Extramuscular myofascial force transmission also occurs between synergistic muscles and antagonistic muscles.

The purpose of the present study was to test the hypothesis that myofascial force transmission may not be limited by compartmental boundaries of a muscle group to synergists. Muscles of the anterior tibial compartment in rat hindlimb as well as of the neighbouring peroneal compartment (antagonistic muscles) were excited maximally. Length-force data, based on proximal lengthening, of EDL, as well as distal lengthening of the tibial muscles (TA+EHL) and the peroneal muscle group (PER) were collected independently, while keeping the other two muscle groups at a constant muscle-tendon complex length. Simultaneously measured, distal and proximal EDL active forces were found to differ significantly throughout the experiment. The magnitude of this difference and its sign was affected after proximal lengthening of EDL itself, but also of the tibial muscle complex and of the peroneal muscle complex. Proximal lengthening of EDL predominantly affected its synergistic muscles within the anterior crural compartment (force decrease <4%). Lengthening of either TA or PER caused a decrease in distal EDL isometric force (by 5-6% of initial force). It is concluded also that mechanisms for mechanical intermuscular interaction extend beyond the limits of muscle compartments in the rat hindlimb. Even antagonistic muscles should not be considered fully independent units of muscular function. Particular, strong mechanical interaction was found between antagonistic tibial anterior muscle and peroneal muscle complexes: Lengthening of the peroneal complex caused tibial complex force to decrease by approximately 25%, whereas for the reverse a 30% force decrease was found.