Hamstring strength and hip mobility associated with pain and disability in lumbar instability

Chronic low back pain (LBP) has been hypothesized to involve lumbar instability, yet the roles of hamstring strength and hip mobility remain underexplored. While earlier studies focused on hamstring tightness, this study examined how these factors are strongly associated with pain and disability in young adults with lumbar instability. A case-control study was conducted on 129 participants (67 symptomatic, 62 asymptomatic) aged 18-35 years. Hamstring strength was assessed using the NordBord dynamometer, while hip mobility was measured using a goniometer. Pain intensity and disability were evaluated using the Numeric Pain Rating Scale and Oswestry Disability Index. Hamstring strength showed a strong negative correlation with pain (r = -0.71, p < 0.001) and disability (r = -0.72, p < 0.001). Regression analysis confirmed hamstring strength and hip mobility as key correlates of LBP severity. Cutoff values were determined for hamstring strength (Female: 178.0 N; Male: 197.5 N), hip internal rotation (Female: 23°; Male: 18°), and hip extension (Female: 21°; Male: 19°). Hamstring strength and hip mobility are key correlates of pain and disability in young adults with clinically defined lumbar instability. Candidate thresholds showed apparent in-sample discrimination and should be interpreted as hypothesis-generating rather than diagnostic.