Dose-Response Effects of Transcutaneous Electrical Nerve Stimulation for Chronic Low Back Pain: A Systematic Review...

Transcutaneous electrical nerve stimulation (TENS) is a widely used non-pharmacological method for pain management, though its effectiveness in individuals with chronic low back pain (CLBP) is uncertain. Previous studies and systematic reviews have not systematically analysed the influence of TENS dosing parameters on treatment outcomes.

To assess the impact of TENS on pain relief in individuals with CLBP and to explore the dose-dependent effects of TENS parameters on pain relief.

A systematic review and meta-analysis was conducted following PROSPERO registration. Searches were performed in PubMed, Cochrane and Scopus databases. A total of 29 studies out of 1162 screened were included. Study quality was assessed using the PEDro scale and RoB-2 tool. Meta-analyses using random- and mixed-effects models were conducted.

The initial random-effects model showed no significant effect of TENS on pain (d₊ = 0.16, p > 0.050, k = 64) when dosing parameters were not considered. However, moderator analyses comparing TENS with control or placebo groups revealed that appropriate intensity was associated with larger effects than inappropriate intensity (Δd₊≈0.67; F(1, 16) = 7.27, p = 0.016), with subgroup estimates of d₊ = 0.97 (95% CI 0.65-1.30; k = 12) versus d₊ = 0.30 (95% CI -0.11 to 0.72; k = 6). Frequency, number of sessions and electrode placement showed no significant impact.

TENS can reduce pain in individuals with CLBP when delivered at a sensory-level intensity that is clearly perceptible and titrated throughout the session. Fixed intensity and stimulation strong enough to elicit muscle contractions are generally not recommended. These findings support the relevance of dosing in optimising TENS effectiveness. Overall, the certainty of evidence appears low due to the high risk of bias and substantial heterogeneity.

This meta-analysis provides a comprehensive synthesis of the evidence on transcutaneous electrical nerve stimulation (TENS) for pain relief in chronic low back pain (CLBP), with a specific focus on the role of stimulation parameters as sources of heterogeneity. By systematically examining dose-related characteristics, particularly stimulation intensity, this work helps clarify why previous reviews have reported inconsistent findings. The results suggest that inadequate dosing may obscure potential analgesic effects, highlighting the importance of parameter reporting and implementation when interpreting existing trials. Overall, this review offers a clinically and methodologically relevant framework to inform the design of future high-quality trials and to guide more nuanced evaluation of TENS within multimodal CLBP management.

PROSPERO: CRD42023468176.