Extramuscular myofascial force transmission for in situ rat medial gastrocnemius and plantaris muscles in progressive stages of dissection

The aim of this study was to establish the extent of extramuscular myofascial force transmission for dissected rat medial gastrocnemius (GM) and plantaris (PL) muscles. Initially, this was done with GM still connected to extramuscular connective tissue (general fascia, neuro-vascular tract and compartmental fascia). Neighbouring muscles were also connected to these tissues. In a later stage, it was dissected progressively until finally a fully dissected in situ GM was obtained, for which the neuro-vascular tract (i.e. the nerves, bloodvessels and the surrounding connective tissue) was the only extramuscular tissue left intact. Force of GM was measured not only at its distal tendon in progressive stages of dissection, but also at its dissected proximal tendon. In the stage where GM was still connected to extramuscular tissues, the experiments showed that up to 40.5±5.9% (mean ± S.E.M.) of the force exerted by the neighbouring PL muscle was transmitted onto the calcaneal bone, even when the PL tendon was not connected to this bone. After distal PL-tenotomy, a difference between proximally and distally measured forces of GM constituted evidence for myofascial force transmission. In the fully dissected in situ GM muscle, no relevant myofascial force transmission occurred in the reference position (the position of the GM origin corresponding to a knee angle of 120°). However, some myofascial force transmission occurred when the relative position of the origin of the fully dissected GM muscle was changed with respect to the neuro-vascular tract.