Back and hip extensor activities during trunk flexion/extension: Effects of low back pain and rehabilitation

Objective: To compare lumbar paraspinal, gluteus maximus, and biceps femori s muscle function during sagittal trunk flexion and extension in patients w ith chronic low back pain and healthy control subjects, and to assess the i nfluence of rehabilitation in the back pain patients. Design: A cross-sectional study comparing chronic low back pain patients an d healthy controls, and a prospective follow-up in back pain patients durin g rehabilitation. Setting: Physical medicine and rehabilitation clinic. subjects: Nineteen wo men with chronic low back pain, and 19 women without pain (controls). Intervention: Five-week active outpatient rehabilitation (1 hour three time s a week) guided by a physiotherapist, followed by 5-week self-motivated ex ercise at home. Outcome Measures: Subjects performed sagittal trunk flexion and extension w hile surface electromyogram was bilaterally recorded of paraspinal (L1-L2 l evel), gluteus maximus, and biceps femoris muscles. The muscle activity was assessed from the average electromyogram and the relative muscle activatio n onsets and their duration were calculated. Results: During early flexion, lumbar paraspinal and biceps femoris were ac tivated simultaneously before gluteus maximus. At the end of flexion and du ring extension all investigated muscles were activated and relaxed in order . Lumbar paraspinal and biceps femoris muscles were activated in a similar order in low back pain patients and healthy controls during flexion and ext ension. However, the duration of gluteus maximus activity was shorter in th e back pain patients than in controls during the trunk flexion (p <.05), an d it ended earlier during extension. Active rehabilitation did not change t he muscle activities of lumbar paraspinal and biceps femoris in the back pa in patients, but in the measurements after rehabilitation the onset of glut eus maximus activity occurred later in flexion and earlier in extension. Conclusions: The activity of the gluteus maximus muscle during the flexion- extension cycle was reduced inpatients with chronic low back pain. The glut eal muscles should be taken into consideration in the rehabilitation of the se patients.