Table 2: Risk of bias assessment of the included studies using the Cochrane Back Review Group risk of bias tool.

Author, year Bias Selection bias: Performance bias: Attrition bias: Reporting bias: Detection bias: Total: (max. 12)a Adequate random sequence generation Adequate allocation concealment Similar baseline characteristics Adequate participant blinding Adequate provider blinding Similar or no co-interventions Acceptable compliance Acceptable and described drop-out rate Inclusion of an intention-to-treat analysis No selective outcome reporting Adequate outcome assessor blinding Similar timing of outcome assessment Afonso et al., 2011 [42] Unclear Unclear No Unclear Unclear Unclear Unclear No No Yes Unclear Yes 2 Carson et al., 2009 [43] Yes Yes Yes Unclear Unclear Yes Yes Yes Yes Yes Yes Yes 10 Chattha et al., 2008 [44] Yes Unclear Yes No No Unclear Yes Yes No No Unclear Yes 5 Elavsky and McAuley, 2007 [45] Yes Unclear No Unclear Unclear Unclear Yes Yes No No Yes Yes 5 Joshi et al., 2011 [46] Yes Yes Yes Unclear Unclear Unclear Yes Yes No Yes Unclear Yes 7

aHigher scores indicate lower risk of bias.