Dynamic relationships between lumbar lordosis, pelvic tilt, and abdominal muscle performance

Pelvic tilt, lumbar lordosis, and abdominal strength are variables frequently assessed in relationship to low back pain. Treatment aimed at reducing the degree of anterior pelvic tilt and concurrently reducing the depth of lumbar lordosis is often prescribed in an attempt to treat the pain and dysfunction. Existing clinical literature suggests that weakened abdominal musculature is a major contributor to excessive anterior pelvic tilt and increased lumbar lordosis. Despite the theoretical reasons for believing this relationship, there has been to date no research confirmation of this hypothesis. The purpose of this study was to examine both statically and dynamically the relationships between abdominal muscle performance, pelvic tilt, and lumbar lordosis. Measurements of abdominal muscle performance, pelvic tilt, and lumbar lordosis were obtained on 28 healthy female subjects aged 20-32. Abdominal muscle performance was measured using the double leg lowering test. Lumbar lordosis and pelvic tilt were measured using a television/computer system that obtained three-dimensional kinematic data at 20ms intervals. All measures were taken three or more times and were shown to be reliable (p <.001). Twenty subjects also assumed maximal anterior and posterior pelvic tilt postures to determine the effects on lumbar lordosis. Assuming a maximal anterior pelvic tilt posture changed the pelvic attitude by an average of 11.3° and increased the depth of lumbar lordosis by an average of 11.1° (p <.001). Assuming a maximal posterior pelvic tilt posture changed the pelvic attitude by an average of 8.8° and decreased the depth of lumbar lordosis by an average of 8.1° (p <.001). Correlations between abdominal muscle performance and pelvic tilt, and between abdominal muscle performance and lumbar lordosis, were not significant, either statically or during gait (p >.05). The results indicated that abdominal muscle performance did not appear to be directly related to either pelvic tilt or lumbar lordosis, measured either statically or dynamically. The results of this study indicate a need to reconsider clinical decision-making based on the assumed relationships between these variables.