Evidence of movement variability patterns during a repetitive pointing task until exhaustion.

Human movement is characterized by its variability: the same task is never performed twice in exactly the same way. This variability is believed to play a functional role in movement performance and adaptability, as well as in preventing musculoskeletal damage. This article focuses on the time-evolution of movement variability throughout a repetitive pointing task until exhaustion. The kinematics of 13 subjects performing the pointing task is analyzed. Principal Component Analysis of joint angles identifies joint coordinations for each pointing cycle, and cycle-by-cycle comparison highlights movement variability. Non-supervised clustering reveals that subjects adopt successive coordination patterns at an intra-individual level. Inter-individual variability is characterized by the number and type of such patterns: from 3 to 5 patterns, mobilizing the trunk, the shoulder and the upper limbs differently. Movement variability exists even in a seemingly basic and constrained task. It appears in the very early stages of fatigue onset, and may correspond to adaptative coordination responses throughout task performance. This observation should encourage workstation designers to better account for movement variability in order to preserve operators' health and safety.

Temporal leeway: can it help to reduce biomechanical load for older workers performing repetitive light assembly tasks?

Current industrial production systems allow assembly of customised products which include additional elements distinguishing them from a reference model. This customisation can result in significant additional time constraints which compel workers to complete their tasks faster, which may pose problems for older workers. The objective of this laboratory study was to investigate the impact of restrictive or flexible pacing during assembly of customised products among groups of younger and older participants. The data gathered were used to analyse cycle-time, assembly performance, muscular load, and kinematic adaptations. The flexible pacing condition was found to improve production performance, increasing customised assembly cycle-time and reducing biomechanical load, for both young and older participants. However, as the task required fine manual dexterity, older participants were subjected to a higher biomechanical load, even in the flexible pacing scenario. These results should encourage assembly-line designers to allow flexible time constraints as much as possible and to be particularly attentive to the needs of older workers.

Poor maternal anthropometric characteristics and newborns' birth weight and length: a cross-sectional study in Benin.

Background: Maternal undernutrition is known to negatively impact newborns' birth weight and length, but this finding is poorly documented in the Beninese population. This study aimed to assess the effect of maternal anthropometry on mean birth weight and length in a Beninese cohort of newborns. Methods: A cross-sectional study was carried out in Tori Bossito, Republic of Benin. Pregnant women attending maternity wards between June 2007 and July 2008 were recruited. At delivery the women's characteristics, including weight and height, were gathered and newborns' birth weights and lengths were measured. Statistical analysis was performed using multiple linear regression. Results: A total of 526 mother-infant pairs were enrolled; 29.8% of women had low weight status and 26.2% had short stature (<155 cm). The mean birth weight was 2985 g (standard deviation [SD] 384) the mean birth length was 48.7 cm (SD 2.2). Maternal low weight status (coefficient=-151.81, p<0.001) and short stature (coefficient=-135.49, p<0.001) reduced the mean birth weight. Similar results were found for mean birth length, which was decreased by maternal low weight status (coefficient=-0.42, p=0.04) and short stature (coefficient=-0.51, p=0.01). Conclusion: Maternal undernutrition expressed by low anthropometry remains problematic in the Beninese population and induces transmission of malnutrition. Nutritional interventions are required to break this vicious cycle.

Prévalence et description des pratiques d'allaitement maternel exclusif dans une zone semi-rurale au sud du Bénin

Introduction : Dans un contexte de non atteinte des recommandations de l'OMS et de l'UNICEF con-cernant l'allaitement maternel exclusif, cette étude avait pour objectif de décrire les pratiques et habi-tudes d'allaitement maternel dans une population semi-rurale au sud du Bénin. Matériel et méthode : Cette enquête s'est déroulée à Sèmè-Kpodji située à 15 km au sud-est de la capitale Porto-Novo. Les pratiques d'allaitement maternel exclusif de 0 à 6 mois ont été observées et notées chez 339 femmes ayant accouché entre janvier 2015 et janvier 2016. Résultats : La plupart des enfants (71,40%) ont été mis au sein dès la première de vie ; l'âge moyen de sevrage était de 4,5 mois. Le taux d'allaitement maternel exclusif était de 53,9% et a diminué pro-gressivement en fonction de l'âge de l'enfant. Les taux d'allaitement maternel prédominant et complété ont varié de 25,4% à 49,6% et de 0 à 40,7% respectivement. La durée moyenne des tétées est passée de 24,1 à 15,1 minutes et la fréquence des repas de 9,5 à 6,4 repas par jour. Conclusion : Cette enquête confirme la nécessité de continuer les interventions de santé publique visant à promouvoir l'allaitement maternel exclusif afin d'améliorer les indicateurs de santé materno-infantile

3D X-Ray Imaging of Continuous Objects beyond the Depth of Focus Limit.

X-ray ptychography is becoming the standard method for sub-30 nm imaging of thick extended samples. Available algorithms and computing power have traditionally restricted sample reconstruction to 2D slices. We build on recent progress in optimization algorithms and high performance computing to solve the ptychographic phase retrieval problem directly in 3D. Our approach addresses samples that do not fit entirely within the depth of focus of the imaging system. Such samples pose additional challenges because of internal diffraction effects within the sample. We demonstrate our approach on a computational sample modeled with 17 million complex variables.

Intrinsic movement variability at work. How long is the path from motor control to design engineering?

For several years, increasing numbers of studies have highlighted the existence of movement variability. Before that, it was neglected in movement analysis and it is still almost completely ignored in workstation design. This article reviews motor control theories and factors influencing movement execution, and indicates how intrinsic movement variability is part of task completion. These background clarifications should help ergonomists and workstation designers to gain a better understanding of these concepts, which can then be used to improve design tools. We also question which techniques--kinematics, kinetics or muscular activity--and descriptors are most appropriate for describing intrinsic movement variability and for integration into design tools. By this way, simulations generated by designers for workstation design should be closer to the real movements performed by workers. This review emphasises the complexity of identifying, describing and processing intrinsic movement variability in occupational activities.

Cardiorespiratory reflex control in rats with left ventricular dysfunction.

Patients with heart failure exhibit a neurohumoral excitatory state and abnormal baroreflex control of the cardiovascular system. We determined whether arterial baroreflexes are impaired during left ventricular dysfunction (LVD) caused by chronic myocardial infarction in the absence of congestive heart failure and whether abnormal central mechanisms contribute to this impairment. Baroreceptors were stimulated in anesthetized rats with and without LVD by increasing arterial pressure with phenylephrine. Lumbar sympathetic nerve and phrenic nerve activity as well as heart rate were recorded. Rats were divided into different groups based on infarct size. Rats with moderate LVD showed impaired baroreflex control of sympathetic, ventilatory, and heart rate responses. Baroreflex gains were inversely related to the size of the infarct. The central gain for sympathetic nerve activity, obtained by using electrical stimulation of the aortic depressor nerve, also was impaired. Baroreflex control of the cardiorespiratory system is thus impaired in rats with moderate LVD in the absence of congestive heart failure. The attenuated baroreflexes are likely due to abnormal afferent mechanisms, although central mechanisms contribute to the impaired barosympathetic reflex.

Stability of water-soluble carbodiimides in aqueous solution.

A dimethylbarbituric acid reagent has been used to follow the kinetics of loss of two water-soluble carbodiimides, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and the structurally related 1-ethyl-3-(4-azonia-4,4-dimethylpentyl) carbodiimide (EAC), in aqueous solution as a function of pH and added chemical reagents. In 50 mM 2-(N-morpholino)ethanesulfonic acid at 25 degrees C, EDC has t1/2 values of 37, 20, and 3.9 h at pH 7.0, 6.0, and 5.0, respectively, while the corresponding values for EAC are 12, 2.9, and 0.32 h. Iodide, bromide, or chloride, at 0.1 M, has very little or no effect on carbodiimide stability. However, 0.1 M glycine methyl ester or 0.1 M ethylenediamine causes a significant increase in the rate of loss of EAC and EDC, while the presence of 0.1 M phosphate, 0.1 M hydroxylamine, or 0.01 M ATP decreases the half-lives to less than or equal to 0.4 h at all pH values.