Electromyographic characteristics of deep, thoracic paraspinal musculature

Introduction

Few researchers have examined the recruitment and activation patterns of deep, thoracic paraspinal muscles. Raw EMG signals from intra-muscular electrodes from different sites within the same muscle are highly variable in magnitude,¹ making direct comparison of raw, fine-wire EMG data from multiple thoracic sites invalid. To overcome this problem, EMG data should be normalised using maximal voluntary contraction (MVC), but the best method for eliciting MVC in deep, thoracic paraspinal muscles is unknown.

Design

Single cohort, repeated measures design.

Methods

Fine-wire, bi-polar intramuscular electrodes were inserted, under real-time ultrasonic guidance, into the deep paravertebral muscle mass underlying three adjacent sites in the thoracic PVG regions of 12 subjects (mean age=25.42 years, range=22–43). EMG activity was recorded under passive and active conditions. Two tasks, active prone extension and holding weights (2kg) in outstretched arms, were expected to elicit MVC.

Results

There were large variations in EMG activity within and between individuals. Peak amplitudes for individual sites were found under every condition, except resting prone. There was a significant difference between activity under the different conditions (F_3.1,102.3=0.04). The lowest mean EMG activity occurred during resting prone (0.11mV, SD=0.12), and the highest mean activity was recorded for passive rotation to the opposite side (0.51mV, SD=0.70). The mean amplitude for holding weights (0.42mV, SD=0.76) was higher than for active thoracic extension (0.34mV, SD=0.48), and there was a weak, inverse correlation (r=−0.23) between the mean values recorded from these tasks.

Conclusions

EMG activity from deep, thoracic paraspinal muscles was highly variable, and no single task elicited MVC from all sites. The highest EMG activity occurred during passive rotation to the opposite side, which may be related to the proposed role of these muscles as spinal stabilisers. Active extension and holding weights in outstretched arms appeared to activate the muscles in different ways. EMG values should be normalised to the peak amplitude of each site.

No full text is available. To read the body of this article, please view the PDF online.