4-8 weeks. Most assessed outcome was isometric muscle strength (8 studies), whereas other functional outcomes were 30-second chair stand and Timed Up and Go test (2 studies). 8 out of 9 studies showed greater improvements in outcomes of muscle strength with NMES/FES (most used frequency: 50 Hz) compared to control conditions. 1 study did not show group differences in outcomes between 50 Hz and 75 Hz frequencies. The stimulation parameters varied from 50-90Hz for frequency, 250-400 microseconds for duration, and 10-40 milliamperes for intensity, with quadriceps being the most targeted group (5 studies)

Conclusions: NMES/FES seems to be a more effective agent compared to standard care (e.g., resistance training) for improving muscle strength among middle-aged and older adults. Secondly, the included studies used a wide range of stimulation parameters without reporting scientific rationale for selection. There is a need to standardize stimulation parameters for inducing optimal NMES/FES effects.

Author(s) Disclosures: None