Effects of epimuscular myofascial force transmission on sarcomere length of passive muscles in the rat hindlimb

Journal of Biomechanics

2016

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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.

Section: Effects Of Epimuscular Myofascial Connections On Ta and Edlcontrasting

confidence: 47%

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

Tijs

Journal of Biomechanics

2016

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“…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.…”

Section: Mechanical Consequences Of Displacements Between Neighboringmentioning

confidence: 85%

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

Bernabei

Journal of Experimental Biology

2017

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The functional consequences of differential muscle activation and contractile behavior between mechanically coupled synergists are still poorly understood. Even though synergistic muscles exert similar mechanical effects at the joint they span, differences in the anatomy, morphology and neural drive may lead to non-uniform contractile conditions. This study aimed to investigate the patterns of activation and contractile behavior of triceps surae muscles, to understand how these contribute to the relative displacement between the one-joint soleus (SO) and two-joint lateral gastrocnemius (LG) muscle bellies and their distal tendons during locomotion in the rat. In seven rats, muscle belly lengths and muscle activation during level and upslope trotting were measured by sonomicrometry crystals and electromyographic electrodes chronically implanted in the SO and LG. Length changes of muscle-tendon units (MTUs) and tendon fascicles were estimated based on joint kinematics and muscle belly lengths. Distances between implanted crystals were further used to assess longitudinal and transversal deformations of the intermuscular volume between the SO and LG. For both slope conditions, we observed differential timing of muscle activation as well as substantial differences in contraction speeds between muscle bellies (maximal relative speed 55.9 mm s −1 ). Muscle lengths and velocities did not differ significantly between level and upslope locomotion, only EMG amplitude of the LG was affected by slope. Relative displacements between SO and LG MTUs were found in both longitudinal and transversal directions, yielding an estimated maximal length change difference of 2.0 mm between their distal tendons. Such relative displacements may have implications for the force exchanged via intermuscular and intertendinous pathways.

“…2008; Maas and Sandercock 2008; Tijs et al. 2015b), imaging studies in humans do imply relevant effects (Bojsen-Moller et al. 2010; Huijing et al.…”

Section: Discussionmentioning

confidence: 99%

“…2010; Tijs et al. 2015b), we assumed that muscle relative position was the sole determinant of force changes in the muscle group. In fact, these local effects occur as a consequence of changes in the imposed relative positions, so that relative position was selected as a global descriptor of length changes for the whole mechanical chain.…”

Section: Discussionmentioning

confidence: 99%

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A lumped stiffness model of intermuscular and extramuscular myofascial pathways of force transmission

Bernabei

Biomech Model Mechanobiol

2016

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Mechanical behavior of skeletal muscles is commonly modeled under the assumption of mechanical independence between individual muscles within a muscle group. Epimuscular myofascial force transmission via the connective tissue network surrounding a muscle challenges this assumption as it alters the force distributed to the tendons of individual muscles. This study aimed to derive a lumped estimate of stiffness of the intermuscular and extramuscular connective tissues and to assess changes in such stiffness in response to a manipulation of the interface between adjacent muscles. Based on in situ measurements of force transmission in the rat plantar flexors, before and after resection of their connective tissue network, a nonlinear estimate of epimuscular myofascial stiffness was quantified and included in a multi-muscle model with lumped parameters which allows for force transmission depending on the relative position between the muscles in the group. Such stiffness estimate was assessed for a group with normal intermuscular connective tissues and for a group with increased connectivity, mimicking scar tissue development. The model was able to successfully predict the amount of epimuscular force transmission for different experimental conditions than those used to obtain the model parameters. The proposed nonlinear stiffness estimates of epimuscular pathways could be integrated in larger musculoskeletal models, to provide more accurate predictions of force when effects of mechanical interaction or altered epimuscular connections, e.g. after surgery or injury, are substantial.