Matching the outcomes to treatment targets of exercise for low back pain: does it make a difference? Results of secondary analyses from individual patient data of randomised controlled trials and pooling of results across trials in comparative meta-analyses

Published:August 04, 2022DOI:


      • Exercise has multiple proposed treatment targets. Few RCTs match their outcomes to these targets.
      • These analyses suggest that outcomes matched to exercise treatment targets may produce greater SMDs than outcomes that are not matched to exercise treatment targets
      • Composite outcomes may generate greater SMDs and less uncertain estimates



      To explore whether using a single matched or composite outcome might impact the results of previous randomised controlled trials (RCTs) testing exercise for non-specific low back pain (NSLBP). The first objective was to explore whether a single matched outcome generated a greater standardised mean differences (SMD) when compared to the original unmatched primary outcome SMD. The second objective was to explore whether a composite measure, comprised of matched outcomes, generated a greater SMD when compared to the original primary outcome SMD.


      We conducted exploratory secondary analyses of data.


      Seven RCTs were included, of which two were based in the USA (University research clinic, Veterans Affairs medical centre) and the UK (primary care clinics, nonmedical centres). One each were based in Norway (clinics), Brazil (primary care), and Japan (outpatient clinics).


      The first analysis comprised 1) five RCTs (n=1,033) that used an unmatched primary outcome but included (some) matched outcomes as secondary outcomes, and the second analysis comprised 2) four RCTs (n=864) that included multiple matched outcomes by developing composite outcomes.


      Exercise compared to no exercise.

      Main Outcome Measures

      The composite consisted of standardised averaged matched outcomes. All analyses replicated the RCTs’ primary outcome analyses.


      Of five RCTs, three had greater SMDs with matched outcomes (pooled effect SMD 0.30 (95% CI 0.04, 0.56), p=0.02) compared to an unmatched primary outcome (pooled effect SMD 0.19 (95% CI -0.03, 0.40) p=0.09). Of four composite outcome analyses, three RCTs had greater SMDs in the composite outcome (pooled effect SMD 0.28 (95%CI 0.05, 0.51) p=0.02) compared to the primary outcome (pooled effect SMD 0.24 (95%CI -0.04, 0.53) p=0.10).


      These exploratory analyses suggest that using an outcome matched to exercise treatment targets in NSLBP RCTs may produce greater SMDs than an unmatched primary outcome. Composite outcomes could offer a meaningful way of investigating superiority of exercise than single domain outcomes.

      Key words

      List of abbreviations:

      NSLBP (non-specific low back pain), RCT (randomised controlled trial), SMD (standardised mean difference), ANOVA (analysis of variance), ANCOVA (analysis of covariance), WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index)
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