Effect of tibial tray inclination on the femoro-tibial contact pattern of a mobile total knee arthroplasty

Introduction: The posterior inclination of the tibial component is an important factor that can affect the success of total knee arthroplasty. It can reduce the posterior impingement and thus increase the range of flexion, but it may also induce instability in flexion, anterior impingement between the polyethylene of postero-stabilizing knee prosthesis, and anterior conflict with the cortical bone and the stem. Although the problem is identified, there is still a debate on the ideal inclination angle and the surgical technique to avoid an excessive posterior inclination. The aim of this study was to predict the effect of a posterior inclination of the tibial component on the contact pattern on the tibial insert, using a numerical musculoskeletal model of the knee joint. Methods: A 3D finite element model of the knee joint was developed to simulate an active and loaded squat movement after total knee arthroplasty. Flexion was actively controlled by the quadriceps muscle and muscle activations were estimated from EMG data and were synchronized by a feedback algorithm. Two inclinations of the tibial tray were considered: a posterior inclination of 0° or 10°. During the entire range of flexion, the following quantities were calculated: the tibiofemoral and patello-femoral contact force, and the contact pattern on polyethylene insert. The antero-posterior displacement of the contact pattern was also measured. Abaqus 6.7 was used for all analyses. Results: The tibio-femoral and patello-femoral contact forces increased during flexion and reached respectively 4 and 7 BW (bodyweight) at 90° of flexion. They were slightly affected by the inclination of the tibial tray. Without posterior inclination, the contact pattern on the tibial insert remained centered. The contact pressure was lower than 5 MPa below 60° of flexion, but exceeded 20 MPa at 90° of flexion. The posterior inclination displaced the contact point posteriorly by 2 to 4 mm. Conclusion: The inclination of the tibial tray displaced the contactpattern towards the posterior border of the tibial insert. However, even for 10° of inclination, the contact center remained far from the posterior border (12 mm). There was no instability predicted for this movement.

Le traitement de l'hypertension artérielle: quel médicament pour quelle malade [The treatment of arterial hypertension: which drug for which patient?]

Hypertension is a multifactorial disease. Various antihypertensive drugs can lower arterial pressure in a given patient in a more or less efficient way. The sequential testing of several drugs is most promising for lowering blood pressure by monotherapy. If necessary a drug combination is preferable to dose adjustments of a single substance because of the risk for side effects growing with the dose.

Diagnostic value of MRI for the detection of suspected placental invasion: Does it depend on observers' experience?

Purpose: To evaluate the diagnostic value of specific MR features for detection of suspected placental invasion according to observers' experience.Methods and Materials: Our study population included 25 pregnant women (mean age 35.16) investigated by prenatal MRI. In twelve out of them placental invasion was histopathologically proven, the 13 other women (52%) without placental invasion served as control group. Multiplanar T1- and T2-weighted sequences had been performed mostly without IV contrast injection (1.5 T). MR examinations of the two groups were rendered anonymous, mixed, then independently and retrospectively reviewed by two senior and two junior radiologists in view of 8 MR features indicating placentar invasion including the degree. Results were compared with surgical diagnosis (placenta normal/increta/accreta/percreta). Interobserver agrement between senior and junior readers were calculated. Stepwise logistic regression and receiver operating (ROC) curvers were performed.Results: Demographics between the two groups were not statistically different. Overall sensitivity and specificity for detecting placentar invasion was 90.9% and 75.0% for senior readers, and 81.8% and 61.8% for junior readers respectively. The most significant MR features indicating placentar invasion were T2 hypointense placental bands, followed by placenta praevia, focally interrupted myometrial border, posterior placental insertion, and heterogeneous placental signal. For each of the evaluated MR features the interobserver agreement kappa between the two senior readers was superior than that between the junior readers, ranging from bad (<0.4) to good (0.4-0.75).Conclusions: MRI can be a reliable and reproducible tool for detection of suspected placentar invasion, however very variable according to the observers' experience.

The Variscan evolution in the External massifs of the Alps and place in their Variscan framework

In the general discussion on the Variscan evolution of central Europe the pre-Mesozoic basement of the Alps is, in many cases, only included with hesitation. Relatively well-preserved from Alpine metamorphism, the Alpine External massifs can serve as an excellent example of evolution of the Variscan basement, including the earliest Gondwana-derived microcontinents with Cadomian relics. Testifying to the evolution at the Gondwana margin, at least since the Cambrian, such pieces took part in the birth of the Rheic Ocean. After the separation of Avalonia, the remaining Gondwana border was continuously transformed through crustal extension with contemporaneous separation of continental blocks composing future Pangea, but the opening of Palaeotethys had only a reduced significance since the Devonian. The Variscan evolution in the External domain is characterised by an early HP-evolution with subsequent granulitic decompression melts. During Visean crustal shortening, the areas of future formation of migmatites and intrusion of monzodioritic magmas in a general strike-slip regime, were probably in a lower plate situation, whereas the so called monometamorphic areas may have been in an upper plate position of the nappe pile. During the Latest Carboniferous, the emplacement of the youngest granites was associated with the strike-slip faulting and crustal extension at lower crustal levels, whereas, at the surface, detrital sediments accumulated in intramontaneous transtensional basins on a strongly eroded surface. To cite this article: J.R von Raumer et al., C. R. Geoscience 341 (2009). (C) 2008 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.

Development of an erythropoietin prescription simulator to improve abilities for the prescription of erythropoietin stimulating agents: is it feasible?

BACKGROUND: The increasing use of erythropoietins with long half-lives and the tendency to lengthen the administration interval to monthly injections call for raising awareness on the pharmacokinetics and risks of new erythropoietin stimulating agents (ESA). Their pharmacodynamic complexity and individual variability limit the possibility of attaining comprehensive clinical experience. In order to help physicians acquiring prescription abilities, we have built a prescription computer model to be used both as a simulator and education tool. METHODS: The pharmacokinetic computer model was developed using Visual Basic on Excel and tested with 3 different ESA half-lives (24, 48 and 138 hours) and 2 administration intervals (weekly vs. monthly). Two groups of 25 nephrologists were exposed to the six randomised combinations of half-life and administration interval. They were asked to achieve and maintain, as precisely as possible, the haemoglobin target of 11-12 g/dL in a simulated naïve patient. Each simulation was repeated twice, with or without randomly generated bleeding episodes. RESULTS: The simulation using an ESA with a half-life of 138 hours, administered monthly, compared to the other combinations of half-lives and administration intervals, showed an overshooting tendency (percentages of Hb values > 13 g/dL 15.8 ± 18.3 vs. 6.9 ± 12.2; P < 0.01), which was quickly corrected with experience. The prescription ability appeared to be optimal with a 24 hour half-life and weekly administration (ability score indexing values in the target 1.52 ± 0.70 vs. 1.24 ± 0.37; P < 0.05). The monthly prescription interval, as suggested in the literature, was accompanied by less therapeutic adjustments (4.9 ± 2.2 vs. 8.2 ± 4.9; P < 0.001); a direct correlation between haemoglobin variability and number of therapy modifications was found (P < 0.01). CONCLUSIONS: Computer-based simulations can be a useful tool for improving ESA prescription abilities among nephrologists by raising awareness about the pharmacokinetic characteristics of the various ESAs and recognizing the factors that influence haemoglobin variability.

Formation of aluminosilicate-bearing quartz veins in the Simano nappe (Central Alps): structural, thermobarometric and oxygen isotope constraints

We combined structural analysis, thermobarometry and oxygen isotope geochemistry to constrain the evolution of kyanite and/or andalusite-bearing quartz veins from the amphibolite facies metapelites of the Simano nappe, in the Central Alps of Switzerland. The Simano nappe records a complex polyphase tectonic evolution associated with nappe stacking during Tertiary Alpine collision (D1). The second regional deformation phase (132) is responsible for the main penetrative schistosity and mineral lineation, and formed during top-to-the-north thrusting. During the next stage of deformation (D3) the aluminosilicate-bearing veins formed by crystallization in tension gashes, in tectonic shadows of boudins, as well as along shear bands associated with top-to-the-north shearing. D2 and D3 are coeval with the Early Miocene metamorphic peak, characterised by kyanite + staurolite + garnet + biotite assemblages in metapelites. The peak pressure (P) and temperature (T) conditions recorded are constrained by multiple-equilibrium thermobarometry at 630 +/- 20 degrees C and 8.5 +/- 1 kbar (similar to 27 km depth), which is in agreement with oxygen isotope thermometry indicating isotopic equilibration of quartz-kyanite pairs at 670 +/- 50 degrees C. Quartz-kyanite pairs from the aluminosilicate-bearing quartz veins yield equilibration temperatures of 645 +/- 20 degrees C, confirming that the veins formed under conditions near metamorphic peak. Quartz and kyanite from veins and the surrounding metapelites have comparable isotopic compositions. Local intergranular diffusion in the border of the veins controls the mass-transfer and the growth of the product assemblage, inducing local mobilization of SiO2 and Al2O3. Andalusite is absent from the host rocks, but it is common in quartz veins, where it often pseudomorphs kyanite. For andalusite to be stable at T-max, the pressure in the veins must have been substantially lower than lithostatic. An alternative explanation consistent with structural observations would be inheritance by andalusite of the kyanite isotopic signature during polymorphic transformation after the metamorphic peak.

Auditory Neurons with Transitory Axons to Visual Areas Form Short Permanent Projections.

The kitten's auditory cortex (including the first and second auditory fields AI and AII) is known to send transient axons to either ipsi- or contralateral visual areas 17 and 18. By the end of the first postnatal month the transitory axons, but not their neurons of origin, are eliminated. Here we investigated where these neurons project after the elimination of the transitory axon. Eighteen kittens received early (postnatal day (pd) 2 - 5) injections of long lasting retrograde fluorescent traces in visual areas 17 and 18 and late (pd 35 - 64) injections of other retrograde fluorescent tracers in either hemisphere, mostly in areas known to receive projections from AI and AII in the adult cat. The middle ectosylvian gyrus was analysed for double-labelled neurons in the region corresponding approximately to AI and AII. Late injections in the contralateral (to the analysed AI, AII) hemisphere including all of the known auditory areas, as well as some visual and 'association' areas, did not relabel neurons which had had transient projections to either ipsi- or contralateral visual areas 17 - 18. Thus, AI and AII neurons after eliminating their transient juvenile projections to visual areas 17 and 18 do not project to the other hemisphere. In contrast, relabelling was obtained with late injections in several locations in the ipsilateral hemisphere; it was expressed as per cent of the population labelled by the early injections. Few neurons (0 - 2.5%) were relabelled by large injections in the caudal part of the posterior ectosylvian gyrus and the adjacent posterior suprasylvian sulcus (areas DP, P, VP). Multiple injections in the middle ectosylvian gyrus relabelled a considerably larger percentage of neurons (13%). Single small injections in the middle ectosylvian gyrus (areas AI, AII), the caudal part of the anterior ectosylvian gyrus and the rostral part of the posterior ectosylvian gyrus relabelled 3.1 - 7.0% of neurons. These neurons were generally near (&lt;2.0 mm) the outer border of the late injection sites. Neurons with transient projections to ipsi- or contralateral visual areas 17 and 18 were relabelled in similar proportions by late injections at any given location. Thus, AI or AII neurons which send a transitory axon to ipsi- or contralateral visual areas 17 and 18 are most likely to form short permanent cortical connections. In that respect, they are similar to medial area 17 neurons that form transitory callosal axons and short permanent axons to ipsilateral visual areas 17 and 18.

Le travail des sans-emploi : analyse sociologique de l'assignation à un programme d'emploi temporaire

RESUMECette recherche empirique porte sur les emplois temporaires subventionnés (ETS) instaurés dans le cadre du chômage et de l'aide sociale en Suisse depuis une dizaine d'années. La mise en place de politiques d'activation dans le cadre de la protection sociale met l'accent sur les liens explicites, souvent réglementaires, qu'entretiennent actuellement la protection sociale, les politiques de l'emploi et le marché du travail dans les pays industrialisés. Ces transformations ont largement contribué au développement d'activités exercées en marge du marché de l'emploi. Dans le cadre du chômage, comme dans celui de l'aide sociale, une mise au travail peut être exigée en contrepartie du versement des indemnités ; en Suisse, on nomme ce procédé l'assignation au travail. L'assignation est le processus par lequel un-e conseiller?ère en placement peut contraindre, sous peine de sanction (suppression des indemnités pour un temps déterminé) une personne au chômage (inscrit-e auprès d'un office régional de placement) à souscrire à une mesure du marché du travail (MMT), particulièrement les ETS.Cette recherche propose une analyse de l'assignation à un programme d'emploi temporaire sous l'éclairage de la sociologie du travail. Elle adopte une perspective compréhensive attentive aux tensions que vivent les individus pris dans une situation de travail hybride et inédite qui les place aux frontières des différentes catégories administratives de chômage, d'inactivité et de population occupée. Partant d'une étude empirique auprès de personnes assignées, cette recherche mène une analyse qualitative des conditions et de l'organisation du travail en ETS, des modalités contractuelles et statutaires des personnes assignées à une activité de travail contrainte et matériellement non reconnue, puisque non salariée. Elle s'attache également à cerner le vécu de l'assignation au travail, ainsi que le sens que les personnes lui attribuent dans leur trajectoire biographique et professionnelle.SUMMARYThis research investigates a specific and new form of labor, namely «temporary subsidized jobs» {emplois temporaires subventionnés, ETS) that have been developed since the late 1990s in Switzerland in the context of unemployment and social assistance benefits. Although ETS are specific to Switzerland, they echo similar «workfare» measures imposed on unemployed and welfare recipients introduced in recent years in almost all industrialized countries. Indeed, the evolution of public policies and the generalization of «active labour-market policies» {politiques d'activation) have become central to social protection in the majority of Western countries and have emerged in parallel to the expansion of work activities situated at the margins of traditional wage- labor.My analysis of the ETS phenomenon is informed by labor sociology and discusses the pertinence of a classical approach in grasping this hybrid and new work situation, which sets individual persons at the border between various administrative categories such as «unemployed», «inactive» and «at work». I investigate in particular the issue of contractual and statutory modalities imposed on persons who have been assigned to a form of activity that is both constraining as well as materially non-recognized (as it remains outside of traditional wage-labor forms). In order to understand ETS conditions and labor organization, my fieldwork consist of interviews of persons who have been assigned to it and observations. I investigate their personal experience, as well as the meaning that these individuals attribute to the ETS experience in the context of their biographical and professional trajectory.

Voir le monde à travers les lunettes du métacontraste : un modèle mathématique inspiré de la psychologie sociale

Résumé La théorie de l'autocatégorisation est une théorie de psychologie sociale qui porte sur la relation entre l'individu et le groupe. Elle explique le comportement de groupe par la conception de soi et des autres en tant que membres de catégories sociales, et par l'attribution aux individus des caractéristiques prototypiques de ces catégories. Il s'agit donc d'une théorie de l'individu qui est censée expliquer des phénomènes collectifs. Les situations dans lesquelles un grand nombre d'individus interagissent de manière non triviale génèrent typiquement des comportements collectifs complexes qui sont difficiles à prévoir sur la base des comportements individuels. La simulation informatique de tels systèmes est un moyen fiable d'explorer de manière systématique la dynamique du comportement collectif en fonction des spécifications individuelles. Dans cette thèse, nous présentons un modèle formel d'une partie de la théorie de l'autocatégorisation appelée principe du métacontraste. À partir de la distribution d'un ensemble d'individus sur une ou plusieurs dimensions comparatives, le modèle génère les catégories et les prototypes associés. Nous montrons que le modèle se comporte de manière cohérente par rapport à la théorie et est capable de répliquer des données expérimentales concernant divers phénomènes de groupe, dont par exemple la polarisation. De plus, il permet de décrire systématiquement les prédictions de la théorie dont il dérive, notamment dans des situations nouvelles. Au niveau collectif, plusieurs dynamiques peuvent être observées, dont la convergence vers le consensus, vers une fragmentation ou vers l'émergence d'attitudes extrêmes. Nous étudions également l'effet du réseau social sur la dynamique et montrons qu'à l'exception de la vitesse de convergence, qui augmente lorsque les distances moyennes du réseau diminuent, les types de convergences dépendent peu du réseau choisi. Nous constatons d'autre part que les individus qui se situent à la frontière des groupes (dans le réseau social ou spatialement) ont une influence déterminante sur l'issue de la dynamique. Le modèle peut par ailleurs être utilisé comme un algorithme de classification automatique. Il identifie des prototypes autour desquels sont construits des groupes. Les prototypes sont positionnés de sorte à accentuer les caractéristiques typiques des groupes, et ne sont pas forcément centraux. Enfin, si l'on considère l'ensemble des pixels d'une image comme des individus dans un espace de couleur tridimensionnel, le modèle fournit un filtre qui permet d'atténuer du bruit, d'aider à la détection d'objets et de simuler des biais de perception comme l'induction chromatique. Abstract Self-categorization theory is a social psychology theory dealing with the relation between the individual and the group. It explains group behaviour through self- and others' conception as members of social categories, and through the attribution of the proto-typical categories' characteristics to the individuals. Hence, it is a theory of the individual that intends to explain collective phenomena. Situations involving a large number of non-trivially interacting individuals typically generate complex collective behaviours, which are difficult to anticipate on the basis of individual behaviour. Computer simulation of such systems is a reliable way of systematically exploring the dynamics of the collective behaviour depending on individual specifications. In this thesis, we present a formal model of a part of self-categorization theory named metacontrast principle. Given the distribution of a set of individuals on one or several comparison dimensions, the model generates categories and their associated prototypes. We show that the model behaves coherently with respect to the theory and is able to replicate experimental data concerning various group phenomena, for example polarization. Moreover, it allows to systematically describe the predictions of the theory from which it is derived, specially in unencountered situations. At the collective level, several dynamics can be observed, among which convergence towards consensus, towards frag-mentation or towards the emergence of extreme attitudes. We also study the effect of the social network on the dynamics and show that, except for the convergence speed which raises as the mean distances on the network decrease, the observed convergence types do not depend much on the chosen network. We further note that individuals located at the border of the groups (whether in the social network or spatially) have a decisive influence on the dynamics' issue. In addition, the model can be used as an automatic classification algorithm. It identifies prototypes around which groups are built. Prototypes are positioned such as to accentuate groups' typical characteristics and are not necessarily central. Finally, if we consider the set of pixels of an image as individuals in a three-dimensional color space, the model provides a filter that allows to lessen noise, to help detecting objects and to simulate perception biases such as chromatic induction.

Stimulated-echo acquisition mode (STEAM) MRI for black-blood delayed hyperenhanced myocardial imaging.

PURPOSE: To develop a breathhold method for black-blood viability imaging of the heart that may facilitate identifying the endocardial border. MATERIALS AND METHODS: Three stimulated-echo acquisition mode (STEAM) images were obtained almost simultaneously during the same acquisition using three different demodulation values. Two of the three images were used to construct a black-blood image of the heart. The third image was a T(1)-weighted viability image that enabled detection of hyperintense infarcted myocardium after contrast agent administration. The three STEAM images were combined into one composite black-blood viability image of the heart. The composite STEAM images were compared to conventional inversion-recovery (IR) delayed hyperenhanced (DHE) images in nine human subjects studied on a 3T MRI scanner. RESULTS: STEAM images showed black-blood characteristics and a significant improvement in the blood-infarct signal-difference to noise ratio (SDNR) when compared to the IR-DHE images (34 +/- 4.1 vs. 10 +/- 2.9, mean +/- standard deviation (SD), P < 0.002). There was sufficient myocardium-infarct SDNR in the STEAM images to accurately delineate infarcted regions. The extracted infarcts demonstrated good agreement with the IR-DHE images. CONCLUSION: The STEAM black-blood property allows for better delineation of the blood-infarct border, which would enhance the fast and accurate measurement of infarct size.

Das Auerhuhn im Jura: Qualität des Lebensraum, Demographie, Habitatwahl und nicht-invasive genetische Untersuchungen

Most Central European Capercaillie populations have been declining during the last century. In the Jura Mountains, at the border between Switzerland and France, remaining Capercaillie populations are now isolated and endangered. In this study, land-use and Capercaillie presence data were used to identify key landscape parameters by logistic regression modelling. We found that Capercaillie prefers areas at the highest altitude in the Jura Mountains that are characterised by continous forests and stands with intermediate canopy cover. At the local scale, winter habitat selection revealed a preference for open forests with a sparse canopy cover dominated by spruce and fir. Capercaillie avoided dense undercanopy and understorey, especially when dominated by beech. Population viability and sensitivity analyses underlined the crucial importance of adult female survival, chick survival and breeding success for populations maintenance. Legal bases, scientific knowledge and technical measures are now available to conserve the flagship species Capercaillie within Jura Mountains. Capercaillie-adapted forestry requires a mosaic distribtution of habitat types, with a matrix of open forests where fir is favoured, and understorey kept sparse. Preliminary essays indicate that grouse-adapted forestry costs are similar or even lower than present costs. To increase survival and breeding sucess, one option is to diminish human distrubance by limiting access to Capercailllie breeding and wintering areas. An action plan for the species should avoid more costly and intensive approaches such as the reintroduction of birds from other populations. Capercaillie conservaiton represents a major challenge rising from various and contradictory leisure, tourist and rural development activities. Collaborations with different stakeholders and state agencies for forestry with an effective protection from human distrubance.

Unsatisfactory outcomes in myasthenia gravis: influence by care providers.

Myasthenia gravis (MG) can be difficult to treat despite an available therapeutic armamentarium. Our aim was to analyze the factors leading to unsatisfactory outcome (UO). To this end we used the Myasthenia Gravis Foundation of America classification system. Forty one patients with autoimmune MG were followed prospectively from January 2003 to December 2007. Outcomes were assessed throughout follow-up and at a final visit. 'Unchanged', 'worse', 'exacerbation' and 'died of MG' post-intervention status were considered UOs. During follow-up, UO rates reached 54% and were related to undertreatment (41%), poor treatment compliance (23%), infections (23%), and adverse drug effects (13%). The UO rate at final study assessment was 20%. UO during follow-up was significantly (P = 0.004) predictive of UOs at final assessment. When care was provided by neuromuscular (NM) specialists, patients had significantly better follow-up scores (P = 0.01). At final assessment UO rates were 7% and significantly better in patients treated by NM specialists, compared to other physicians where UO rates reached 27%. UO was a frequent finding occurring in more than half our patients during follow-up. Nearly two-thirds of the UOs could have been prevented by appropriate therapeutic adjustments and improved compliance. The differential UO rates at follow-up, their dependency on the degree to which the management was specialized and their correlation with final outcomes suggest that specialized MG care improves outcomes.

Physiological traits affecting the distribution and wintering strategy of the bat Tadarida teniotis

The ability to enter torpor at low ambient temperature, which enables insectivorous bats to survive seasonal food shortage, is often seen as a prerequisite for colonizing cold environments. Free-tailed bats (Molossidae) show a distribution with a maximum latitudinal extension that appears to be intermediate between truly tropical and temperate-zone bat families. We therefore tested the hypothesis that Tadarida teniotis, the molossid species reaching the highest latitude worldwide (46 degrees N), lacks the extreme physiological adaptations to cold that enable other sympatric bats to enter further into the temperate zone. We studied the metabolism of individuals subjected to various ambient temperatures in the laboratory by respirometry, and we monitored the body temperature of free-ranging individuals in winter and early spring in the Swiss Alps using temperature-sensitive radio-tags. For comparison, metabolic data were obtained from Nyctalus noctula, a typically hibernating vespertilionid bat of similar body size and convergent foraging tactics. The metabolic data support the hypothesis that T. teniotis cannot experience such low ambient temperatures as sympatric temperate-zone vespertilionid bats without incurring much higher energetic costs for thermogenesis. The minimum rate of metabolism in torpor was obtained at 7.5 degrees-10 degrees C in T. teniotis, as compared to 2.5 degrees-5 degrees C in N. noctula. Field data showed that T. teniotis behaves as a classic thermo-conforming hibernator in the Alps, with torpor bouts lasting up to 8 d. This contradicts the widely accepted opinion that Molossidae are nonhibernating bars. However, average body temperature (10 degrees-13 degrees C) and mean arousal frequency (3.4 d in one bat in January) appear to be markedly higher than in other temperate-zone bat species. At the northern border of its range T. teniotis selects relatively warm roosts (crevices in tall, south-exposed limestone cliffs) in winter where temperatures oscillate around 10 degrees C. By this means, T. teniotis apparently avoids the risk of prolonged exposure to energetically critical ambient temperatures in torpor (<6.5 degrees-7.5 degrees C) during cold spells. Possibly shared by other Molossidae, the physiological pattern observed in T. teniotis may clearly be linked to the intermediate latitudinal extension of this bat family.

Changes in leg spring behaviour, plantar loading and foot mobility magnitude induced by an exhaustive treadmill run in adolescent middle-distance runners.

OBJECTIVES: This study aimed to determine adjustments in spring-mass model characteristics, plantar loading and foot mobility induced by an exhaustive run. DESIGN: Within-participants repeated measures. METHODS: Eleven highly-trained adolescent middle-distance runners ran to exhaustion on a treadmill at a constant velocity corresponding to 95% of velocity associated with VO₂max (17.8 ± 1.4 kmh(-1), time to exhaustion=8.8 ± 3.4 min). Contact time obtained from plantar pressure sensors was used to estimate spring-mass model characteristics, which were recorded (during 30 s) 1 min after the start and prior to exhaustion using pressure insoles. Foot mobility magnitude (a composite measure of vertical and medial-lateral mobility of the midfoot) was measured before and after the run. RESULTS: Mean contact area (foot to ground), contact time, peak vertical ground reaction force, centre of mass vertical displacement and leg compression increased significantly with fatigue, while flight time, leg stiffness and mean pressure decreased. Leg stiffness decreased because leg compression increased to a larger extent than peak vertical ground reaction forces. Step length, step frequency and foot mobility magnitude did not change at exhaustion. CONCLUSIONS: The stride pattern of adolescents when running on a treadmill at high constant velocity deteriorates near exhaustion, as evidenced by impaired leg-spring behaviour (leg stiffness) and altered plantar loading.

Heritability of the retinal microcirculation in flemish families.

BACKGROUND Few population studies have described the heritability and intrafamilial concordance of the retinal microvessels, or the genetic or environmental correlations of the phenotypes of these vessels. METHODS We randomly selected 413 participants from 70 families (mean age, 51.5 years; 50.1% women) from a Flemish population. We postprocessed retinal images using IVAN software to generate the central retinal arteriole equivalent (CRAE), central retinal venule equivalent (CRVE), and arteriole-to-venule-ratio (AVR) from these images. We used SAGE version 6.2 and SAS version 9.2 to compute multivariate-adjusted estimates of heritability and intrafamilial correlations of the CRAE, CRVE, and AVR of the retinal microvessels in the images. RESULTS Sex, age, mean arterial pressure, and smoking explained up to 12.7% of the variance of the phenotypes of the retinal microvessels of the study participants. With adjustments applied for these covariates, the heritability estimates of CRAE, CRVE, and AVR were 0.213 (P = 0.044), 0.339 (P = 0.010), and 0.272 (P = 0.004), respectively. The parent-offspring correlations for CRAE, CRVE, and AVR were 0.118 (NS), 0.225 (P < 0.01), and 0.215 (P < 0.05), respectively. The corresponding values were 0.222 (P < 0.05), 0.213 (P < 0.05), and 0.390 (P < 0.001) for sib-sib correlations, respectively. The genetic and environmental correlations between CRAE and CRVE were 0.360 and 0.545 (P < 0.001 for both). CONCLUSION Our study showed moderate heritability for CRAE, CRVE, and AVR, and a significant genetic correlation of CRAE with CRVE in the Flemish population of our study. These findings suggest that genetic factors influence the diameter of the retinal microvessels, and that CRAE and CRVE share some genetic determinants.