Limited mechanical effects of intermuscular myofascial connections within the intact rat anterior crural compartment

Abstract

a b s t r a c tSkeletal muscles of the rat anterior crural compartment are mechanically connected by epimuscular myofascial connections, but the relevance for mechanical muscle function within physiological ranges of joint motion is unclear. We evaluated the net effect at the ankle joint of epimuscular myofascial connections between tibialis anterior (TA) and extensor digitorum longus (EDL) muscles in the rat (n ¼ 8) and determined which anatomical structures may mediate such epimuscular mechanical interactions. We assessed (1) effects of knee angle (i.e. changes in EDL length and position relative to TA) and interactions of knee angle with fasciotomy and proximal EDL tenotomy on TA ankle moment and (2) the effect of knee angle on TA and EDL ankle moment summation. Knee angle was varied between 60°and 130°. Ankle angle was kept constant (90°). TA and EDL were excited individually and simultaneously (TA&EDL). The mathematical sum of individual TA and EDL moments was compared with the moment exerted by TA&EDL to assess the extent of non-additive ankle moment summation. Magnitude of TA ankle moment was not affected by knee angle, but frontal plane moment direction was. However, dissections indicated that this was not caused by the compartmental fascia or EDL length changes. Moment summation was non-additive in magnitude ( þ1.1 7 1.1% mean7 s.d.) and frontal plane direction. The latter was affected by knee angle and ranged from þ 0.27 0.3°at 60°to þ1.1 7 0.6°at 130°. As the net effects found were very limited, we conclude that myofascial connections between muscles in the anterior crural compartment have limited mechanical relevance during normal movement.

Mechanical Coupling Between Muscle-Tendon Units Reduces Peak Stresses

“…Thus for this muscle pair, intermuscular mechanical interaction should lead to changes in the direction of the 3-D moment vector. Instead, no effects of knee extension (decreasing EDL length) on the moment exerted by TA muscle were observed (22). Therefore, these results must be considered as evidence against the hypothesis of the present article.…”

“…The same experimental approach was applied also to study mechanical interaction between one-joint TA and extensor hallucis longus muscles and the multiple-joint EDL muscle (22). These muscles do not share a distal tendon and, hence, exert moments in different directions (i.e., TAankle inversion, EDLankle eversion, both musclesankle dorsiflexion).…”

“…A bipolar cuff electrode was placed on the tibial nerve to maximally activate all muscles. Right: The femur was fixed and the foot was attached to a 6 degrees-of-freedom load cell using custom-made clamps (21,22). The ankle and knee joints were aligned with the setup's rotational axes.…”

Synergistic Co-activation Increases the Extent of Mechanical Interaction between Rat Ankle Plantar-Flexors

“…As a consequence, any epimuscular myofascial force transmission may not be reflected in the moments exerted at the ankle (Tijs et al, 2015 ). However, similar results were found for the muscles in the anterior crural compartment, which do not share a tendon distally (Tijs et al, 2016 ). Secondly, the level of muscle activation and number of simultaneously excited muscles differed between the studies.…”

Longitudinal and transversal displacements between triceps surae muscles during locomotion of the rat

“…6A). However, in the study by Bernabei et al (2015), both muscles were maximally activated, while the extent of mechanical interaction has been shown to decrease with submaximal activation and passive muscle conditions (Tijs et al, 2015a(Tijs et al, , 2016a. Moreover, the maximal MTU relative displacement imposed in the study by Bernabei et al LG proximal tendon is detached from its origin on the lateral epicondyle of the femur to show the intermuscular connective tissues and SO muscle belly lying more anterior in the triceps surae compartment.…”