Muscle Architecture and Adaptations to Functional Requirements

Narici, Marco V.; Maganaris, C.N.

doi:10.1007/1-4020-5177-8_9

Cited by 5 publications

(4 citation statements)

References 52 publications

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“…While we lack the necessary data to discern the relative roles of hypertrophy versus hyperplasia, two anecdotal pieces of evidence suggest that hypertrophy is not fully responsible for the observed differences in jaw-muscle mass between tufted and untufted capuchins. First, muscle hypertrophy typically involves increases in pinnation angle given that the larger fibers must be spatially accommodated within an existing myotendinous aponeurosis (Narici and Maganaris, 2006). The jaw muscles of tufted capuchins, however, did not exhibit significantly greater pinnation angles (Table 2).…”

Section: Discussionmentioning

confidence: 99%

Jaw-muscle fiber architecture in tufted capuchins favors generating relatively large muscle forces without compromising jaw gape

Taylor

Vinyard

2009

Journal of Human Evolution

105

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Cebus apella is renowned for its dietary flexibility and capacity to exploit hard and tough objects. Cebus apella differs from other capuchins in displaying a suite of craniodental features that have been functionally and adaptively linked to their feeding behavior, particularly the generation and dissipation of relatively large jaw forces. We compared fiber architecture of the masseter and temporalis muscles between the tufted capuchin (C. apella; n = 12 ) and two "untufted" capuchins (C. capuchinus, n = 3; C. albifrons, n = 5). These three species share broadly similar diets, but tufted capuchins occasionally exploit mechanically challenging tissues. We tested the hypothesis that C. apella exhibits architectural properties of their jaw muscles that facilitate relatively large forces, including relatively greater physiologic cross-sectional areas (PCSA), more pinnate fibers, and lower ratios of mass to tetanic tension (Mass/P 0 ). Results show some evidence supporting these predictions, as C. apella has relatively greater superficial masseter, whole masseter, and temporalis PCSAs, significantly so only for the temporalis following Bonferroni adjustment. Capuchins did not differ in pinnation angle or Mass/P 0 . As an architectural trade-off between maximizing muscle force and muscle excursion/contraction velocity, we also tested the hypothesis that C. apella exhibits relatively shorter muscle fibers. Contrary to our prediction, there are no significant differences in relative fiber lengths between tufted and untufted capuchins. Therefore, we attribute the relatively greater PCSAs in C. apella primarily to their larger muscle masses. These findings suggest that relatively large jaw-muscle PCSAs can be added to the suite of masticatory features that have been functionally linked to the exploitation of a more resistant diet by C. apella. By enlarging jaw-muscle mass to increase PCSA, rather than reducing fiber lengths and increasing pinnation, tufted capuchins appear to have increased jaw-muscle and bite forces without markedly compromising muscle excursion and contraction velocity. One performance advantage of this morphology is that it promotes relatively large bite forces at wide jaw gapes, which may be useful for processing large food items along the posterior dentition. We further

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Section: Discussionmentioning

confidence: 99%

Jaw-muscle fiber architecture in tufted capuchins favors generating relatively large muscle forces without compromising jaw gape

Taylor

Vinyard

2009

Journal of Human Evolution

105

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“…For instance, their analysis did not include changes in muscle architecture or specific tension, which are known to strongly influence maximal force (cf. Fitts et al 2001, Narici & Maganaris 2007 for reviews).…”

Section: Electromyographic Activitymentioning

confidence: 99%

Early structural adaptations to unloading in the human calf muscles

et al. 2008

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“…Whilst MRI provides good resolution of anatomical cross‐sectional area of muscle, allowing for distinction between muscle, fat and connective tissue, this does not tell us anything about the alignment of the muscle fibres. Here developments in ultrasound imaging allow fascicles to be identified and measured in terms of their lengths and their angles of pennation (see Narici & Maganaris, 2006). Following strength training, increases in the region of 10% may be expected in terms of anatomical cross‐sectional area of the quadriceps, as determined by MRI (Aagaard et al 2001).…”

Section: Functional Implications Of Increasing Muscle Sizementioning

confidence: 99%

Plasticity of human skeletal muscle: gene expression to in vivo function

Harridge

2007

Experimental Physiology

143

124

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Human skeletal muscle is a highly heterogeneous tissue, able to adapt to the different challenges that may be placed upon it. When overloaded, a muscle adapts by increasing its size and strength through satellite-cell-mediated mechanisms, whereby protein synthesis is increased and new nuclei are added to maintain the myonuclear domain. This process is regulated by an array of mechanical, hormonal and nutritional signals. Growth factors, such as insulin-like growth factor I (IGF-I) and testosterone, are potent anabolic agents, whilst myostatin acts as a negative regulator of muscle mass. Insulin-like growth factor I is unique in being able to stimulate both the proliferation and the differentiation of satellite cells and works as part of an important local repair and adaptive mechanism. Speed of movement, as characterized by maximal velocity of shortening (V max ), is regulated primarily by the isoform of myosin heavy chain (MHC) contained within a muscle fibre. Human fibres can express three MHCs: MHC-I, -IIa and -IIx, in order of increasing V max and maximal power output. Training studies suggest that there is a subtle interplay between the MHC-IIa and -IIx isoforms, with the latter being downregulated by activity and upregulated by inactivity. However, switching between the two main isoforms appears to require significant challenges to a muscle. Upregulation of fast gene programs is caused by prolonged disuse, whilst upregulation of slow gene programs appears to require significant and prolonged activity. The potential mechanisms by which alterations in muscle composition are mediated are discussed. The implications in terms of contractile function of altering muscle phenotype are discussed from the single fibre to the whole muscle level.

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Muscle Architecture and Adaptations to Functional Requirements

Cited by 5 publications

References 52 publications

Jaw-muscle fiber architecture in tufted capuchins favors generating relatively large muscle forces without compromising jaw gape

Jaw-muscle fiber architecture in tufted capuchins favors generating relatively large muscle forces without compromising jaw gape

Early structural adaptations to unloading in the human calf muscles

Plasticity of human skeletal muscle: gene expression to in vivo function

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