Bramberg 2017.

Study characteristics
Methods	Randomized controlled parallel‐group trial.
Participants	159 participants with non‐disabling non‐specific LBP, with or without neck pain, of whom > 90% had chronic non‐specific LBP. Settings: university/medical school. Yoga classes held at a yoga studio. Country: Sweden. Recruitment: April to September 2010, 8 participants recruited from occupational health service units in Stockholm County, Sweden, in accordance with the original plan. However, due to the low influx of people with back and neck pain from the occupational health service, 302 participants were thereafter recruited by advertising in local media. Inclusion criteria: presence of non‐disabling, non‐specific LBP, with or without neck pain, and score ≥ 90 points on the Örebro Musculoskeletal Pain Screening Questionnaire (non‐disabling defined from the perspective of work disability). People were not on sick leave or on sick leave for < 8 weeks; aged 18–60 years and proficient in Swedish. Exclusion criteria: spinal pathology (e.g. tumors or spinal fractures), continuous ongoing sick listing ≥ 8 weeks, comorbidities that could affect the ability to fully participate in the study (e.g. physical disability, psychosis), existing weekly yoga practice or strength training and verified pregnancy.
Interventions	Yoga group: (n = 52) 2 × 60‐min standardized kundalini yoga group classes per week for 6 weeks, followed by encouragement to continue home practice at least twice per week for 12 months. Home practice: participants received a CD with instructions and written information, including drawings of each posture. At end of intervention, i.e. after 6 weeks, participants were encouraged to continue practicing yoga programs at least twice a week. Strength training: (n = 52) 5 × 60‐min supervised strength‐training sessions over 6 weeks, followed by encouragement to continue home practice. Home practice: of strength training program ≥ 2 times per week guided by written material and a follow‐up telephone call from physiotherapist 8 weeks after intervention. Advice: (n = 59) control group received a booklet (The Back Book) that contained evidence‐based advice on back pain, and a verbal recommendation to remain active. Common interventions: a minimal intervention comprising self‐care advice was given to all participants. Co‐interventions: no mention of included or excluded co‐interventions. Duration and follow‐up: interventions were provided for 6 weeks and follow‐up ended at 12 months.
Outcomes	Back‐specific disability subscale of the Swedish version of the Chronic Pain Grade Scale, calculated as the mean intensity and transformed into 0–100, reported at 6 months. Back pain subscale of the Swedish version of the Chronic Pain Grade Scale, calculated as the mean intensity and transformed into 0–100, reported at 6 months. Sickness absenteeism, reported as the mean number of days in past month that participants were absent from work due to illness. Other outcomes collected: sickness presenteeism, process outcomes (number of times exercised per week).
Notes	Adverse events: no discussion of safety or adverse events. Measurement of expectations or treatment preferences at baseline: none. Unpublished data: none. Funding: non‐profit. Funded by Swedish Research Council for Health, Working life and Welfare (2008‐0849). Clinical trials registration: NCT01653782. Note: LSW contacted the primary author in October 2019 to check the number of participants at each time point in Table 5 and received information by e‐mail on 5 November 2019.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "The study used a block randomization design. A random allocation sequence was generated by the statistician (JH)."
Allocation concealment (selection bias)	Low risk	Quote: "For each participant an opaque envelope was opened, in consecutive order, by an external research assistant not involved in the inclusion process."
Blinding of participants	High risk	Quote: "The participants did not know the content of the different intervention arms." Comment: although the participants did not initially know the content of the intervention groups, they were aware of their intervention after they were allocated to groups.
Blinding of personnel/providers	High risk	Quote: "The yoga leader and physiotherapist were not blinded."
Blinding of outcome assessors	High risk	Quote: "The research group assessing the study's outcome was blinded during the data collection and data analysis." Comment: although the researchers collecting the data may have been blinded, the participants reporting their subjective states were not blinded.
Incomplete outcome data (attrition bias) All outcomes	High risk	Quote: "Forty participants were lost to follow‐up, i.e. those who discontinued and the non‐responders (yoga 6 (11.5%); strength training 16 (30.7%); CG 18 (32.7%)) at the 12‐month follow‐up. The yoga group had a statistically significantly lower loss to follow‐up than the strength training and CG (Fisher's exact test = 0.017). Sixty percent of those lost to follow‐up were women, mean age was 42.0 years (SD 11.3), mean neck pain intensity was 45.0 (SD 25.3) and mean back pain intensity was 61.6 (SD 14.8). However, there were no significant differences between those who were lost to follow‐up and participants in terms of age, sex, or pre‐intervention values on neck and back pain." Comment: at all follow‐up points, participants were not followed up if they were not responders (Figure 1).
Selective reporting (reporting bias)	Unclear risk	Comment: primary outcome of sickness absence was described in ClinicalTrials.gov but the secondary outcomes of back and neck pain and disability were not mentioned in the trial registration. However, these are reasonable outcomes to measure for the condition and there is no positive evidence of selective reporting.
Group similarity at baseline	Low risk	Comment: groups appeared similar on all important factors.
Co‐interventions	Unclear risk	Comment: it does not appear that any co‐interventions were planned or prohibited and there is no reporting on co‐interventions used by participants, other than the minimal intervention of self‐care advice, which was given to all participants (page 3). There is no mention of medication or other treatments received among participants at baseline.
Compliance	Unclear risk	Quote: "The proportion of participants who adhered to the recommendations (exercised at least 2 times/week) during the 6 month follow‐up was: 54% (yoga), 34% (strength training) and 42% (CG)." Comment: 54% attended yoga but attendance rates for strength training was 34% and for non‐exercise control group was 42%.
ITT analysis	Low risk	Quote: "An intention‐to‐treat analysis was conducted which included all randomized individuals, irrespective of whether they had adhered to the intervention programme or not. Two conservative imputation analyses were performed on the primary outcome sickness absenteeism. In the first analysis, we used the relative frequencies of zeros and ones in each group to randomly generate zeroes and ones for the drop‐outs. In the second analysis we used "Last value carried forward." Both analyses generated similar results (data not presented) to those presented in the results section."
Timing of outcome assessments	Low risk	Comment: outcomes assessed at 6, 24, and 52 weeks for all groups (page 6).
Other bias	Low risk	No other biases identified.