A Combined Lifestyle Intervention Delivered by Physio/exercise Therapists for Patients with Persistent Low Back Pain and Overweight or Obesity

The activPAL is a small non-invasive electronic logger designed to quantify free-living daily activities. The activPAL measures physical activity and sedentary behaviour through measuring accelerations and posture of the thigh.

The RMDQ is a reliable tool to measure the impact of LBP on physical functioning. It is a 24-item self-report questionnaire about how low back pain affects functional activities. Each question is worth one point, therefore scores can range from 0 (no disability) to 24 (severe disability).

The NPRS is a 11-point scale consisting of integers from 0 to 10; 0 representing "no pain" and 10 represents "worst possible pain".

Weight will be objectively measured via a standardized procedure using the same scale throughout the study. Weight status will be classified using Body Mass Index by dividing body weight (kg) by height (m²).

The PSQI 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 summed to derive a sleep quality score, higher scores indicate worse sleep quality.

The FFQ is an adapted version of the Dietary Instrument for Nutrition Education. It consists of 20 food items and has a reference period of one month.

The process evaluation will study the implementation and mechanism of impact of the intervention. Both participants and physio/exercise therapists will be asked to fill in questionnaires at baseline, 6 and 24 months. A selection of participants will be invited to join a focus group and a selection of physio/exercise therapists will be invited for a semi-structured interview about their experiences during the intervention.

Three times, one vacutainer (7ml blood) will be extracted using venipuncture and serum will be stored at -80 degrees Celcius untill all data has been collected. Serum inflammatory concentrations (TNF-alpha, hsCRP) will be measured using highly sensitive ELLA by an experience laboratory technician. The choice of inflammatory markers may change before analyses due to new insights.

The EuroQol 5 Dimension 5 Level (EQ-5D-5L) is a self-report survey that measures a participants' health state across 5 domains: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. Each dimension is scored on a 5-level severity ranking that ranges from "no problems" through "extreme problems". The participants' health states will be converted into utility values using the Dutch tariff, after which Quality Adjusted Life Years (QALYs) will be calculated by multiplying the participants spent in a certain health state by the respective utility value (45). In addition, each subject will rate their own perceived health status on a visual analogue scale (VAS) of 0 to 100.

Costs will be measured from a societal and a healthcare perspective. From the societal perspective, costs will include the cost of the intervention, other healthcare use (i.e., primary, secondary, and medication), informal care, sports memberships and equipment, as well as the cost of productivity losses from paid (i.e. absenteeism and presenteeism) and unpaid work. From the healthcare perspective, only costs accruing to the formal Dutch healthcare sector will be included. Intervention costs will be micro-costed, meaning that detailed data will be collected regarding the number of resources used and their respective unit prices. For this, data will be gathered from questionnaires filled in by participating physio/exercise therapists. Information on all other kinds of resource use will be collected using cost questionnaires. These questionnaires are based on the various iMTA questionnaires but tailored to the specific patient population and intervention under study.

Each point on the scale indicates a different level of improvement; 1 representing "very much improved", 2 representing "much improved", 3 representing "minimally improved", 4 representing "no change", 5 representing "minimally worse", 6 representing "much worse" and 7 represent "very much worse". Participants will be asked to rate their overall status since the start of the study. The participants' responses to the GPE will be dichotomized into "Recovered" (1 and 2), and "Not Recovered" (3, 4, 5, 6, and 7).

The B-IPQ is a tool used to evaluate cognitive and emotional representations of illness. It is an 8-item questionnaire where each item is rated on a 0-10 scale, with higher scores indicating a more threatening perception of the illness. Total score can be between 0 and 80, higher scores indicate worse illness perception. Cut-off points for the B-IPQ total score as follows: <42 indicating low experienced threat, 42-49 indicating moderate experienced threat, and ≥50 indicating high experienced threat in patients.

The PSEQ is developed to assess the confidence people with ongoing pain have in performing activities while in pain. The PSEQ is applicable to all persisting pain presentations. The questionnaire consists of 10 questions scored between 0 (no confidence) and 6 (full confidence). Total score can be between 0 and 60, where a higher score indicates greater levels of confidence in dealing with pain.

The Tampa scale for kinesiophobia is a 17-item questionnaire which are scored between 1 (low fear of movement) and 4 (high fear of movement). Total score can be between 17 and 68. A score ≤37 is interpreted as absence of fear of movement, a score of >37 is interpreted as fear of movement.

Education will be considered as a fundamental indicator of socioeconomic status.