Feed-forward activation role in low back pain unclear
MedWire News: Exercise does not improve feed-forward activation of deep abdominal muscles in patients with low back pain (LBP), show findings from a randomized trial.
There were no improvements from baseline across three exercise regimens, including core stability exercises, which are thought to help restore control of trunk muscles in patients with LBP.
Although the findings "strongly indicate no clinically important short-term effects of exercises, the long-term effects and whether exercises are superior to natural recovery need further exploration," say Ottar Vasseljen (Norwegian University of Science and Technology, Trondheim) and team.
All 109 patients in the study were assigned to do supervised exercise, either core stability exercises, high-load stabilizing exercises in a sling, or general exercise (strengthening and stretching exercises).
There was no nonexercise control group; however, the team detected no changes from baseline in any of the exercise groups.
Feed-forward activation of deep abdominal muscles in response to rapid shoulder flexion (ie, activation of muscle in anticipation of upset balance), relative to activation of the anterior deltoid muscle, changed by an average of 0 ms across the groups during 8 weeks of exercise.
"Because deep trunk muscles contribute to stabilization of the spine, it is hypothesized that a deficit in feed-forward activation increases the susceptibility of injury to spinal structures," the researchers comment in Spine.
There were some changes, such as a 12.4 ms improvement in the sling exercise group in response to flexion of the dominant shoulder, and about a 7 ms reduction in activation time in the general exercise group in response to dominant shoulder flexion. But the overall pattern of changes implied regression to the mean, with the fastest baseline activation times slowing and the slowest speeding up.
Also, deep abdominal muscle activation times varied widely between patients. For example, the average baseline -8 ms activation time (relative to anterior deltoid) in the general exercise group had a standard deviation of 29 ms.
Finally, Vasseljen et al note that almost all patients in the study had activation times that met the criterion for feed-forward activation (-100 to +50 ms relative anterior deltoid), which rather contradicts the notion that delayed feed-forward activation is a problem in LBP patients.
They conclude: "It is possible that patients with higher pain and disability levels or clearly reduced onset latency at baseline may experience more favorable exercise effects than observed in this study."
By Eleanor McDermid