Purpose This trial study the association between SBT subgroups and postural stability. It is theorized that cognitive impairment is more pronounced among patients in SBT group three compared to SBT group one and two. Therefore, it is hypothesized that challenging patients' balance will have a greater impact on the postural sway among patients in SBT group three compared to SBT group one and two in conditions where sensory information is reduced and cognitive load is increased.

Globally low back pain (LBP) and neck pain are the leading causes of disability (1). Consequently, improvements in the assessment and treatment of LBP can have an extensive impact. Patients with LBP constitute a heterogeneous group and to improve treatment there is much focus on identifying subgroups of patients and tailor treatment accordingly. An example of this is the STarT Back Tool (SBT) which has been translated to more than 20 languages and is probably the most used tool for subgrouping of patients with LBP. The SBT sub-groups patients into three groups with a progressing need for treatment. Patients in group one should be given information on LBP and advice to stay active, patients in group two are also recommended supplementary treatment in primary care, and in addition patients in group three need attention to psycho-social issues (2-3). Accordingly to the SBT, patient in group three should be treated with cognitive therapy by a physiotherapist undergoing special training. This training includes mentorship and professional support to enable physiotherapists to elicit and address complex issues in patients with psycho-social barriers to recovery. Subgrouping by SBT and thereby treating patients in group three with cognitive therapy has been found effective in improving their functional outcomes (4-5).

Patients with LBP have found to have different postural control strategies than patients without LBP especially during tasks involving increased task complexity (6-7). However, some studies have not found decreased postural control among patients whit LBP (8-9). Heterogeneous study populations may explain the discrepancy in findings especially if subgroups of patients with LBP have affected postural control while other subgroups are not affected.

Patients with pain often present with some degree of cognitive impairments which could limit the extent to which daily activities could be performed. This may be particularly present among SBT group three patients. Cognitive impairments have been associated with decreased function and consequently reduced balance in elderly, indicating that postural stability requires significant amount of cognitive resource. Since the cognitive resources are limited, if additional tasks compete for these resources, performance in one or more tasks can become affected. The conscious interpretation of (or attention towards) painful stimulations is a costly process that uses significant amount of the cognitive resources available which could impair physical performance. Consequently, this may lead to additional postural sway and thereby restricted balance.

After given written informed consent patients fill in a questionnaire including age, gender, educational level (bachelor, yes/no), employment, sick leave, co-morbidity (other than LBP, yes/no), pain duration (2-6 weeks/sub-acute or chronic), pain intensity (NPR), Roland Morris Disability Questionnaire (23 question, RMDQ), self-reported health status (EQ-5D visual analogue scale). After filling in the questionnaire patients will be asked to take of their jacket and shoes and to empty their pockets, before measuring height, weight, and testing for static balance.

Postural sway will be measured using a force plate (Metitur Good Balance System®). The force plate will be placed with a distance of 100 cm to a wall in front of the patient and with more than 100 cm of free space to the sides and behind the force plate. The force plate, an equilateral triangle (800 mm), had four strain gauge transducer signals converted by a three-channel DC amplifier and transformed to digital data (50 Hz) and subsequently filtered digitally, using a three-point median filter and IRR filter, with 20 Hz cut-off frequency. On the wall in front of the patient a 12 cm circular green plate will be place in the patients' eye level. Patients will be asked to stand with their feet as closed positioned as possible, without lifting their feet, and to focus on the green plate in front of them. Patients will be asked to replicate this position for each test. The static balance test will require that the subjects stand as quiet as possible during 35 seconds in 4 different conditions in the following order: (i) eyes open and easy counting, (ii) eyes closed and easy counting, (iii) eyes closed and counting in multiples of seven, and (iv) eyes closed and counting backward from 500 in multiples of seven.

The force platform, scale, and person altimeter will be calibrated every fortnight or more frequent. Data will be extracted, checked for any abnormal discrepancies, and saved on a secure driver frequently (at least every fortnight).

Inclusion Criteria:

• Low back pain for more than 14 days

Exclusion Criteria:

• Signs of serious pathology (e.g. signs of fracture, cauda equina syndrome, malignancy, osteoporosis, or spinal inflammatory arthritis)
• Blindness
• Dyslexia and not able to reply questionnaires unassisted
• Pregnancy
• Not able to walk unassisted

The data analysed will be available from the corresponding author on reasonable request.

Balance testing will be performed and data saved without the testers knowing the results. Afterwards the testers will ask patients to fill in questionnaires. An assessor (not participating in testing) will be cleaning the data and establishing the models without knowledge of the SBT score. The STarT Back score will be cleaned, saved in another data set and established by another assessor. When agreed upon the model, the two data sets will be merged.