Patients with chronic low back pain demonstrated poorer postural control of the lumbar spine and longer trunk muscle response times than healthy control volunteers. Correlation between these two phenomena suggests a common underlying pathology in the lumbar spine.

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Study Design: Observational case control design. Objectives: To examine muscle response to sudden trunk loading in athletes with and without a recent history of acute low back injury (LBI). Background: Impaired neuromuscular function is associated with chronic low back pain. This study examined whether such impairment persists after recovery from an acute LBI. Methods and Measures:Seventeen athletes who had a recent history of acute LBI and 17 matched healthy controls were tested. At the time of testing (mean = 56 days postinjury, range = 7-120 days postinjury), all athletes were symptom free and had returned to regular competition. Subjects performed isometric exertions in trunk flexion, extension, and left and right lateral bending against a trunk restraining cable. Upon reaching the target isometric force, the cable was released to impose sudden loading on the lumbar spine. Surface EMG signals from 12 major trunk muscles were recorded. The shut-off and switch-on latencies and number of muscles responding to sudden loading were compared between the 2 groups. Results: In all 4 testing directions, the athletes with a recent history of acute LBI shut off significantly fewer muscles and did so with delayed latency. On average, the injured subjects shut off 4.0 out of 6.0 (SD = 1.3) muscles compared to 4.6 out of 6.0 (SD = 1.3) muscles in the control group. The average muscle shut-off latency was 71 (SD = 31) milliseconds for the injured and 50 (SD = 21) milliseconds for the control subjects. No differences were found in number or latency of muscles switching on. Conclusions: These objective measures of neuromuscular function indicated an altered muscle response pattern to sudden trunk loading in athletes following their clinical recovery from a recent acute LBI.

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