Differentiating temporal electromyographic waveforms between those with chronic low back pain and healthy controls

Objectives. Temporal activation patterns from abdominal and lumbar muscles were compared between healthy control subjects and those with chronic low back pain. Study design. A cross-sectional comparative study. Background. Synergist and antagonist coactivity has been considered an important neuromuscular control strategy to maintain spinal stability. Differences in onset times and amplitudes have been reported from trunk muscle EMG recordings between healthy subjects and those with low back pain;however, evaluating temporal EMG waveforms should demonstrate whether differences exist in the ability of those with and those without low back pain to respond to changing perturbations. Methods. The Karhunen-Loève expansion was applied to the ensemble-average EMG profiles recorded from four abdominal and three trunk extensor muscle sites while subjects performed a leg-lifting task aimed at challenging lumbar spine stability. The principal patterns were derived and the weighting coefficients for each pattern were the main dependent variables in a series of two-factor (group and muscle) mixed ANOVA models. Results. Three principal patterns explained 96% of the variance in the temporal EMG profiles. The ANOVAs revealed statistically significant group and muscle main effects (P<0.05) for the principal pattern and significant group by muscle interactions (P<0.05) for patterns two and three. Post hoc analysis showed that patterns were not different among all muscle sites for the healthy controls, but differences were significant for the low back pain group. Conclusions. The healthy group coactivated all seven sites with the same temporal pattern of activation. The low back pain group used different activation patterns indicative of a lack of synergistic coactivitation among the muscle sites examined.