Comparisons of hamstring flexibility between individuals with and without low back pain: systematic review with meta-analysis

Background: There is no robust evidence on the contribution of reduced hamstring flexibility to the development of low back pain (LBP) in cohort studies. Purpose: To investigate whether individuals with LBP have impaired hamstring flexibility and stiffness and what measures have been used to compare hamstring flexibility and stiffness between individuals with and without LBP. Methods: A systematic literature search was undertaken in PubMed, EMBASE, MEDLINE, CINAHL, SCOPUS, and Cochrane databases from inception to April 2018. The GRADE system was used to determine the quality of evidence for each measure evaluated in meta-analysis. Results: Respectively, seventeen and two studies having acceptable methodological quality were analyzed with regard to hamstring flexibility and stiffness. Four measures were identified for hamstring flexibility and five for stiffness. Meta-analyses were undertaken in straight leg raising (SLR), sit and reach and knee extension in 90 degrees hip flexion for hamstring flexibility and for hamstring stiffness measures of stiffness at 50 degrees SLR and gradient of stiffness from 20 degrees to 50 degrees SLR (Me-grad). Significantly reduced hamstring flexibility or increased stiffness (P < .05) was detected in SLR, 90/90 knee extension and Me-grad. However, the validity of measures for hamstring flexibility was problematic and GRADE scores for all measures in the meta-analyses were very low. Conclusion: There have been four measures for hamstring flexibility and five for stiffness to evaluate individuals with and without LBP. It was impossible to conclude whether individuals with LBP have impaired hamstring flexibility and stiffness due to very low quality of evidence for meta-analyses.