Myofascial Loads Can Occur without Fascicle Length Changes

Abstract

Many studies have shown that connective tissue linkages can transmit force between synergistic muscles and that such force transmission depends on the position of these muscles relative to each other and on properties of their intermuscular connective tissues. Moving neighboring muscles has been reported to cause longitudinal deformations within passive muscles held at a constant muscle-tendon unit (MTU) length (e.g., soleus [SO]), but muscle forces were not directly measured. Deformations do not provide a direct measure of the force transmitted between muscles. We combined two different muscle preparations to assess whether myofascial loads exerted by neighboring muscles result in length changes of SO fascicles. We investigated the effects of proximal MTU length changes of two-joint gastrocnemius (GA) and plantaris (PL) muscles on the fascicle length of the one-joint SO muscle within (1) an intact muscle compartment and (2) a disrupted compartment that allowed measurements of fascicle length and distal tendon force of SO simultaneously. SO muscle bellies of Wistar rats (n = 5) were implanted with sonomicrometry crystals. In three animals, connectivity between SO and GA+PL was enhanced. Measurements were performed before and during maximal excitation of all plantar flexor muscles. In both setups, MTU length of GA+PL did not affect the length of SO fascicles, neither during passive nor active conditions. However, lengthening the MTU of GA+PL increased distal tendon force of SO by 43.3-97.8% (P < 0.001) and 27.5-182.6% (P < 0.001), respectively. This indicates that substantial myofascial force transmission between SO and synergistic muscle can occur via a connective tissue network running parallel to the series of SO sarcomeres without substantial length changes of SO fascicles.

Does epimuscular myofascial force transmission occur between the human quadriceps muscles in vivo during passive stretching?

“…aponeurosis), and do not achieve the muscle bellies. Interestingly, a recent study reported that the fascicles length of soleus from Wistar rats did not changed when the gastrocnemius and plantaris muscle-tendon units length was increased, but it was noted a considerable high increase of force at the tendon level from the soleus (Tijs et al, 2018). Important to note that (fascicles) deformation measurements do not represent a direct force measurement.…”

Significance of epimuscular myofascial force transmission under passive muscle conditions

“…48). The first study that simultaneously measured muscle forces and deformations in response to epimuscular myofascial loads reported no changes in muscle fascicle length (75). Note that length changes of sarcomeres locally were not measured and thus cannot be excluded.…”

“…Note that none of the other human studies using this experimental paradigm measured ankle movement. In experiments in other animals, rigid fixation of segments is obtained by attaching clamps directly onto bone (40,75,77,82). Ankle angle is generally defined as the angle between the lower leg and the foot, but the ankle consists of three joints (i.e., talocrural joint, subtalar joint, and inferior tibiofibular joint).…”

Changes in neural drive to calf muscles during steady submaximal contractions after repeated static stretches

“…2018) or via connective tissues between synergists independent of changes in fascicle length (Tijs et al . 2018). Variation in force‐sharing strategies (Crouzier et al .…”