Reduced Order Modeling for Real-Time Stent Deformation Simulations of Transcatheter Aortic Valve Prostheses

Computational modeling can be a critical tool to predict deployment behavior for transcatheter aortic valve replacement (TAVR) in patients with aortic stenosis. However, due to the mechanical complexity of the aortic valve and the multiphysics nature of the problem, described by partial differential equations (PDEs), traditional finite element (FE) modeling of TAVR deployment is computationally expensive. In this preliminary study, a PDEs-based reduced order modeling (ROM) framework is introduced for rapidly simulating structural deformation of the Medtronic Evolut R valve stent frame. Using fifteen probing points from an Evolut model with parametrized loads enforced, 105 FE simulations were performed in the so-called offline phase, creating a snapshot library. The library was used in the online phase of the ROM for a new set of applied loads via the proper orthogonal decomposition-Galerkin (POD-Galerkin) approach. Simulations of small radial deformations of the Evolut stent frame were performed and compared to full order model (FOM) solutions. Linear elastic and hyperelastic constitutive models in steady and unsteady regimes were implemented within the ROM. Since the original POD-Galerkin method is formulated for linear problems, specific methods for the nonlinear terms in the hyperelastic case were employed, namely, the Discrete Empirical Interpolation Method. The ROM solutions were in strong agreement with the FOM in all numerical experiments, with a speed-up of at least 92% in CPU Time. This framework serves as a first step toward real-time predictive models for TAVR deployment simulations.

A comprehensive update on the morphology and distribution of the invasive scaffold-web spider Eidmannella pallida (Araneae, Nesticidae) with a focus on new records from Italy

Updated non-native distributional data of the invasive spider Eidmannella pallida (Emerton, 1875), Nesticidae, are herein summarized together with the morphological characters of the species. We report all the known localities from the literature. Furthermore, we present and discuss recent findings for the Italian peninsula. In particular, the species has been consistently found in vineyards and annual crop fields in North Italy and in olive groves in South Italy. We include a redescription of the species, and detailed illustrations of the diagnostic characters of both males and females, based on stereomicroscope and SEM images. The spreading potential of the species and its possible impacts on local communities are discussed. Our data suggest that E. pallida has high invasiveness potential and several new findings in non-native areas were recorded in the last years. We found that E. pallida can establish permanent populations in crop-dominated landscapes and has a tendency to exploit vulnerable ecosystems such as the subterranean environment. We thus recommend new and more comprehensive studies on this species to investigate in deeper detail its phylogeny, ecology, and micro-habitat preferences. A high effort should be placed to assess the potential negative effects of E. pallida on the endemic fauna in invaded areas, especially in caves.

Integrative taxonomic revision of the genera Nesticella and Howaia in Japan with the description of five new species (Araneae, Nesticidae, Nesticellini)

The Japanese species of the genera Nesticella Lehtinen & Saaristo, 1980 and Howaia Lehtinen & Saaristo, 1980 (Araneae, Nesticidae, Nesticellini) are revised using an integrative taxonomic approach. Their morphology, phylogenetic position within the genera, assignment to species groups, and distribution in mainland Japan and the Ryukyu islands are discussed herein. A phylogenetic and species delimitation analysis was conducted to confirm the boundaries between the putative species that were initially discriminated based on external and genital morphology. As a result of the present study, six species of Nesticella and three species of Howaia are proposed for the fauna of Japan based on the combined results of morphology and molecular analyses. Male and female of the previously known species H.mogera (Yaginuma, 1972), N.brevipes (Yaginuma, 1970), and N.okinawaensis (Yaginuma, 1979) are redescribed and illustrated using type specimens or specimens collected at the type locality. Nesticellaterrestris (Yaginuma, 1970) is resurrected as a valid species and distinguished from the closely related N.brevipes based on morphological and molecular evidence. The male of N.terrestris is described for the first time. We herein describe three new species of Nesticella and two new species of Howaia from different islands in the Ryukyu Archipelago, southwest Japan: N.insulanasp. nov. (♂, ♀) from Yonaguni-jima Island, N.occultasp. nov. (♀) from Ishigaki-jima Island, N.silvicolasp. nov. (♂, ♀) from Yakushima Island, H.albasp. nov. (♂, ♀) from Miyako-jima Island and H.subterraneasp. nov. (♀) from Okinoerabu-jima Island. Nesticellaoccultasp. nov., H.albasp. nov. and H.subterraneasp. nov. dwell exclusively in caves and show extensive morphological adaptation to subterranean life.

Life history and biogeography of the enigmatic mantid Nilomantisfloweri (Mantodea, Nanomantidae)

The biology and distribution patterns of the Sahelian mantid species Nilomantisfloweri are still insufficiently known. For the first time, records are confirmed of this species from Iran and the distribution map of its native range is updated. Records are compiled from the Sahel zone of North Africa, the Arabian Peninsula, and Iran. Detailed information on its biology, oothecal characteristics, male genitalia variation, and intraspecific molecular diversity in the mitochondrial gene cytochrome c oxidase are provided, and ecological niche modelling was used to gain insight into the overall species distribution and understand its climatic niche limits. Genetic analysis revealed only one haplotype shared between Iran and Oman. The Iranian populations likely represent two distinct clusters, both more related to the diverse Oman haplotypes than to each other. Based on new data, N.floweri appears to be mostly associated with coastal areas in southwestern Asia, with the vast majority of records found along the Red Sea, Persian Gulf, and Oman Gulf coasts. This distribution contrasts markedly with N.floweri records in the Sahel, where most collections have been reported in the transitional zone between the southern Sahara and arid thorn savannah, far off the coast. This study contributes to a comprehensive understanding of this still enigmatic mantid species.

Marine-montane transitions coupled with gill and genetic convergence in extant crustacean

Marine-terrestrial transition represents an important aspect of organismal evolution that requires numerous morphological and genetic innovations and has been hypothesized to be caused by geological changes. We used talitrid crustaceans with marine-coastal-montane extant species at a global scale to investigate the marine origination and terrestrial adaptation. Using genomic data, we demonstrated that marine ancestors repeatedly colonized montane terrestrial habitats during the Oligocene to Miocene. Biological transitions were well correlated with plate collisions or volcanic island formation, and top-down cladogenesis was observed on the basis of a positive relationship between ancestral habitat elevation and divergence time for montane lineages. We detected convergent variations of convoluted gills and convergent evolution of SMC3 associated with montane transitions. Moreover, using CRISPR-Cas9 mutagenesis, we proposed that SMC3 potentially regulates the development of exites, such as talitrid gills. Our results provide a living model for understanding biological innovations and related genetic regulatory mechanisms associated with marine-terrestrial transitions.

Baiyuerius gen. nov., a new genus of Coelotinae (Araneae, Agelenidae) spiders from China and Vietnam

Baiyueriusgen. nov., a new genus of the subfamily Coelotinae F. O. Pickard-Cambridge, 1893 is described, including five new species: B.daxisp. nov. (♀), B.pindongsp. nov. (♂), B.tamdaosp. nov. (♀), B.zhupingsp. nov. (♂) and B.zuojiangsp. nov. (♂♀), from southern China and northern Vietnam. Our molecular phylogenetic analyses support Baiyuerius gen. nov. as monophyletic and as a sister group of the newly established genus Yunguirius Li, Zhao & Li, 2023.

Enhancing high-fidelity nonlinear solver with reduced order model

We propose the use of reduced order modeling (ROM) to reduce the computational cost and improve the convergence rate of nonlinear solvers of full order models (FOM) for solving partial differential equations. In this study, a novel ROM-assisted approach is developed to improve the computational efficiency of FOM nonlinear solvers by using ROM’s prediction as an initial guess. We hypothesize that the nonlinear solver will take fewer steps to the converged solutions with an initial guess that is closer to the real solutions. To evaluate our approach, four physical problems with varying degrees of nonlinearity in flow and mechanics have been tested: Richards’ equation of water flow in heterogeneous porous media, a contact problem in a hyperelastic material, two-phase flow in layered porous media, and fracture propagation in a homogeneous material. Overall, our approach maintains the FOM’s accuracy while speeding up nonlinear solver by 18–73% (through suitable ROM-assisted FOMs). More importantly, the proximity of ROM’s prediction to the solution space leads to the improved convergence of FOMs that would have otherwise diverged with default initial guesses. We demonstrate that the ROM’s accuracy can impact the computational efficiency with more accurate ROM solutions, resulting in a better cost reduction. We also illustrate that this approach could be used in many FOM discretizations (e.g., finite volume, finite element, or a combination of those). Since our ROMs are data-driven and non-intrusive, the proposed procedure can easily lend itself to any nonlinear physics-based problem.

Projection Based Semi-Implicit Partitioned Reduced Basis Method for Fluid-Structure Interaction Problems

In this manuscript a POD-Galerkin based Reduced Order Model for unsteady Fluid-Structure Interaction problems is presented. The model is based on a partitioned algorithm, with semi-implicit treatment of the coupling conditions. A Chorin-Temam projection scheme is applied to the incompressible Navier-Stokes problem, and a Robin coupling condition is used for the coupling between the fluid and the solid. The coupled problem is based on an Arbitrary Lagrangian Eulerian formulation, and the Proper Orthogonal Decomposition procedure is used for the generation of the reduced basis. We extend existing works on a segregated Reduced Order Model for Fluid-Structure Interaction to unsteady problems that couple an incompressible, Newtonian fluid with a linear elastic solid, in two spatial dimensions. We consider three test cases to assess the overall capabilities of the method: an unsteady, non-parametrized problem, a problem that presents a geometrical parametrization of the solid domain, and finally, a problem where a parametrization of the solid's shear modulus is taken into account.

An unexpected occurrence: discovery of the genus Cybaeopsis Strand, 1907 in Europe with the description of a new species from Italy (Arachnida, Araneae, Amaurobiidae)

We report on the unexpected finding of a new species of the genus Cybaeopsis Strand, 1907, C. lodoviciisp. nov. from the Northern Apennine Mountains in Italy. This is the first documented record of a Cybaeopsis species in Europe. Other currently known species of this genus have been previously recorded in North America, the Russian Far-East and Japan. The new species is illustrated and described based on both sexes. Another species from Portugal, Cybaeopsis theoblicki (Bosmans, 2021) comb. nov., recently described in the genus Callobius Chamberlin, 1947, is hereby transferred to Cybaeopsis on the basis of morphological characters. An updated key to the European genera of Amaurobiidae is provided.

Consistency of the full and reduced order models for evolve-filter-relax regularization of convection-dominated, marginally-resolved flows

Numerical stabilization is often used to eliminate (alleviate) the spurious oscillations generally produced by full order models (FOMs) in under-resolved or marginally-resolved simulations of convection-dominated flows. In this article, we investigate the role of numerical stabilization in reduced order models (ROMs) of marginally-resolved, convection-dominated incompressible flows. Specifically, we investigate the FOM-ROM consistency, that is, whether the numerical stabilization is beneficial both at the FOM and the ROM level. As a numerical stabilization strategy, we focus on the evolve-filter-relax (EFR) regularization algorithm, which centers around spatial filtering. To investigate the FOM-ROM consistency, we consider two ROM strategies: (i) the EFR-noEFR, in which the EFR stabilization is used at the FOM level, but not at the ROM level; and (ii) the EFR-EFR, in which the EFR stabilization is used both at the FOM and at the ROM level. We compare the EFR-noEFR with the EFR-EFR in the numerical simulation of a 2D incompressible flow past a circular cylinder in the convection-dominated, marginally-resolved regime. We also perform model reduction with respect to both time and Reynolds number. Our numerical investigation shows that the EFR-EFR is more accurate than the EFR-noEFR, which suggests that FOM-ROM consistency is beneficial in convection-dominated, marginally-resolved flows.

Seasonal abundance and spatio-temporal distribution of the troglophylic harvestman Ischyropsalis ravasinii (Arachnida, Opiliones, Ischyropsalididae) in the Buso del Valon ice cave, Eastern Italian Prealps

We explore the population of the troglophilic harvestman Ischyropsalis ravasinii inhabiting the Buso del Valon ice cave located in the Italian Prealps. Spatial and temporal distributions of the specimens are investigated in relation to the variation of environmental abiotic conditions in the cave, such as the seasonal temperature and substrate surface typology. Our results show that I. ravasinii is distributed unevenly in the cave, most of individuals being present in the scree-covered section of the cave with superficial activities limited to the warm seasons only. In addition, our data suggests that the presence of a thick layer of rocky debris, together with high humidity and cold temperatures, are important limiting factors for the species. Seven additional species of harvestman are recorded in the cave, including the congeneric troglophilic species Ischyropsalis strandi. This is the first known record of these two troglophilic Ischyropsalis species coexisting within the same cave. An updated map of the distribution of I. ravasinii and I. strandi in the Italian Prealps is provided.

Reduced order methods for parametric optimal flow control in coronary bypass grafts, toward patient-specific data assimilation

Coronary artery bypass grafts (CABG) surgery is an invasive procedure performed to circumvent partial or complete blood flow blockage in coronary artery disease. In this work, we apply a numerical optimal flow control model to patient-specific geometries of CABG, reconstructed from clinical images of real-life surgical cases, in parameterized settings. The aim of these applications is to match known physiological data with numerical hemodynamics corresponding to different scenarios, arisen by tuning some parameters. Such applications are an initial step toward matching patient-specific physiological data in patient-specific vascular geometries as best as possible. Two critical challenges that reportedly arise in such problems are: (a) lack of robust quantification of meaningful boundary conditions required to match known data as best as possible and (b) high computational cost. In this work, we utilize unknown control variables in the optimal flow control problems to take care of the first challenge. Moreover, to address the second challenge, we propose a time-efficient and reliable computational environment for such parameterized problems by projecting them onto a low-dimensional solution manifold through proper orthogonal decomposition-Galerkin.

An optimal control approach to determine resistance-type boundary conditions from in-vivo data for cardiovascular simulations

The choice of appropriate boundary conditions is a fundamental step in computational fluid dynamics (CFD) simulations of the cardiovascular system. Boundary conditions, in fact, highly affect the computed pressure and flow rates, and consequently haemodynamic indicators such as wall shear stress (WSS), which are of clinical interest. Devising automated procedures for the selection of boundary conditions is vital to achieve repeatable simulations. However, the most common techniques do not automatically assimilate patient-specific data, relying instead on expensive and time-consuming manual tuning procedures. In this work, we propose a technique for the automated estimation of outlet boundary conditions based on optimal control. The values of resistive boundary conditions are set as control variables and optimized to match available patient-specific data. Experimental results on four aortic arches demonstrate that the proposed framework can assimilate 4D-Flow MRI data more accurately than two other common techniques based on Murray's law and Ohm's law.

Five new species of Macrothele Ausserer, 1871 from China (Araneae, Macrothelidae)

Five new species of the genus Macrothele Ausserer, 1871 are described from China: Macrotheleemei Lin & Li, sp. nov. (♂♀, Sichuan), M.hanfeii Lin & Li, sp. nov. (♂♀, Hainan), M.hungae Lin & Li, sp. nov. (♂♀, Taiwan), M.limenghuai Lin & Li, sp. nov. (♂♀, Sichuan), and M.nanning Lin & Li, sp. nov. (♂♀, Guangxi). Types of the new species are deposited in the Institute of Zoology, Chinese Academy of Sciences in Beijing, China.

A survey on poorly known rainforest litter-dwelling spiders of Orchid Island (Lanyu, Taiwan) with the description of a new species (Araneae: Linyphiidae, Tetrablemmidae, and Theridiosomatidae)

Representatives of some poorly known spider species collected in the rainforest litter of the Orchid Island (Taiwan) are illustrated and discussed here. A new species, Brignoliella tao sp. nov. (Fam. Tetrablemmidae), endemic to Orchid Island, is described based on both sexes. The previously unknown female of Theridiosoma triumphale Zhao Li, 2012 (Fam. Theridiosomatidae), is described for the first time. Zoma taiwanica (Zhang, Zhu Tso 2006) comb. nov., from the same family, is illustrated and its transfer from the genus Theridiosoma O. Pickard-Cambridge, 1879 to Zoma Saaristo, 1996 is proposed on the basis of morphological characters. Habitus and genitalia of the endemic species Gongylidioides angustus Tu Li, 2006 (Fam. Linyphiidae) are also illustrated.

Nesticus kosodensis Yaginuma, 1972 bona species. Molecular and morphological separation from N. latiscapus Yaginuma, 1972 with notes on cave scaffold-web spiders subspecies in Japan (Araneae, Nesticidae)

The troglophilic spider subspecies Nesticus latiscapus kosodensis Yaginuma, 1972 is compared with its nominal species N. latiscapus Yaginuma, 1972 using an integrated taxonomic approach. Both morphological and molecular analysis suggest the two taxa are distinct, rejecting the status of subspecies. In the light of these results, N. kosodensisstat. nov. is elevated to species level and both species are redescribed. We expect that future revisions of Japanese Nesticidae will find that many currently designated subspecies are in fact distinct species. Taxonomic revision of long-established and unrevised subspecies may help to improve the conservation efforts aiming to protect the Japanese endemic cave fauna.

Elevation to species level and redescription of Xysticus alpinus Kulczyński, 1887 stat. n. (Araneae, Thomisidae)

Xysticus alpinus Kulczyński, 1887 stat. n. from Central-Eastern Alps, previously considered a subspecies of X. lanio C. L. Koch, 1835, is analyzed in detail. Redescription of both sexes and illustrations of habitus and genitalia are provided. A careful comparison with the nominal species is carried out revealing clear differences in morphology and habitat preferences. In light of this evidence, its elevation to species level is proposed.

Diversification in tropics and subtropics following the mid-Miocene climate change: A case study of the spider genus Nesticella

Caves may offer suitable refugia for troglophilic invertebrates during periods of unfavourable climatic conditions because of their stable microclimates. As a consequence, allopatric divergence from their epigean counterparts may occur, leading to formation of truly hypogean communities (the Climatic Relict Hypothesis). Unlike the well-studied effects of Pleistocene glaciations, we know little about how ancient climate changes drove the development of cave-dwelling organisms living at both middle and lower latitudes. We investigate the evolutionary history of the troglophilic spider genus Nesticella (Araneae, Nesticidae) in relation to Asian Neogene (23-2.6 Ma) climatic changes. Our analyses discern clear differences in the evolution of the two main clades of Nesticella, which occur in temperate/subtropical and tropical latitudes. Eastern Asian Nesticella gradually evolved greater sedentariness and a strict subterranean lifestyle starting from the middle Miocene Epoch (~15-14 Ma) in conjunction with the progressive deterioration of the climate and vegetational shifts. Caves appear to have acted as refugia because of their internally uniform temperature and humidity, which allowed these spiders to survive increasing external seasonality and habitat loss. In contrast, a uniform accumulation of lineages, long-lasting times for dispersals and the lack of a comparable habitat shifting characterized the tropical lineage. This difference in pattern likely owes to the mild effects of climate change at low latitudes and the consequent lack of strong climatic drivers in tropical environments. Thus, the mid-Miocene climatic shift appears to be the major evolutionary force shaping the ecological differences between Asian troglophilic invertebrates and the driver of the permanent hypogean communities in middle latitudes.

A survey of the spider family Nesticidae (Arachnida, Araneae) in Asia and Madagascar, with the description of forty-three new species

Forty-three new species of Nesticidae are described from China, Indonesia, Philippines, Singapore, Thailand, Vietnam and Madagascar, and two new junior synonyms are suggested. A new genus, Speleoticusgen. n., is described with Nesticus navicellatus Liu & Li, 2013 as the type species, and four species are transferfed from Nesticus, i.e., Speleoticus globosus (Liu & Li, 2013), comb. n., Speleoticus libo (Chen & Zhu, 2005), comb. n., Speleoticus navicellatus (Liu & Li, 2015), comb. n. and Speleoticus uenoi (Yaginuma, 1972), comb. n. The new species described in this paper belong to four genera and are: Hamus cornutussp. n. (♂♀), Hamus kangdingensissp. n. (♂), Hamus luzonsp. n. (♀), Hamus mangunensissp. n. (♂), Nescina kohisp. n. (♂♀), Nesticella baiseensissp. n. (♂♀), Nesticella baobabsp. n. (♂), Nesticella caecasp. n. (♂♀), Nesticella chongqingsp. n. (♀), Nesticella dazhuangensissp. n. (♂♀), Nesticella fuliangensissp. n. (♂♀), Nesticella gazuidasp. n. (♀), Nesticella gongshanensissp. n. (♀), Nesticella griswoldisp. n. (♂♀), Nesticella hongheensissp. n. (♂♀), Nesticella huomachongensissp. n. (♂♀), Nesticella jingposp. n. (♀), Nesticella kaohsiungensissp. n. (♂♀), Nesticella lisusp. n. (♂♀), Nesticella liuzhaiensissp. n. (♀), Nesticella nandanensissp. n. (♂♀), Nesticella phamisp. n. (♂♀), Nesticella potalasp. n. (♀), Nesticella qiaoqiensissp. n. (♀), Nesticella qiongensissp. n. (♂♀), Nesticella robustasp. n. (♂♀), Nesticella rongtangensissp. n. (♂), Nesticella sanchaheensissp. n. (♂♀), Nesticella sulawesisp. n. (♀), Nesticella sumatranasp. n. (♂), Nesticella tibetanasp. n. (♂♀), Nesticella vanlangsp. n. (♀), Nesticella wanzaiensissp. n. (♂♀), Nesticella xiongmaosp. n. (♂♀), Nesticella xixiasp. n. (♂♀), Nesticella yanbeiensissp. n. (♂♀), Nesticella yaosp. n. (♀), Nesticella zhiyuanisp. n. (♂♀), Pseudonesticus dafangensissp. n. (♂♀), Pseudonesticus miaosp. n. (♂♀), Pseudonesticus spinosussp. n. (♂♀), Pseudonesticus wumengensissp. n. (♀), Pseudonesticus ziyunensissp. n. (♂♀). Nesticella inthanoni (Lehtinen & Saaristo, 1980), syn. n. is synonymised with Nesticella mollicula (Thorell, 1898); Nesticella taiwan Tso & Yoshida, 2000, syn. n. is synonymised with Nesticella odonta (Chen, 1984). The female of Nesticella connectens Wunderlich, 1995, so far unknown, is described and recorded from Thailand. Nesticidae are reported from Madagascar for the first time. Nesticella nepalensis (Hubert, 1973) is recorded for the first time from China. Types of Nesticella odonta (Chen, 1984), Nesticella songi Chen & Zhu, 2004 and Nesticella yui Wunderlich & Song, 1995 are re-examined and photographed. The entire genus Nesticella is reviewed, and four species groups are recognised. DNA barcodes of the new species are obtained to confirm their correct identifications.

On the spider genus Amaurobius (Araneae, Amaurobiidae) in India and Nepal

A new species, Amaurobius koponenisp. n., is described from Himachal Pradesh on the basis of a male specimen. A key to all five genera of Amaurobiidae that occur in Asia is provided. Four species from India and Nepal incorrectly assigned to Amaurobius are transferred to three genera of Titanoecidae: Anuvinda milloti (Hubert, 1973), comb. n., Pandava andhraca (Patel & Reddy, 1990), comb. n., Pandava nathabhaii (Patel & Patel, 1975), comb. n., and Titanoeca sharmai (Bastawade, 2008), comb. n.

Characterisation of elastin and collagen in aortic bioprostheses

Porcine aortic valves used as cardiac valve bioprostheses are well adapted to physiological functions in the short term, but they lack long-term durability. Several multi-step extractions have been performed to obtain a perfectly acellular matrix. A new physical methodology is proposed to evaluate the resulting fibrous protein damage after biochemical extraction (TRI-COL and SDS). Thermal analysis techniques are adapted to collagen and elastin characterisation in the solid state. The aortic tissue thermal transitions are determined by differential scanning calorimetry (DSC): elastin glass transition is observed around 200 degrees C, and collagen denaturation is observed around 230 degrees C. These parameters are characteristic of the elastin network arrangement and of collagen triple-helix stability. The technique of thermostimulated currents (TSC) is well suited to specify the chain dynamics of proteins. The low-temperature relaxations observed in both collagen and elastin are associated with localised motions, whereas the high-temperature modes are attributed to more delocalized motions of the chains. Therefore TSC and DSC spectrometries allow physical parameters specific to collagen and elastin to be obtained and their interaction in aortic tissues to be determined. According to the significant evolution of these parameters on SDS samples, the destabilizing effect of this detergent is highlighted.

Gender- and thyroid hormone-related transitions of essential myosin light chain isoform expression in rat soleus muscle during ageing

In this brief review, the modulatory influence of essential myosin light chain (MLC) isoforms on muscle cell contractility is discussed. Specific interest is focused on the expression of the MLC1Sa and MLC1Sb isoforms in the slow-twitch soleus muscle in male and female rats, during ageing and after thyroid hormone treatment. According to two-dimensional gel electrophoresis analysis, the MLC1Sa/MLC1SB ratio increased during ageing in both males and females in parallel with the age-related decrease in shortening velocity reported in muscle fibres expressing the slow (type 1) myosin heavy chain (MHC) isoform. However, the MLC1Sa and MLC1Sb isoform expression responded to thyroid hormone treatment in a complex manner which did not parallel the age-related changes in shortening velocity reported in hyperthyroid animals. Thus, if MLC1Sa and MLC1Sb isoforms modulate shortening velocity in type 1 fibres, then other modulators of shortening velocity are not regulated by thyroid hormone in co-ordination with these essential MLCs.