Intact muscle compartment exposed to botulinum toxin type A shows compromised intermuscular mechanical interaction

We tested the hypothesis that BTX-A diminishes epimuscular myofascial force transmission (EMFT) within an intact muscle compartment.

The tibialis anterior (TA) and extensor hallucis longus (EHL) muscles were kept at constant length, whereas the position of the extensor digitorum longus (EDL) muscle was changed exclusively. Two groups of Wistar rats were tested: a control group (no BTX-A injected) and a BTX group (0.1 unit of BTX-A injected into the mid-belly of TA).

In controls, distally altered EDL position affected EDL distal and proximal forces and proximodistal force differences, indicating substantial EMFT. In the BTX group, EDL forces measured at the most proximal position did not change significantly with altered muscle position, and EDL proximodistal force differences became minimized.

Use of BTX-A diminishes EMFT. It may be relevant clinically that BTX-A compromises intermuscular mechanical interaction, as recent studies have shown that such an interaction plays a role in the abnormal mechanics of spastic muscle.