Muscle fiber angle, segment bulging and architectural gear ratio in segmented musculature

Brainerd, Elizabeth L.; Azizi, Emanuel

doi:10.1242/jeb.01770

Cited by 97 publications

(135 citation statements)

References 43 publications

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“…The prominence of lateral trunk movements during locomotion in salamanders has also made them favorite subjects in investigations of epaxial and hypaxial muscle function in tetrapods (Blight, 1976;Frolich and Biewener, 1992;Carrier, 1993;Delvolve et al, 1997;Bennett et al, 2001;Azizi and Horton, 2004;Brainerd and Azizi, 2005). Despite this attention, the locomotor functions of relatively few trunk muscles have been examined electromyographically, and additional muscles must be investigated to assemble a complete picture of trunk muscle function in salamanders.…”

Section: Introductionmentioning

confidence: 99%

Activity of trunk muscles during aquatic and terrestrial locomotion inAmbystoma maculatum

Deban

Schilling

2009

Journal of Experimental Biology

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SUMMARYThe activity of seven trunk muscles was recorded at two sites along the trunk in adult spotted salamander, Ambystoma maculatum, during swimming and during trotting in water and on land. Several muscles showed patterns of activation that are consistent with the muscles producing a traveling wave of lateral bending during swimming and a standing wave of bending during aquatic and terrestrial trotting: the dorsalis trunci, subvertebralis lateralis and medialis, rectus lateralis and obliquus internus. The interspinalis showed a divergent pattern and was active out of phase with the other muscles suggesting that it functions in vertebral stabilization rather than lateral bending. The obliquus internus and rectus abdominis showed bilateral activity indicating that they counteract sagittal extension of the trunk that is produced when the large dorsal muscles are active to produce lateral bending. Of the muscles examined, only the obliquus internus showed a clear shift in function from lateral bending during swimming to resistance of long-axis torsion during trotting. During terrestrial trotting, muscle recruitment was greater in several muscles than during aquatic trotting, despite similar temporal patterns of muscle activation, suggesting that the trunk is stiffened during terrestrial locomotion against greater gravitational forces whereas the basic functions of the trunk muscles in trotting are conserved across environments.

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Section: Introductionmentioning

confidence: 99%

Activity of trunk muscles during aquatic and terrestrial locomotion inAmbystoma maculatum

Deban

Schilling

2009

Journal of Experimental Biology

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“…1B) (5,(8)(9)(10). As a result, the muscle's velocity along its line of action can exceed the velocity of the contracting fibers (3,8,10). This velocity amplification can be measured as the ratio of muscle fiber velocity to whole-muscle velocity, a relationship that describes a muscle's architectural gear ratio (AGR).…”

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confidence: 99%

“…A less obvious potential gearing mechanism resides within the architecture of the muscles themselves (3). It is generally recognized that skeletal muscle architecture influences the force and velocity of a muscle, but in most cases, the analysis of the effects of muscle architecture on force or velocity output has been limited to predictions based on static anatomy.…”

mentioning

confidence: 99%

“…This velocity amplification can be measured as the ratio of muscle fiber velocity to whole-muscle velocity, a relationship that describes a muscle's architectural gear ratio (AGR). The ampli- fying effects of changes in fiber pennation angle (i.e., fiber rotation) with shortening generally result in AGRs Ͼ1 (3).…”

mentioning

confidence: 99%

“…A recent analysis of muscle architecture predicts that AGR can vary depending on the relative magnitude of muscle-shape changes in the directions orthogonal to the muscle's line of action (3). Some degree of orthogonal shape change is necessary in any contracting muscle because total muscle volume must remain constant (11) while fibers decrease in length and increase in diameter.…”

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confidence: 99%

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Variable gearing in pennate muscles

Azizi

Brainerd

Roberts

2008

Proc. Natl. Acad. Sci. U.S.A.

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305

406

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Muscle fiber architecture, i.e., the physical arrangement of fibers within a muscle, is an important determinant of a muscle's mechanical function. In pennate muscles, fibers are oriented at an angle to the muscle's line of action and rotate as they shorten, becoming more oblique such that the fraction of force directed along the muscle's line of action decreases throughout a contraction. Fiber rotation decreases a muscle's output force but increases output velocity by allowing the muscle to function at a higher gear ratio (muscle velocity/fiber velocity). The magnitude of fiber rotation, and therefore gear ratio, depends on how the muscle changes shape in the dimensions orthogonal to the muscle's line of action. Here, we show that gear ratio is not fixed for a given muscle but decreases significantly with the force of contraction (P < 0.0001). We find that dynamic muscle-shape changes promote fiber rotation at low forces and resist fiber rotation at high forces. As a result, gearing varies automatically with the load, to favor velocity output during low-load contractions and force output for contractions against high loads. Therefore, muscle-shape changes act as an automatic transmission system allowing a pennate muscle to shift from a high gear during rapid contractions to low gear during forceful contractions. These results suggest that variable gearing in pennate muscles provides a mechanism to modulate muscle performance during mechanically diverse functions.biomechanics ͉ force-velocity tradeoff ͉ gear ratio ͉ muscle architecture T he force, speed, and power that can be harnessed from skeletal muscles to power movement are ultimately limited by the mechanical behavior of myofibers, the muscles' contractile cells. Two features of the contractile behavior of myofibers that likely constrain locomotor performance are the well defined limits to contraction velocity and contractile force. The maximum shortening velocity of a myofiber can be characterized by allowing the muscle to contract against near-zero loads, and a maximum isometric force can be defined when a muscle contracts at a fixed length. To understand how these limits to speed and force at the level of skeletal muscle cells translate to limits to speed or force of movement requires a consideration of musculoskeletal components that modulate force and velocity ''downstream'' of the force-producing cells. The most familiar of these are the skeletal lever systems, which define the mechanical advantage (gearing) through which muscle force is transmitted (1, 2). Like any lever or gear, skeletal gearing influences the ratio of muscle force or velocity to output force or velocity.A less obvious potential gearing mechanism resides within the architecture of the muscles themselves (3). It is generally recognized that skeletal muscle architecture influences the force and velocity of a muscle, but in most cases, the analysis of the effects of muscle architecture on force or velocity output has been limited to predictions based on static anatomy. Dynamic changes...

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Regional differences in hyoid muscle activity and length dynamics during mammalian head shaking

2010

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The sternohyoid (SH) and geniohyoid (GH) are antagonist strap-muscles that are active during a number of different behaviors, including sucking, intraoral transport, swallowing, breathing, and extension/flexion of the neck. Because these muscles have served different functions through the evolutionary history of vertebrates, it is quite likely they will have complex patterns of electrical activity and muscle fiber contraction. Different regions of the sternohyoid exhibit different contraction and activity patterns during a swallow. We examined the dynamics of the sternohyoid and geniohyoid muscles during an unrestrained, and vigorous head-shake behavior in an animal model of human head, neck and hyolingual movement. A gentle touch to infant pig ears elicited a head shake of several head revolutions. Using sonomicrometry and intramuscular EMG we measured regional (within) muscle strain and activity in SH and GH. We found that EMG was consistent across three regions (anterior, belly and posterior) of each muscle. Changes in muscle length however, were more complex. In the SH, mid-belly length-change occurred out of phase with the anterior and posterior end-regions, but with a zero-lag timing; the anterior region shortened prior to the posterior. In the GH, the anterior region shortened prior to, and out of phase with the mid-belly and posterior regions. Head-shaking is a relatively simple reflex behavior, yet the underlying patterns of muscle length-dynamics and EMG activity are not. The regional complexity in SH and GH, similar to regionalization of SH during swallowing, suggests that these ‘simple hyoid strap muscles’ are more complex than textbooks often suggest.

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Muscle fiber angle, segment bulging and architectural gear ratio in segmented musculature

Cited by 97 publications

References 43 publications

Activity of trunk muscles during aquatic and terrestrial locomotion inAmbystoma maculatum

Activity of trunk muscles during aquatic and terrestrial locomotion inAmbystoma maculatum

Variable gearing in pennate muscles

Regional differences in hyoid muscle activity and length dynamics during mammalian head shaking

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