The relationship between epimuscular myofascial loads and deformations within skeletal muscles

When forces are exerted on muscle, the different tissues within this structure will deform. Pulling on the insertion of a passive muscle will lengthen the muscle fibers and, hence, the in series arranged sarcomeres and the tendon. Besides at the origin and insertion, forces can also be exerted directly onto the muscle belly surface (the epimysium), mediated by connective tissues linked to surrounding structures [1,2]. Such epimuscular myofascial loads are also expected to cause deformations of the structures involved (i.e. intramuscular connective tissues, muscle fibers). Because it is not possible to obtain direct evidence of epimuscular myofascial force transmission in human subjects, deformations of muscle tissue have been applied [2,3]. What is the magnitude of forces causing such deformations? For a more compliant spring, the same force will cause more lengthening (Fig. 1). This paper describes recent studies aimed at investigating the relationship between myofascial loads and muscle deformations.