Altered trunk muscle recruitment in people with low back pain with upper limb movement at different speeds.

OBJECTIVE To compare trunk muscle coordination in people with and without low back pain with varying speeds of limb movement. STUDY DESIGN Abdominal and back extensor muscle activity in association with upper limb movement was compared among three speeds of movement and between people with and without low back pain. PARTICIPANTS Fourteen subjects with a history of recurrent low back pain and a group of age- and sex-matched control subjects. MEASURES The onsets of electromyographic activity of the trunk and limb muscles, frequency of trunk muscle responses, and angular velocity of arm movements. RESULTS Early activation of transversus abdominis (TrA) and obliquus internus abdominis (OI) occurred in the majority of trials, with movement at both the fast and intermediate speeds for the control group. In contrast, subjects with low back pain failed to recruit TrA or OI in advance of limb movement with fast movement, and no activity of the abdominal muscles was recorded in the majority of intermediate speed trials. There was no difference between groups for slow movement. CONCLUSION The results indicate that the mechanism of preparatory spinal control is altered in people with lower back pain for movement at a variety of speeds.