A mass-length scaling law for modeling muscle strength in the lower limb

Musculoskeletal computer models are often used to study muscle function in children with and without impaired mobility. Calculations of muscle forces depend in part on the assumed strength of each muscle, represented by the peak isometric force parameter, which is usually based on measurements obtained from cadavers of adult donors. The aim of the present study was twofold: first, to develop a method for scaling lower-limb peak isometric muscle forces in typically-developing children; and second, to determine the effect of this scaling method on model calculations of muscle forces obtained for normal gait. Muscle volumes were determined from magnetic resonance (MR) images obtained from ten children aged from 7 to 13yr. A new mass-length scaling law was developed based on the assumption that muscle volume and body mass are linearly related, which was confirmed by the obtained volume and body mass data. Two musculoskeletal models were developed for each subject: one in which peak isometric muscle forces were estimated using the mass-length scaling law; and another in which these parameters were determined directly from the MR-derived muscle volumes. Musculoskeletal modeling and quantitative gait analysis were then used to calculate lower-limb muscle forces in normal walking. The patterns of muscle forces predicted by the model with scaled peak isometric force values were similar to those predicted by the MR-based model, implying that assessments of muscle function obtained from these two methods are practically equivalent. These results support the use of mass-length scaling in the development of subject-specific musculoskeletal models of children.     

Morphological traits determine the winner of “symmetric” fights in hermit crabs

This study aimed at investigating in the hermit crab Pagurus longicarpus whether some morphological traits and their slight variations might determine the winner of a contest in symmetric pairs, i.e. pairs composed of individuals matched by their overall size. In the pre-experimental phase, 400 crabs were individually kept in isolation for a week to eliminate the effects of their previous social experiences and were allowed to enter adequate shells to equalize their motivation to fight. Then, we formed 200 pairs matched for shell and body size and observed their agonistic behaviour for 15 min. Alphas (and betas) were deemed as those individuals that won more than half of the recorded fights. Finally, crabs were sacrificed and sexed, and 6 and 8 measures were taken of their shells and bodies, respectively. Raw data were converted to compositional data and subjected to an isometric log-ratio transformation prior to statistical analysis. Alphas were found to occupy heavier and wider shells than betas, both characteristics that, together with the correlated high level of encrustation, make the apparent dimension of the crab larger and thus favour that individual during agonistic encounters. As expected, hermit crabs were sexually dimorphic in their chelae, but sexes differed also in the length of the dactylus of their third walking leg and in their body weight. Alphas were heavier than betas and had longer propodi and wider dactyli on the third walking legs than betas. The latter character might be advantageous during shell fights when the walking legs of the attacker are used to hold the defender's shell in the spasmodic shaking and their wider dactyli might assure a firmer seizing of it. Indeed, a correct execution of this pattern allows for the eviction of the defender. Our results suggest that more attention towards variations in morphological traits other than body size might improve our understanding of the factors that affect individual Resource Holding Power and fight dynamics.     

Human upper-limb force capacities evaluation with robotic models for ergonomic applications: effect of elbow flexion

The aim of this study was to apply models derived from the robotics field to evaluate the human upper-limb force generation capacity. Four models were compared: the force ellipsoid (FE) and force polytope (FP) based on unit joint torques and the scaled FE (SFE) and scaled FP (SFP) based on maximum isometric joint torques. The four models were assessed from four upper-limb postures with varying elbow flexion (40°, 60°, 80° and 100°) measured by an optoelectronic system and their corresponding isometric joint torques. Ten subjects were recruited. Three specific ellipsoids and polytopes parameters were compared: isotropy, principal force orientation and volume. Isotropy showed that the ellipsoids and polytopes were elongated. The angle between the two ellipsoids main axis and the two polytopes remained low but increased with the elbow flexion. The FE and FP volumes increased and those of SFE and SFP decreased with the elbow flexion. The interest and limits of such models are discussed in the framework of ergonomics and rehabilitation.     

Growth During the Bacterial Cell Cycle: Analysis of Cell Size Distribution

Cell volume distributions were determined electronically for steady-state cultures of Escherichia coli, Bacillus megaterium, Bacillus subtilis, and Salmonella typhimurium by use of a Coulter transducer-multichannel analyzer system of good resolution. All of the cell volume distributions had the same general shape, even though cultures were grown at widely different rates. Some results were independent of any particular growth model. Both the variability in the volumes of dividing cells and the fraction of constricted and unseparated doublet cells increased with growth rate. The greater separation to single cells at slow growth rates is in agreement with the general finding that filamentous and hyphal forms are greatly reduced in slowly growing chemostat cultures. The distributions were fitted equally well by simple models which assumed that cell growth was either linear or exponential throughout the entire cell cycle. It is concluded that methods of determining growth rate by analysis of distributions of bacterial volumes do not yet have sufficient resolution to distinguish between a variety of alternative models for growth of bacteria.     

Moment-generating capacity of upper limb muscles in healthy adults

Muscle strength and volume vary greatly among individuals. Maximum isometric joint moment, a standard measurement of strength, has typically been assessed in young, healthy subjects, whereas muscle volumes have generally been measured in cadavers. This has made it difficult to characterize the relationship between isometric strength and muscle size in humans. We measured maximum isometric moments about the shoulder, elbow, and wrist in 10 young, healthy subjects, ranging in size from a 20th percentile female to a 97th percentile male. The volumes of 32 upper limb muscles were determined from magnetic resonance images of these same subjects, and grouped according to their primary function. The maximum moments produced using the shoulder adductors (67.9+/-28.4 Nm) were largest, and were approximately 6.5(+/-1.2) times greater than those produced using the wrist extensors (10.2+/-4.6 Nm), which were smallest. While there were substantial differences in moment-generating capacity among these 10 subjects, moment significantly covaried with muscle volume of the appropriate functional group, explaining between 95% (p<0.0001; shoulder adductors) and 68% (p=0.004; wrist flexors) of the variation in the maximum isometric joint moments among subjects. While other factors, such as muscle moment arms or neural activation and coordination, can contribute to variation in strength among subjects, they either were relatively constant across these subjects compared to large differences in muscle volumes or they covaried with muscle volume. We conclude that differences in strength among healthy young adults are primarily a consequence of variation in muscle volume, as opposed to other factors.     

Effects of shell stress on the growth of hermit crabs

Growth rates of the hermit crabs Pagurus longicarpus Say and P. pollicaris Say maintained in preferred shells and in shells smaller than the preferred size have been compared. Changes in wet weight, shield length, and duration of the molt cycle were determined. Crabs in preferred shells grew significantly faster than those in small shells. P. pollicaris molted at approximately the same rate in both cases but grew more each molt in preferred shells. Von Bertalanffy growth curves were fitted to changes in shield length among crabs in preferred shells. These curves indicate that P. longicarpus may mature four months after settling from the plankton and reach its asymptotic size within the next eight months while P. pollicaris also matures four months after leaving the plankton but does not reach its asymptotic size for approximately three years. The rapid growth of P. longicarpus may enable it to preempt shells which are required for the successful brooding of a large clutch before these shells are required by more aggressive competitors, such as P. pollicaris and Clibanarius vittatus.     

Growth trajectories of some major ammonoid sub‐clades revealed by serial grinding tomography data

Molluscs such as ammonoids record their growth in their accretionary shells, making them ideal for the study of evolutionary changes in ontogeny through time. Standard methods usually focus on two‐dimensional data and do not quantify empirical changes in shell and chamber volumes through ontogeny, which can possibly be important to disentangle phylogeny, interspecific variation and palaeobiology of these extinct cephalopods. Tomographic and computational methods offer the opportunity to empirically study volumetric changes in shell and chamber volumes through ontogeny of major ammonoid sub‐clades in three dimensions (3‐D). Here, we document (1) the growth of chamber and septal volumes through ontogeny and (2) differences in ontogenetic changes between species from each of three major sub‐clades of Palaeozoic ammonoids throughout their early phylogeny. The data used are three‐dimensional reconstructions of specimens that have been subjected to grinding tomography. The following species were studied: the agoniatitid Fidelites clariondi and anarcestid Diallagites lenticulifer (Middle Devonian) and the Early Carboniferous goniatitid Goniatites multiliratus. Chamber and septum volumes were plotted against the septum number and the shell diameter (proxies for growth) in the three species; although differences are small, the trajectories are more similar among the most derived Diallagites and Goniatites compared with the more widely umbilicate Fidelites. Our comparisons show a good correlation between the 3‐D and the 2‐D measurements. In all three species, both volumes follow exponential trends with deviations in very early ontogeny (resolution artefacts) and near maturity (mature modifications in shell growth). Additionally, we analyse the intraspecific differences in the volume data between two specimens of Normannites (Middle Jurassic).     

The interaction of muscle moment arm,knee laxity,and torque in a multi-scale musculoskeletal model of the lower limb

IntroductionMusculoskeletal modeling allows insight into the interaction of muscle force and knee joint kinematics that cannot be measured in the laboratory. However, musculoskeletal models of the lower extremity commonly use simplified representations of the knee that may limit analyses of the interaction between muscle forces and joint kinematics. The goal of this research was to demonstrate how muscle forces alter knee kinematics and consequently muscle moment arms and joint torque in a musculoskeletal model of the lower limb that includes a deformable representation of the knee.MethodsTwo musculoskeletal models of the lower limb including specimen-specific articular geometries and ligament deformability at the knee were built in a finite element framework and calibrated to match mean isometric torque data collected from 12 healthy subjects. Muscle moment arms were compared between simulations of passive knee flexion and maximum isometric knee extension and flexion. In addition, isometric torque results were compared with predictions using simplified knee models in which the deformability of the knee was removed and the kinematics at the joint were prescribed for all degrees of freedom.ResultsPeak isometric torque estimated with a deformable knee representation occurred between 45° and 60° in extension, and 45° in flexion. The maximum isometric flexion torques generated by the models with deformable ligaments were 14.6% and 17.9% larger than those generated by the models with prescribed kinematics; by contrast, the maximum isometric extension torques generated by the models were similar. The change in hamstrings moment arms during isometric flexion was greater than that of the quadriceps during isometric extension (a mean RMS difference of 9.8 mm compared to 2.9 mm, respectively).DiscussionThe large changes in the moment arms of the hamstrings, when activated in a model with deformable ligaments, resulted in changes to flexion torque. When simulating human motion, the inclusion of a deformable joint in a multi-scale musculoskeletal finite element model of the lower limb may preserve the realistic interaction of muscle force with knee kinematics and torque.     

ADAPTATION FROM RESTRICTED GEOMETRIES: THE SHELL INCLINATION OF TERRESTRIAL GASTROPODS

The adaptations that occur for support and protection can be studied with regard to the optimal structure that balances these objectives with any imposed constraints. The shell inclination of terrestrial gastropods is an appropriate model to address this problem. In this study, we examined how gastropods improve shell angles to well‐balanced ones from geometrically constrained shapes. Our geometric analysis and physical analysis showed that constantly coiled shells are constrained from adopting a well‐balanced angle; the shell angle of such basic shells tends to increase as the spire index (shell height/width) increases, although the optimum angle for stability is 90° for flat shells and 0° for tall shells. Furthermore, we estimated the influences of the geometric rule and the functional demands on actual shells by measuring the shell angles of both resting and active snails. We found that terrestrial gastropods have shell angles that are suited for balance. The growth lines of the shells indicated that this adaptation depends on the deflection of the last whorl: the apertures of flat shells are deflected downward, whereas those of tall shells are deflected upward. Our observations of active snails demonstrated that the animals hold their shells at better balanced angles than inactive snails.     

Ligamental increments of the mid-Holocene Pacific oyster Crassostrea gigas are reliable independent proxies for seasonality in the western Bohai Sea,China

Modern living and mid-Holocene shells of Crassostrea gigas from the western Bohai Sea in China were subjected to sclerochronological analysis with the aim of determining whether their concave bottoms and growth breaks on resilifer surfaces, as well as corresponding translucent growth bands visible in cross-section, have seasonal significance. An additional aim was to obtain ontogenetic information from mid-Holocene fossil shells. We compared δ¹⁸O and δ¹³C profiles compiled with high and low sampling resolution for the same shell in order to test the consistency of the results and identify a suitable sampling strategy for future sclerochronological studies. The results show that concave bottoms on the resilifer surface and corresponding translucent growth bands in cross-section formed during the cold season. These features are appropriate indicators of annual growth increments in fossil C. gigas shells. Moreover, growth breaks located near convex tops indicate annual growth increments for that part of the shell which grew when the organism was sexually mature. Therefore, spawning-related growth breaks and alternating winter freeze shocks (concave bottoms) are excellent morphological features in determining annual growth increments. Consequently, the life span, growth rate, and timing of spawning and death can be determined from the increments of ligament growth of these fossil oyster shells. For future sclerochronological studies, an adaptive micro-sampling strategy could be used for different increments of ligament growth that represent different seasons. Such a strategy would be more efficient in providing reliable insights into growth history of shells with variable growth rates of annual increments.     

The dependence of chamber dynamics on chamber dimensions

One can learn something about the determinants of ventricular dimensions and dynamics from a simple spherical model. We have derived equations showing how isometric pressure, compliance, isometric P-V curves and viscous resistance to wall displacement depend on dimensions of a spherical chamber whose fibers adjust for a "normal" stretch at a particular point in the pump cycle. The derivations show: (a) that isometric pressure at this point is proportional to the logarithm of total chamber volume (cavity plus wall) relative to cavity volume; (b) that compliance at this point is proportional to cavity volume and to total chamber volume relative to wall volume; (c) that the rate of wall displacement relative to the disparity between isometric pressure and actual pressure depends on dimensions like compliance depends on dimensions; and (d) since reciprocal compliance does not increase with wall/cavity ratios as much as isometric pressure at the normal-stretch volume, the P-V curves spread out on either side of the normal-stretch volume as the chamber undergoes adaptive thickening, resulting in disproportionate increases of isometric pressure at low cavity volumes. This tends to increase ejection fraction and reduce cavity volumes relative to stroke volume, and it is partly responsible for the "concentric" character of hypertrophy in response to high systolic pressure.     

Isomap transform for segmenting human body shapes

Segmentation of the 3D human body is a very challenging problem in applications exploiting volume capture data. Direct clustering in the Euclidean space is usually complex or even unsolvable. This paper presents an original method based on the Isomap (isometric feature mapping) transform of the volume data-set. The 3D articulated posture is mapped by Isomap in the pose of Da Vinci's Vitruvian man. The limbs are unrolled from each other and separated from the trunk and pelvis, and the topology of the human body shape is recovered. In such a configuration, Hoshen-Kopelman clustering applied to concentric spherical shells is used to automatically group points into the labelled principal curves. Shepard interpolation is utilised to back-map points of the principal curves into the original volume space. The experimental results performed on many different postures have proved the validity of the proposed method. Reliability of less than 2?cm and 3° in the location of the joint centres and direction axes of rotations has been obtained, respectively, which qualifies this procedure as a potential tool for markerless motion analysis.     

Development of an orthotopic human pancreatic cancer xenograft model using ultrasound guided injection of cells

Mice have been employed as models of cancer for over a century, providing significant advances in our understanding of this multifaceted family of diseases. In particular, orthotopic tumor xenograft mouse models are emerging as the preference for cancer research due to increased clinical relevance over subcutaneous mouse models. In the current study, we developed orthotopic pancreatic cancer xenograft models in mice by a minimally invasive method, ultrasound guided injection (USGI) comparable to highly invasive surgical orthotopic injection (SOI) methods. This optimized method prevented injection complications such as recoil of cells through the injection canal or leakage of cells out of the pancreas into the peritoneal cavity. Tumor growth was monitored in vivo and quantified by ultrasound imaging weekly, tumors were also detected by in vivo fluorescence imaging using a tumor targeted molecular probe. The mean tumor volumes for the USGI and SOI models after 2 weeks of tumor growth were 205 mm(3) and 178 mm(3) respectively. By USGI of human pancreatic cancer cell lines, human orthotopic pancreatic cancer xenografts were established. Based on ultrasound imaging, the orthotopic human pancreatic cancer xenograft take rate was 100% for both human pancreatic cancer cell lines used, MiaPaCa-2 and Su86.86, with mean tumor volumes of 28 mm(3)and 30 mm(3). We demonstrated that this USGI method is feasible, reproducible, facile, minimally invasive and improved compared to the highly-invasive SOI method for establishing orthotopic pancreatic tumor xenograft models suitable for molecular imaging.     

Using critical path method to analyse the radiation of rudist bivalves

It has been suggested that certain families of rudist bivalves (superfamily Hippuritoidea) were 'preadapted' to inhabit different environments and radiated to fill them. This scenario was based on a hypothesis of a geometric constraint of shell growth, a differential increase in the number of rudist genera possessing uncoiled shells relative to those possessing spirogyrate (i.e. coiled) shells, and a speculative phylogeny. In this paper, these ideas are reformulated and tested by comparing a postulated sequence of structural changes, expressed according to critical path method of management theory, and phylogeny, inferred from cladistic analysis. The hypothesis of constraint is unfalsified, and the cladogram is consistent with a proliferation of rudists possessing uncoiled shells. The proliferation may be attributed to the origin of an invaginated ligament, which should be considered as a direct adaptation.     

Large-Scale Trade in Legally Protected Marine Mollusc Shells from Java and Bali,Indonesia

Background

Tropical marine molluscs are traded globally. Larger species with slow life histories are under threat from over-exploitation. We report on the trade in protected marine mollusc shells in and from Java and Bali, Indonesia. Since 1987 twelve species of marine molluscs are protected under Indonesian law to shield them from overexploitation. Despite this protection they are traded openly in large volumes.

Methodology/Principal Findings

We collected data on species composition, origins, volumes and prices at two large open markets (2013), collected data from wholesale traders (2013), and compiled seizure data by the Indonesian authorities (2008–2013). All twelve protected species were observed in trade. Smaller species were traded for <USD1.00 whereas prices of larger species were USD15.00–40.00 with clear price-size relationships. Some shells were collected locally in Java and Bali, but the trade involves networks stretching hundreds of kilometres throughout Indonesia. Wholesale traders offer protected marine mollusc shells for the export market by the container or by the metric ton. Data from 20 confiscated shipments show an on-going trade in these molluscs. Over 42,000 shells were seized over a 5-year period, with a retail value of USD700,000 within Indonesia; horned helmet (Cassis cornuta) (>32,000 shells valued at USD500,000), chambered nautilus (Nautilus pompilius) (>3,000 shells, USD60,000) and giant clams (Tridacna spp.) (>2,000 shells, USD45,000) were traded in largest volumes. Two-thirds of this trade was destined for international markets, including in the USA and Asia-Pacific region.

Conclusions/Significance

We demonstrated that the trade in protected marine mollusc shells in Indonesia is not controlled nor monitored, that it involves large volumes, and that networks of shell collectors, traders, middlemen and exporters span the globe. This impedes protection of these species on the ground and calls into question the effectiveness of protected species management in Indonesia; solutions are unlikely to be found only in Indonesia and must involve the cooperation of importing countries.     

Volume Estimates by Imaging Methods: Model Comparisons with Visible Woman as the Reference

Objective: To compare the accuracy of four volume estimation models to actual tissue and organ volumes measured in the visible woman. Methods: Actual volumes were calculated from 1‐mm‐thick visible woman images that were segmented for five major components including subcutaneous and visceral adipose tissue across the 1730 available slices. Four available models resolved to two equations: truncated cone/truncated pyramid vs. two‐column/parallel trapezium. Between‐slice interval and initial slice were systematically varied when deriving component volumes using the two equations in four regions. Results: For each compartment and each between‐slice interval, the means of the two‐column model were always the same as the corresponding reference volumes, whereas those of the truncated cone model were smaller than the reference volumes. Similarly, the coefficient variation for the two‐column model was always smaller than for the truncated cone model. Discussion: The equation based on the parallel trapezium and the two‐column models is more accurate in estimating tissue volumes than the corresponding equation for truncated pyramid and truncated cone models. This finding has important implications for the volume calculations of imaging‐based body compartments such as adipose tissue.     

Indirect Estimation of Poly-β-Hydroxybutyric Acid by Cell Carbon Analysis

Nitrogen-limited batch cultures of Alcaligenes eutrophus were characterised by two phases: an exponential growth phase followed by a PHB accumulation phase where the increase in cell carbon concentration was caused exclusively by PHB accumulation. Consequently, the PHB concentration could be estimated indirectly by cell carbon analysis. The conventional spectrophotometric method for PHB estimation and the method described in this paper gave identical results. However, our method is more rapid and requires smaller sample volumes.     

Isomap transform for segmenting human body shapes

Segmentation of the 3D human body is a very challenging problem in applications exploiting volume capture data. Direct clustering in the Euclidean space is usually complex or even unsolvable. This paper presents an original method based on the Isomap (isometric feature mapping) transform of the volume data-set. The 3D articulated posture is mapped by Isomap in the pose of Da Vinci's Vitruvian man. The limbs are unrolled from each other and separated from the trunk and pelvis, and the topology of the human body shape is recovered. In such a configuration, Hoshen–Kopelman clustering applied to concentric spherical shells is used to automatically group points into the labelled principal curves. Shepard interpolation is utilised to back-map points of the principal curves into the original volume space. The experimental results performed on many different postures have proved the validity of the proposed method. Reliability of less than 2 cm and 3° in the location of the joint centres and direction axes of rotations has been obtained, respectively, which qualifies this procedure as a potential tool for markerless motion analysis.     

The effect of digenea larvae on calcium content in the shells of Lymnaea stagnalis (L.) individuals

The objective of this work was to examine the calcium concentration in the shells of naturally infected individuals of Lymnaea stagnalis. Calcium concentration in the water of lakes and in snail shells was examined by the EDTA method. Calcium concentration in the shells of infected snails was found to be higher than that in the shells of uninfected ones only in the lake with the lowest calcium concentration in water. However, this difference is not evidence of hypercalcification of snail shells caused by trematode larvae but suggests that the limited calcium concentration in the environment can be a very good factor for studying snail shell calcification under natural conditions. Moreover, small adult snails from 2 lakes had more calcium in their shells than did large ones. Different reproductive rates of different-sized snails could be the cause of this phenomenon.     

人工长白落叶松幼龄林树冠比叶重

比叶重(LMA)是构建生态系统过程模型的重要参数之一,准确预测树冠比叶重的动态变化对提高模型精度有重要意义。本研究以黑龙江省尚志市帽儿山林场人工长白山落叶松为对象,分别在生长季针叶不同发育时期对树冠内不同垂直位置的针叶比叶重进行测量,分析针叶比叶重在树冠垂直方向及针叶不同发育时期的变化规律,探讨导致其时间和空间差异的主要因子,建立长白落叶松幼龄林比叶重动态预估模型。结果表明: 比叶重在树冠垂直方向表现为随着相对着枝深度(RDINC)的增加而减小,完全展叶后比叶重在垂直方向的变化幅度明显高于展叶初期。比叶重在不同发育时期表现为随发育进程先增大后趋于稳定,该趋势随着树冠深度的增加而逐渐减弱。分别以RDINC和年度积日(DOY)为单一变量预测比叶重时,模型的调整后决定系数(R_a²)低于0.6,当同时以RDINC和DOY为自变量构建比叶重预估模型时,R_a²提高0.19,且模型检验效果良好(ME=0.54 g·m^-2, MAE=5.74 g·m^-2)。研究表明长白落叶松比叶重在树冠不同轮层和不同针叶发育期间均存在显著差异,以RDINC和DOY为自变量构建的比叶重预测模型可以很好描述长白落叶松比叶重的空间及生长季针叶发育期变化,为阐明树冠发育机理提供理论依据,为提高生态过程模型精度奠定基础。