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

Exercise and Sport Sciences Reviews

Finni

2018

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Section: Mechanical Interactions Between Muscles -Human Studiesmentioning

confidence: 89%

Section: Mechanical Interactions Between Muscles -Studies On Other Anmentioning

confidence: 99%

Mechanical Coupling Between Muscle-Tendon Units Reduces Peak Stresses

Exercise and Sport Sciences Reviews

Finni

2018

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“…A critical difference is that in the passive state the stiffness of the muscle belly is much lower than in the active state. The stiffness of epimuscular connections may also be affected by the level of muscle activation (48,51,76). These changes between passive and active muscle state may affect the relative stiffness and, hence, the magnitude of force transmitted via the different pathways.…”

Section: Introductionmentioning

confidence: 99%

Significance of epimuscular myofascial force transmission under passive muscle conditions

Journal of Applied Physiology

2019

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In the past 20 yr, force transmission via connective tissue linkages at the muscle belly surface, called epimuscular myofascial force transmission, has been studied extensively. In this article, the effects of epimuscular linkages under passive muscle conditions are reviewed. Several animal studies that included direct (invasive) measurements of force transmission have shown that different connective tissue structures serve as an epimuscular pathway and that these tissues have sufficient stiffness, especially at supraphysiological muscle lengths and relative positions, to transmit substantial passive forces (up to 15% of active optimal force). Exact values of lumped tissue stiffness for different connective tissue structures have not yet been estimated. Experiments using various imaging techniques (ultrasound, MRI, shear wave elastography) have yielded some, but weak, evidence of epimuscular myofascial force transmission for passive muscles in humans. At this point, the functional consequences of epimuscular pathways for muscle and joint mechanics in the intact body are still unknown. Potentially, however, these pathways may affect sensory feedback and, thereby, neuromuscular control. In addition, altered epimuscular force transmission in pathological conditions may also contribute to changes in passive range of joint motion.

“…This could partially explain the limited or no mechanical interaction between muscles when intact muscle compartments and physiological joint excursions in rats and cats hindlimb muscles were tested (Sandercock and Maas, 2009;Tijs et al, 2015b). According to previous studies relating the amount of intermuscularly transmitted force with the active and passive state of muscles (Bernabei et al, 2016a;Tijs et al, 2016b), the largest effects of intermuscular force transmission are expected during the pre-stance and stance phases, when both the LG and SO are active. When the relative position changes between passive muscles, compliant intramuscular structures will likely fully absorb the resulting shear strain and, hence, the strain on intermuscular connections will be minimal.…”

Section: Mechanical Consequences Of Displacements Between Neighboringmentioning

confidence: 99%

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

Bernabei

Dieën

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.