Task-specificity of bilateral anticipatory activation of the deep abdominal muscles in healthy and chronic low back pain populations

- TrA/IO activity is symmetrical and anticipatory for bilateral but not for unilateral limb movements.
- Anticipatory activation of TrA/IO is task-specific owing to the conditions of postural demands.
- Hamstring is delayed during shoulder flexion in CLBP suggesting a role in lumbopelvic control.

Study designCross-sectional study of lumbopelvic muscle activation during rapid limb movements in chronic low back pain (CLBP) patients and healthy controls.IntroductionControversy exists over whether bilateral anticipatory activation of the deep abdominal muscles represents a normal motor control strategy prior to all rapid limb movements, or if this is simply a task-specific strategy appropriate for only certain movement conditions.ObjectiveTo assess the onset timing of the transversus abdominis/internal oblique muscles (TrA/IO) during two rapid limb movement tasks with different postural demands - bilateral shoulder flexion in standing, unilateral hip extension in prone lying - as well as differences between CLBP and controls.MethodsTwelve CLBP and 13 controls performed the two tasks in response to an auditory cue. Surface EMG was acquired bilaterally from five muscles, including TrA/IO.ResultsIn both groups, 50% of bilateral shoulder flexion trials showed bilateral anticipatory TrA/IO activation. This was rare, however, in unilateral hip extension for which only the TrA/IO contralateral to the moving leg showed anticipatory activation. The only significant difference in lumbo-pelvic muscle onset timing between CLBP and controls was a delay in semitendinosus activation during bilateral shoulder flexion in standing.ConclusionOur data suggest that bilateral anticipatory TrA/IO activation is a task-specific motor control strategy, appropriate for only certain rapid limb movement conditions. Furthermore, the presence of altered semitendinosus onset timing in the CLBP group during bilateral shoulder flexion may be reflective of other possible lumbo-pelvic motor control alterations among this population.