Comparison of EMG Activity during Trunk Forward Bending with and without Limited Lumbar Flexion Angle

Background: Several studies have evaluated the relationship of low back pain with lumbar flexion angle and muscle activity. However, there are scant studies on the relationship between the ratio of normalized muscle activities and lumbar flexion angle. The lumbar flexion angle has been used to diagnose low back pain and to determine the predominantly used muscles during trunk forward bending in asymptomatic individuals. Prolonged sitting is associated with a slumped or upright sitting posture, which can affect the soft tissues in the lumbar region. Objectives: The purpose of this study was to determine the predominantly used muscles during forward bending, holding, and re-extension based on EMG data. Methods: In total, 20 participants were screened for inclusion. The activities of the longissimus [ES (T12)], erector spinae [ES (L3)], gluteus maximus, and hamstring muscles were examined during forward bending, holding the posture, and re-extension. The mean lumbar flexion angle was used to categorize the patients. Patients with a short hamstring length during forward bending were excluded. Results: The ES (T12) and gluteus maximus : hamstring, and ES (L3) : hamstring activity ratios were compared between the groups during the three phases. The data were normalized to calculate the percent reference voluntary contraction (%RVC). The gluteus maximus : hamstring and ES (L3) : hamstring ratios during re-extension were significantly different between the groups. Conclusions: In the experimental group, the participants showed greater activation of the hamstrings than the gluteus maximus and erector spinae during re-extension. Future studies should include a larger sample size and use more precise eligibility criteria.