This study aims to determine the optimal parameters of lumbar sensory stimulation in office workers with chronic nonspecific low back pain. Participants will attend two laboratory sessions. The first session will characterize baseline clinical and sensorimotor function using clinical assessments, transcranial magnetic stimulation, functional near-infrared spectroscopy during unstable sitting, inertial measurement units, decomposition electromyography, and rehabilitative ultrasound imaging. The second session will use a randomized within-participant crossover design in which participants receive eight combinations of lumbar vibration frequency, amplitude, and direction while bilateral primary somatosensory cortex hemodynamic responses are continuously measured using functional near-infrared spectroscopy. The primary objective is to identify vibration parameters that produce a favorable and consistent cortical response while meeting predefined comfort, safety, and technical criteria.
Office workers who currently sit for at least 6 hours per workday.
Age 20-60 years.
Chronic nonspecific low back pain for at least 3 months.
Current pain intensity of at least 2/10 on the Numeric Pain Rating Scale.
History of seizure for either the subject or any family member
Implanted pacemaker
Contraindications for TMS and fNIRS, including open wound, infection, lesions, arteriosclerosis, history of hemophilia, or demand-type pacemaker
Acute cerebral hemorrhage
Single group
Lumbar sensory stimulation
DeviceA customized vibration apparatus will deliver controlled mechanical stimulation over the bilateral lumbar multifidus region. Participants will receive eight randomized combinations of vibration frequency, amplitude, and direction. Each condition will be delivered for 1 minute, followed by a 5-minute passive rest period.
Change in oxygenated hemoglobin concentration in bilateral primary somatosensory cortex
Baseline-corrected change in oxygenated hemoglobin concentration (ΔHbO) recorded from the bilateral primary somatosensory cortex using an eight-channel functional near-infrared spectroscopy system during lumbar vibration.
Change in deoxygenated hemoglobin concentration in the bilateral primary somatosensory cortex
Deoxygenated hemoglobin concentration (ΔHHb) will be recorded from the bilateral primary somatosensory cortex using an eight-channel functional near-infrared spectroscopy (fNIRS) system. The outcome will be expressed as the baseline-corrected change in HHb during each lumbar vibration condition relative to the immediately preceding resting baseline
Change in total hemoglobin concentration in the bilateral primary somatosensory cortex
Total hemoglobin concentration (ΔHbT), calculated from oxygenated and deoxygenated hemoglobin signals, will be recorded from the bilateral primary somatosensory cortex using fNIRS. The outcome will be expressed as the baseline-corrected change in HbT during each lumbar vibration condition
Peak oxygenated hemoglobin response in the bilateral primary somatosensory cortex
The maximum baseline-corrected increase in oxygenated hemoglobin concentration (peak ΔHbO) within the predefined response window will be determined for each vibration condition. Left and right S1 responses may also be summarized separately and bilaterally
Area under the oxygenated hemoglobin response curve in the bilateral primary somatosensory cortex
The area under the curve (AUC) of the baseline-corrected oxygenated hemoglobin response will be calculated over the predefined response window for each vibration condition to quantify the magnitude and duration of the S1 hemodynamic response
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