Electrophysiological Characteristics of Localized Twitch Responses in Responsive Taut Bands of Rabbit Skeletal Muscle Fibers

Abstract

Objective: This study was designed to investigate the electromyographic characteristics of the Rabbit Localized Twitch Response [R-LTR], a brisk contraction of a certain group of rabbit skeletal muscle fibers [a responsive band] elicited by mechanical stimulation of the most pressure-sensitive site [TrS]. Methods: In this study, R-LTRs were electromyographically investigated on 9 rabbits [ages 2-12 months]. Each animal was anesthetized in a way that preserved most peripheral reflexes mediated by the central nervous system. R-LTRs were elicited by one of three different mechanical stimuli; manual-probe stimulus [similar to snapping palpation], mechanical-tap stimulus [delivered by a solenoid driven blunt metal probe], or needle insertion using a solenoid-driven needle. Results: R-LTRs were best recorded from the responsive band [but not the other spots in the responsive band, or any spot in the non-responsive fibers] was mechanically stimulated. Responses to snapping stimulation were longer in duration than those to mechanical tap stimulation, which in turn were longer than R-LTRs produced by needle stimulation. This observation supports the impression that one trigger spot of the rabbit may contain multiple loci of hypersensitivity. The nearly complete loss of R-LTRs following lidocaine block or transection of the motor nerve indicates that propagation of the R-LTR is primarily via a central nervous system reflex rather than exclusively via director muscle-fiber transmission. Conclusion: The rabbit localized twitch responses [R-LTRs] show several similarities to and no incompatibility with, the human local twitch response [LTR]. The rabbit shows promise as an animal model for study of LTRs and possibly of taut bands and TrPs that are characteristic of myofascial pain syndrome.