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.
Phase II is an experimental laboratory study designed to optimize the neurophysiological parameters of lumbar sensory stimulation in office workers with chronic nonspecific low back pain. The primary objective is to determine which combination of vibration frequency, amplitude, and direction produces the most favorable cortical response in the bilateral primary somatosensory cortex (S1), while meeting predefined safety, comfort, and technical criteria. Participants will complete two laboratory visits separated by approximately 48-72 hours. The two visits have different purposes and are not intended to constitute a pre- and post-intervention comparison. Visit 1: Baseline clinical and sensorimotor characterization During the first visit, participants will undergo clinical and neurophysiological assessments to characterize their baseline clinical and sensorimotor profiles. Clinical assessments will include pain intensity, low back pain-related disability, work-related musculoskeletal discomfort, movement-control testing, tactile acuity, and pressure pain threshold. 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 S1 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. Finally, lumbar multifidus morphology and contractile response will be assessed using rehabilitative ultrasound imaging (RUSI) at rest and during contralateral arm lifting. The measurements obtained during Visit 1 are intended to characterize individual baseline sensorimotor function and to permit exploratory analyses of associations between clinical characteristics, corticospinal excitability, cortical responses, postural control, motor-unit behavior, lumbar multifidus contractile response, and responses to lumbar sensory stimulation. These measurements are not intended to serve as pre-intervention values for an acute pre-post comparison with Visit 2. Visit 2: Randomized within-participant vibration-parameter optimization During the second visit, participants will undergo the vibration-fNIRS parameter-optimization experiment. Participants will lie prone in a relaxed position while an eight-channel fNIRS system records hemodynamic responses over the bilateral primary somatosensory cortex. A customized vibration apparatus will be positioned over the bilateral lumbar multifidus region. Each participant will receive all eight vibration conditions generated from a 2 × 2 × 2 factorial combination of two vibration frequencies, two vibration amplitudes, and two stimulation directions. The order of the eight conditions will be randomized by computer for each participant to minimize systematic order effects. Randomization therefore applies to the sequence of stimulation conditions within each participant rather than allocation of participants to separate study arms. Each vibration condition will be applied for 1 minute. A 5-minute passive rest period will be provided between successive vibration conditions to minimize fatigue and potential carryover effects and to allow the hemodynamic response to return toward baseline before the next condition. The primary neurophysiological outcome will be the baseline-corrected change in oxygenated hemoglobin concentration (ΔHbO) in the bilateral S1 measured using fNIRS during each vibration condition. Secondary fNIRS outcomes will include changes in deoxygenated hemoglobin and total hemoglobin concentrations, peak oxygenated hemoglobin response, time to peak response, and area under the oxygenated hemoglobin response curve. The effects of vibration frequency, amplitude, and direction, including their interactions, on the primary fNIRS outcome will be evaluated using a linear mixed-effects model with participant treated as a repeated or random effect. Condition order, testing period, baseline response, and preceding condition may be considered to evaluate potential sequence or carryover effects. The optimal vibration parameters will not be selected solely on the basis of the largest cortical response. Parameter selection will integrate the magnitude and consistency of the bilateral S1 hemodynamic response with predefined criteria related to participant comfort, biomechanical safety, technical stability and performance of the stimulation apparatus, and suitability for subsequent incorporation into a wearable sensory stimulation belt. The selected parameters will subsequently be used in the Phase III randomized controlled trial.
Study Type
INTERVENTIONAL
Allocation
NA
Purpose
OTHER
Masking
NONE
Enrollment
36
A 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.
Faculty of Physical Therapy, Mahidol University
Salaya, Changwat Nakhon Pathom, Thailand
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.
Time frame: During each 1-minute vibration condition relative to its corresponding pre-stimulation baseline during the single Phase II parameter-optimization session.
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
Time frame: During each vibration condition relative to the immediately preceding resting baseline during the Phase II parameter-optimization session
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
Time frame: During each vibration condition relative to the immediately preceding resting baseline during the Phase II parameter-optimization session
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
Time frame: During each vibration condition relative to the immediately preceding resting baseline during the Phase II parameter-optimization session
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
Time frame: During each vibration condition relative to the immediately preceding resting baseline during the Phase II parameter-optimization session
Corticospinal excitability of the lumbar multifidus measured by transcranial magnetic stimulation
Corticospinal excitability will be assessed using single-pulse transcranial magnetic stimulation with surface EMG recording from the lumbar multifidus.
Time frame: During Visit 1 of Phase II, prior to the vibration-parameter optimization session
Corticospinal excitability of the lumbar erector spinae measured by transcranial magnetic stimulation
Corticospinal excitability will be assessed using single-pulse transcranial magnetic stimulation with surface EMG recording from the lumbar erector spinae.
Time frame: During Visit 1 of Phase II, prior to the vibration-parameter optimization session
Change in oxygenated hemoglobin concentration during unstable sitting
Cortical hemodynamic responses over the bilateral primary somatosensory cortex will be recorded using fNIRS during unstable sitting with eyes open and eyes closed.
Time frame: During each sitting condition relative to the immediately preceding resting baseline in visit 1.
Postural-control response during unstable sitting
Postural-control behavior will be quantified during unstable sitting using inertial measurement units positioned at L1, S1, and the unstable chair.
Time frame: During each vibration condition relative to the immediately preceding resting baseline in visit 1
Lumbar multifidus motor-unit behavior during loaded forward bending
Motor-unit behavior of the bilateral lumbar multifidus will be assessed using decomposition electromyography during repeated 45° trunk flexion-extension while holding a load equivalent to 5% of body weight.
Time frame: During the loaded forward-bending assessment at baseline in Visit 1.
Lumbar multifidus contractile response measured by rehabilitative ultrasound imaging
Lumbar multifidus thickness will be measured at rest and during contralateral arm lifting using B-mode rehabilitative ultrasound imaging at the L4-L5 level.
Time frame: During the baseline assessment in Visit 1
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