Meeting Abstract
Many studies have shown that connective tissue linkages are able to transmit force between synergistic muscles. Recently, knee joint movement have been found to cause deformations of muscles that only span the ankle joint (e.g. soleus, SO). Such deformations, involving changes in the distributions of sarcomere length within and between muscles, may affect the mechanical function of these muscles. Although muscle deformations may be caused by myofascial loads (i.e. forces exerted on the muscle belly via intermuscular connective tissues), they do not provide a direct measure of the force transmitted intermuscularly. While we have previously found some force transmission between plantar flexor muscles using invasive experiments on rats and cats, no effects were found on joint level mechanical function. However, in those studies no assessment of muscle deformations was performed. To bridge the gap between the observations from non-invasive kinematic and invasive mechanical measures, we assessed in situ effects of knee joint angle (from 70° to 130°) on SO muscle belly length, using sonomicrometry crystals, within an intact ankle plantar flexors compartment of anesthetized Wistar rats (n=3). For each knee angle, passive and active lengths were measured before and during maximal excitation of all plantar flexor muscles, respectively. Varying knee joint angle resulted in limited changes in SO muscle belly length, both during passive (mean: 2.4%) and active (mean: 1.6%) conditions. This indicates that during normal movements in rats myofascial connections between SO and synergistic muscles cause only small deformations of SO muscle belly. This is agreement with the previously reported limited effects of myofascial force transmission on the 3D ankle joint moment of SO.
