Design of a 3 DOF displacement stage based on ferrofluids.

International audienceThis paper presents the design of a 3 DOF (Degrees Of Freedom) displacement stage. This stage is composed of a mobile platform in suspension on three ferrofluid bubbles as an hydrostatic suspension. Bubbles stay attached to the platform thanks to three permanent magnets fixed on this platform. The actuation is obtained by fixing and controlling three coils on the support near the magnets. The dynamical characteristics of the stage are tuning by choosing appropriate volumes and properties for the ferrofluid and permanent magnets. The control in open loop permits a resolution of 50 nm but unfortunately a lower repeatability. The stage will be improved in the future by using a position feedback control

Is altitude training an efficient treatment for obesity?

Worldwide, about half the adult population is considered overweight as defined by a body mass index (BMI - calculated by body weight divided by height squared) ratio in excess of 25 kg.m-2. Of these individuals, half are clinically obese (with a BMI in excess of 30) and these numbers are still increasing, notably in developing countries such as those of the Middle East region. Obesity is a disorder characterised by increased mass of adipose tissue (excessive fat accumulation) that is the result of a systemic imbalance between food intake and energy expenditure. Although factors such as family history, sedentary lifestyle, urbanisation, income and family diet patterns determine obesity prevalence, the main underlying causes are poor knowledge about food choice and lack of physical activity3. Current obesity treatments include dietary restriction, pharmacological interventions and ultimately, bariatric surgery. The beneficial effects of physical activity on weight loss through increased energy expenditure and appetite modulation are also firmly established. Another viable option to induce a negative energy balance, is to incorporate hypoxia per se or combine it with exercise in an individual's daily schedule. This article will present recent evidence suggesting that combining hypoxic exposure and exercise training might provide a cost-effective strategy for reducing body weight and improving cardio-metabolic health in obese individuals. The efficacy of this approach is further reinforced by epidemiological studies using large-scale databases, which evidence a negative relationship between altitude of habitation and obesity. In the United States, for instance, obesity prevalence is inversely associated with altitude of residence and urbanisation, after adjusting for temperature, diet, physical activity, smoking and demographic factors

Coordination pattern adaptability: energy cost of degenerate behaviors.

This study investigated behavioral adaptability, which could be defined as a blend between stability and flexibility of the limbs movement and their inter-limb coordination, when individuals received informational constraints. Seven expert breaststroke swimmers performed three 200-m in breaststroke at constant submaximal intensity. Each trial was performed randomly in a different coordination pattern: 'freely-chosen', 'maximal glide' and 'minimal glide'. Two underwater and four aerial cameras enabled 3D movement analysis in order to assess elbow and knee angles, elbow-knee pair coordination, intra-cyclic velocity variations of the center of mass, stroke rate and stroke length and inter-limb coordination. The energy cost of locomotion was calculated from gas exchanges and blood lactate concentration. The results showed significantly higher glide, intra-cyclic velocity variations and energy cost under 'maximal glide' compared to 'freely-chosen' instructional conditions, as well as higher reorganization of limb movement and inter-limb coordination (p<0.05). In the 'minimal glide' condition, the swimmers did not show significantly shorter glide and lower energy cost, but they exhibited significantly lower deceleration of the center of mass, as well as modified limb movement and inter-limb coordination (p<0.05). These results highlight that a variety of structural adaptations can functionally satisfy the task-goal

Does the Running Economy Really Increase after Ultra-Marathons?

[no abstract available

Microvascular and oxidative stress responses to acute high-altitude exposure in prematurely born adults.

Premature birth is associated with endothelial and mitochondrial dysfunction, and chronic oxidative stress, which might impair the physiological responses to acute altitude exposure. We assessed peripheral and oxidative stress responses to acute high-altitude exposure in preterm adults compared to term born controls. Post-occlusive skeletal muscle microvascular reactivity and oxidative capacity from the muscle oxygen consumption recovery rate constant (k) were determined by Near-Infrared Spectroscopy in the vastus lateralis of seventeen preterm and seventeen term born adults. Measurements were performed at sea-level and within 1 h of arrival at high-altitude (3375 m). Plasma markers of pro/antioxidant balance were assessed in both conditions. Upon acute altitude exposure, compared to sea-level, preterm participants exhibited a lower reperfusion rate (7 ± 31% vs. 30 ± 30%, p = 0.046) at microvascular level, but higher k (6 ± 32% vs. -15 ± 21%, p = 0.039), than their term born peers. The altitude-induced increases in plasma advanced oxidation protein products and catalase were higher (35 ± 61% vs. -13 ± 48% and 67 ± 64% vs. 15 ± 61%, p = 0.034 and p = 0.010, respectively) and in xanthine oxidase were lower (29 ± 82% vs. 159 ± 162%, p = 0.030) in preterm compared to term born adults. In conclusion, the blunted microvascular responsiveness, larger increases in oxidative stress and skeletal muscle oxidative capacity may compromise altitude acclimatization in healthy adults born preterm

Emotional Intelligence in Ultra-Marathon Runners: Implications for Recovery Strategy and Stress Responses during an Ultra-Endurance Race.

The aim of this research was to investigate the role of trait emotional intelligence (EI) in recovery stress states in a mountain ultra-marathon (MUM) race. Recovery stress states of 13 finishers were assessed before, during, and immediately after the end of an extreme MUM, whereas emotional intelligence was assessed 2 days before the MUM race. Temporal evolutions of recovery stress states were examined. Stress states increased after the race whereas recovery states decreased in all participants. In addition, recovery states were influenced by the trait EI level assessed before the competition. Results supported the hypothesis that trait EI tends to have a positive effect by boosting recovery strategies. In this perspective, trait EI could have a protective role against stress and improve pre-competition mental preparation. High scores of trait EI (in comparison to low scores of trait EI) could have helped athletes to increase recovery states in order to improve their psychological adaptation to one of the most difficult races in the world

Ground state of the Kagome-like S=1/2 antiferromagnet, Volborthite Cu3V2O7(OH)2.2H2O

Volborthite compound is one of the very few realizations of S=1/2 quantum spins on a highly frustrated kagome-like lattice. Low-T SQUID measurements reveal a broad magnetic transition below 2K which is further confirmed by a peak in the 51V nuclear spin relaxation rate (1/T1) at 1.4K$\pm$0.2K. Through 51V NMR, the ground state (GS) appears to be a mixture of different spin configurations, among which 20% correspond to a well defined short range order, possibly of the $\sqrt{3} \times \sqrt{3}$ type. While the freezing involve all the Cu$^{2+}$ spins, only 40% of the copper moment is actually frozen which suggests that quantum fluctuations strongly renormalize the GS.Comment: 4 pages, 4 figures, to appear in PR

Ventilatory responses to independent and combined hypoxia, hypercapnia and hypobaria in healthy pre-term-born adults.

Pre-term birth is associated with physiological sequelae that persist into adulthood. In particular, modulated ventilatory responsiveness to hypoxia and hypercapnia has been observed in this population. Whether pre-term birth per se causes these effects remains unclear. Therefore, we aimed to assess pulmonary ventilation and blood gases under various environmental conditions, comparing 17 healthy prematurely born individuals (mean ± SD; gestational age, 28 ± 2 weeks; age, 21 ± 4 years; peak oxygen uptake, 48.1 ± 11.2 ml kg <sup>-1</sup> min <sup>-1</sup> ) with 16 well-matched adults born at term (gestational age, 40 ± 1 weeks; age, 22 ± 2 years; peak oxygen uptake, 51.2 ± 7.7 ml kg <sup>-1</sup> min <sup>-1</sup> ). Participants were exposed to seven combinations of hypoxia/hypobaria (equivalent to ∼3375 m) and/or hypercapnia (3% CO <sub>2</sub> ), at rest for 6 min. Pulmonary ventilation, pulse oxygen saturation and the arterial partial pressures of O <sub>2</sub> and CO <sub>2</sub> were similar in pre-term and full-term individuals under all conditions. Higher ventilation in hypoxia compared to normoxia was only observed at terrestrial altitude, despite an equivalent (normobaric) hypoxic stimulus administered at sea level (0.138 ). Assessment of oscillations in key variables revealed that combined hypoxic hypercapnia induced greater underlying fluctuations in ventilation in pre-term individuals only. In general, higher pulse oxygen saturation fluctuations were observed with hypoxia, and lower fluctuations in end-tidal CO <sub>2</sub> with hypercapnia, despite similar ventilatory oscillations observed between conditions. These findings suggest that healthy prematurely born adults display similar overall ventilation to their term-born counterparts under various environmental stressors, but that combined ventilatory stimuli could induce an irregular underlying ventilatory pattern. Moreover, barometric pressure may be an important factor when assessing ventilatory responsiveness to moderate hypoxic stimuli. KEY POINTS: Evidence exists for unique pulmonary and respiratory function under hypoxic conditions in adult survivors of pre-term birth. Whether pre-term birth per se causes these differences requires a comparison of conventionally healthy prematurely born adults with an appropriately matched sample of term-born individuals. According to the present data, there is no difference between healthy pre-term and well-matched term-born individuals in the magnitude of pulmonary ventilation or arterial blood gases during independent and combined hypobaria, hypoxia and hypercapnia. Terrestrial altitude (hypobaria) was necessary to induce differences in ventilation between normoxia and a hypoxic stimulus equivalent to ∼3375 m of altitude. Furthermore, peak power in pulse oxygen saturation was similar between hypobaric normoxia and normobaric hypoxia. The observed similarities between groups suggest that ventilatory regulation under various environmental stimuli is not impaired by pre-term birth per se. Instead, an integrated combination of neonatal treatment strategies and cardiorespiratory fitness/disease status might underlie previously observed chemosensitivity impairments