Table 5

Size and statistical significance of treatment–variable interactions (unadjusted and adjusted results) on continuous functional outcome (0–100) at follow-up closest to 3 months*

VariableUnadjustedAdjusted
StudiesParticipantsInteraction
MD (95% CI)
P valueStudiesParticipantsInteraction
MD (95% CI)
P value
Age (years)2529960.07 (−0.04 to 0.19)0.212529960.07 (−0.04 to 0.19)0.21
Sex253000252996
 Male
 Female−1.62 (−4.38 to 1.15)0.25−1.71 (−4.44 to 1.02)0.22
High school education101204101202
 High school or less
 Beyond high school−0.53 (−4.83 to 3.77)0.81−0.24 (−4.54 to 4.05)0.91
Current smoker9142091416
 No
 Yes0.16 (−3.99 to 4.30)0.94−0.36 (−4.52 to 3.80)0.87
Regular physical activity121758121756
 No
 Yes−0.96 (−4.59 to 2.67)0.60−0.75 (−4.38 to 2.89)0.69
BMI1519840.11 (−0.31 to 0.52)0.611519810.11 (−0.30 to 0.52)0.60
History of LBP88308830
 No
 Yes0.16 (−8.23 to 8.56)0.970.39 (−7.99 to 8.76)0.93
Sick leave (past 12 months)131451131448
 No
 Yes−0.35 (−6.65 to 5.94)0.91−0.03 (−6.24 to 6.17)0.99
Work status172321172319
 Unemployed
 Employed0.96 (−2.93 to 4.85)0.630.58 (−3.24 to 4.40)0.76
Heavy physical demands8139181389
 No
 Yes5.81 (0.73 to 10.88)0.0256.02 (1.00 to 11.04)0.019
General health (0–100)101337−0.06 (−0.25 to 0.14)0.56101334−0.06 (−0.25 to 0.14)0.56
Mental health (0–100)7956−0.03 (−0.20 to 0.15)0.757953−0.02 (−0.19 to 0.15)0.82
Fear avoidance beliefs (0–100)911100.09 (−0.003 to 0.18)0.059911090.09 (−0.002 to 0.18)0.054
Social support9138191380
 No
 Yes2.2 (−2.08 to 6.48)0.311.94 (−2.40 to 6.29)0.38
Episode duration (months)1315730.01 (−0.01 to 0.04)0.291315700.02 (−0.01 to 0.04)0.25
Functional limitations (0–100)253000−0.08 (−0.18 to 0.02)0.14252996−0.06 (−0.16 to 0.03)0.21
Pain intensity (0–100)2429230.03 (−0.04 to 0.10)0.382429190.03 (−0.04 to 0.10)0.36
Any leg pain151950151946
 No
 Yes0.86 (−3.21 to 4.94)0.680.54 (−3.53 to 4.61)0.80
Any LBP medication use131795131793
 No
 Yes−5.11 (−9.03 to 1.19)0.011−4.81 (−8.72 to 0.90)0.016
  • A negative interaction coefficient indicates decreased function for the variable level (eg, female) with exercise vs any non-exercise comparison (ie, all other conservative and no treatment/usual care comparisons.

  • *Unadjusted models include baseline functional limitations, potential treatment effect-modifying variable, treatment group (exercise or comparison treatment), and trial at the random-effects level and the variable–treatment group interaction at the fixed-effects level. Adjusted models add age and sex (at the random-effects level). All participant-level covariates are centred around their trial-specific means.

  • BMI, body mass index; LBP, low back pain; MD, mean difference.