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Table 1 Detailed description of measures

From: Cohort profile: why do people keep hurting their back?

Measure Description Units/range
Demographic, health & function
Age, height, weight, sex Self-reported age, height, weight and sex Years, cm, kg, male/female
BMI Weight (kg) divided by the squared height (cm) Numerical
Co-morbidities Self-selected disease(s)/condition(s) other than LBP from a list (including “other”) Yes/no, type
Previous LBP Self-reported previous incidence(s) of LBP not including the current (study entry) episode Yes/no
Health care/medication usage Self-reported health care and medication frequency of use and type for LBP Yes/no, frequency, type
Low-Back Outcome Scale (LBOS [17], measured in LBP only) Questionnaire: evaluates pain and physical function. Consists of 13 differently weighted items that assess current pain, function (e.g., employment, domestic chores and sport activities), and the frequency of use of medical treatments/consultations and analgesics with respect to the respondent’s LBP 0–75: ↑score = ↑function, 0–29 = poor, 30–49 = fair, 50–64 = good, ≥ 65 = excellent
Psychological
Centre for Epidemiological Studies of Depression Scale (CES-D [18]) Questionnaire: evaluates depressive symptoms. Consists of 20 items. Respondents’ rate how often over the past week they experienced symptoms associated with depression using a four-point Likert scale ranging from 0 (“rarely or none of the time”) to 3 (“most or all of the time”) 0–60: ↑score = ↑depressive symptoms, > 15 = clinically significant depressive symptoms
Pain catastrophizing scale (PCS [19]) Questionnaire: evaluates thoughts and feelings related to pain suggestive of catastrophic cognitions. Consists of 13 items. Responses to questions are quantified on a five-point Likert scale ranging from 0 (“not at all”) to 4 (“all the time”) with respect to how often the respondent experiences certain thoughts and feelings when in pain. Yields a total score as well as three subscale scores of magnification (“I become afraid that the pain will get worse”: 3 items), rumination (“I worry all the time whether the pain will end”: 4 items) and helplessness (“I feel I can't go on”: 6 items) 0–52: ↑score = ↑pain catastrophizing
Subscales: magnification (0–12), rumination (0–16) helplessness (0–24)
Fear-Avoidance Beliefs Questionnaire (FABQ [20], measured in LBP only) Questionnaire: evaluates fearful and avoidant behaviours. Consists of 16 items in which participants’ rate their agreement with each statement on a seven-point Likert scale ranging from 0 (“completely disagree”) to 7 (“completely agree”). Two subscales measure the agreement of statements related to physical activity (FABQ-PA: 4 items) and work (FABQ-W: 7 items) 0–96: ↑score = fear-avoidance beliefs
Subscales: FABQ-PA (0–24), FABQ-W (0–42)
Pain Self-Efficacy Questionnaire (PSEQ [21], measured in LBP only) Questionnaire: evaluates the confidence individuals have in performing activities while in pain. Consists of 10 items. Respondents’ rate how confidently they can perform a range of activities using a seven-point Likert scale 0–60: ↑score = ↑self-efficacy beliefs
Social
Marital status Self-selected marital status (e.g., never/currently married, separated, cohabitating, etc.) from a list Type
Education level Self-selected education level (e.g., school certificate, bachelor/postgraduate degree, etc.) from a list Type
Employment status Self-selected employment status (e.g., full-time/full duties, part-time, unemployed, etc.) from a list Type
Type of work Self-selected primary occupation (e.g., professional, technician, clerk, etc.) in the last 12 months from a list Type
Job satisfaction Self-reported job satisfaction using a seven-point NRS ranging from “extremely dissatisfied” to “extremely satisfied” 0–6: ↑score = ↑job satisfaction
Job Content Questionnaire (JCQ [22]) Questionnaire: evaluates psychosocial demands resulting from the respondent’s job. Consists of 27 items re-grouped into several dimensions. Responses to each item are quantified on a four-point Likert scale from 1 (“totally disagree”) to 4 (“totally agree”) Job skill discretion (12–48, ↑score = ↑discretion), job decision-making authority (12–48, ↑score = ↑authority), job demands (12–48, ↑score = ↑demands), job decision latitude (24–96, ↑score = ↑latitude), co-worker support (4–16, ↑score = ↑support), supervisor support (4–16, ↑score = ↑support), job insecurity (3–12, ↑score = ↑insecurity)
Sick days over last 12 months Self-reported number of sick-days taken from work over the previous 12 months Numerical
Reason(s) for not working Self-selected reason(s) for not working for pay (e.g., caring for family, studies/training, ill health, etc.) from a list Yes/no, type
Sickness benefits Self-reported sickness benefits associated or not associated with the participants’ LBP Yes/no, for LBP/other
Impending compensation Self-reported impending compensation associated with the participants’ LBP Yes/no
Biological
Systemic inflammation Laboratory measure: Serum concentrations of TNF, IL-6, IL-1β and CRP. Venous blood was drawn, clotted (30 min, room temperature), and serum was separated by centrifugation (2500 rpm, 15 min) before storing at − 80 °C. Concentrations of each biomarker were determined in duplicate using “high sensitive” (assay sensitivity: CRP = 0.022 ng/ml, IL-6 = 0.110 pg/ml, IL-1β = 0.14 pg/ml, TNF = 0.191 pg/ml) enzyme-linked immunosorbent assays (ELISA, R&D Systems, Minneapolis, MN). Zero was allocated for values below the reported sensitivity of the test [14, 16] TNF (pg/ml), IL-6 (pg/ml), IL-1β (pg/ml), CRP (ng/ml)
Pain processing Laboratory measure: Pain thresholds to pressure (PPT), heat (HPT) and cold (CPT) were assessed at the back (LBP – site of most pain on palpation; control – fixed site ~ 5 cm rostral [toward the head] and lateral to the center of the lumbo-sacral junction divided randomly between the left and right side) and either the thumb nail bed (PPT) or proximal volar aspect of the forearm (HPT and CPT) [12, 15]. CPM was assessed based on our previous work [23] that validated the use of PPT as a test stimulus (TS) and noxious contact heat as the conditioning stimulus (CS). TS and CS were applied to the lower back or forearm. CPM was measured on three occasions (separated by a 15-min break) using different anatomical locations and stimuli (TS/CS) arrangements as reported previously [12, 15]. The CPM response was calculated as the difference between the TS scores obtained before and during the CS. A higher TS score during the CS than baseline indicated pain inhibition (expressed as a positive value). A lower TS score during the CS than baseline indicated pain facilitation (negative value) PPT (kPa, ↑score = ↑pain threshold), HPT (°C, ↑score = ↑pain threshold), CPT (°C, ↑score = ↓pain threshold), CPM (kPa, > 0 = pain inhibition, < 0 = pain facilitation)
Multifidus muscle morphology Laboratory measure: Multifidus muscle cross sectional area was measured at the level of each spinous process between the first lumbar (L1) and first sacral (S1) vertebra on both sides of the body (totalling 12 images) using a high resolution ultrasound system (LOGIC 9; GE Company, Milwaukee, WI), with a linear array 10 MHz transducer [24] Cross-sectional area (cm2)
Trunk muscle coordination Laboratory measure: Latency of response of superficial trunk muscle activity to unloading was assessed using an established paradigm [25]. Participants sat in a semi-sitting position with their pelvis fixed and a cable attached either behind or in front of their trunk via a harness. On instruction, participants pulled against the cable with a force of 12.5% of their body weight using visual feedback (target on a computer screen). The cable was released at an unpredictable time for 10 repetitions in each direction and the response of 12 abdominal and back muscles were recorded with surface EMG electrodes using placement described previously Muscle activity (EMG)
Trunk mechanical properties Laboratory measure: Effective trunk stiffness, mass and damping was estimated following trunk perturbation with the trunk modeled as a linear second-order system [26]. Participants sat in a frame with equal weights (7.5% body weight) attached to the front and back of the trunk via pulleys such that the masses were balanced and the trunk could move freely with minimal muscle activity. The trunk was perturbed by the unexpected release of one of the weights. The task was repeated 10 times in each direction with the order of directions randomised. Trunk kinematics and cable force were used to estimate system properties Mass (kg), stiffness (N/m), damping (Ns/m)
Trunk postural control Laboratory measure: Dynamic trunk control was assessed with participants balancing on a seat with a curved base placed on a force plate to record centre of pressure (CoP) [27]. Participants performed three 30-s trials (separated by a 1 min rest period) with eyes open, eyes closed and with feedback of the seat position in the anteroposterior direction (target on a computer screen). In an additional trial, participants were perturbed by release, at an unexpected time, of a weight (3% body weight) attached behind the trunk. Feedback was provided until the perturbation. Participants were instructed to regain balance as fast as possible three times under four conditions: eyes open, eyes closed, feedback (as above), and feedback up until perturbation induced by release of the weight. Coordinates of CoP were recorded as well as trunk muscle activity (as for trunk muscle coordination) and kinematics using a motion capture system Balance (CoP), muscle activity (EMG), kinematics (degrees)
Standing postural control Laboratory measure: Postural control was measured with participants standing barefoot and blindfolded on a force plate for 75 s. To test the effect of disruption of proprioception at the calf and lower back, the task was repeated with vibrators (~ 60 Hz, 1 mm amplitude) attached bilaterally over the Achilles tendon and lumbar paraspinal muscles [28], separately, in random order. Vibrators were switched on for 15 s at ~ 15 s after the start of the trial. Coordinates of CoP were recorded Balance (CoP)
Lumbopelvic motion Laboratory measure: Angular measures of limb movement and lumbopelvic motion were calculated across time during active/passive knee flexion and active/passive hip rotation (both lateral and medial) in prone using a motion capture system [29] Kinematics (degrees)
Lumbopelvic control during gait Laboratory measure: Lumbopelvic/trunk kinematics and trunk muscle activity (EMG) was assessed during 3 min of treadmill walking at 3 km/h and 5 km/h [30, 31] Muscle activity (EMG), kinematics (degrees)
Behavioural
Pittsburgh Sleep Quality Index (PSQI [32]) Questionnaire: evaluates sleep duration and quality. Consists of 19 items that cover seven dimensions, including subjective sleep quality, sleep duration and latency (time it takes to fall asleep), and the frequency and severity of specific sleep-related complaints in the previous month. Scores from each dimension (range: 0–3) are individually reported as component scores and summed to derive a sleep quality maximum score 0–21: ↑score = ↓sleep quality, > 5 = poor sleeper
Component scores (all 0–3): duration of sleep, sleep disturbance, sleep latency, day dysfunction due to sleepiness, sleep efficacy, overall sleep quality, sleep medications
Sleep hours per night (h)
International Physical Activity Questionnaire (IPAQ [33]) Questionnaire: evaluates health-related physical activity. Consists of seven items that assess four domains of physical activity over the previous week, including vigorous activity (activities that make breathing much harder than normal), moderate activity (activities that make breathing somewhat harder than normal), walking and time spent sitting ↑score = ↑physical activity (refer to scoring manual for calculating and interpreting MET scores and activity categories)
Alcohol Use Disorders Identification Test (AUDIT [34]) Questionnaire: evaluates alcohol consumption, dependence and drinking-related problems. Consists of 8 items (i.e., shortened version of the full 10-item AUDIT) that address four areas: alcohol consumption (quantity and frequency), drinking behaviour and dependence, alcohol related psychological effects and alcohol related problems. Responses to each item are quantified on a five-point Likert scale from 0 to 4 0–32: ↑score = ↑level of alcohol problem
Past/current smoking status Self-reported past and current smoking history Yes/no, duration, quantity
Fortnightly (for 12 months)
Pain Self-reported pain intensity over the last week using an 11-point NRS ranging from “none” to “worst imaginable” 0–10: ↑score = ↑pain
Roland Morris Disability Questionnaire (RMDQ [35]) Questionnaire: evaluates disability caused by LBP. Involves 28 items (i.e., extended version of the standard 24-item RMDQ) associated with physical functions likely to be affected by LBP. An item receives a score of 1 if it is applicable to the respondent or a score of 0 if it is not 0–28: ↑score = ↑disability
12-month LBP trajectory Questionnaire: evaluates the trajectory of LBP symptoms over 12 months from study commencement. Consists of a series of questions (asked at 12 months) that address how the respondent’s current LBP compares with their LBP at the start of the study, the frequency and duration at which the responder experienced periods without pain, periods of recurrence/persistence, and/or periods of markedly worse symptoms, based on their 12-month recall. In addition, respondents are asked to classify their LBP experience into one of seven trajectories using visual and word descriptions Yes/no, duration, frequency, trajectory type
  1. TNF tumor necrosis factor, IL-6 interleukin-6, IL-1β interleukin-1β, CRP C-reactive protein, PPT pressure pain threshold, CPT cold pain threshold, HPT heat pain threshold, CPM conditioned pain modulation, TS test stimulus, CS conditioning stimulus, EMG electromyography, CoP centre of pressure