Exploring hamstrings flexion-relaxation phenomenon in experimental low back pain

Abstract

BACKGROUND: Flexion-relaxation phenomenon in lumbar erector spinae muscles is a normal phenomenon which is notably altered in cases of low back pain; however the characteristics of this phenomenon in the hamstring muscles is not well understood. OBJECTIVE: To investigate if the hamstrings extension-relaxation ratio was affected by experimental low back pain. Participants: Nineteen healthy, pain-free volunteers with mean age (SD) = 28.7 (6.7) years participated in the study. METHODS: Surface electromyography was used to measure activity in the bilateral hamstring and lumbar erector spinae muscles before and after hypertonic-saline-induced experimental pain of the lumber erector spinae muscles during trunk flexion-extension tasks. Average muscle activity during each phase and extension-relaxation ratio values were analysed for each muscle group (lumbar erector spinae, biceps femoris, and medial hamstrings) using repeated measure ANOVAs. RESULTS: Although pain conditions affected biceps femoris activity in full trunk flexion (P < 0.001), and medial hamstrings activity in extension (P = 0.025), the hamstring extension-relaxation ratio was not affected significantly by the experimental pain. CONCLUSION: Low back pain does not seem to directly affect hamstrings extension-relaxation ratio in an experimental setting