Sensory Stimulation Belt for Chronic Low Back Pain in Office Workers (LSS-BELT)

Phase III is a prospective, double-blind, sham-controlled randomized clinical trial designed to evaluate the clinical effectiveness and potential sensorimotor mechanisms of a wearable sensory stimulation belt in office workers with chronic nonspecific low back pain.

After eligibility screening and written informed consent, participants will undergo a baseline laboratory assessment. Baseline clinical assessments will include pain intensity, low back pain-related disability, work-related musculoskeletal discomfort, movement-control testing, tactile acuity, and pressure pain threshold.

Baseline mechanistic assessments will characterize corticospinal, cortical, postural, motor-unit, and lumbar multifidus function. Corticospinal excitability will be assessed using single-pulse transcranial magnetic stimulation (TMS), with motor-evoked potentials recorded from the lumbar multifidus and erector spinae muscles. Somatosensory cortical and postural responses will be assessed during unstable sitting using functional near-infrared spectroscopy (fNIRS) over the bilateral primary somatosensory cortex together with inertial measurement units (IMUs). Participants will also perform a repeated loaded forward-bending task while lumbar multifidus motor-unit behavior is recorded using decomposition electromyography (dEMG) and trunk movement is recorded using IMUs. Lumbar multifidus morphology and contractile response will be assessed using rehabilitative ultrasound imaging (RUSI) at rest and during contralateral arm lifting.

Following completion of the baseline assessment, participants will be randomly allocated in a 1:1 ratio to an active sensory stimulation belt group or a sham belt group using a computer-generated block randomization sequence. Allocation will be concealed using sequentially numbered, opaque, sealed envelopes prepared by a research assistant who is not involved in outcome assessment.

Participants assigned to the active intervention group will receive a sensory stimulation belt programmed with the lumbar vibration parameters identified during the preceding Phase II parameter-optimization study. Participants assigned to the sham group will receive a belt designed to have similar appearance, weight, sound, and user interface. The sham belt will provide only a brief, low-level surface vibration at the beginning of use and will subsequently cease active stimulation so that it does not provide the intended sustained sensory stimulation.

Participants and outcome assessors will be blinded to group allocation. Device programming and allocation management will be performed by research personnel who are not involved in clinical or mechanistic outcome assessment.

Participants will be instructed to wear their assigned belt during their usual office working hours for at least 4 hours per day, 5 days per week, for 4 consecutive weeks. Participants may continue their usual occupational activities while wearing the belt.

Throughout the 4-week intervention period, participants will complete a daily study logbook documenting belt-wear duration, number of wear sessions, pain intensity before and after belt use, local discomfort or skin reactions, technical or device-related problems, and reasons for missed use when applicable. A member of the research team will conduct weekly follow-up to review adherence, identify technical problems, reinforce study procedures, and document adverse events.

At the end of the 4-week intervention, participants will return to the laboratory for post-intervention assessments using procedures comparable to the baseline assessment. Clinical assessments will include pain intensity, low back pain-related disability, work-related musculoskeletal discomfort, movement-control testing, tactile acuity, and pressure pain threshold. Mechanistic assessments will include corticospinal excitability using TMS, somatosensory cortical and postural responses during unstable sitting using fNIRS and IMUs, lumbar multifidus motor-unit behavior during loaded forward bending using dEMG, and lumbar multifidus contractile response using RUSI.

The primary efficacy analysis will compare changes in clinical outcomes between the active and sham groups over the 4-week intervention period. Linear mixed-effects models will be used to evaluate group, time, and group-by-time interaction effects for continuous outcomes. Repeated daily pain or discomfort measurements will also be evaluated using mixed-effects models. The frequency of pain or discomfort episodes may be analyzed using Poisson or negative-binomial regression, depending on the distribution of the data.

The primary analysis will follow the intention-to-treat principle. A complementary per-protocol analysis will be performed for participants who complete at least 75% of the prescribed belt use. Treatment effects will be reported with 95% confidence intervals.

Safety, adherence, comfort, usability, and device-related problems will be monitored throughout the intervention. Belt use will be discontinued if a participant requests discontinuation, develops clinically important symptom aggravation, experiences a significant adverse event, or develops a device-related problem that makes continued use inappropriate.