Participants enrolled into the intervention group receive specific sleep ergonomics guidance

Participants enrolled into the control group will receive general sleep ergonomics guidance

Participants receive a detailed instruction in sleep ergonomics. Participants are instructed to maintain either side lying or supine sleeping posture, depending on which is less painful. Neutral position of spine supported by specific placement of body pillow. Changing of posture during sleep is prevented. The participants are recommended to replace their mattress if they feel that it is too hard or too soft. Instruction is given by a physiotherapist during one personal therapy session and the participants also receive a printed instruction.

Low back pain reported with Visual Analog Scale (VAS) during rest, after getting up and during day; 0-100 mm scales, 0 mm = no pain, 100 mm = worst possible pain. Change from baseline to 12 month follow-up is reported in mm for each sub-scale (during rest, after getting up and during day).

Oswestry Disability Index Finnish version 2.0 total score (scale 0-100%): 0 = minimal disability, 100 = bed-bound or exaggeration of symptoms; and sub-scores (scale 0-5): 0 = minimal disability, 5 = worst disability. Change is reported for total ODI score and sub-scores from baseline to 12 month follow-up.

Perceived sufficiency of sleep based on question: "Do you feel that you have got sufficient sleep during last week?", reported with 5 step Likert scale (scale 1-5), 1 = not sufficient at all, 5 = totally sufficient. Change in perceived sufficiency of sleep is reported from baseline to 12 month follow-up.