Prevalence of Spontaneous Electrical Activity at Trigger Spots and at Control Sites in Rabbit Skeletal Muscle

Abstract

Objective: To determine whether the spontaneous electrical activity observed in trigger spots of rabbit skeletal muscle is restricted only to trigger spots, and to compare that electrical activity to descriptions of potentials from neuromuscular junctions of rabbits from trigger points in human subjects. Methods: Fourteen paired examinations of trigger spots and control sites were performed on surgically exposed biceps femoris muscles in six anesthetized New Zealand Albino rabbits. Each examination involved 24 needle advances in three tracks [eight advances per track]. The trigger spot was identified as the location along a palpable taut band of muscle where snapping palpitation elicited the largest rabbit localized twitch response. The number of active loci [minute regions from which spontaneous potentials were recorded electromyographically] found in trigger spots was compared to the number of active loci found in control sites [where no taut band was identified by palpation]. Results: Spontaneous electrical activity was observed at 70 loci in trigger spots and at 15 loci in control sites [a significant difference, P < 0.01 using the Fischer exact test]. In addition to low-amplitude uninterrupted spontaneous electrical activity, the recordings occasionally showed high-amplitude intermittent spikes, as described by others. Conclusion: These results suggest that the observed spontaneous electrical activity has an important relation to the pathophysiology responsible for trigger-spot phenomena. The potentials observed at trigger spots appear to be the same in character as the potentials identified at neuromuscular junctions and at human trigger points. Active loci of trigger spots and control sites should be examined for pathophysiological differences.