Muscle Fiber Architecture Research Articles

Discovering fiber type architecture over the entire muscle using data-driven analysis.

Skeletal muscle function is inferred from the spatial arrangement of muscle fiber architecture, which corresponds to myofiber molecular and metabolic features. Myofiber features are often determined using immunofluorescence on a local sampling, typically obtained from a median region. This median region is assumed to represent the entire muscle. However, it remains largely unknown to what extent this local sampling represents the entire muscle. We present a pipeline to study the architecture of muscle fiber features over the entire muscle, including sectioning, staining, imaging to image quantification and data‐driven analysis with Myofiber type were identified by the expression of myosin heavy chain (MyHC) isoforms, representing contraction properties. We reconstructed muscle architecture from consecutive cross‐sections stained for laminin and MyHC isoforms. Examining the entire muscle using consecutive cross‐sections is extremely laborious, we provide consideration to reduce the dataset without loosing spatial information. Data‐driven analysis with over 150,000 myofibers showed spatial variations in myofiber geometric features, myofiber type, and the distribution of neuromuscular junctions over the entire muscle. We present a workflow to study histological changes over the entire muscle using high‐throughput imaging, image quantification, and data‐driven analysis. Our results suggest that asymmetric spatial distribution of these features over the entire muscle could impact muscle function. Therefore, instead of a single sampling from a median region, representative regions covering the entire muscle should be investigated in future studies.

Using DiceCT to evaluate the functional correlates of masticatory muscle architecture

Diffusible iodine-based contrast-enhanced computed tomography (DiceCT) is a process in which the radiopacity of soft-tissues is enhanced by binding them to a dense molecule (in this case, Lugol's iodine) so that they can be viewed using x-ray-based visualization. Although DiceCT has previously been used to examine masticatory muscle fiber architecture, including in some lemurs, for the first time we have applied this technique to a large enough interspecific sample size to evaluate the functional adaptations of these muscles in three-dimensional space. We performed this analysis on 5 lemurids (Hapalemur, Lemur, Varecia,and two species of Eulemur) and three other strepsirrhines (Propithecus, Daubentonia,and Otolemur) as increasingly distant phylogenetic brackets. While our analysis confirms the findings of previous studies based on traditional gross dissection (i.e., more folivorous species have relatively shorter fascicle lengths and higher PCSA than do frugivorous taxa, giving them relatively higher bite force though lower linear gape abilities) these new analyses reveal more about the arrangement of these muscles. Namely, this approach shows, for the first time, 1) how these muscles are angled in three dimensional space - a necessary step to fully resolving the effects of pennation in these complex muscles, 2) that the jaw adductor muscles, in near occlusion, are curved and in a state of gross compression - thus changing our understanding of the force potential of these muscles in this state, and 3) the detailed gross and fascicular morphology of these muscles, particularly the deep muscles, in greater detail than can be accomplished using traditional methods. While these advantages improve our understanding of the function of these muscles, the technique is still extremely expensive in both material costs and scan time and the data collection is very time consuming. While these disadvantages currently preclude the application of this approach to large enough samples to explore broad functional questions across multiple lineages, if the costs in time and materials can be reduced, this three-dimensional visualization approach (or cheaper/easier approaches that can accomplish the same level of analysis) has the potential to yield new insights into the evolution of the functional anatomy of soft-tissues in three-dimensions.

3D Anatomy of the Jaw Muscles of the Spiny‐Tailed Dogfish ( Squalus acanthius )

New technologies are enabling anatomists to see inside animals to better understand the organization and function of the musculoskeletal system. Among the great transformations in vertebrate evolution is the acquisition and diversification of jaws and jaw musculature. Sharks are key species used in anatomy courses as well as research in organismal evolutionary biology where there is considerable diversity in cranial function and feeding behavior in the clade. Here, we use contrast imaging and 3D muscle fiber architecture visualization approaches to model and demonstrate the jaws and jaw muscles of the spinytailed dogfish (Sqaulus acanthius). A specimen was microCTed following immersion in an iodine-ethanol solution. Muscles and cartilages were segmented using Avizo. Muscle fascicles were then modeled using automated methods followed by manual noise reduction approaches. Colors of modeled fascicles were modeled to reflect orientations of muscles to reveal qualitative patterns in fiber organization. These segmented models of fascicles were then projected in quantitative space to show the orientations of muscle fascicles and moments of the quadratomandibularis, preorbitalis and levator hyomandibulae muscles among others. This 3D model will be shared with educators to include in comparative vertebrate anatomy courses. The results from the muscle architecture and mechanics data will be used to compare with other fishes and tetrapods as part of a growing study on the evolution of jaw muscles in vertebrates.

Vitamin D Promotes Skeletal Muscle Regeneration and Mitochondrial Health

Vitamin D is an essential nutrient for the maintenance of skeletal muscle and bone health. The vitamin D receptor (VDR) is present in muscle, as is CYP27B1, the enzyme that hydroxylates 25(OH)D to its active form, 1,25(OH)D. Furthermore, mounting evidence suggests that vitamin D may play an important role during muscle damage and regeneration. Muscle damage is characterized by compromised muscle fiber architecture, disruption of contractile protein integrity, and mitochondrial dysfunction. Muscle regeneration is a complex process that involves restoration of mitochondrial function and activation of satellite cells (SC), the resident skeletal muscle stem cells. VDR expression is strongly upregulated following injury, particularly in central nuclei and SCs in animal models of muscle injury. Mechanistic studies provide some insight into the possible role of vitamin D activity in injured muscle. In vitro and in vivo rodent studies show that vitamin D mitigates reactive oxygen species (ROS) production, augments antioxidant capacity, and prevents oxidative stress, a common antagonist in muscle damage. Additionally, VDR knockdown results in decreased mitochondrial oxidative capacity and ATP production, suggesting that vitamin D is crucial for mitochondrial oxidative phosphorylation capacity; an important driver of muscle regeneration. Vitamin D regulation of mitochondrial health may also have implications for SC activity and self-renewal capacity, which could further affect muscle regeneration. However, the optimal timing, form and dose of vitamin D, as well as the mechanism by which vitamin D contributes to maintenance and restoration of muscle strength following injury, have not been determined. More research is needed to determine mechanistic action of 1,25(OH)D on mitochondria and SCs, as well as how this action manifests following muscle injury in vivo. Moreover, standardization in vitamin D sufficiency cut-points, time-course study of the efficacy of vitamin D administration, and comparison of multiple analogs of vitamin D are necessary to elucidate the potential of vitamin D as a significant contributor to muscle regeneration following injury. Here we will review the contribution of vitamin D to skeletal muscle regeneration following injury.

Identification of muscle innervation zones using linear electrode arrays: a fundamental step to measure fibers conduction velocity

Fiber conduction velocity (CV) is a parameter correlated to the physiological membrane properties of the skeletal muscle fibers. Changes in muscle fiber CV are correlated to the gradation of force and fatigue, and can be measured by means of surface electromyography EMG (sEMG). sEMG measurement of CV during muscle contractions requires the correct identification of the skeletal muscle innervation zone (IZ). In superficial muscles, IZ location can be detected using linear electrode arrays and visually identified as the point of inversion of the detected motor unit action potential (MUAP) propagation. In the present work, we present a method for the effective and fast detection of the IZ location, through the following procedures: (1) identification of the target superficial muscle considering the muscle fiber architecture; (2) electrode array selection based on interelectrode distance and number of electrodes; (3) subject training to perform submaximal isometric contractions of the target muscle/s; (4) electrode array positioning along the muscle surface to investigate the IZ position during the contractions by visual identification of MUAP patterns.

In Situ Fiber Length Estimates from Sectioned Muscle Bellies are not Systematically Shorter Compared with Fiber Length Estimates Obtained Using Chemical Digestion

Architectural characteristics of skeletal muscles are important determinants of whole muscle function. Fiber length (Lf) and physiologic cross‐sectional area (PCSA) are correlated with skeletal muscle excursion/contraction velocity and force, respectively. Thus, fiber architecture provides important insights into muscle function and performance. A variety of methods are available for estimating Lf and PCSA, including traditional gross anatomical dissection and chemical digestion, imaging methods such as ultrasound and magnetic resonance imaging, and newer applications of iodine‐based contrast using computed tomography. A considerable body of work on muscle fiber architecture has been accomplished using chemical digestion as well as cadaver dissection in which in situ Lf measurements are sampled from muscle bellies that have been sectioned parallel to probable lines of action. Recently, the validity of findings based on in situ measurements sampled from sectioned muscle bellies has been questioned on the grounds that sectioning muscles theoretically results in shorter fascicle measurements compared to chemical digestion. To date, no study has compared measurements obtained from these two methods.We compared Lf estimates obtained using both data collection methods to determine if the in situ measurement technique systematically results in shorter fibers compared with those obtained using chemical digestion. We sectioned masseter and temporalis muscles and obtained in situ Lf estimates for a maximum of 14 species of strepsirrhine primates (n=38 specimens). Most of our samples ranged between n=2 and n=6 per species, but we were limited to n=1 for four species. We compared our results with previously published data based on chemical dissection methods for strepsirrhines (Perry et al., 2011; samples per species ranged between n=1 and n=3; n=20 specimens).Our results showed that in 5/14 species (36%) chemical digestion‐based Lf estimates for the masseter fell within or below our ranges for in situ Lf measurements; in 4/14 species (29%), masseter Lf estimates fell above our ranges. Masseter Lf estimates using chemical digestion were shorter than our single in situ Lf estimates in 3/14 species (21%) and greater in 2/14 species (14%). For the temporalis, in 5/10 species (50%), chemical digestion‐based Lf estimates fell within or below our ranges; in 2/10 species (20%) temporalis Lf estimates fell above our range. Temporalis Lf estimates using chemical digestion were shorter than our single in situ Lf estimates in 2/10 species and greater in 1/10 species. Thus, chemical digestion‐based Lf estimates either fell within our ranges or were actually shorter in 8/14 species for the masseter and in 7/10 species for the temporalis, compared with our in situ measurements. We observe similar results when we compare our in situ masseter and temporalis Lf estimates for platyrrhines with those previously published based on chemical digestion (Hartstone‐Rose et al., 2018).We conclude that there is no empirical support for the contention that in situ Lf estimates derived from sectioned muscle bellies result in systematically shorter fibers compared with estimates based on chemical digestion.Support or Funding InformationNSF (BCS 0452160, 0962677) and NIH (R24 HD050837‐1).

3D Muscle Fiber Architecture of Avian Jaw Muscles and their Significance for Avian cranial functional morphology evolution

Birds evolved a diversity of head shapes, feeding behaviors and jaw muscles which drive the feeding apparatus. However, capturing the anatomical and functional diversity of these muscles remains challenging and we know little about how jaw muscles develop, function and evolve among lineages of the clade and this hampers our ability to understand skeletal tissue biology, joint function, and patterns of evolution in bird skulls. Here we use contrast imaging, 3D muscle fiber tracking and new data visualization methods to explore the morphology, architecture and functional significance of the jaw muscles of a sample of birds to highlight the potential of these approaches. First, we show differences in functional morphology of jaw muscles between a hatchling and adult Mallard duck (Anas platyrhynchos). Ducks show a marked change in adductor chamber shape during ontogeny including an elongated postorbital process, quadrate orbital process and retroarticular process along with a broad temporal fossa which likely track with changes in muscle function and cranial kinesis. Indeed, we found m. depressor mandibulae in baby and adult ducks shifts from a rostrocadual orientation to a more dorsoventral orientation that offers additional mechanical advantage to jaw opening and propalinal mandible movement as well as concomitant changes in the 3D resultant and pennation of other jaw muscle bellies. Second, we show differences between a long‐ and short‐faced, dabbling birds (mallard, green‐wing teal), long faced orthally‐biting bird (belted kingfisher) and a short‐faced, hard‐biting bird, the grey parrot (Psittacus erithacus). We expected position, architecture and biomechanics of homologous muscles to differ substantially between these avian species given their different behaviors and overall cranial morphology. Although some muscles showed marked differences in resultant and pennation, others, including protractor pterygoideus, the primary actuator of kinesis, were remarkably similar in morphology suggesting a mosaic of changes happening during avian evolution. Together, these new, 3D high fidelity anatomical data on jaw muscle functional morphology in birds will not only better illuminate ecomorphological evolution but also illustrate how other clades of birds and vertebrates adapt their muscle architecture to meet functional demands.

Intraspecific and intrafamilial variation in primate forearm muscle architecture

Recent studies have examined locomotion and postural correlates of primate forearm muscle architecture. However, these have done so using relatively small sample sizes – usually one or two specimens per species, and relatively few species per genus and family. Thus, little is known about intraspecific variation in forearm muscle fiber architecture in primates, and whether there are notable differences in these variables between closely related taxa. The current study addresses these deficits by assessing both qualitative (presence/absence of specific muscles) and quantitative (physiological cross‐sectional area [PCSA], fascicle length [FL] and muscle mass [MM]) differences in forearm muscle architecture of larger intraspecific and samples with greater coverage of specific primate families than had been included in previous work. Namely, we studied 30 callitrichid specimens from 11 species, 15 lemurid specimens from 7 species and 9 cebids from two species ‐ a total sample size of 54 specimens from 20 species. Within species, FL varied the greatest among architectural variables and MM varied the least. We also found that there is great variation in both the extent of separation and fusion of flexor digitorum superficialis and profundus, and in the extent of accessory extensors in most species of callitrichids and Saimiri, but no variation in the gross forearm muscle architecture within lemurids. More than a quarter of the callitrichid specimens had forearm muscle configurations that deviate from their standard published description, suggesting that blanket characterizations of anatomical configurations at the genus or family level may obscure potentially important intra‐ and inter‐specific trends.Support or Funding InformationNational Science Foundation: IOS‐15‐57125, BCS‐14‐40599

Scaling of Anatomically Derived Maximal Bite Force in Primates

By combining muscle architectural data with biomechanical variables relating to the jaw, we produce anatomically derived maximum bite force estimations for 23 species of catarrhine and platyrrhine primates. We investigate how bite force scales across the sample as a whole (and within each parvorder) relative to two size proxies, body mass and cranial geometric mean, and the effect of diet upon bite force. Bite force is estimated at three representative bite points along the dental row: the first maxillary incisor, canine, and third-most mesial paracone. We modeled bite force by combining calculated physiological cross-sectional area of the jaw adductors from Hartstone-Rose et al. [Anat Rec 301 (2018) 311-324] with osteological measurements of lever- and load-arm lengths from the same specimens [Hartstone-Rose et al., Anat Rec 295 (2012) 1336-1351]. Bite force scales with positive allometry relative to cranial geometric mean across our entire sample and tends toward positive allometry relative to body mass. Bite force tends toward positive allometry within platyrrhines but scales isometrically within catarrhines. There was no statistically significant scaling difference with diet. Our findings imply an absence of a dietary signal in the scaling of bite force, a result that differs from the scaling of physiological cross-sectional area alone. That is, although previous studies have found a dietary signal in the muscle fiber architecture in these species, when these are combined with their leverages, that signal is undetectable. On the parvorder level, our data also demonstrate that the platyrrhine masticatory system appears more mechanically advantageous than that of catarrhines. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:2026-2035, 2020. © 2019 American Association for Anatomy.

MRI-Derived Biomarkers Related to Sarcopenia: A Systematic Review.

MRI allows quantitatively assessing muscle quantity and quality. To summarize the role of MRI as a noninvasive technique for the identification of in vivo surrogate biomarker of sarcopenia. Systematic review. In April 2019, a systematic literature search (Medline/EMBASE) was performed to identify articles on the topic at issue. No field strength or sequence restrictions. After a literature search, study design, aim, sample size, demographics, magnetic field strength, imaged body region, MRI sequences, and imaging biomarker were extracted. Data are presented as frequencies and percentages. From 69 records identified through search query, 18 articles matched the inclusion criteria. All articles were published from 2012 and had a mainly prospective design (14/18, 78%). Sample size ranged from 9 to 284 subjects, for a total of 1706 enrolled subjects. Healthy subjects were enrolled or retrospectively selected in 8/18 (44%) articles, corresponding to 658 (39%) healthy subjects. Magnetic field strength was 1.5 or 3T in 14/18 (78%) studies. The most analyzed body regions were the thigh (7/18, 39%) and the trunk (6/18, 33%). Stratifying studies according to their aim, 13/18 (72%) studies focused on muscle quality and quantity, 3/18 (17%) studies on outcome prediction, and 2/18 articles (11%) addressed both aims. A wide set of MRI biomarkers have been proposed. Muscle cross-sectional area was the most used for muscle quantity estimation, while quantitative biomarkers of muscle fat content or fiber architecture were proposed to assess muscle quality. The proposed biomarkers were assessed using different MRI sequences for different body regions in different subjects/patient cohorts, pointing out a lack of standardization on this topic. Future studies should test and compare the performance of proposed MRI biomarkers for sarcopenia characterization and quantification using a standardized experimental setup. 1 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2020;51:1117-1127.

Bite Force and Masticatory Muscle Architecture Adaptations in the Dietarily Diverse Musteloidea (Carnivora).

Dietary ecology and its relationship with both muscle architecture and bite force potential has been studied in many mammalian (and non-mammalian) taxa. However, despite the diversity of dietary niches that characterizes the superfamily Musteloidea, the masticatory muscle fiber architecture of its members has yet to be investigated anatomically. In this study, we present myological data from the jaw adductors in combination with biomechanical data derived from craniomandibular measurements for 17 species representing all four families (Ailuridae, Mephitidae, Mustelidae, and Procyonidae) of Musteloid. These data are combined to calculate bite force potential at each of three bite points along the dental row. Across our sample as a whole, masticatory muscle mass scaled with isometry or slight positive allometry against both body mass and skull size (measured via a cranial geometric mean). Total jaw adductor physiological cross-sectional area scaled with positive allometry against both body mass and skull size, while weighted fiber length scaled with negative allometry. From a dietary perspective, fiber length is strongly correlated with dietary size such that taxa that exploit larger foods demonstrated myological adaptations toward gape maximization. However, no consistent relationship between bite force potential and dietary mechanical resistance was observed. These trends confirm previous findings observed within the carnivoran family Felidae (as well as within primates), suggesting that the mechanisms by which masticatory anatomy adapts to dietary ecology may be more universally consistent than previously recognized. Anat Rec, 302:2287-2299, 2019. © 2019 American Association for Anatomy.

A Comparative Histological and Immunohistochemical Study of the Effect of Oxandrolone and Whey Protein on Disuse Induced Muscle Atrophy in old aged male rats

Background: Periods of immobilization are often associated with pathologies and/or aging. These periods of disuse muscle atrophy could worsen the pathology or elderly frailty. Exercise, the best way to recover muscle mass, is not always applicable. Aim of Work: This study aimed to compare the therapeutic effect of oxandrolone versus whey protein on disuse induced muscle atrophy in old aged male rats with low testosterone level and mobility limitation.Materials and Methods: Twenty four aged male albino rats were included: 6 rats as control (group I). Eighteen rats were subjected to hind limb suspension (HLS) for 2 weeks then were divided into: 6 rats as group II (disuse atrophy) and 12 rats as group III (treated group) which was equally subdivided into: group IIIa (oxandrolone treated) and IIIb (whey protein treated) where oxandrolone 1.23 mg/kg and whey protein 9.25 gm/kg were given orally daily for 4 weeks. Rats were sacrificed after 6 weeks. Gastrocnemius muscle weight and total protein content were measured. Muscle specimens were stained with Hematoxylin and Eosin, PAS and immunohistochemical staining for Myogenin. Morphometric measurements of type I and type II fibers number and cross sectional area (CSA), number of myogenin positive cells (differentiated satellite cells) were taken and statistically analyzed. Results: Group II showed atrophic angulated muscle fibers and significant increase in type II fibers compared to the control. Subgroup IIIa showed muscle fibers with large diameter. Many rounded vesicular nuclei were observed among muscle fibers. A significant increase in type I fibers and number of myogenin positive cells as compared to the control and subgroup IIIb. Conclusion: Oxandrolone and whey protein treated subgroups showed improved muscle mass, CSA, total protein content, histological architecture of muscle fibers and increase of satellite cells number. However, oxandrolone showed better therapeutic potential in ameliorating disuse muscle atrophy.

Microstructure-based finite element model of left ventricle passive inflation

Isolating the role(s) of microstructural pathological features in affecting diastolic filling is important in developing targeted treatments for heart diseases. We developed a microstructure-based constitutive model of the myocardium and implemented it in an efficient open-source finite element modeling framework to simulate passive inflation of the left ventricle (LV) in a representative 3D geometry based on experimentally measured muscle fiber architecture. The constitutive model was calibrated using previous tissue-level biaxial mechanical test data derived from the canine heart and validated with independent sets of measurements made at both the isolated constituent and organ level. Using the validated model, we investigated the load taken up by each tissue constituent and their effects on LV passive inflation. The model predicts that the LV compliance is sensitive to the collagen ultrastructure, specifically, the collagen fiber azimuthal angle with respect to the local muscle fiber direction and its waviness. The model also predicts that most of the load in the sub-epicardial and sub-endocardial regions is taken up, respectively, by the muscle fibers and collagen fiber network. This result suggests that normalizing LV passive stiffness by altering the collagen fiber network and myocyte stiffness is most effective when applied to the sub-endocardial and sub-epicardial regions, respectively. This finding may have implication for the development of new pharmaceutical treatments targeting individual cardiac tissue constituents to normalize LV filling function in heart diseases. Statement of SignificanceCurrent constitutive models describing the tissue mechanical behavior of the myocardium are largely phenomenological. While able to represent the bulk tissue mechanical behavior, these models cannot distinguish the contribution of the tissue constituents and their ultrastructure to heart function. Although microstructure-based constitutive models can be used to isolate the role of tissue ultrastructure, they have not been implemented in a computational framework that can accommodate realistic 3D organ geometry. The present study addresses these issues by developing and validating a microstructure-based computational modeling framework, which is used to investigate the role of tissue constituents and their ultrastructure in affecting heart function.

Alteration of T-Tubular Architecture and Capacitance Changes in Huntington's Disease

Huntington's disease (HD) is an inherited disorder with debilitating motor, cognitive, and psychiatric dysfunction. Motor symptoms, including chorea, rigidity, dystonia, and weakness, have principally been attributed to central neurodegeneration, but recent work suggests that primary skeletal muscle defects may also contribute to the motor symptoms. Electrophysiology studies in our lab have revealed a marked decrease in specific capacitance in HD muscle fibers from R6/2 transgenic mice compared with controls. This reduced capacitance is greater than expected when accounting for the smaller size of HD fibers. Because the transverse tubular system (TTS) in skeletal muscle makes up a significant proportion of total cell membrane, we hypothesized that structural changes in the TTS were responsible for reduced capacitance in the disease state. A loss or disruption of membrane in the TTS could directly contribute to weakness in HD. Decreased t-tubule diameters in HD fibers without changes in overall cellular TTS density were confirmed using quantitative electron and confocal microscopy. Here, we present results of calculations based on a cylindrical model of skeletal muscle incorporating these changes in muscle fiber and TTS architecture that account for reduced specific capacitance in HD. These results may help our understanding of muscle function in HD and provide a foundation for modeling electrical activity in disease and normal skeletal muscle.

Uncertainty in cardiac myofiber orientation and stiffnesses dominate the variability of left ventricle deformation response.

Computational cardiac modelling is a mature area of biomedical computing and is currently evolving from a pure research tool to aiding in clinical decision making. Assessing the reliability of computational model predictions is a key factor for clinical use, and uncertainty quantification (UQ) and sensitivity analysis are important parts of such an assessment. In this study, we apply UQ in computational heart mechanics to study uncertainty both in material parameters characterizing global myocardial stiffness and in the local muscle fiber orientation that governs tissue anisotropy. The uncertainty analysis is performed using the polynomial chaos expansion (PCE) method, which is a nonintrusive meta‐modeling technique that surrogates the original computational model with a series of orthonormal polynomials over the random input parameter space. In addition, in order to study variability in the muscle fiber architecture, we model the uncertainty in orientation of the fiber field as an approximated random field using a truncated Karhunen‐Loéve expansion. The results from the UQ and sensitivity analysis identify clear differences in the impact of various material parameters on global output quantities. Furthermore, our analysis of random field variations in the fiber architecture demonstrate a substantial impact of fiber angle variations on the selected outputs, highlighting the need for accurate assignment of fiber orientation in computational heart mechanics models.

The importance of muscle architecture in biomechanical reconstructions of extinct animals: acase study using Tyrannosaurus rex.

Functional reconstructions of extinct animals represent a crucial step towards understanding palaeocological interactions, selective pressures and macroevolutionary patterns in the fossil record. In recent years, computational approaches have revolutionised the field of 'evolutionary biomechanics' and have, in general, resulted in convergence of quantitative estimates of performance on increasingly narrow ranges for well studied taxa. Studies of body mass and locomotor performance of Tyrannosaurus rex - arguably the most intensively studied extinct animal - typify this pattern, with numerous independent studies predicting similar body masses and maximum locomotor speeds for this animal. In stark contrast to this trend, recent estimates of maximum bite force in T.rex vary considerably (>50%) despite use of similar quantitative methodologies. Herein we demonstrate that the mechanistic causes of these disparate predictions are indicative of important and underappreciated limiting factors in biomechanical reconstructions of extinct organisms. Detailed comparison of previous models of T.rex bite force reveals that estimations of muscle fibre lengths and architecture are the principal source of disagreement between studies, and therefore that these parameters represents the greatest source of uncertainty in these reconstructions, and potentially therefore extinct animals generally. To address the issue of fibre length and architecture estimation in extinct animals we present data tabulated from the literature of muscle architecture from over 1100 muscles measured in extant terrestrial animals. Application of this dataset in a reanalysis of T.rex bite force emphasises the need for more data on jaw musculature from living carnivorous animals, alongside increased sophistication of modelling approaches. In the latter respect we predict that implementing limits on skeletal loading into musculoskeletal models will narrow predictions for T.rex bite force by excluding higher-end estimates.

Characterization of local muscle fiber anisotropy using shear wave elastography in patients with chronic myofascial pain

Myofascial trigger points (MTrPs) are common in soft tissue musculoskeletal pain conditions. It is believed that MTrPs are local contractures within the extrafusal fibers of skeletal muscles. Further characterizing muscle pathophysiology is desirable to design effective treatments. This study was designed to measure muscle fiber architecture in the neighbourhood of MTrPs using ultrasound Shear Wave Elastography (SWE), a novel approach for quantitatively assessing muscle fiber. We hypothesized that muscle containing active (symptomatic) MTrPs has disorganized fiber architecture. Twenty-four participants (14 women, ages 20–60 years) met criteria for chronic myofascial pain affecting the neck region. All underwent a clinical history and physical examination of the neck and upper trapezius to identify MTrPs and pain self-report. A Supersonic Aixplorer ultrasound imaging system with an L10-4 ultrasound transducer was used to image the upper trapezius muscle. A custom transducer holder ( Fig. 1 ) enabled imaging through a 20 mm diameter window placed over the palpable MTrP or normal tissue, and rotation of the imaging plane to precise angles from 0° (along fibers) to 90° (perpendicular to fibers). Peak shear wave velocity (SWV) is observed longitudinally along muscle fibers (0°), and is minimum across fibers (90°). Muscle fiber anisotropy (a measure of fiber alignment and organization) was quantified as the asymmetry (degrees) in the shear-wave velocity profile around the peak SWV. Muscles with active (symptomatic) MTrPs ( n = 24) exhibited greater anisotropy (14.25 ± 11.01°), compared to normal, asymptomatic muscle tissue ( n = 12), which is more isotropic (7.16 ± 6.70°) ( P < 0.05) ( Fig. 2 ). A positive correlation was found between the maximum anisotropy and average pain (Pearson's r = 0.54). Muscle containing active MTrPs is anisotropic compared to normal muscle tissue, suggesting muscle contractures are in regions of anisotropy. The degree of anisotropy correlates with pain levels.

3D Contrast Techniques for Visualizing Anatomy and Their Application for Human Education, Vertebrate Biomechanics and Paleobiology

New contrast techniques for visualizing 3D anatomy of soft tissues using tomography are revealing outstanding new opportunities for understanding the internal anatomy of humans and other animals. Iodine‐contrast (DiceCT) combined with 3D modeling and computational approaches now enables new directions in anatomy education, body composition, muscle fiber architecture, biomechanics and evolutionary biology. Here we present several new applications of DiceCT‐derived soft‐tissue data used in education and research approaches. First we illustrate new methods using human material that reveal new data on complicated, high‐yield soft‐tissue centric regions including the infratemporal fossa and ear, throat, pelvic floor and wrist. Second we share new methods in applying 3D muscle fiber architecture estimates to biomechanical investigations of vertebrate function. Finally we show how soft‐tissue data help test taphonomic and paleobiological hypotheses of body composition in soft‐bodied fossils derived from conservat‐lagerstatten. These vignettes offer incredible utility for hypothesis testing, biomechanical modeling and anatomy education.Support or Funding InformationNSF IOS 1457319, NSF EAR 163753, Missouri Research Council, NSF CAREER 1652351, NSF IF 1636643This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Exploration of male urethral sphincter complex using diffusion tensor imaging (DTI)-based fiber-tracking.

Urinary incontinence is a major clinical problem arising primarily from age-related degenerative changes to the sphincter muscles. However, the precise anatomy of the normal male sphincter muscles has yet to be established. Diffusion tensor imaging (DTI) may offer a unique insight into muscle microstructure and fiber architecture. To explore the anatomy of the urethral sphincter muscles pertinent to urinary continence function using DT-MRI. Prospective cohort study. Eleven normal male subjects (mean age: 25.4 years); two subjects were scanned in three separate sessions to assess reproducibility. 3T; using a diffusion-weighted spin echo planar sequence. DT parameters including fractional anisotropy (FA), primary (λ1 ), secondary (λ2 ), and tertiary (λ3 ) eigenvalues, Apparent diffusion coefficient and radial diffusivity were analyzed statistically, while tracked muscle fibers were assessed visually. Regional differences (sphincters and longitudinal muscle of the urethra) in the DTI indices were assessed by one-way analysis of variance. A Tukey post-hoc test was used to identify significant differences between muscle regions. Two sphincter muscles, one proximal near the base of the bladder, corresponding to the lisso-sphincter, and the other distal to the end of the prostate corresponding to the rhabdo-sphincter, surrounding a central urethral muscle fiber bundle, were clearly identified. FA was higher and λ3 lower in the proximal sphincter muscle compared to the central urethral muscle and the distal sphincter (P < 0.05). The average coefficient of variation ranged from 5-12% for the DTI indices. Since DTI values are known to reflect underlying tissue microarchitecture, significant differences in DTI indices identified here between the muscles of the urethral complex may potentially arise from differences in tissue microarchitecture that may in turn be related to the specific function of the sphincter and other muscles. 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;48:1002-1011.

Extraocular muscle architecture in hawks and owls.

A complete and accurate understanding of extraocular muscle function is important to the veterinary care of the avian eye. This is especially true for birds of prey, which rely heavily on vision for survival and yet are prone to ocular injury and disease. To better understand the function of extraocular muscles in birds of prey, we studied extraocular muscle architecture grossly and histologically. This sample was composed of two each of the following species: red-tailed hawk (Buteo jamaicensis), Harris's hawk (Parabuteo unicinctus), great horned owl (Bubo virginianus), and barn owl (Tyto alba). All extraocular muscles were dissected and weighed. To analyze muscle fiber architecture, the superior oblique and quadratus muscles were dissected, weighed, and sectioned at 5μm thickness in the transverse plane. We calculated the physiologic cross-sectional area and the ratio of muscle mass to predicted effective maximum tetanic tension. Hawk and owl extraocular muscles exhibit significant physiological differences that play roles in ocular movements and closure of the nictitating membrane. Owls, which do not exhibit extraocular movement, have muscle architecture suited to stabilize the position of a massive, tubular eye that protrudes significantly from the orbit. Hawks, which have a more globose eye that is largely contained within the orbit, do not require as much muscular stability and instead have muscle architecture that facilitates rapid eye movement.