This proposed study will use a sample of convenience between the ages of 18 and 40.
Subjects who has low back pain more than 3 months or a recurrent pattern of low back pain
at least two episodes that interfered with activities of daily living and/or required
treatment will be recruited by flyers posted in 2 university physical therapy clinics, as
well as word of mouth from subjects and friends. Subjects without a history of low back
pain in lifetime will be also recruited to establish normative data. Subjects who are
interested in participation will undergo a screening process using inclusion-exclusion
criteria checklist and receive brief information regarding the study. If they meet all
inclusion criteria, the consent process will be performed.
All subjects will fill out the information sheet for demographic data. Subjects in CLBP
will undergo standardized movement system impairment examination and transverse abdominis
muscle thickness measurement, self-report questionnaires; pain, disability, quality of
life, and fear of movement) and functional tests (5-time sit to stand test, 2-minute step
test, functional reach test, prone trunk extension test and abdominal curl test). The
project manager responsible for organizing the data collection and blindness will arrange
the appointments with the subjects for 2 biomechanical data collection. For the subjects
who refuse to participate in biomechanical lab testing, they will proceed to 6-week
intervention.
In the first visit (pre-intervention visit#1), biomechanical data including motion and
clinical data, lumbar stability, and cortical excitability will be collected. The body
landmarks will be identified. These landmarks include 1) lumbar spinous process of
T12-S2, 2) lumbar erector spinae (ES) and multifidus (LM) (3 cm lateral to L3 spinous
process and 2 cm lateral to L3 spinous process, respectively), 3) bilateral lateral
epicondyle of femur, and 4) bilateral lateral malleolus. Spinous process of L1, S2,
bilateral lateral epicondyle of femur, and bilateral lateral malleolus will be used as
locations for motion tracking sensors, while ES and LM location will be used to place
surface electrode for cortical excitability measurement.
For motion and clinical observation data collection, subjects will be instructed to
perform 1) sustained positions including usual sitting, corrected position in sitting,
usual standing, corrected position in standing, as well as 2) functional movements
including active forward bend, stand to sit, sit to stand, walking for 30 seconds, stair
ascending, stair descending, and pick up a box from the floor. Then, the subjects will be
asked to perform clinical movement tests including active forward bend (waiter's bow),
standing with posterior tilt, single leg stance on left and right foot, single leg squat
on left and right leg, supine with right and left straight leg raise tests, supine with
right and left hip abduction with knee flexion tests, quadruped backward rock test, prone
with right and left knee flexion tests, prone with right and left hip internal/external
rotation tests, prone with right and left hip extension tests. 1-2 repetitions of
practice trial will be provided to familiarize with the movement. Each subject performs 2
sets of 3 consecutive repetitions of each functional movement and clinical movement test
in fixed order, while 2 assessors independently rate presence/absence of aberrant
movement. Thirty-second rest will be provided between movement tests (rest period can be
longer if necessary). Pain intensity, heart rate and rating of perceive exertion (RPE)
will be monitored after each test. Motion sensors will be removed.
After that, subjects will undergo lumbar stability test. Two electromagnetic tracking
sensors will be placed on T12 and S2 spinous processes, while one sensor will be attached
to hand-held dynamometer. Subjects will be asked to position in prone on the treatment
bed with both feet on the floor. A researcher will apply 10-kg compression force on L1 to
L5 spinous processes for 2 seconds. This 10-kg compression force is derived from the
pilot work in which the researchers plotted the graph between compression force in X-axis
and posteroanterior displacement in Y-axis. The graph demonstrated plateau (no
displacement even increasing in compression force) at approximately 10 kg. Then, subjects
will be asked to lift both legs away from the floor presumably activating LM, while the
researcher re-apply the same compression force on L1 to L5 again. Pain will be recorded
when applying compression force on each spinal level. Sensor displacement will be
collected to represent lumbar stability.
For cortical excitability measurement, the subjects will undergo corticospinal
excitability measurement using transcranial magnetic stimulation (TMS). The researcher
will use ES and LM landmarks for EMG electrode placement. Before placing surface EMG
electrodes, the skin will be lightly abraded using abrasive paper and cleaned using
cotton with alcohol to lower the skin impedance. Electrodes will be aligned parallel to
the muscle fibers. Then, Subjects seat comfortably in a reclined chair with both arms
supported. They will be asked to wear a swim cap used to identify stimulation areas for
ES and LM. The researcher uses TMS with single-pulse monophasic to stimulate each point
over pre-marked scalp sites on a 5 X 7 grid (0-5 cm lateral and from 5 cm anterior to 2
cm posterior to the vertex). Motor cortex stimulation is conducted during submaximal
muscle contractions (at 20% MVIC) via EMG visual feedback. Five stimuli will be delivered
at each point across the grid with 5-second interval between stimuli and 1-minute rest
after each point stimulation. Motor evoke potentials (MEPs) will be recorded. These MEPs
will be used to represent corticospinal excitability at baseline. After completion of
corticospinal excitability data collection. All electrodes will be removed, and marks on
the subject's skin will be erased.
The second visit (pre-intervention visit#2) will be scheduled 1-3 day apart from the
first visit (pre-intervention visit#1). Evidence demonstrates the retention of changes in
cortical excitability can last for 24 hours; thus, the second visit aims to wash out the
effects of TMS on corticospinal excitability from TMS measurement before receiving tDCS
or NMES. LM activation measurement at baseline will be collected. The subjects will be in
prone position on treatment table with thorax (T3 level) and pelvis (S2 level) securely
fastened to the bed. Then, ultrasound transducer will be placed at right L4-5 facet joint
by the researcher who is blinded to the group assignment. Right LM thickness at rest will
be recorded. After that, the subject will be asked to perform 2 repetitions of maximum
voluntary isometric contraction (MVIC) of back extension with rotation to the left to
activate right LM with 1-minute rest between repetitions. The researcher will measure
right LM thickness during MVIC for both repetitions. Subject will be asked to rate the
rating of perceived exertion (RPE) and take 5-minute rest to prevent muscle fatigue. The
neuromuscular electrical stimulation (NMES) electrodes will be placed to bilateral LM,
and the system will be set at interferential mode (6000 Hz, beat frequency 20-50 Hz,
scanning effect). Then, ultrasound transducer will be placed at right L4-5 facet joint by
the researcher. The NMES intensity will be set at maximal tolerance to presumably
activate most motor units available in the LM. The subject will be asked to perform 2
repetitions of MVIC simultaneously with the NMES.
After LM activation measurement, subjects will be randomly assigned into 3 groups (tDCS
priming with MCE group, NMES priming with MCE group, and MCE alone group). For the first
visit, we aim to determine the effects of tDCS and NMES against MCE. The subjects in tDCS
priming with MCE group will receive the tDCS using 5X7 cm electrodes in which anodal
electrode will be placed on M1 representing the back muscles (1 cm anterior and 4 cm
lateral to the vertex), while cathodal electrode will be placed on contralateral
supraorbital area. The intensity will be set at 2 mA with 10-second fade in/out. The
subject will be stimulated by tDCS for 20 minutes. The subjects in NMES priming with MCE
group will receive the NMES using interferential mode (6000 Hz, beat frequency 20-50 Hz,
scanning effect) on bilateral LM. The intensity will be set at the subject's maximum
tolerance. Stimulation will be set at 10 seconds on and 60 seconds off to minimize muscle
fatigue. The subjects in MCE group will receive MCE for 20 minutes. After that, all
subjects will undergo LM activation, lumbar stability and cortical excitability
measurements using the same protocol. These data will be used to determine the immediate
effects of tDCS and NMES against MCE (Objective 1 and 3). The researcher will make an
appointment with the subjects for 6-week intervention program.
The 6-week intervention program can start at any day based on the subject's preference
but should no longer than 1 week after baseline measurement. For 6-week intervention
program, the subjects in tDCS priming with MCE group will receive a 20-minute tDCS, while
the subjects in NMES priming with MCE group will receive a 20-minute NMES using the same
setting as previously mentioned, and the subjects in MCE alone group will receive a
20-minute sham tDCS by setting the intensity at zero mA. After 20 minutes, the subject
will receive MCE.
The subject will receive tDCS, sham-tDCS or NMES for 20 minutes followed by 20-minute
supervised MCE for every session. The subject is encouraged to perform the same exercise
as physical therapy session for 15 minutes once a day and keep record in the exercise
logbook. The subject will receive assigned intervention twice a week for 6 weeks. The
total number of interventions is 12 sessions. To increase the generalizability of the
study, the researchers will not fix the day of the week. The subjects can select any days
in the week that is suitable for them. However, we keep twice a week as the evidence
shows improvement in pain and disability. Subjects will be asked to fill out pain and
disability questionnaires, as well as undergo functional tests at week 2.
After completion of 6-week intervention program, the subjects will undergo biomechanical
data collection including motion, clinical observation, LM activation, lumbar stability,
and cortical excitability. Clinical outcomes including pain, disability, quality of life,
fear of movement, global rating of change, as well as patient's satisfaction will be also
collected. Functional tests will be performed after 6-week intervention as well. Baseline
and post 6-week data will be used to compare the effectiveness of 6-week intervention
program among tDCS priming with MCE, NMES priming with MCE, and MCE alone in patients
with CLBP (Objective 3). In addition, corticospinal excitability, LM activation, lumbar
stability, movement patterns, and clinical outcomes will be used to determine the
associations among parameters (Objective 4).