Neuromuscular electrical stimulation combined with protein supplementation may improve muscle mass and strength: a scoping review of randomized controlled trials

Neuromuscular electrical stimulation (NMES) and protein supplementation are individually effective anabolic strategies. Their potential additive effects on muscle mass and strength remain unclear. This scoping review explored the effects of NMES combined to protein supplementation on muscle strength and mass. A literature search was conducted from November 1 to 15, 2025, using PubMed, Scopus, and Web of Science databases. Inclusion criteria were: (1) English full-text manuscripts; (2) adult participants (≥18 years); (3) clear NMES protocol description; and (4) clear protein supplementation source and dosage. Methodological quality was assessed using the 11-point PEDro scale. Ten studies (n = 333) were included, predominantly involving older adults with muscle wasting conditions such as sarcopenic obesity and limited mobility. Mean daily protein dosage was 38.9 ± 29.2 g, with whey protein as the primary source. Mean NMES pulse frequency and duration were 50 ± 30 Hz and 288 ± 52 µs, respectively. Muscle strength was assessed mainly through maximal isometric contraction tests, while muscle mass assessment methods varied considerably. Most studies were rated "fair" quality and indicated that combined NMES and protein supplementation may effectively improve muscle strength and mass. Combined protein supplementation and NMES may improve muscle mass and strength. However, further studies employing larger sample sizes, double-blind designs, adequate familiarization to strength tests, and reliable muscle mass assessment methods are required to enhance clinical application.