Unraveling Back Pain Chronicity: an EMG and EEG Study

This study aims at examining the influence of both threat of experimentally induced pain and clinical low back pain (LBP) on trunk motor control on the one hand and brain activity related to movement preparation on the other hand. Therefore, 3 groups are studied: healthy controls, people with recurrent LBP, and people with chronic LBP. A comparison in electromyography (EMG) of the trunk muscles and electroencephalography (EEG) activity between the 3 groups will be made in 2 conditions: a control condition without experimental pain on 1 test day, and a fear condition with experimental pain on another test day. In both conditions a motor control task will be performed and muscle and brain activity will be measured during each motor control task.

It is hypothesised that motor control will be different between the 3 groups in both conditions, i.e. delayed trunk muscle onset in LBP groups compared with controls. With regards to the brain activity, it is expected that preparation for movement will also be delayed in the LBP groups. Furthermore, it is expected that the fear condition will entail differences in both EMG and EEG within each group.

March 2017 - April 2018. 30 healthy participants, 30 recurrent and 30 chronic LBP patients all aged 18-45 and of both genders were tested for 2 conditions on 2 separate days, i.e. a control condition (C) on 1 test day; a fear (F) condition consisting out of threat (T) and no threat trials (NT) on another test day. The order of test days was randomized.

1 block of 240 rapid arm movements (RAM) with the dominant arm was performed per condition, while electroencephalography (EEG) of the brain and surface electromyography (sEMG) of the Internal Oblique/Transversus Abdominis, External Oblique, Multifidus and Iliocostalis Lumborum pars Thoracis muscles were measured bilaterally. sEMG of the Anterior Deltoid muscle of the dominant arm was also measured. This RAM was used to induce an internal perturbation to the postural balance of subjects and is an often used task in the study of trunk motor control. Midway the RAM block, the participants got a short intermission of 90 seconds seated rest. Both conditions consisted of a warning cue (colored dot on a screen) followed by a go cue (arrow indicating either an upwards or downwards rapid arm movement) or a no-go cue ('STOP') and 12 seconds rest before the next trial. Harmless vibrotactile stimuli were always administered to the low back region during the appearance of the warning cue. During the C, a white warning cue was presented (safe cue), meaning that the RAM would never be accompanied by a painful electrocutaneous stimulus in that condition. During the F a safe (no threat) or a threatening warning cue could be presented (50-50%); in 25% of the trials after the threatening cue an electrocutaneous stimulus was given to the lower back region; the trials after the no threat cue were never accompanied with painful stimuli.

The intensity of the electrocutaneous stimulus was self-determined by participants through a staircase paradigm and was administered by a digitimer system.

At the beginning of each test day several questionnaires were also administered to control for psychological factors and physical activity, i.e. Central Sensitization Index (CSI), Hospital Anxiety and Depression Scale (HADS), Tampa Scale for Kinesiophobia (TSK), Pain Catastrophizing Scale (PCS), Pain Vigilance and Awareness Questionnaire (PVAQ), Roland-Morris Disability Questionnaire (RMDQ), International Physical Activity Questionnaire (IPAQ) and a general questionnaire regarding socio-demographic information and history of complaints. Furthermore, complaint specific questionnaires were also administered, but only for the clinical populations (RLBP and CLBP)

Statistical analysis will be performed to assess whether and to what extent both threat and LBP might influence motor control as measured with EMG during RAM. Furthermore, the effect of both on cortical movement preparation and somatosensory processing will also be assessed based on the EEG measurements.

Eligibility Criteria:
Healthy controls

Inclusion Criteria:

* Healthy adult subjects.

Exclusion Criteria:

* People with a history of pain or current pain
* severe pathologies
* traumata
* cardiorespiratory disorders
* neurological disorders
* vestibular disorders
* endocrinologic disorders
* psychiatric and cognitive disorders
* colour blindness
* sleeping disorders
* psychological disorders or major depressions
* major surgery to the spine or upper limbs
* clinically relevant malalignments and deformities
* malignancies
* substance abuse of alcohol or drugs
* consumption of analgesics without prescription 24 hours or with prescription two weeks before testing
* use of psychotropic medication
* extreme physical activities two days before testing
* professional athletes
* pregnant women or women \< 1 year postnatally

RLBP

Inclusion Criteria:

* People with non-specific recurrent LBP for at least 2 episodes last year. (1 episode = \>24h complaints; 2 episodes are separated by a painfree period of at least 1 month)

Exclusion Criteria:

* specific reason for LBP (e.g. herniation \<2y, fracture, rheumatic disease,...)
* severe pathologies
* traumata
* cardiorespiratory disorders
* neurological disorders
* vestibular disorders
* endocrinologic disorders
* psychiatric and cognitive disorders
* colour blindness
* sleeping disorders
* psychological disorders or major depressions
* major surgery to the spine or upper limbs
* clinically relevant malalignments and deformities
* malignancies
* substance abuse of alcohol or drugs
* consumption of analgesics without prescription 24 hours or with prescription two weeks before testing
* use of psychotropic medication
* extreme physical activities two days before testing
* professional athletes
* pregnant women or women \< 1 year postnatally

CLBP

Inclusion Criteria:

* People with non-specific chronic LBP for at least 3 days a week and this for at least 3 months on a row.

Exclusion Criteria:

* specific reason for LBP (e.g. herniation \<2y, fracture, rheumatic disease,...)
* severe pathologies
* traumata
* cardiorespiratory disorders
* neurological disorders
* vestibular disorders
* endocrinologic disorders
* psychiatric and cognitive disorders
* colour blindness
* sleeping disorders
* psychological disorders or major depressions
* major surgery to the spine or upper limbs
* clinically relevant malalignments and deformities
* malignancies
* substance abuse of alcohol or drugs
* consumption of analgesics without prescription 24 hours or with prescription two weeks before testing
* use of psychotropic medication
* extreme physical activities two days before testing
* professional athletes
* pregnant women or women \< 1 year postnatally