Penttinen 2002.

Methods	RCT
Participants	93 participants. 1. Back School group n = 47. 2. Fitness training n = 46. Inclusion criteria: age between 35 and 50 years, non‐specific back pain (excluded if an exact diagnosis was present), gradual development of back pain lasting at least 1 month at the time of selection, no medical problems preventing physical training, and full consent to participate in the Back School. Exclusion criteria: not described.
Interventions	1. Back School group: 21 sessions (8 supervised and 13 voluntary group meetings) of 85 minutes each over 10 weeks. Swedish type of Back School including fitness training (muscle force, endurance, and stretching exercises for upper and lower back, trunk flexors, upper arm and leg muscles, and ergonomic work techniques), group discussions (structure, functioning and strain of the back, lifting, principles of physical exercises during leisure time and at work), and extra meetings consisting of physical training and social intercourse. 2. Fitness training: 10 sessions of 1 hour each over 5 weeks.
Outcomes	1. Disability: Oswestry Disability Questionnaire.
Notes	Occupational setting. Funding: N/A.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	The sequence generation procedure or the method of allocation were not mentioned. The title and abstract indicate that it is an RCT.
Allocation concealment (selection bias)	Unclear risk	The sequence generation procedure or the method of allocation were not mentioned. The title and abstract indicate that it is an RCT.
Blinding of participants and personnel (performance bias) All outcomes	High risk	No mention of any attempts to blind the participants
Blinding (performance bias and detection bias) All outcomes	High risk	No mention of any attempts to blind the care providers
Blinding of outcome assessment (detection bias) All outcomes	High risk	No mention of any attempts to blind the assessors
Incomplete outcome data (attrition bias) All outcomes	High risk	Dropouts exceeded 20%.
Intention‐to‐treat Analysis	Unclear risk	Not mentioned
Selective reporting (reporting bias)	Unclear risk	It was unclear if the published report included all expected outcomes.
Similarity of baseline characteristics?	Low risk	Based on Table 1, participants did not differ in baseline characteristics.
Co‐interventions avoided or similar?	Unclear risk	There were few reported co‐interventions in the study.
Compliance acceptable?	Unclear risk	There are insufficient data about the control group.
Timing outcome assessments similar?	Low risk	All important outcomes assessments for both groups were measured at the same time.