Immediate Effects of TENS on Lumbar Erector Spinae Stiffness in Low Back Pain

Low back pain (LBP) is one of the most common musculoskeletal problems and often presents with increased paraspinal muscle activity and perceived stiffness around the lumbar region. Increased stiffness of the lumbar erector spinae may perpetuate pain and restrict movement. TENS provides afferent stimulation that can modulate pain through gate-control and descending inhibitory mechanisms and may secondarily reduce muscle tone. However, evidence about its acute influence on objective muscle stiffness parameters in LBP is limited. This single-center, parallel-group, randomized controlled trial will recruit adults with chronic or recurrent non-specific low back pain who meet the eligibility criteria. Participants will be randomly assigned (1:1) to (1) an experimental group receiving conventional TENS applied bilaterally over the lumbar paraspinal area for 20 minutes (frequency \~80-100 Hz, pulse width \~100-150 μs), or (2) a control group undergoing the same positioning and timing without active TENS. All assessments will be performed immediately before and immediately after the intervention by an outcome assessor blinded to group allocation. Primary outcomes are: (a) lumbar erector spinae muscle stiffness measured with a handheld myotonometer (e.g. Myoton) at standardized lumbar levels, and (b) pain intensity measured with a 10-cm visual analog scale (VAS). Secondary observations may include participant-reported comfort/tolerance of TENS and adverse events. The study is designed as a short-term physiological and symptomatic trial; no long-term follow-up is planned. Ethical approval was obtained from the Erzurum Technical University Ethics Committee (Meeting 13, Decision 04, 18.09.2025)