Effects of combined blood flow restriction and neuromuscular electrical stimulation on skeletal muscle hypertrophy in adults: a systematic review and meta analysis

Background: Traditional resistance training is often prescribed to stimulate skeletal muscle hypertrophy in adults, however voluntary mechanical movement is not possible for all individuals. The combination of blood flow restriction and neuromuscular electrical stimulation (C-BFR-NMES) has recently been shown to be a passive intervention to promote skeletal muscle hypertrophy in adults. However, due to various protocols being used in the literature, varying amounts of skeletal muscle hypertrophy have been reported. Purpose: The aim of this systematic review and meta-analysis was to quantitatively investigate the effectiveness of C-BFR-NMES compared to BFR or NMES alone, or no intervention to induce skeletal muscle mass in adults. The secondary aims were to compare muscle hypertrophy outcomes when different measurement devices are used following C-BFR-NMES, and to investigate the C-BFR-NMES protocols used to induce skeletal muscle hypertrophy in adults. Methods: A PRISMA-compliant systematic review and meta-analysis was conducted. PubMed, MEDLINE, Web of Science, Scopus and CINAHL were searched from inception to 28 ^{February 2025 using the following inclusion criteria: (1) untrained healthy adults (between the age of 18 – 64 years), (2) study design allowed comparison between C-BFR-NMES and CONTROL (BFR or NMES alone, or no intervention), (3) lower limb skeletal muscle hypertrophy was assessed pre/post intervention, (4) interventions included study periods ≥14 days , and (5) manuscripts written in English. A random-effects meta-analysis was performed and reported in standardised mean differences. Results: A total of 615 articles were screened, three studies with a total population of N = 37 were included, and seven meta-analyses were conducted. C-BFR-NMES induced significantly greater muscle hypertrophy compared to CONTROL (Z = 2.66, p = 0.008), with a medium pooled effect size (ES) of 0.61 (95% CI 0.11 to 1.6) in favour of C-BFR-NMES. Conclusion: A pooled analysis of current data suggests the C-BFR-NMES promotes a medium effect on skeletal muscle hypertrophy in lower body musculature compared to BFR or NMES alone, or no exercise in healthy adults. Further research is needed to determine the effectiveness of C-BFR-NMES in upper body musculature, as well as different cohorts such as adolescent and older populations.}