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1
Moro, Tatiana, Camille R. Brightwell, Elena Volpi, Blake B. Rasmussen, and Christopher S. Fry. "Resistance exercise training promotes fiber type-specific myonuclear adaptations in older adults." Journal of Applied Physiology 128, no. 4 (April 1, 2020): 795–804. http://dx.doi.org/10.1152/japplphysiol.00723.2019.
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Aging induces physiological decline in human skeletal muscle function and morphology, including type II fiber atrophy and an increase in type I fiber frequency. Resistance exercise training (RET) is an effective strategy to overcome muscle mass loss and improve strength, with a stronger effect on type II fibers. In the present study, we sought to determine the effect of a 12-wk progressive RET program on the fiber type-specific skeletal muscle hypertrophic response in older adults. Nineteen subjects [10 men and 9 women (71.1 ± 4.3 yr)] were studied before and after the 12-wk program. Immunohistochemical analysis was used to quantify myosin heavy chain (MyHC) isoform expression, cross-sectional area (CSA), satellite cell abundance, myonuclear content, and lipid droplet density. RET induced an increase in MyHC type II fiber frequency and a concomitant decrease in MyHC type I fiber frequency. Mean CSA increased significantly only in MyHC type II fibers (+23.3%, P < 0.05), but myonuclear content increased only in MyHC type I fibers ( P < 0.05), with no change in MyHC type II fibers. Satellite cell content increased ~40% in both fiber types ( P > 0.05). RET induced adaptations to the capillary supply to satellite cells, with the distance between satellite cells and the nearest capillary increasing in type I fibers and decreasing in type II fibers. Both fiber types showed similar decrements in intramuscular lipid density with training ( P < 0.05). Our data provide intriguing evidence for a fiber type-specific response to RET in older adults and suggest flexibility in the myonuclear domain of type II fibers during a hypertrophic stimulus. NEW & NOTEWORTHY In older adults, progressive resistance exercise training (RET) increased skeletal muscle fiber volume and cross-sectional area independently of myonuclear accretion, leading to an expansion of the myonuclear domain. Fiber type-specific analyses illuminated differential adaptation; type II fibers underwent hypertrophy and exhibited myonuclear domain plasticity, whereas myonuclear accretion occurred in type I fibers in the absence of a robust hypertrophic response. RET also augmented satellite cell-capillary interaction and reduced intramyocellular lipid density to improve muscle quality.
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Billeter, R., M. Messerli, E. Wey, A. Puntschart, K. Jostarndt, H. M. Eppenberger, and J. C. Perriard. "Fast myosin light chain expression in chicken muscles studied by in situ hybridization." Journal of Histochemistry & Cytochemistry 40, no. 10 (October 1992): 1547–57. http://dx.doi.org/10.1177/40.10.1382092.
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We have studied the fiber type-specific expression of the fast myosin light chain isoforms LC 1f, LC 2f, and LC 3f in adult chicken muscles using in situ hybridization and two-dimensional gel electrophoresis. Type II (fast) fibers contain all three fast myosin light chain mRNAs; Types I and III (slow) fibers lack them. The myosin light chain patterns of two-dimensional gels from microdissected single fibers match their mRNA signals in the in situ hybridizations. The results confirm and extend previous studies on the fiber type-specific distribution of myosin light chains in chicken muscles which used specific antibodies. The quantitative ratios between protein and mRNA content were not the same for all three fast myosin light chains, however. In bulk muscle samples, as well as in single fibers, there was proportionally less LC 3f accumulated for a given mRNA concentration than LC 1f or LC 2f. Moreover, the ratio between LC 3f mRNA and protein was different in samples from muscles, indicating that LC 3f is regulated somewhat differently than LC 1f and LC 2f. In contrast to other in situ hybridization studies on the fiber type-specific localization of muscle protein mRNAs, which reported the RNAs to be located preferentially at the periphery of the fibers, we found all three fast myosin light chain mRNAs quite evenly distributed within the fiber's cross-sections, and also in the few rare fibers which showed hybridization signals several-fold higher than their surrounding counterparts. This could indicate principal differences in the intracellular localization among the mRNAs coding for various myofibrillar protein families.
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Kucera, J., J. M. Walro, and L. Gorza. "Expression of type-specific MHC isoforms in rat intrafusal muscle fibers." Journal of Histochemistry & Cytochemistry 40, no. 2 (February 1992): 293–307. http://dx.doi.org/10.1177/40.2.1552171.
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Myosin heavy chain (MHC) expression by intrafusal fibers was studied by immunocytochemistry to determine how closely it parallels MHC expression by extrafusal fibers in the soleus and tibialis anterior muscles of the rat. Among the MHC isoforms expressed in extrafusal fibers, only the slow-twitch MHC of Type 1 extrafusal fibers was expressed along much of the fibers. Monoclonal antibodies (MAb) specific for this MHC bound to the entire length of bag2 fibers and the extracapsular region of bag1 fibers. The fast-twitch MHC isoform strongly expressed by bag2 and chain fibers had an epitope not recognized by MAb to the MHC isoforms characteristic of developing muscle fibers or the three subtypes (2A, 2B, 2X) of Type 2 extrafusal fibers. Therefore, intrafusal fibers may express a fast-twitch MHC that is not expressed by extrafusal fibers. Unlike extrafusal fibers, all three intrafusal fiber types bound MAb generated against mammalian heart and chicken limb muscles. The similarity of the fast-twitch MHC of bag2 and chain fibers and the slow-tonic MHC of bag1 and bag2 fibers to the MHC isoforms expressed in avian extrafusal fibers suggests that phylogenetically primitive MHCs might persist in intrafusal fibers. Data are discussed relative to the origin and regional regulation of MHC isoforms in intrafusal and extrafusal fibers of rat hindlimb muscles.
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Eggers, Britta, Karin Schork, Michael Turewicz, Katalin Barkovits, Martin Eisenacher, Rolf Schröder, Christoph S. Clemen, and Katrin Marcus. "Advanced Fiber Type-Specific Protein Profiles Derived from Adult Murine Skeletal Muscle." Proteomes 9, no. 2 (June 8, 2021): 28. http://dx.doi.org/10.3390/proteomes9020028.
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Skeletal muscle is a heterogeneous tissue consisting of blood vessels, connective tissue, and muscle fibers. The last are highly adaptive and can change their molecular composition depending on external and internal factors, such as exercise, age, and disease. Thus, examination of the skeletal muscles at the fiber type level is essential to detect potential alterations. Therefore, we established a protocol in which myosin heavy chain isoform immunolabeled muscle fibers were laser microdissected and separately investigated by mass spectrometry to develop advanced proteomic profiles of all murine skeletal muscle fiber types. All data are available via ProteomeXchange with the identifier PXD025359. Our in-depth mass spectrometric analysis revealed unique fiber type protein profiles, confirming fiber type-specific metabolic properties and revealing a more versatile function of type IIx fibers. Furthermore, we found that multiple myopathy-associated proteins were enriched in type I and IIa fibers. To further optimize the assignment of fiber types based on the protein profile, we developed a hypothesis-free machine-learning approach, identified a discriminative peptide panel, and confirmed our panel using a public data set.
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Lee, Young Jae, Jae Hyung Kim, Jang Soon Kim, Dong Bok Lee, Jae Chun Lee, Yun Jung Chung, and Yun Soo Lim. "Fabrication of Activated Carbon Fibers from Stabilized PAN-Based Fibers by KOH." Materials Science Forum 449-452 (March 2004): 217–20. http://dx.doi.org/10.4028/www.scientific.net/msf.449-452.217.
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Activated carbon fibers were prepared from stabilized PAN-based fibers by chemical activation using potassium hydroxide at different concentration. The experimental data showed variations in specific surface area, microstructure by the activated carbon fibers. Specific surface area of about 2545 m2/g was obtained in the KOH/stabilized PAN-based fiber ratio of 1:1 at 800°. An abrupt reduction of specific surface area was observed in the experiments with the ratio of 3:1 of OH/stabilized PAN-based fiber, being dissimilar with the result of KOH/fiber ratios of 1:1 and 2:1 in the similar experiments. The high concentration of KOH led to the destruction of micropore walls instead of forming mesopores.
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Lassche, Saskia, Nicol C. Voermans, Robbert van der Pijl, Marloes van den Berg, Arend Heerschap, Hieronymus van Hees, Benno Kusters, Silvère M. van der Maarel, Coen A. C. Ottenheijm, and Baziel G. M. van Engelen. "Preserved single muscle fiber specific force in facioscapulohumeral muscular dystrophy." Neurology 94, no. 11 (January 21, 2020): e1157-e1170. http://dx.doi.org/10.1212/wnl.0000000000008977.
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ObjectiveTo investigate single muscle fiber contractile performance in muscle biopsies from patients with facioscapulohumeral muscular dystrophy (FSHD), one of the most common hereditary muscle disorders.MethodsWe collected 50 muscle biopsies (26 vastus lateralis, 24 tibialis anterior) from 14 patients with genetically confirmed FSHD and 12 healthy controls. Single muscle fibers (n = 547) were isolated for contractile measurements. Titin content and titin phosphorylation were examined in vastus lateralis muscle biopsies.ResultsSingle muscle fiber specific force was intact at saturating and physiologic calcium concentrations in all FSHD biopsies, with (FSHDFAT) and without (FSHDNORMAL) fatty infiltration, compared to healthy controls. Myofilament calcium sensitivity of force is increased in single muscle fibers obtained from FSHD muscle biopsies with increased fatty infiltration, but not in FSHD muscle biopsies without fatty infiltration (pCa50: 5.77–5.80 in healthy controls, 5.74–5.83 in FSHDNORMAL, and 5.86–5.90 in FSHDFAT single muscle fibers). Cross-bridge cycling kinetics at saturating calcium concentrations and myofilament cooperativity did not differ from healthy controls. Development of single muscle fiber passive tension was changed in all FSHD vastus lateralis and in FSHDFAT tibialis anterior, resulting in increased fiber stiffness. Titin content was increased in FSHD vastus lateralis biopsies; however, titin phosphorylation did not differ from healthy controls.ConclusionMuscle weakness in patients with FSHD is not caused by reduced specific force of individual muscle fibers, even in severely affected tissue with marked fatty infiltration of muscle tissue.
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Li, Baoxia, Liuqin Zhang, Jing Xi, Lei Hou, Xingxian Fu, Yan Pei, and Mi Zhang. "An Unexpected Regulatory Sequence from Rho-Related GTPase6 Confers Fiber-Specific Expression in Upland Cotton." International Journal of Molecular Sciences 23, no. 3 (January 19, 2022): 1087. http://dx.doi.org/10.3390/ijms23031087.
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Cotton fibers, single seed trichomes derived from ovule epidermal cells, are the major source of global textile fibers. Fiber-specific promoters are desirable to study gene function and to modify fiber properties during fiber development. Here, we revealed that Rho-related GTPase6 (GhROP6) was expressed preferentially in developing fibers. A 1240 bp regulatory region of GhROP6, which contains a short upstream regulatory sequence, the first exon, and the partial first intron, was unexpectedly isolated and introduced into transgenic cotton for analyzing promoter activity. The promoter of GhROP6 (proChROP6) conferred a specific expression in ovule surface, but not in the other floral organs and vegetative tissues. Reverse transcription PCR analysis indicated that proGhROP6 directed full-length transcription of the fused ß-glucuronidase (GUS) gene. Further investigation of GUS staining showed that proChROP6 regulated gene expression in fibers and ovule epidermis from fiber initiation to cell elongation stages. The preferential activity was enriched in fiber cells after anthesis and reached to peak on flowering days. By comparison, proGhROP6 was a mild promoter with approximately one-twenty-fifth of the strength of the constitutive promoter CaMV35S. The promoter responded to high-dosage treatments of auxin, gibberellin and salicylic acid and slightly reduced GUS activity under the in vitro treatment. Collectively, our data suggest that the GhROP6 promoter has excellent activity in initiating fibers and has potential for bioengineering of cotton fibers.
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Moon, Sook Young, Myung Soo Kim, and Yun Soo Lim. "Preparation and Characterization of Chemical Activated Fibers on Various Carbon Fibers." Materials Science Forum 510-511 (March 2006): 314–17. http://dx.doi.org/10.4028/www.scientific.net/msf.510-511.314.
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OXI-PAN fibers, Kynol fibers, and rayon fibers were used as precursors for the preparation of activated carbon fibers (ACFs) by chemical activation with KOH at 800°C. The effects of different precursor fibers and fiber/KOH ratios on the final ACFs are discussed. The precursor fibers used were appropriate for the ACFs in a single stage pyrolysis process. The OXI-PAN fibers, which were activated with KOH of 2.0M, showed a specific surface area of 2328m2/g, however, lost the fiber shape because of low yields. The Kynol fibers and Rayon fibers showed the high yields, but lower specific surface areas of 900m2/g and 774m2/g, respectively, at KOH of 1.5M. The OXI-PAN fibers, which were activated with KOH of 1.5M, have a specific surface area of 1028m2/g and higher micro-pore volumes and lower yields rather than Kynol-1.5 and Rayon-1.5 samples. This phenomenon is attributed to higher chemical resistance of the Kynol and Rayon fibers rather than OXI-PAN fibers. However, the Kynol fibers were the best precursors on KOH activation at 800°C when carbon yields, surface areas, and micropore volumes are condisered.
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Guo, Xing Mei, and Yi Ping Qiu. "Hemp Fiber Reinforced Composites: Morphological and Mechanical Properties." Advanced Materials Research 332-334 (September 2011): 121–25. http://dx.doi.org/10.4028/www.scientific.net/amr.332-334.121.
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The use of natural plant fibers as reinforcing fillers in fiber-polymer composites has drawn much interest in recent years. Natural plant fibers as reinforcing fillers have several advantages over inorganic fillers such as glass fibers; they are abundant, readily available, renewable, inexpensive, biodegradable, of low density, and of high specific strength. Hemp fibers are one of the most attractive natural plant fibers for fiber-reinforced composites because of their exceptional specific stiffness. In this review, we summarize recent progress in developments of the hemp fiber reinforced composites such as hemp fiber reinforced unsaturated polyester (UPE), hemp fiber reinforced polypropylene (PP), hemp fiber reinforced epoxy composites, and so on, illustrate with examples how they work, and discuss their intrinsic fundamentals and optimization designs. We are expecting the review to pave the way for developing fiber-polymer composites with higher strength.
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Hallauer, P. L., H. L. Bradshaw, and K. E. Hastings. "Complex fiber-type-specific expression of fast skeletal muscle troponin I gene constructs in transgenic mice." Development 119, no. 3 (November 1, 1993): 691–701. http://dx.doi.org/10.1242/dev.119.3.691.
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We analyzed, in transgenic mice, the cellular expression pattern of the quail fast skeletal muscle troponin I (TnIfast) gene and of a chimeric reporter construct in which quail TnIfast DNA sequences drive expression of E. coli beta-galactosidase (beta-gal). Both constructs were actively expressed in skeletal muscle and specifically in fast, as opposed to slow, muscle fibers. Unexpectedly, both constructs showed a marked differential expression among the adult fast fiber subtypes according to the pattern IIB > IIX > IIA. This expression pattern was consistent in multiple lines and differed from the endogenous mouse TnIfast pattern, which shows approximately equal expression in all fast fibers. These observations indicate that distinct regulatory mechanisms contribute to high-level expression of TnIfast in the various fast fiber subtypes and suggest that the outwardly simple pattern of equal expression in all fast fiber types shown by the endogenous mouse TnIfast gene is based on an intricate system of counterbalancing mechanisms. The adult expression pattern of the TnIfast/beta-gal construct emerged in a two-stage developmental process. Differential expression in fast versus slow fibers was evident in neonatal animals, although expression in fast fibers was relatively weak and homogeneous. During the first two weeks of postnatal life, expression in maturing IIB fibers was greatly increased whereas that in IIA/IIX fibers remained weak, giving rise to marked differential expression among fast fiber types. Thus at least two serially acting (pre- and post-natal) fiber-type-specific regulatory mechanisms contribute to high-level gene expression in adult fast muscle fibers. Unexpected similarities between TnIfast transgene expression and that of the myosin heavy chain gene family (which includes differentially expressed IIB-, IIX- and IIA-specific members) suggest that similar mechanisms may regulate adult fast muscle gene expression in a variety of unrelated muscle gene families.
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Sultan, Karim R., Bernd T. Dittrich, Elmi Leisner, Nina Paul, and Dirk Pette. "Fiber type-specific expression of major proteolytic systems in fast- to slow-transforming rabbit muscle." American Journal of Physiology-Cell Physiology 280, no. 2 (February 1, 2001): C239—C247. http://dx.doi.org/10.1152/ajpcell.2001.280.2.c239.
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The present study investigates the role of two major proteolytic systems in transforming rabbit and rat muscles. The fast-to-slow transformation of rabbit muscle by chronic low-frequency stimulation (CLFS) induces fast-to-slow transitions of intact, mature fibers and replacement of degenerating fibers by newly formed slow fibers. Ubiquitination, an indicator of the ATP-dependent proteasome system, and calpain activity were measured in homogenates of control and stimulated extensor digitorum longus muscles. Calpain activity increased similarly (∼2-fold) in stimulated rat and rabbit muscles. CLFS had no effect on protein ubiquitination in rat muscle but led to elevations in ubiquitin protein conjugates in rabbit muscle. Immunohistochemistry was used to study the distribution of μ-calpain and m-calpain and of ubiquitinated proteins in myosin heavy chain-based fiber types. The findings suggest that both proteolytic systems are involved in fiber transformation and replacement. Transforming mature fibers displayed increases in μ-calpain and accumulation of ubiquitin protein conjugates. The majority of these fibers were identified as type IIA. Enhanced ubiquitination was also observed in degenerating and necrotic fibers. Such fibers additionally displayed elevated m-calpain levels. Conversely, p94, the skeletal muscle-specific calpain, decayed rapidly after stimulation onset and was hardly detectable after 4 days of CLFS.
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Waters, Richard E., Svein Rotevatn, Ping Li, Brian H. Annex, and Zhen Yan. "Voluntary running induces fiber type-specific angiogenesis in mouse skeletal muscle." American Journal of Physiology-Cell Physiology 287, no. 5 (November 2004): C1342—C1348. http://dx.doi.org/10.1152/ajpcell.00247.2004.
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Adult skeletal muscle undergoes adaptation in response to endurance exercise, including fast-to-slow fiber type transformation and enhanced angiogenesis. The purpose of this study was to determine the temporal and spatial changes in fiber type composition and capillary density in a mouse model of endurance training. Long-term voluntary running (4 wk) in C57BL/6 mice resulted in an approximately twofold increase in capillary density and capillary-to-fiber ratio in plantaris muscle as measured by indirect immunofluorescence with an antibody against the endothelial cell marker CD31 (466 ± 16 capillaries/mm2 and 0.95 ± 0.04 capillaries/fiber in sedentary control mice vs. 909 ± 55 capillaries/mm2 and 1.70 ± 0.04 capillaries/fiber in trained mice, respectively; P < 0.001). A significant increase in capillary-to-fiber ratio was present at day 7 with increased concentration of vascular endothelial growth factor (VEGF) in the muscle, before a significant increase in percentage of type IIa myofibers, suggesting that exercise-induced angiogenesis occurs first, followed by fiber type transformation. Further analysis with simultaneous staining of endothelial cells and isoforms of myosin heavy chains (MHCs) showed that the increase in capillary contact manifested transiently in type IIb + IId/x fibers at the time ( day 7) of significant increase in total capillary density. These findings suggest that endurance training induces angiogenesis in a subpopulation of type IIb + IId/x fibers before switching to type IIa fibers.
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Lee-Young, Robert S., Benedict J. Canny, Damian E. Myers, and Glenn K. McConell. "AMPK activation is fiber type specific in human skeletal muscle: effects of exercise and short-term exercise training." Journal of Applied Physiology 107, no. 1 (July 2009): 283–89. http://dx.doi.org/10.1152/japplphysiol.91208.2008.
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AMP-activated protein kinase (AMPK) has been extensively studied in whole muscle biopsy samples of humans, yet the fiber type-specific expression and/or activation of AMPK is unknown. We examined basal and exercise AMPK-α Thr172 phosphorylation and AMPK subunit expression (α1, α2, and γ3) in type I, IIa, and IIx fibers of human skeletal muscle before and after 10 days of exercise training. Before training basal AMPK phosphorylation was greatest in type IIa fibers ( P < 0.05 vs. type I and IIx), while an acute bout of exercise increased AMPK phosphorylation in all fibers ( P < 0.05), with the greatest increase occurring in type IIx fibers. Exercise training significantly increased basal AMPK phosphorylation in all fibers, and the exercise-induced increases were uniformly suppressed compared with pretraining exercise. Expression of AMPK-α1 and -α2 was similar between fibers and was not altered by exercise training. However, AMPK-γ3 was differentially expressed in skeletal muscle fibers (type IIx > type IIa > type I), irrespective of training status. Thus skeletal muscle AMPK phosphorylation and AMPK expression are fiber type specific in humans in the basal state, as well as during exercise. Our findings reveal fiber type-specific differences that have been masked in previous studies examining mixed muscle samples.
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LIN, J. Z., X. C. CHAI, and X. J. FAN. "STRUCTURE AND PROPERTIES OF CONCENTRATED FIBER SUSPENSIONS IN A SHEAR FLOW." Modern Physics Letters B 22, no. 09 (April 10, 2008): 643–59. http://dx.doi.org/10.1142/s0217984908015152.
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The concentrated fiber suspensions in a simple shear flow are simulated numerically by taking into account the hydrodynamic interactions and fiber–fiber mechanical contacts. The orientation probability distribution of fibers, the specific viscosity and the first normal stress difference are obtained. The comparison of the specific viscosity to experimental data is made and the agreement is good. The results show that initially randomly-oriented fibers are re-oriented in the flow direction. The hydrodynamic interactions and fiber–fiber mechanical contacts result in an increase in the spread of the orientation distribution and asymmetric orientation distribution about the flow direction. Fiber's alignment with the flow direction becomes more obvious with an increasing shear rate. In a concentrated fiber suspension, the force induced by the fiber–fiber mechanical contact plays a more important role than that induced by hydrodynamic interactions. The specific viscosity of fiber suspension grows with concentration for various aspect ratios. For a fixed concentration, the larger the aspect ratio is, the higher the specific viscosity is. The specific viscosity calculated by taking into account both hydrodynamic interactions and fiber–fiber mechanical contacts is larger than that only taking into account the fiber–fiber mechanical contacts. The effect of aspect ratio on the first normal stress difference is more obvious at high concentration. Taking into account the hydrodynamic interactions or not will make a big difference in the first normal stress difference.
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Choi, Seung Jun, and Jeffrey J. Widrick. "Calcium-activated force of human muscle fibers following a standardized eccentric contraction." American Journal of Physiology-Cell Physiology 299, no. 6 (December 2010): C1409—C1417. http://dx.doi.org/10.1152/ajpcell.00226.2010.
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Peak Ca2+-activated specific force (force/fiber cross-sectional area) of human chemically skinned vastus lateralis muscle fiber segments was determined before and after a fixed-end contraction or an eccentric contraction of standardized magnitude (+0.25 optimal fiber length) and velocity (0.50 unloaded shortening velocity). Fiber myosin heavy chain (MHC) isoform content was assayed by SDS-PAGE. Posteccentric force deficit, a marker of damage, was similar for type I and IIa fibers but threefold greater for type IIa/IIx hybrid fibers. A fixed-end contraction had no significant effect on force. Multiple linear regression revealed that posteccentric force was explained by a model consisting of a fiber type-independent and a fiber type-specific component ( r2 = 0.91). Preeccentric specific force was directly associated with a greater posteccentric force deficit. When preeccentric force was held constant, type I and IIa fibers showed identical susceptibility to damage, while type IIa/IIx fibers showed a significantly greater force loss. This heightened sensitivity to damage was directly related to the amount of type IIx MHC in the hybrid fiber. Our model reveals a fiber-type sensitivity of the myofilament lattice or cytoskeleton to mechanical strain that can be described as follows: type IIa/IIx > type IIa = type I. If these properties extend to fibers in vivo, then alterations in the number of type IIa/IIx fibers may modify a muscle's susceptibility to eccentric damage.
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Langston, Tye. "The Tensile Behavior of High-Strength Carbon Fibers." Microscopy and Microanalysis 22, no. 4 (June 9, 2016): 841–44. http://dx.doi.org/10.1017/s143192761601134x.
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AbstractCarbon fibers exhibit exceptional properties such as high stiffness and specific strength, making them excellent reinforcements for composite materials. However, it is difficult to directly measure their tensile properties and estimates are often obtained by tensioning fiber bundles or composites. While these macro scale tests are informative for composite design, their results differ from that of direct testing of individual fibers. Furthermore, carbon filament strength also depends on other variables, including the test length, actual fiber diameter, and material flaw distribution. Single fiber tensile testing was performed on high-strength carbon fibers to determine the load and strain at failure. Scanning electron microscopy was also conducted to evaluate the fiber surface morphology and precisely measure each fiber’s diameter. Fiber strength was found to depend on the test gage length and in an effort to better understand the overall expected performance of these fibers at various lengths, statistical weak link scaling was performed. In addition, the true Young’s modulus was also determined by taking the system compliance into account. It was found that all properties (tensile strength, strain to failure, and Young’s modulus) matched very well with the manufacturers’ reported values at 20 mm gage lengths, but deviated significantly at other lengths.
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Rastogi, Vipul. "Application specific leaky optical fibers." Journal of Optics 42, no. 1 (October 18, 2012): 42–50. http://dx.doi.org/10.1007/s12596-012-0095-8.
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Taylor, B. J., and L. M. Knittel. "Sex-specific differentiation of a male-specific abdominal muscle, the Muscle of Lawrence, is abnormal in hydroxyurea-treated and in fruitless male flies." Development 121, no. 9 (September 1, 1995): 3079–88. http://dx.doi.org/10.1242/dev.121.9.3079.
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A prominent sex-specific abdominal muscle in male Drosophila is the Muscle of Lawrence (MOL), which is induced by male-specific innervation. We have examined MOL development in wild-type males, in males fed hydroxyurea to ablate the muscle precursors and in fruitless mutants, in which the MOL muscle develops aberrantly. One striking feature of MOLs in wild-type males was the presence of additional muscle nuclei compared with neighboring muscles or MOL-homologues in females. We tested whether muscle length and the sex-specific expression of a reporter gene depended critically on the number of nuclei present within a MOL fiber. MOL fibers developing from a reduced myoblast pool in hydroxyurea-affected hemisegments were recognizable by their attachment points and still contained more nuclei than did neighboring medial fibers, suggesting that these MOL fibers were able to actively recruit myoblasts nearly as well as wild-type MOLs. However, many of the hydroxyurea-affected MOL fibers were incapable of the normal male-specific expression of a muscle-specific reporter gene. We suggest that early events in MOL development, such as finding the correct muscle attachment points, are relatively insensitive to the number of MOL nuclei compared with later events, such as the sex-specific expression of a reporter gene. In fruitless mutant males, MOL-position fibers are smaller and had substantially fewer nuclei compared to wild-type MOLs. Since the number and distribution of muscle precursors was the same in fruitless mutant and wild-type animals, we propose that one fru+ function is to direct the male-specific recruitment of myoblasts into MOL-myotubes. However, fruitless+ must have more than one role in MOL fiber development, since simple reduction in the number of muscle nuclei, as demonstrated by the hydroxyurea ablations, is insufficient to account for all of the MOL muscle phenotypes in fruitless mutant males.
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Geremew, Anteneh, Pieter De Winne, Tamene Adugna Demissie, and Hans De Backer. "Treatment of Natural Fiber for Application in Concrete Pavement." Advances in Civil Engineering 2021 (February 13, 2021): 1–13. http://dx.doi.org/10.1155/2021/6667965.
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Concrete crack is one of the main problems observed in concrete technology due to drying shrinkage. Incorporating fibers in concrete production is one of the mechanisms implemented to mitigate cracks. Nowadays, investigators concentrate on different techniques to replace human-made fiber with existing natural fibers for fiber-reinforced composite material. Utilization of natural fiber has an initiation for the development of eco-friendly materials by reducing damages caused by human-made materials and saving nonrenewable resources. Natural fibers are readily and abundantly available, sustainable, and biodegradable, with low cost and low density, and have superior specific properties. Nevertheless, there are some limitations of natural fiber compared to human-made fiber. Consequently, significant energy was applied to alter natural fiber’s surface and morphology using physical, chemical, and biological treatment techniques to overcome the limitation. The primary intention of surface treatment is to modify the bond between the fiber surface and the polymer matrix. However, based on this literature review, there were no specific treatment techniques to be followed to select the best one from the others as criteria. It should include all parameters to consider starting from the stage from the cradle to the grave, cost of chemicals, transportation, and labors, including energy consumption and effluent energy. Additionally, their environmental effect also investigated in detail to compare each other.
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Al Bakri, A. M. Mustafa, J. Liyana, M. N. Norazian, H. Kamarudin, and C. M. Ruzaidi. "Mechanical Properties of Polymer Composites with Sugarcane Bagasse Filler." Advanced Materials Research 740 (August 2013): 739–44. http://dx.doi.org/10.4028/www.scientific.net/amr.740.739.
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Natural fibers reinforced polymer composites have gained more interest because of their biodegradable, light weight, less expensive sources, easy processing, high specific modulus and also environmentally friendly appeal. This paper presents an overview of a study aimed at showing on how the bio-composites which is bagasse fibers combined with resins as an alternative of bagasse-fiber-based composites panel. Transforming bagasse fibers into panel products provides a prospective solution. Bagasse-fiber-based composites offer potential as the core material replacing high density and expensive wood-based fiberboard. Biodegradable composites reinforced with bagasse fibres after being modified or treated by alkali treatment were prepared and also the mechanical properties were investigated. The bio-composites panel samples were processed by hot press machine. All panels were made with aspect ratios between bagasse fibers and polystyrene thermoplastics resins and also the sieve size of bagasse fibers which has short fibers and combination of short fiber and granules fibers. The polystyrene was added as a modified from natural fibers to determine the effect it had on physical and mechanical properties of the panel. Resin content level and panel density were very important in controlling the strength properties of the panels. Surface hardness value, compressive strength, bending strength and bending modulus values all increases in resin content level and panel density. Bagasse-based-panel products can be commercialize successfully if have good development of a cost manufacturing process on an establishment of a market base for the products.
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Park, Junbeom, Sung-Hyun Lee, Jaegeun Lee, Dong-Myeong Lee, Hayoung Yu, Hyeon Su Jeong, Seung Min Kim, and Kun-Hong Lee. "Accurate measurement of specific tensile strength of carbon nanotube fibers with hierarchical structures by vibroscopic method." RSC Advances 7, no. 14 (2017): 8575–80. http://dx.doi.org/10.1039/c6ra26607j.
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Since carbon nanotube (CNT) fibers have a hierarchical structure, the specific strength of CNT fibers can be estimated to be much higher than its real value when the linear density of the fiber is measured using the vibroscopic method.
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Wyckelsma, V. L., M. J. McKenna, F. R. Serpiello, C. R. Lamboley, R. J. Aughey, N. K. Stepto, D. J. Bishop, and R. M. Murphy. "Single-fiber expression and fiber-specific adaptability to short-term intense exercise training of Na+-K+-ATPase α- and β-isoforms in human skeletal muscle." Journal of Applied Physiology 118, no. 6 (March 15, 2015): 699–706. http://dx.doi.org/10.1152/japplphysiol.00419.2014.
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The Na+-K+-ATPase (NKA) plays a key role in muscle excitability, but little is known in human skeletal muscle about fiber-type-specific differences in NKA isoform expression or adaptability. A vastus lateralis muscle biopsy was taken in 17 healthy young adults to contrast NKA isoform protein relative abundance between type I and IIa fibers. We further investigated muscle fiber-type-specific NKA adaptability in eight of these adults following 4-wk repeated-sprint exercise (RSE) training, comprising three sets of 5 × 4-s sprints, 3 days/wk. Single fibers were separated, and myosin heavy chain (I and IIa) and NKA (α1–3 and β1–3) isoform abundance were determined via Western blotting. All six NKA isoforms were expressed in both type I and IIa fibers. No differences between fiber types were found for α1-, α2-, α3-, β1-, or β3-isoform abundances. The NKA β2-isoform was 27% more abundant in type IIa than type I fibers ( P < 0.05), with no other fiber-type-specific trends evident. RSE training increased β1 in type IIa fibers (pretraining 0.70 ± 0.25, posttraining 0.84 ± 0.24 arbitrary units, 42%, P < 0.05). No training effects were found for other NKA isoforms. Thus human skeletal muscle expresses all six NKA isoforms and not in a fiber-type-specific manner; this points to their different functional roles in skeletal muscle cells. Detection of elevated NKA β1 after RSE training demonstrates the sensitivity of the single-fiber Western blotting technique for fiber-type-specific intervention effects.
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Jostarndt, K., A. Puntschart, H. Hoppeler, and R. Billeter. "Fiber-type-specific expression of essential (alkali) myosin light chains in human skeletal muscles." Journal of Histochemistry & Cytochemistry 44, no. 10 (October 1996): 1141–52. http://dx.doi.org/10.1177/44.10.8813079.
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We studied the expression patterns of the essential (alkali) myosin light-chain isoforms in adult human skeletal muscles, using in situ hybridization and single-fiber protein analysis. In analogy to other species, we found that the fiber type-specific expression of essential myosin light chains is regulated via the availability of the respective mRNAs in a given fiber. In contrast to other species, the slow isoform 1sa was only expressed in the most oxidative Type I fibers (Subtype IA) in addition to 1sb. These fibers also contained high levels of carbonic anhydrase III. Within the fibers, the essential myosin light-chain mRNAs were located preferentially in the perinuclear regions and to a lesser extent in the intermyofibrillar spaces, a distribution that excludes cotranslational assembly of these light chains into the myofibrils as the main mechanism. In comparing leg and shoulder muscles, we found less distinct fiber typing in the expression patterns of the essential myosin light chains in the leg muscles than in muscles from the shoulder region.
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Do, Nhi Thi, Hop Quang Tran, Hanh Thi My Diep, and Vi Thi Vi Do. "Study on properties of composites polyurethane foam reinforced by bamboo fiber." Science and Technology Development Journal 19, no. 4 (December 31, 2016): 212–20. http://dx.doi.org/10.32508/stdj.v19i4.693.
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This study focuses on the development and characterization of polyurethane/bamboo fiber composites foams which have the specific properties to participate both in the thermal insulation and regulation of the humidity inside the building. The polyurethane foam reinforced by bamboo fibers (5–20 wt%) were produced to investigate the mechanical test, the morphological characterization and thermal properties. The result from mechanical test showed that the compressive strength was increased at 5 wt % of bamboo fiber. Likewise, the effects of the fibre diameter and nature of bamboo fibers on some properties (compressive test, thermal analyses, surface morphology) of bamboo fibre reinforced rigid polyurethane foam were studied. The bamboo Gai and Luong fibres result in composites with better mechanical strength than the other fiber composites.
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Gallagher, Philip M., Chad D. Touchberry, Kelli Teson, Everlee McCabe, Michelle Tehel, and Michael J. Wacker. "Effects of an acute bout of resistance exercise on fiber-type specific GLUT4 and IGF-1R expression." Applied Physiology, Nutrition, and Metabolism 38, no. 5 (May 2013): 581–86. http://dx.doi.org/10.1139/apnm-2012-0301.
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The effects of resistance exercise on fiber-type–specific expression of insulin-like growth factor I receptor (IGF-1R) and glucose transporter 4 (GLUT4) was determined in 6 healthy males. The expression of both genes increased in Type I fibers (p < 0.05), but only GLUT4 increased (p < 0.05) in Type II fibers. These data demonstrates that an acute bout of resistance exercise can up-regulate mechanisms of glucose uptake in slow and fast-twitch fibers, but the IGF signaling axis may not be as effective in fast-twitch fibers.
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CHIHAI (PEȚU), Rodica, Claudia UNGUREANU, and Vasile BRIA. "Effect of the Fiber Orientation of Glass Fiber Reinforced Polymer Composites on Mechanical Properties." Annals of “Dunarea de Jos” University of Galati. Fascicle IX, Metallurgy and Materials Science 45, no. 2 (June 15, 2022): 16–21. http://dx.doi.org/10.35219/mms.2022.2.03.
Full textAbstract:
Fiber reinforced polymer (FRP) composites possess excellent specific strength, specific stiffness and controlled anisotropy for which these are extensively used in various engineering applications, like automobile industries, aerospace industries, marine industries, space industries, electronics industries and many more. Glass fibers (GF), carbon fibers (CF) and aramid fibers (AF) are common reinforcements for polymer matrix composites (PMCs). High mechanical properties and wear resistance behaviour of glass fiber reinforced composites are the premises for the current experimental research on the effect of fiber orientation on the tensile strength of the polymeric composite materials. The glass fiber reinforced epoxy resin composite was prepared by wet lay-up method, followed by thermal treatment.
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Geiger, Paige C., Mark J. Cody, Rebecca L. Macken, and Gary C. Sieck. "Maximum specific force depends on myosin heavy chain content in rat diaphragm muscle fibers." Journal of Applied Physiology 89, no. 2 (August 1, 2000): 695–703. http://dx.doi.org/10.1152/jappl.2000.89.2.695.
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In the present study, myosin heavy chain (MHC) content per half sarcomere, an estimate of the number of cross bridges available for force generation, was determined in rat diaphragm muscle (Diam) fibers expressing different MHC isoforms. We hypothesize that fiber-type differences in maximum specific force [force per cross-sectional area (CSA)] reflect the number of cross bridges present per CSA. Studies were performed on single, Triton X-100-permeabilized rat Diam fibers. Maximum specific force was determined by activation of single Diamfibers in the presence of a high-calcium solution (pCa, −log Ca2+ concentration of 4.0). SDS-PAGE and Western blot analyses were used to determine MHC isoform composition and MHC content per half sarcomere. Differences in maximum specific force across fast MHC isoforms were eliminated when controlled for half-sarcomere MHC content. However, the force produced by slow fibers remained below that of fast fibers when normalized for the number of cross bridges available. On the basis of these results, the lower force produced by slow fibers may be due to less force per cross bridge compared with fast fibers.
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Yeh, Jen-taut, Chuen-Kai Wang, Lu-Kai Huang, Chih-Chen Tsai, and Wei-Yu Lai. "Ultradrawing and Ultimate Tenacity Properties of Ultrahigh Molecular Weight Polyethylene Composite Fibers Filled with Nanosilica Particles with Varying Specific Surface Areas." Journal of Nanomaterials 2015 (2015): 1–16. http://dx.doi.org/10.1155/2015/146718.
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Original and/or functionalized nanosilica particles with a quoted specific surface area of 100, 300, and 600 m2/g, respectively, were used to investigate the influence of specific surface areas of nanosilica particles on ultradrawing and ultimate tensile properties of ultrahigh molecular weight polyethylene (UHMWPE), UHMWPE/nanosilica, and UHMWPE/functionalized nanosilica fibers. The specific surface areas of well-dispersed functionalized nanosilica particles in UHMWPE/functionalized nanosilica fibers can positively affect their ultradrawing, orientation, ultimate tensile properties, and “micro-fibrils” morphologies. Excellent orientation and ultimate tensile properties of UHMWPE/nanofiller fibers can be prepared by ultradrawing the UHMWPE/functionalized nanosilica as-prepared fibers with optimal contents of the best prepared functionalized nanosilica particles well dispersing in the as-prepared fibers. The ultimate tensile strength value of the best prepared UHMWPE/functionalized nanosilica drawn fiber reaches 7.6 GPa, which is about 2.3 times of those of the best prepared UHMWPE drawn fiber without addition of any nanofiller. Specific surface area, morphological and Fourier transform infrared analyses of original and functionalized nanosilica particles, and/or investigations of thermal, orientation factor, and ultimate tensile properties of as-prepared and/or drawn UHMWPE/functionalized nanosilica fibers were performed to understand the above improved ultradrawing and ultimate tensile properties of the UHMWPE/functionalized nanosilica as-prepared and/or drawn fibers.
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Idrees, Maria. "Comparative study of hybrid fiber cementitious composites." Independent Journal of Management & Production 11, no. 3 (June 1, 2020): 1034. http://dx.doi.org/10.14807/ijmp.v11i3.1081.
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Different types of fibers impart specific characteristics to concrete, including crack bridging, early age crack resistance, ductility, toughness, strength, and loss of workability. It seems that if these fibers are combined, then specific characteristics of each fiber may be imparted to concrete and the desired characteristics of the concrete composite may be achieved. Thus, this investigation has been conducted to study the properties of concrete composites composed of four different types of fibers used singly or in hybrid form. The effectiveness of hybrid fibers in cementitious composites to achieve better characteristics; strengths, toughness, workability, and cost, was investigated and compared. Composites made of carbon fiber, plain steel fiber, polypropylene fiber, and glass fiber and their hybrid combinations (2, 3 and 4 fibers mixed), at constant volume of fiber 1.25%, along 4% styrene-butadiene rubber latex and 1.5% superplasticizer, are prepared and tested. The composites are compared and investigated for their feasibility in terms of their properties and cost. The comparison showed the suitability of some bi-hybrid composites, and incompatibility of tri-hybrid and tetra-hybrid composites in terms of effectiveness and feasibility.
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Shaw, C. S., C. Swinton, M. G. Morales-Scholz, N. McRae, T. Erftemeyer, A. Aldous, R. M. Murphy, and K. F. Howlett. "Impact of exercise training status on the fiber type-specific abundance of proteins regulating intramuscular lipid metabolism." Journal of Applied Physiology 128, no. 2 (February 1, 2020): 379–89. http://dx.doi.org/10.1152/japplphysiol.00797.2019.
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Endurance training enhances the capacity for fat oxidation during exercise due to increased utilization of intramuscular lipid (IMCL). This study quantitatively investigated the impact of exercise training status on muscle fiber type-specific abundance of regulatory proteins involved in IMCL utilization. Endurance-trained [ n = 7 subjects, peak oxygen consumption (V̇o2peak) 62.6 ± 4.1 (SD) mL·min−1·kg−1] and non-endurance-trained ( n = 8 subjects, V̇o2peak 44.9 ± 5.3 mL·min−1·kg−1) young men completed an incremental exercise test to determine maximal fat oxidation (MFO) and maximal oxygen uptake. Fiber type-specific IMCL content and protein abundance were assessed with immunofluorescence microscopy and immunoblot analysis of pooled single muscle fibers and whole muscle. Endurance-trained individuals displayed a higher MFO rate (0.45 ± 0.15 vs. 0.19 ± 0.07 g/min, P < 0.05), a greater proportion of type I muscle fibers, and higher IMCL content compared with untrained individuals ( P < 0.05). Adipose triglyceride lipase, hormone-sensitive lipase, perilipin 2, perilipin 5, and hydroxyacyl-coenzyme A dehydrogenase abundances were ~2–3-fold higher in type I muscle fibers compared with type IIa fibers ( P < 0.05). Correspondingly, these lipid proteins and oxidative enzymes were higher in endurance-trained individuals when assessed in whole muscle. MFO rate was strongly related to the proportion of type I fibers ( R = 0.81, P < 0.01). The abundance of proteins involved in the regulation of IMCL storage and oxidation is highly muscle fiber type specific. The increased capacity for fat oxidation in endurance-trained individuals corresponded with increased IMCL content and elevated abundance of lipolytic and oxidative enzymes in combination with a greater proportion of type I muscle fibers. NEW & NOTEWORTHY We have utilized contemporary techniques to compare the fiber type-specific characteristics of skeletal muscle from endurance-trained athletes and untrained individuals. We show that type I muscle fibers have a coordinated upregulation of proteins controlling intramuscular lipid storage, mobilization, and oxidation. Furthermore, the enhanced capacity for intramuscular lipid storage and utilization in endurance-trained individuals is related to the increased expression of lipid regulatory proteins combined with a greater proportion of type I muscle fibers.
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Forster, E., C. Kaltschmidt, J. Deng, H. Cremer, T. Deller, and M. Frotscher. "Lamina-specific cell adhesion on living slices of hippocampus." Development 125, no. 17 (September 1, 1998): 3399–410. http://dx.doi.org/10.1242/dev.125.17.3399.
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Laminar distribution of fiber systems is a characteristic feature of hippocampal organization. Ingrowing afferents, e.g. the fibers from the entorhinal cortex, terminate in specific layers, which implies the existence of laminar recognition cues. To identify cues that are involved in the laminar segregation of fiber systems in the hippocampus, we used an in vitro assay to study the adhesion of dissociated entorhinal cells on living hippocampal slices. Here we demonstrate that dissociated entorhinal cells adhere to living hippocampal slices with a lamina-specific distribution that reflects the innervation pattern of the entorhino-hippocampal projection. In contrast, laminae which are not invaded by entorhinal fibers are a poor substrate for cell adhesion. Lamina-specific cell adhesion does not require the neural cell adhesion molecule or the extracellular matrix glycoprotein reelin, as revealed in studies with mutants. However, the pattern of adhesive cues in the reeler mouse hippocampus mimics characteristic alterations of the entorhinal projection in this mutant, suggesting a role of layer-specific adhesive cues in the pathfinding of entorhinal fibers. Lamina-specific cell adhesion is independent of divalent cations, is abolished after cryofixation or paraformaldehyde fixation and is recognized across species. By using a novel membrane adhesion assay, we show that lamina-specific cell adhesion can be mimicked by membrane-coated fluorescent microspheres. Recognition of the adhesive properties of different hippocampal laminae by growing axons, as either a growth permissive or a non-permissive substrate, may provide a developmental mechanism underlying the segregation of lamina-specific fiber projections.
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Mokaloba, N., and V. P. Kommula. "Exploration of Local cellulosic-fiber; its Modification and Potential use by the Industry." MRS Advances 3, no. 34-35 (2018): 2015–25. http://dx.doi.org/10.1557/adv.2018.400.
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ABSTRACTDemand for newer, stronger, stiffer, yet lighter-weight and environmental friendly (biodegradable) materials in the fields such as automobile for non-structural applications are ever increasing. The principal reasons for using natural (cellulosic) fibers is they possess several attractive properties such their economic feasibility, enhanced sustainability, good specific mechanical properties, and desirable aspect ratio for good performance after melt-processing. Natural fiber composite materials are now being rapidly utilized in automobile industries, and they have become the forefront of research and development activity. An interesting alternative for reinforcing soft polymeric matrices with short fibers is the use of cellulose fibers which show remarkable reinforcing effects in thermoplastics such as polypropylene. The current study made an attempt to investigate the suitability of sisal fibers for automobile industry for non-structural and low-strength interior applications. In this work native sisal fibers were extracted and the effect of alkali treatment on their morphological, tensile, moisture absorption and thermal properties were studied. Scanning electron micrographs indicated roughening of the surface of the fiber strands due to the removal of the hemicellulose layer on alkali treatment. The maximum weight-gain for the composite prepared from treated fibers was 2.12 %, while that for the composite prepared from untreated fiber was 4.33 %. From the thermograms, the results indicate initial degradation for the treated fiber to have improved from 174 °C to 230 °C (56 °C shift) when compared to the untreated fiber. This fiber has competitive advantages when evaluated with other natural fibers. A polymer composite was processed from the chemically modified fiber, profiled against equivalent material systems in Ashby material property charts exhibited its suitability for light, low strength and low flexure material applications which can use a potential replacement of fibres being used currently.
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Dickinson, J. M., J. D. Lee, B. E. Sullivan, M. P. Harber, S. W. Trappe, and T. A. Trappe. "A new method to study in vivo protein synthesis in slow- and fast-twitch muscle fibers and initial measurements in humans." Journal of Applied Physiology 108, no. 5 (May 2010): 1410–16. http://dx.doi.org/10.1152/japplphysiol.00905.2009.
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The aim of this study was to develop an approach to directly assess protein fractional synthesis rate (FSR) in isolated human muscle fibers in a fiber type-specific fashion. Individual muscle fibers were isolated from biopsies of the vastus lateralis (VL) and soleus (SOL) obtained from eight young men during a primed, continuous infusion of [5,5,5-2H3]leucine performed under basal conditions. To determine mixed protein FSR, a portion of each fiber was used to identify fiber type, fibers of the same type were pooled, and the [5,5,5-2H3]leucine enrichment was determined via GC-MS. Processing isolated slow-twitch [myosin heavy chain (MHC) I] and fast-twitch (MHC IIa) fibers for mixed protein bound [5,5,5-2H3]leucine enrichment yielded mass ion chromatographic peaks that were similar in shape, abundance, and measurement reliability as tissue homogenates. In the VL, MHC I fibers exhibited a 33% faster ( P < 0.05) mixed protein FSR compared with MHC IIa fibers (0.068 ± 0.006 vs. 0.051 ± 0.003%/h). MHC I fibers from the SOL (0.060 ± 0.005%/h) and MHC I fibers from the VL displayed similar ( P > 0.05) mixed protein FSR. Feasibility of processing isolated human muscle fibers for analysis of myofibrillar protein [5,5,5-2H3]leucine enrichment was also confirmed in non-fiber-typed pooled fibers from the VL. These methods can be applied to the study of fiber type-specific responses in human skeletal muscle. The need for this level of investigation is underscored by the different contributions of each fiber type to whole muscle function and the numerous distinct adaptive functional and metabolic changes in MHC I and MHC II fibers originating from the same muscle.
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Nelson, G., P. F. Hamlyn, L. Holden, and B. J. McCarthy. "A Species-Specific DNA Probe for Goat Fiber Identification." Textile Research Journal 62, no. 10 (October 1992): 590–95. http://dx.doi.org/10.1177/004051759206201006.
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The development of a species-specific DNA probe for identifying goat (e.g., cashmere and mohair) fibers is described. A 54-base oligonucleotide probe hybridizes with single stranded target goat fiber DNA under conditions of low stringency. DNA isolated from as little as 100 mg of raw goat fiber can be clearly detected. Visualization of the DNA isolated from a 100% cashmere processed garment is also demonstrated.
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Straight, Chad R., Olivia R. Ringham, Jenna M. Bartley, Spencer R. Keilich, George A. Kuchel, Laura Haynes, and Mark S. Miller. "Influenza Infection has Fiber Type-Specific Effects on Cellular and Molecular Skeletal Muscle Function in Aged Mice." Journals of Gerontology: Series A 75, no. 12 (June 3, 2020): 2333–41. http://dx.doi.org/10.1093/gerona/glaa136.
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Abstract Skeletal muscle myopathies represent a common non-pulmonary manifestation of influenza infection, leading to reduced physical function and hospitalization in older adults. However, underlying mechanisms remain poorly understood. Our study examined the effects of influenza virus A pulmonary infection on contractile function at the cellular (single fiber) and molecular (myosin-actin interactions and myofilament properties) levels in soleus and extensor digitorum longus muscles of aged (20 months) C57BL/6 male mice that were healthy or flu-infected for 7 (7-days post-infection; 7-DPI) or 12 days (12-DPI). Cross-sectional area (CSA) of myosin heavy chain (MHC) IIA and IIB fibers was reduced at 12-DPI relative to 7-DPI and healthy. Maximal isometric force in MHC IIA fibers was also reduced at 12-DPI relative to 7-DPI and healthy, resulting in no change in specific force (maximal isometric force divided by CSA). In contrast, MHC IIB fibers produced greater isometric force and specific force at 7-DPI compared to 12-DPI or healthy. The increased specific force in MHC IIB fibers was likely due to greater myofilament lattice stiffness and/or an increased number or stiffness of strongly bound myosin-actin cross-bridges. At the molecular level, cross-bridge kinetics were slower in MHC IIA fibers with infection, while changes in MHC IIB fibers were largely absent. In both fiber types, greater myofilament lattice stiffness was positively related to specific force. This study provides novel evidence that cellular and molecular contractile function is impacted by influenza infection in a fiber type-specific manner, suggesting potential molecular mechanisms to help explain the impact of flu-induced myopathies.
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Tonoli, Gustavo Henrique Denzin, Rafael F. Mendes, Gilberto Siqueira, Julien Bras, Mohamed N. Belgacem, and Holmer Savastano. "Isocyanate-treated cellulose pulp and its effect on the alkali resistance and performance of fiber cement composites." Holzforschung 67, no. 8 (December 1, 2013): 853–61. http://dx.doi.org/10.1515/hf-2012-0195.
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Abstract The impact of grafted surface of cellulose fibers on the mechanical and physical properties of fiber-cement composites (FCC) has been investigated. The grafting was performed with n-octadecyl isocyanate [i.e., with an aliphatic isocyanate (AI)], with the intention to protect the cellulose fiber from alkali degradation in the cement matrix. The chemical changes, observed by contact angle measurements and X-ray photoelectron spectroscopy, showed a higher hydrophobic character of AI-treated fibers. The strength of FCC was tested during 28 days of curing treatment. The extracted AI-treated fibers contributed to higher specific energy and final specific deflection after accelerated aging cycles in comparison with the reference composites reinforced with untreated fibers. The higher values of limit of proportionality and modulus of elasticity for composites with AI-treated fibers are an evidence of the densification of the fiber-matrix transition zone. The modulus of rupture values were higher for composites with AI-treated and Soxhlet-extracted fibers after 200 soak and dry aging cycles. In comparison with the reference, AI-treated fibers decreased the water absorption and the apparent porosity of the FCC. The modification of fibers could be a new strategy to improve the performance and stability of cement products reinforced with natural fibers.
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Nabinejad, Omid, Sujan Debnath, Jack Kai Beh, and Mohammad Yeakub Ali. "Mechanical Performance and Moisture Absorption of Unidirectional Bamboo Fiber Polyester Composite." Materials Science Forum 911 (January 2018): 88–94. http://dx.doi.org/10.4028/www.scientific.net/msf.911.88.
Full textAbstract:
Bamboo fibers as a natural fiber offer numerous advantages such as high specific strength over synthetic fiber when used as reinforcing fiber for polymer composites. Yet the hydrophilic nature of bamboo fibers with high moisture absorption results in incompatibility in between bamboo fibers and unsaturated polyester resin. An experimental study was carried out to investigate the effects of alkali treatment of bamboo fiber on the mechanical properties and water sorption properties of polyester composite. The result revealed that, the bamboo fiber polyester composite with 5% Alkali treated bamboo fiber possesses the highest mechanical properties. Besides, Alkali treated fibers composite showed a significant reduction in moisture uptake compared to untreated fibers, where composite with 7% Alkali treated showed the lowest moisture uptake.
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Kirilovs, Edgars, Rita Soliženko, and Silvija Kukle. "Specific of Hemp Fiber ’ S Plastic Composite Projection." Environment. Technology. Resources. Proceedings of the International Scientific and Practical Conference 1 (August 5, 2015): 310. http://dx.doi.org/10.17770/etr2011vol1.900.
Full textAbstract:
In the report there are reflected research results of new board type biocomposites creation for furniture and equipment manufacturing for public segment, replacing traditional petroleum-based components with fully or partly renewable, biodegradable raw materials as one of the major global environmental problems today is non-renewable resource depletion and waste of petroleum-based plastic products. Performed research of biopolymer composites development shows that they are cheaper, environmentally friendlier, lighter, more easily to recycle and to dispose at the end of the product life cycle. For biopolymer’s reinforcement industrial flax and hemp fibers in terms of mechanical qualities are competitive with the glass fiber, they are strong enough in many applications, CO2 neutral, have a relatively low cost, low production energy requirements. By creating new biocomposites it is taken into account that the designed material mechanical properties are mainly dependent on the fiber mass in the matrix, orientation and adhesion to the matrix material. The maximum theoretical amount of fiber weight in composite can reach 91%, specific weight of the fiber component used in practice is usually between 45-65%, but can reach also 70%. For improvement of the adhesion the chemical treatment and drying of the fibers need to be done, also adjuvants that promote development of the hydroxyl group links should be incorporated in the matrix.
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Thibodeaux, Noah, Daniel E. Guerrero, Jose L. Lopez, Matthew J. Bandelt, and Matthew P. Adams. "Effect of Cold Plasma Treatment of Polymer Fibers on the Mechanical Behavior of Fiber-Reinforced Cementitious Composites." Fibers 9, no. 10 (October 18, 2021): 62. http://dx.doi.org/10.3390/fib9100062.
Full textAbstract:
Fiber-reinforced cementitious composites (FRCC) are a class of materials made by adding randomly distributed fibers to a cementitious matrix, providing better material toughness through the crack bridging behavior of the fibers. One of the primary concerns with FRCCs is the behavior of the fiber when a crack is formed. The fibers provide a stress-bridging mechanism, which is largely determined by the bond that exists between the concrete and the fiber’s outer surface. While many studies have determined the properties of FRCCs and potential benefits of using specific fiber types, the effects of low temperature or cold plasma treatment of polymer fibers on the mechanical behavior of the composite material are limited. Polymer fibers are notable for their low density, ductility, ease of manufacture, and cost-effectiveness. Despite these advantages, the surface properties of polymers do not enable the bonding potential given by steel or glass fibers when used in untreated FRCC, resulting in pull-out failures before the full displacement capacity of the fiber is utilized. For this reason, modification of the surface characteristics of polymer fibers can aid in higher bonding potential. Plasma treatment is a process wherein surfaces are modified through the kinetics of electrically charged and reactive species in a gaseous discharge environment. This paper is a preliminary study on the use of atmospheric pressure plasma generated at approximately room temperature. This atmospheric, cold plasma treatment is a method for improving the mechanical properties of FRCC using polymeric fibers. In this study, polypropylene and polyvinyl-alcohol fibers were cold plasma treated for 0, 30, 60, and 120 s before being used in cementitious mortar mixtures. Compression and flexure tests were performed using a displacement-based loading protocol to examine the impact of plasma treatment time on the corresponding mechanical performance of the fiber-reinforced cementitious composite. The experimental results obtained from this study indicate that there is a positive correlation between fiber treatment time and post-peak load-carrying capacity, especially for specimens subjected to flexural loading.
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Patterson, M. F., G. M. M. Stephenson, and D. G. Stephenson. "Denervation produces different single fiber phenotypes in fast- and slow-twitch hindlimb muscles of the rat." American Journal of Physiology-Cell Physiology 291, no. 3 (September 2006): 518–28. http://dx.doi.org/10.1152/ajpcell.00013.2006.
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Using a single, mechanically skinned fiber approach, we tested the hypothesis that denervation (0 to 50 days) of skeletal muscles that do not overlap in fiber type composition [extensor digitorum longus (EDL) and soleus (SOL) muscles of Long-Evans hooded rats] leads to development of different fiber phenotypes. Denervation (50 day) was accompanied by 1) a marked increase in the proportion of hybrid IIB/D fibers (EDL) and I/IIA fibers (SOL) from 30% to >75% in both muscles, and a corresponding decrease in the proportion of pure fibers expressing only one myosin heavy chain (MHC) isoform; 2) complex muscle- and fiber-type specific changes in sarcoplasmic reticulum Ca2+-loading level at physiological pCa ∼7.1, with EDL fibers displaying more consistent changes than SOL fibers; 3) decrease by ∼50% in specific force of all fiber types; 4) decrease in sensitivity to Ca2+, particularly for SOL fibers (by ∼40%); 5) decrease in the maximum steepness of the force-pCa curves, particularly for the hybrid I/IIA SOL fibers (by ∼35%); and 6) increased occurrence of biphasic behavior with respect to Sr2+activation in SOL fibers, indicating the presence of both slow and fast troponin C isoforms. No fiber types common to the two muscles were detected at any time points ( day 7, 21, and 50) after denervation. The results provide strong evidence that not only neural factors, but also the intrinsic properties of a muscle fiber, influence the structural and functional properties of a particular muscle cell and explain important functional changes induced by denervation at both whole muscle and single cell levels.
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Tupling, A. R., E. Bombardier, R. D. Stewart, C. Vigna, and A. E. Aqui. "Muscle fiber type-specific response of Hsp70 expression in human quadriceps following acute isometric exercise." Journal of Applied Physiology 103, no. 6 (December 2007): 2105–11. http://dx.doi.org/10.1152/japplphysiol.00771.2007.
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To investigate the time course of fiber type-specific heat shock protein 70 (Hsp70) expression in human skeletal muscle after acute exercise, 10 untrained male volunteers performed single-legged isometric knee extensor exercise at 60% of their maximal voluntary contraction (MVC) with a 50% duty cycle (5-s contraction and 5-s relaxation) for 30 min. Muscle biopsies were collected from the vastus lateralis before (Pre) exercise in the rested control leg (C) and immediately after exercise (Post) in the exercised leg (E) only and on recovery days 1 (R1), 2 (R2), 3 (R3), and 6 (R6) from both legs. As demonstrated by Western blot analysis, whole muscle Hsp70 content was unchanged ( P > 0.05) immediately after exercise (Pre vs. Post), was increased ( P < 0.05) by ∼43% at R1, and remained elevated throughout the entire recovery period in E only. Hsp70 expression was also assessed in individual muscle fiber types I, IIA, and IIAX/IIX by immunohistochemistry. There were no fiber type differences ( P > 0.05) in basal Hsp70 expression. Immediately after exercise, Hsp70 expression was increased ( P < 0.05) in type I fibers by ∼87% but was unchanged ( P > 0.05) in type II fibers (Pre vs. Post). At R1 and throughout recovery, Hsp70 content in E was increased above basal levels ( P < 0.05) in all fiber types, but Hsp70 expression was always highest ( P < 0.05) in type I fibers. Hsp70 content in C was not different from Pre at any time throughout recovery. Glycogen depletion was observed at Post in all type II, but not type I, fibers, suggesting that the fiber type differences in exercise-induced Hsp70 expression were not related to glycogen availability. These results demonstrate that the time course of exercise-induced Hsp70 expression in human skeletal muscle is fiber type specific.
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Elsasser, Ted H., German Romo, Janet Eastridge, Stanislaw Kahl, Alfredo Martinez, Changge Feng, Cong Jung Li, James L. Sartin, Frank Cuttitta, and Ronald Fayer. "Protein tyrosine nitration in chronic intramuscular parasitism: immunohistochemical evaluation of relationships between nitration, and fiber type-specific responses to infection." Veterinary Science Development 1, no. 1 (May 18, 2011): 3. http://dx.doi.org/10.4081/vsd.2011.2416.
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The present study was conducted to determine whether preferential muscle catabolism [psoas major (PM) > rectus femoris (RF)] observed during the chronic intramuscular stage of <em>Sarcocystis cruzi</em> infection could be associated with the pathological consequences of increased protein tyrosine nitration in fibers characteristically more metabolically active due to higher mitochondrial density. Holstein calves were assigned to control (C), or <em>S. cruzi</em>-infected (I) groups, n=5/group. Calves were euthanized on day 63 of infection. Samples of RF and PM were prepared for metabolic fiber typing (MFT: slow oxidative, SO – Type I; fast oxidative glycolytic, FOG - Type IIa; fast glycolytic, FG – Type IIb), fiber area, and immunohistochemical localization of fast myosin heavy chain 2a and 2b, nitrotyrosine (NT), and mitochondrial Complex V ATP-synthase. MFT analysis documented that PM contained twice the number of SO fibers compared to RF (32 v 16%, P<0.002). SO and FOG fibers (Both higher in mitochondrial density than FG fibers) in both PM and RF were significantly smaller in area in I calves with mean FG areas not different between C and I. Muscle NT content (Western blot of myofibrillar protein fraction) increased with infection; NT was immunohistochemically localized into three distinct patterns in fibers: i) sparse fiber staining, ii) dense punctuate intrafiber staining, and iii) pericystic staining. By image analysis, the greatest punctuate intrafiber pixel density of NT was associated with SO fibers from I calves with the NT colocalizing with mitochondrial Complex V – F1F0 ATP synthase. More fibers were positive for the colocalization in PM than RF (P<0.04). The data are consistent with the concept that fibers rich in mitochondria possessing more inherent oxidative energy capacity generate more nitrated proteins than glycolytic fibers and as such are more affected by the proinflammatory response to infections like Sarcocystosis.
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Choi, Eusoo, Ha-Vinh Ho, and Junwon Seo. "Dynamic Behaviors of Mortar Reinforced with NiTi SMA Fibers under Impact Compressive Loading." Materials 14, no. 17 (August 30, 2021): 4933. http://dx.doi.org/10.3390/ma14174933.
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In this study, a compressive impact test was conducted using the split Hopkinson pressure bar (SHPB) method to investigate SMA fiber-reinforced mortar’s impact behavior. A 1.5% fiber volume of crimped fibers and dog-bone-shaped fibers was used, and half of the specimens were heated to induce recovery stress. The results showed that the appearance of SMA fibers, recovery stress, and composite capacity can increase strain rate. For mechanical properties, the SMA fibers reduced dynamic compressive strength and increased the peak strain. The specific energy absorption of the reinforced specimens slightly increased due to the addition of SMA fibers and the recovery stress; however, the effect was not significant. The composite behavior between SMA fibers and the mortar matrix, however, significantly influenced the dynamic compressive properties. The higher composite capacity of the SMA fibers produced lower dynamic compressive strength, higher peak strain, and higher specific energy absorption. The composite behavior of the dog-bone-shaped fiber was less than that of the crimped fiber and was reduced due to heating, while that of the crimped fiber was not. The mechanical properties of the impacted specimen followed a linear function of strain rate ranging from 10 to 17 s−1; at the higher strain rates of about 49–67 s−1, the linear functions disappeared. The elastic modulus of the specimen was independent of the strain rate, but it was dependent on the correlation between the elastic moduli of the SMA fibers and the mortar matrix.
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Brunner, Florian, Annina Schmid, Ali Sheikhzadeh, Margareta Nordin, Jangwhon Yoon, and Victor Frankel. "Effects of Aging on Type II Muscle Fibers: A Systematic Review of the Literature." Journal of Aging and Physical Activity 15, no. 3 (July 2007): 336–48. http://dx.doi.org/10.1123/japa.15.3.336.
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The authors conducted a systematic review of the literature for scientific articles in selected databases to determine the effects of aging on Type II muscle fibers in human skeletal muscles. They found that aging of Type II muscle fibers is primarily associated with a loss of fibers and a decrease in fiber size. Morphological changes with increasing age particularly included Type II fiber grouping. There is conflicting evidence regarding the change of proportion of Type II fibers. Type II muscle fibers seem to play an important role in the aging process of human skeletal muscles. According to this literature review, loss of fibers, decrease in size, and fiber-type grouping represent major quantitative changes. Because the process of aging involves various complex phenomena such as fiber-type coexpression, however, it seems difficult to assign those changes solely to a specific fiber type.
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Ullegaddi, Kalmeshwar, C. R. Mahesha, and Shivarudraiah. "Tribological Properties of Basalt Fibers - A Review." Materials Science Forum 969 (August 2019): 335–42. http://dx.doi.org/10.4028/www.scientific.net/msf.969.335.
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Now a days natural fibers are progressively projected as a choice of conventional synthetic fibers which causes an adverse impact on the surroundings. Rise within the utilization of environment-friendly natural fibers as reinforcement for the manufacture of lightweight, low-cost polymer with excellent mechanical, thermal and tribological properties can be made globally. One such material of interesting material being presently used is basalt fiber, which is the most-efficient and provides important properties over Carbon fibers, Glass fiber, and some other fibers. In this attempt, an effort made to showcase the tribological properties achieved for application in specific wear conditions like abrasive, sliding and erosion of basalt fiber reinforced polymer composites.
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Chu, Zeng Yong, Rong An He, Hai Feng Cheng, Xiao Dong Li, and Jun Wang. "Effect of Heat Treatment on Specific Surface Area of Si-C-O Fibers." Key Engineering Materials 368-372 (February 2008): 1639–41. http://dx.doi.org/10.4028/www.scientific.net/kem.368-372.1639.
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In this paper, effect of heat treatment on the SSA of Si-C-O fibers was investigated and morphologies of the treated fibers were studied using SEM. The results revealed that weight loss was proportional to the treatment time at 1573K and the specific surface area (SSA) increased sharply when the weight loss reached above 6wt%. A rough and porous ceramic fiber with SSA of 23.76m2/g could be obtained at the weight loss of 9.1wt%, as a result of the treatment at 1573K for 32h.
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Takagi, Ryo, Riki Ogasawara, Junya Takegaki, Arata Tsutaki, Koichi Nakazato, and Naokata Ishii. "Influence of past injurious exercise on fiber type-specific acute anabolic response to resistance exercise in skeletal muscle." Journal of Applied Physiology 124, no. 1 (January 1, 2018): 16–22. http://dx.doi.org/10.1152/japplphysiol.00480.2017.
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We investigated the influence of past injurious exercise on anabolic response of skeletal muscle fibers to resistance exercise (RE). Wistar rats were divided into exercise (E) and exercise-after-injury (I-E) groups. At age 10 wk, the right gastrocnemius muscle in each rat in the I-E group was subjected to strenuous eccentric contractions. Subsequently, RE was imposed on the same muscle of each rat at 14 wk of age in both groups. Peak joint torque and total force generation per body mass during RE were similar between the groups. Muscle protein synthesis (MPS) in the I-E group was higher than that in the E group 6 h after RE. Furthermore, levels of phospho-p70S6 kinase (Thr389) and phospho-ribosomal protein S6 (phospho-rpS6) (Ser240/244), a downstream target of p70S6 kinase, were higher in the I-E group than in the E group. For the anabolic response in each fiber type, the I-E group showed a higher MPS response in type IIb, IIa, and I fibers and a higher phospho-rpS6 response in type IIx, IIa, and I fibers than the E group. In the I-E group, the relative content of myosin heavy chain (MHC) IIa was higher and that of MHC IIb was lower than those in the E group. In addition, type IIa fibers showed a lower MPS response to RE than type IIb fibers in the I-E group. In conclusion, the past injurious exercise enhanced the MPS and phospho-rpS6 responses in type IIb, IIa, and I fibers and type IIx, IIa, and I fibers, respectively. NEW & NOTEWORTHY Past injurious exercise increased the muscle protein synthesis (MPS) response and mammalian target of rapamycin complex 1 (mTORC1) signaling activation to resistance exercise. In the responses of each fiber type, the past injurious exercise increased the MPS and phosphorylation ribosomal protein (Ser240/244) responses in type IIb, IIa, and I fibers and type IIx, IIa, and I fibers, respectively.
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Janardhnan, Sreekumar, and Mohini Sain. "Isolation of Cellulose Nanofibers: Effect of Biotreatment on Hydrogen Bonding Network in Wood Fibers." International Journal of Polymer Science 2011 (2011): 1–6. http://dx.doi.org/10.1155/2011/279610.
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The use of cellulose nanofibres as high-strength reinforcement in nano-biocomposites is very enthusiastically being explored due to their biodegradability, renewability, and high specific strength properties. Cellulose, through a regular network of inter- and intramolecular hydrogen bonds, is organized into perfect stereoregular configuration called microfibrils which further aggregate to different levels to form the fibre. Intermolecular hydrogen bonding at various levels, especially at the elementary level, is the major binding force that one need to overcome to reverse engineer these fibres into their microfibrillar level. This paper briefly describes a novel enzymatic fibre pretreatment developed to facilitate the isolation of cellulose microfibrils and explores effectiveness of biotreatment on the intermolecular and intramolecular hydrogen bonding in the fiber. Bleached Kraft Softwood Pulp was treated with a fungus (OS1) isolated from elm tree infected with Dutch elm disease. Cellulose microfibrils were isolated from these treated fibers by high-shear refining. The % yield of nanofibres and their diameter distribution (<50 nm) isolated from the bio-treated fibers indicated a substantial increase compared to those isolated from untreated fibers. FT-IR spectral analysis indicated a reduction in the density of intermolecular and intramolecular hydrogen bonding within the fiber. X-ray spectrometry indicated a reduction in the crystallinity. Hydrogen bond-specific enzyme and its application in the isolation of new generation cellulose nano-fibers can be a huge leap forward in the field of nano-biocomposites.
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De Bock, K., W. Derave, M. Ramaekers, E. A. Richter, and P. Hespel. "Fiber type-specific muscle glycogen sparing due to carbohydrate intake before and during exercise." Journal of Applied Physiology 102, no. 1 (January 2007): 183–88. http://dx.doi.org/10.1152/japplphysiol.00799.2006.
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The effect of carbohydrate intake before and during exercise on muscle glycogen content was investigated. According to a randomized crossover study design, eight young healthy volunteers ( n = 8) participated in two experimental sessions with an interval of 3 wk. In each session subjects performed 2 h of constant-load bicycle exercise (∼75% maximal oxygen uptake). On one occasion (CHO), they received carbohydrates before (∼150 g) and during (1 g·kg body weight−1·h−1) exercise. On the other occasion they exercised after an overnight fast (F). Fiber type-specific relative glycogen content was determined by periodic acid Schiff staining combined with immunofluorescence in needle biopsies from the vastus lateralis muscle before and immediately after exercise. Preexercise glycogen content was higher in type IIa fibers [9.1 ± 1 × 10−2 optical density (OD)/μm2] than in type I fibers (8.0 ± 1 × 10−2 OD/μm2; P < 0.0001). Type IIa fiber glycogen content decreased during F from 9.6 ± 1 × 10−2 OD/μm2 to 4.5 ± 1 × 10−2 OD/μm2 ( P = 0.001), but it did not significantly change during CHO ( P = 0.29). Conversely, in type I fibers during CHO and F the exercise bout decreased glycogen content to the same degree. We conclude that the combination of carbohydrate intake both before and during moderate- to high-intensity endurance exercise results in glycogen sparing in type IIa muscle fibers.
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DeNardi, C., S. Ausoni, P. Moretti, L. Gorza, M. Velleca, M. Buckingham, and S. Schiaffino. "Type 2X-myosin heavy chain is coded by a muscle fiber type-specific and developmentally regulated gene." Journal of Cell Biology 123, no. 4 (November 15, 1993): 823–35. http://dx.doi.org/10.1083/jcb.123.4.823.
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We have previously reported the identification of a distinct myosin heavy chain (MyHC) isoform in a major subpopulation of rat skeletal muscle fibers, referred to as 2X fibers (Schiaffino, S., L. Gorza, S. Sartore, L. Saggin, M. Vianello, K. Gundersen, and T. Lømo. 1989. J. Muscle Res. Cell Motil. 10:197-205). However, it was not known whether 2X-MyHC is the product of posttranslational modification of other MyHCs or is coded by a distinct mRNA. We report here the isolation and characterization of cDNAs coding a MyHC isoform that is expressed in type 2X skeletal muscle fibers. 2X-MyHC transcripts differ from other MyHC transcripts in their restriction map and 3' end sequence and are thus derived from a distinct gene. In situ hybridization analyses show that 2X-MyHC transcripts are expressed at high levels in the diaphragm and fast hindlimb muscles and can be coexpressed either with 2B- or 2A-MyHC transcripts in a number of fibers. At the single fiber level the distribution of each MyHC mRNA closely matches that of the corresponding protein, determined by specific antibodies on serial sections. In hindlimb muscles 2X-, 2A-, and 2B-MyHC transcripts are first detected by postnatal day 2-5 and display from the earliest stages a distinct pattern of distribution in different muscles and different fibers. The emergence of type 2 MyHC isoforms thus defines a distinct neonatal phase of fiber type differentiation during muscle development. The functional significance of MyHC isoforms is discussed with particular reference to the velocity of shortening of skeletal muscle fibers.