The electromyographic activity of thoracic paraspinal muscles identified as abnormal with palpation.

Objective: The aim of this study was to compare the electromyographic (EMG) activity of deep muscles in the thoracic paravertebral gutter (PVG) detected as abnormal to palpation (AbPT) and reported as tender by the subject with muscles underlying nontender (NT), normal to palpation sites under various experimental conditions.

Methods: Twelve subjects (mean age, 25.42 years; range, 22-43 years) participated in this study. Fine-wire, bipolar intramuscular electrodes were inserted, under real-time ultrasonic guidance, into the deep paravertebral muscle mass underlying 1 AbPT and 2 NT sites (1 segment above and below the AbPT site) in the thoracic PVG regions. Electromyographic activity was recorded under the following conditions: resting prone, prone active trunk extension, application of pressure (300 kPa) to adjacent spinous processes, resting seated, passive and active seated trunk rotation, and supporting 2-kg weights in outstretched arms.

Results: Mean EMG activity was highest at the AbPT site, relative to NT sites, under all conditions, with a significant between-group effect of site (F2,31 = 4.13, P = .03) and large between-group effect size (eta2 = 0.21). There was also a trend for lower percentage change from baseline resting at the AbPT sites, relative to the NT sites, in response to the demand of other conditions. There were large variations in EMG activity within and between individuals, and large SDs accompanied the mean values of EMG activity in all cases.

Conclusion: Increased motor activity may be a contributing factor to tissue changes in the PVG detected with palpation. However, caution must be used when interpreting these results because of the large variations, small sample size, and issues associated with EMG normalization.