Effects of botox on non-injected muscles' mechanics and myofascial force transmission

Abstract

Studies show that Botulinum toxin type A (BTX) injection causes a force decrease in the injected muscle. However, if BTX has e ects beyond the injected muscle via di usion and altered epimuscular myofascial force transmission (EMFT) is not known. It is hypothesized in this study that (1) BTX injection into the rat tibialis anterior (TA) has an impact on mechanics of adjacent extensor digitorum muscle (EDL) and (2) BTX has an impact on EMFT. The goal of this study was to test these hypotheses by measuring changes in total and passive forces exerted proximally and distally by the EDL muscle on both muscle length changes and muscle relative position changes. Two groups of Wistar rats were tested: Control (no BTX injected) and BTX (0.1 U of BTX injected to the mid-belly of the TA). Five days after injection, injection of BTX into the TA: (1) altered total and passive EDL forces exerted proximally and distally and after imposing muscle length changes. This does indicate that BTX changed EDL mechanics. The passive forces showed an increase (up to 13 folds) and the total forces showed a decrease (up to 81.7%). (2) Changed EMFT. EDL relative position changes towards the distal positions caused EDL total forces to signi cantly decrease also in the BTX group (64.1% decrease in BTX compared to Control) The ndings indicate that BTX administration diminishes EMFT. Our ndings support our hypotheses and improve our understanding of BTX e ects on muscular mechanics and EMFT showing that BTX injected into one muscle a ects the remainder of the compartment via leakage into other muscles and altered EMFT.|Keywords : Botulinum toxin type-A, epimuscular myofascial force transmission, muscular mechanics.