Study design: This was a cross sectional study measuring onsets of six trunk and hip muscles in subjects with back and leg pain (BLP) compared to healthy controls with and without an application of a pelvic belt.
Objective: To determine whether muscle activation was different when wearing a belt between control and BLP subjects during hip extension and flexion.
Background: Muscle activation of the trunk and gluteal muscles stabilize the spine in preparation for movement. In back pain delayed onset of oblique internus (OI) and multifidus indicates a deficient motor control. While several hypotheses have been suggested regarding the biomechanics of pelvic belts. Little is known about their effect on the temporal pattern of muscle activation.
Methods: 7 patients with BLP and 12 control subjects participated. Surface electromyography (sEMG) of six lumbo-pelvic muscles was recorded during hip flexion in standing and hip extension in the prone position. The onset of muscle activation was compared between groups and between the two belt conditions (without and with belt).
Results: None of the muscles consistently activated before beginning of movement. Subjects with BLP showed delayed onset times of oblique internus on the symptomatic side, compared with control subjects. Onset sEMG of the transverses abdominus and multifidus was significantly earlier in BLP when wearing the belt (P<.05). In the control group, no consistent differences were found between the muscle onsets with and without the belt (P >.05).
Isolated differences were noted in the other muscles.
Conclusion: In subjects without back pain a belt has no effect; but in patients with BLP wearing a belt may alter muscle activation patterns. It may reverse to a degree the abnormal activation pattern.
Clinical relevance: Assuming that delayed onset of transverse abdominus and multifidus leads to inefficient ability of muscles to stabilize the lumbar spine, wearing the belt contributes to stabilization during the tasks assessed. Knowledge of these differences in muscle activation patterns in patients with BLP when wearing the belt broadens the understanding of clinicians treating low back pain.
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