Muscle mass (kg) will be measured by Bioelectrical Impedance Analysis (BIA)

Fat mass (kg) will be measured by Bioelectrical Impedance Analysis (BIA)

Total body water (l) will be measured by Bioelectrical Impedance Analysis (BIA)

Insulin sensitivity will be estimated using homeostasis model assessment index (HOMA)

Inflammation status will be assessed by measuring blood levels (mg/L) of c-reactive protein (CRP) and high-sensitivity c-reactive protein (hs-CRP)

Health-related quality of life will be assessed by using the standardized and validated EQ-5D-5L Questionnaire, consisting of 2 pages: the EQ-5D descriptive system and the EQ visual analogue scale (EQ VAS). The descriptive system comprises five dimensions: mobility, self-care, usual activities, pain/discomfort and anxiety/depression. Each dimension has 5 levels: no problems, slight problems, moderate problems, severe problems and extreme problems. The patient ticks the box next to the most appropriate statement in each dimension (scale: 1-5; lower value = better outcome). The digits for the 5 dimensions can be combined into a 5-digit number that describes the patient's health state.The EQ VAS records the patient's self-rated health on a vertical visual analogue scale (0-100, higher value = better outcome).

Pain scores will be assessed by using the standardized and validated Chronic Pain Grade Questionnaire (CPGQ). The CPGQ is a seven-item instrument to evaluate overall severity of chronic pain based on 2 dimensions: pain intensity and pain-related disability. The responses on the 7 items are used to compute scores for 3 subscales: pain intensity (0-100), disability score (0-3), and disability Points (0-3). Lower values indicate better outcomes.

moderately limiting intensity (Grade III), high disability and severely limiting intensity (Grade IV) (see Von Korff et al 1992).

Perceived stress will be assessed by using the standardized and validated Perceived Stress Questionnaire (PSQ). The PSQ comprises different components of stress (worries, tension, joy, demands), with 5 items each. It contains both positively and negatively formulated items in order to reduce acquiescent bias. Each item is answered using a four-point Likert-type scale, ranging from 1 to 4. Higher scores indicate more severe perceived stress.

Subjective work ability will be assessed by using the standardized and validated Work Ability Index Questionnaire (WAI). WAI obtains information related to diseases, functional limitations, sick leave, and mental resources. The questionnaire consistes of 7 items, including current work ability compared with the lifetime best (item 1, 0-10), work ability in relation to the demands of the job (item 2, 2-10), number of current disease groups diagnosed by a physician (item 3, 1-7), estimated work impairment due to diseases (item 4, 1-6), sick leave during the past year (item 5, 1-5), personal prognosis of work ability for 2 years from now (item 6, 1,4 or 7) and mental resources, referring to the workers life in general, both at work and during leisure time(item 7, 1-4). The total WAI score is calculated by summing up the scores of all items and is ranged from 7 to 49. The total WAI scores are categorized into 4 levels: poor (7-27), moderate (28-36), good (37-43), and excellent (44-49).