Donchin 1990.

Methods	Randomised, controlled, and intention‐to‐treat basis. No reports of concealed allocation and blinding.
Participants	Hospital employees reporting at least 3 annual episodes of LBP. Total of 142 hospital employees were assigned to: Calisthetics for the back (CAL) group, N = 46; Back school group, N = 46; Control group, N = 50; 48 men and 94 women, mean age 45 years in Calisthenics group, 48 years in Back school group, and 45 years in Control group. All who agreed took part in the study.
Interventions	Post‐ treatment Calisthenics exercise group: Subjects underwent 45 minutes exercise, bi‐weekly for 3 months. Flexion and pelvic tilt exercise, based on the Williams method, aimed at strengthening the abdominal muscles, expanding spinal forward flexion, and rectifying the general posture. Back school group: Subjects received four 90 minutes sessions during a 2‐week period plus a fifth session after 2 months. The physiotherapist taught proper body mechanics and exercises for back and abdominal muscles. Home exercise was encouraged for the subjects. Control group: No intervention.
Outcomes	Number of subjects with recurrent low‐back pain.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Adequate sequence generation?	Low risk	The subjects were allocated to the three groups by a systematic random sampling method.
Allocation concealment?	Unclear risk	Unclear.
Blinding? All outcomes	High risk	No blinding reported.
Incomplete outcome data addressed? All outcomes ‐ drop‐outs?	High risk	Not stated.
Incomplete outcome data addressed? All outcomes ‐ ITT analysis?	Low risk	ITT analysis was used.
Similarity of baseline characteristics?	High risk	Calisthenics group had more subjects with a more recent episode and more painful days before intervention.
Co‐interventions avoided or similar?	Low risk
Compliance acceptable?	Unclear risk	Not stated.
Timing of outcome assessments similar?	Low risk	Outcomes were assessed after 3 months of intervention and after an additional 6 months of follow‐up.