Bellido‐Fernandez 2018.

Study characteristics
Methods	Study design: RCT (NCT02721914) Setting: Spain, healthcare Exercise groups: 2 Comparison groups: 1
Participants	Number of participants: 27 (E1 = 9, E2 = 9, C1 = 9) Chronic LBP duration: Not specified (not specified) Neurological/radicular symptoms: Not specified Mean age (years): 29 Sex (female): 85%
Interventions	Exercise Group 1 (E1): Combined abdominal hypopressive gymnastics and massage therapy: abdominal hypopressive gymnastics are static postural exercises that aim to strengthen the abdominal girdle and stabilise the spine; type = core strengthening; duration = 5 weeks; dose = low; design = standardised; delivery = individual; additional intervention = manual therapy Exercise Group 2 (E2): Abdominal hypopressive gymnastics alone, static postural exercises that aim to strengthen the abdominal girdle and stabilise the spine; type = core strengthening; duration = 5 weeks; dose = low; design = standardised; delivery = individual; additional intervention = none Comparison Group 1 (C1): Other conservative treatment (manual therapy)
Outcomes	Core outcomes reported: Pain (Numerical Rating Scale); function (Oswestry Disability Index); HRQoL (12‐Item Short Form Survey (Spanish)) Follow‐up time periods available for syntheses: 5 weeks (short)
Notes	Conflicts of interest: None to declare Funding source: Not reported Other: None
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Simple random sampling, "drawing from a hat"
Allocation concealment (selection bias)	Low risk	Treatment allocation was concealed, as patients directly selected their random assignment from an opaque container.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	1. Patients could not be blinded to the intervention due to the nature of the difference interventions (massage versus exercise); 2. Both groups getting sufficient treatment, unlikely to be dissatisfied; experimental hard to access outside of study.
Blinding of care provider (performance bias)	Low risk	1. Care provider could not be blinded because a single physiotherapist performed the treatments for all intervention groups; 2. Explicit set of exercises in protocol
Blinding of outcome assessment (detection bias) All outcomes	High risk	1. Outcome assessors for pain intensity and disability were the patients themselves, who could not be blinded to intervention due to the nature of the interventions; 2. Pain and functional questionnaires are subjective, and responses could be altered by awareness of intervention; 3. Likely that massage group was perceived as more effective because it was more direct.
Incomplete outcome data (attrition bias) All outcomes	Low risk	1. None of the patients dropped out of the study; all who were randomised were analysed.
Participants analysed in group allocated (attrition bias)	Low risk	1. "The effectiveness of the three applied interventions was examined by the intention‐to‐treat method".
Selective reporting (reporting bias)	Low risk	1. No linked protocol or statistic analysis plan found: within this publication all outcomes and analyses were fully reported; no obvious lapses.
Groups similar at baseline (selection bias)	Low risk	Groups were relatively similar at baseline for age, sex, function and pain intensity; did not report baseline duration of symptoms.
Co‐interventions avoided or similar (performance bias)	Low risk	One of the exclusion criteria was being under pharmacological treatment (co‐intervention), though it did not specify whether this treatment had to be directly for low back pain.
Compliance acceptable in all groups (performance bias)	Low risk	No direct reporting of compliance, though there seemed to be implication that attendance to treatment sessions was 100%.
Timing of outcome assessment similar in all groups (detection bias)	Low risk	1. All participants were assessed on pain intensity and function identically, regardless of treatment group assignment; 2. Numeric rating scale (for pain) and Oswestry Disability Index (for function) are well‐validated tools in the low back pain context.
Other bias	Low risk	Appeared free from other sources of bias