Low back pain (LBP) patients may have reduced hamstring extensibility. The Instrumented Straight Leg Raise (ISLR) has been proposed as an objective extensibility measure; however, appropriate quantification methods, and test-retest reliability, are lacking. The lumbar flexion-relaxation response (FRR) is abnormal in LBP patients. The hamstring FRR has been identified in asymptomatic participants, but has not been explored in LBP participants. The...