Melt viscoelastic assessment of Poly(Lactic Acid) composting: Influence of UV Ageing

This study is devoted to the degradation pathway (bio, photo degradation and photo/bio) of Poly(Lactic acid) PLA polymers by means of melt viscoelasticity. A comparison was made between three PLA polymers with different microstructures (L, D stereoisomers). Biodegradability was determined during composting by burying the polymer films in compost at 58 _C. Melt viscoelasticity was used to assess the molecular evolution of the materials during the composting process. Viscoelastic data were plotted in the complex plane. We used this methodology to check the kinetics of the molecular weight decrease during the initial stages of the degradation, through the evolution of Newtonian viscosity. After a few days in compost, the Newtonian viscosity decreased sharply, meaning that macromolecular chain scissions began at the beginning of the experiments. However, a double molar mass distribution was also observed on Cole-Cole plots, indicating that there is also a chain recombination mechanism competing with the chain scission mechanism. PLA hydrolysis was observed by infra-red spectroscopy, where acid characteristic peaks appeared and became more intense during experiments, confirming hydrolytic activity during the first step of biodegradation. During UV ageing, polymer materials undergo a deep molecular evolution. After photo-degradation, lower viscosities were measured during biodegradation, but no significant differences in composting were found. © 2018 by the authors

Long-term effects of high intensity resistance and endurance exercise on plasma leptin and ghrelin in overweight individuals:the RESOLVE Study

International audienceThe objective of this study was to evaluate the effects of high-intensity resistance and endurance exercise on body composition and plasma leptin and ghrelin concentrations in overweight individuals. One hundred participants were randomly assigned to 3 exercise interventions: high-resistance–low-aerobic exercise (Re), low-resistance–high-aerobic exercise (rE), low-resistance–low-aerobic exercise (re). Interventions began with 3 weeks of residential supervision (phase 1) after which participants had to manage the physical activity programs individually (phase 2). Body composition and plasma variables were measured at baseline and after phase 1 as well as after 3, 6, and 12 months. Significant decreases in body weight and fat were observed after phase 1 (p < 0.001) and continued at a lower rate for up to 3 months and then remained stable for the rest of the protocol. Once a body weight plateau was reached, body fat loss after the Re and rE conditions exceeded the fat loss observed in the re condition by 1.5–2 kg (p < 0.05). Leptin was significantly decreased after day 21 and month 3 (p < 0.001) and remained stable for the rest of the study. Ghrelin was significantly increased after day 21 and month 3 (p < 0.001) and returned to a level comparable to baseline between month 6 and 12 when body weight and fat had reached a plateau. In conclusion, this study reinforces the idea that an increase in exercise intensity may accentuate body fat loss before the occurrence of a body weight plateau. Resistance to further fat loss was accompanied by a decrease in plasma leptin and an increase in plasma ghrelin

Running from Paris to Beijing: biomechanical and physiological consequences

Abstract The purpose of this study was to examine the physiological and biomechanical changes occurring in a subject after running 8,500 km in 161 days (i.e. 52.8 km daily). Three weeks before, 3 weeks after (POST) and 5 months after (POST?5) running from Paris to Beijing, energy cost of running (Cr), knee flexor and extensor isokinetic strength and biomechanical parameters (using a treadmill dynamometer) at different velocities were assessed in an experienced ultra-runner. At POST, there was a tendency toward a &apos;smoother&apos; running pattern, as shown by (a) a higher stride frequency and duty factor, and a reduced aerial time without a change in contact time, (b) a lower maximal vertical force and loading rate at impact and (c) a decrease in both potential and kinetic energy changes at each step. This was associated with a detrimental effect on Cr (?6.2%) and a loss of strength at all angular velocities for both knee flexors and extensors. At POST?5, the subject returned to his original running patterns at low but not at high speeds and maximal strength remained reduced at low angular velocities (i.e. at high levels of force). It is suggested that the running pattern changes observed in the present study were a strategy adopted by the subject to reduce the deleterious effects of long distance running. However, the running pattern changes could partly be linked to the decrease in maximal strength

Melatonin Promotes Oligodendroglial Maturation of Injured White Matter in Neonatal Rats

OBJECTIVE:To investigate the effects of melatonin treatment in a rat model of white matter damage (WMD) in the developing brain. Additionally, we aim to delineate the cellular mechanisms of melatonin effect on the oligodendroglial cell lineage. METHODS:A unilateral ligation of the uterine artery in pregnant rat at the embryonic day 17 induces fetal hypoxia and subsequent growth restriction (GR) in neonatal pups. GR and control pups received a daily intra-peritoneal injection of melatonin from birth to post-natal day (P) 3. RESULTS:Melatonin administration was associated with a dramatic decrease in microglial activation and astroglial reaction compared to untreated GR pups. At P14, melatonin prevented white matter myelination defects with an increased number of mature oligodendrocytes (APC-immunoreactive) in treated GR pups. Conversely, melatonin was not found to be associated with an increased density of total oligodendrocytes (Olig2-immunoreactive), suggesting that melatonin is able to promote oligodendrocyte maturation but not proliferation. These effects appear to be melatonin-receptor dependent and were reproduced in vitro. INTERPRETATION:These data suggest that melatonin has a strong protective effect on developing damaged white matter through decreased microglial activation and oligodendroglial maturation leading to a normalization of the myelination process. Consequently, melatonin should be a considered as an effective neuroprotective candidate not only in perinatal brain damage but also in inflammatory and demyelinating diseases observed in adults

Conséquences musculaires d'un entraînement sollicitant endurance et force chez un même sujet âgé (aspects fonctionnels et histomorphologiques)

Nous avons voulu étudier les effets à la fois spécifiques et non spécifiques de l'entraînement en endurance et en musculation chez un même sujet au niveau fonctionnel mais également au niveau cellulaire. Nous avons entraîné chez dix sujets âgés (73 + - 4 ans) l'hémicorps supérieur en musculation et l'hémicorps inférieur en endurance durant 14 semaines (3 fois par semaine). Des biopsies musculaires ont été effectuées sur le deltoïde (Del) et le vaste externe (VLat) avant et après entraînement pour mesurer des activités enzymatiques musculaires, analyser la typologie et la taille des fibres musculaires, quantifier la population des cellules satellites (SC) ou évaluer l'indice de capillarisation LC/PF (longueur de contact capillaire/périmètre de la fibre). Les membres inférieurs ont augmenté significativement VO2 pic, les activités enzymatiques oxydatives (CS, HAD) et LC/PF. Les membres entraînés en musculation ont montré une augmentation significative du couple maximal isocinétique ainsi qu'une hypertrophie musculaire (IRM). En réponse à l'entraînement, seules les cellules satellites associées aux fibres de type II ont augmenté significativement et cette augmentation n'était pas significativement supérieure dans le muscle entraîné en musculation. Il semble donc que l'entraînement en endurance génère une adaptation de la population des SC similaire à celle observée en réponse à un entraînement en musculation. Enfin ce programme d'entraînement combiné a amélioré la composition corporelle et le bilan lipidique des sujets, ce qui ouvre des perspectives d'application de ce type d'entraînement à des populations sujettes à une altération du métabolisme glucido-lipidiqueWe aimed to investigate both specific and unspecific adaptations to combined lower body endurance and upper body resistance training in the same healthy elderly. Ten subjects (73 + - 4 years) were trained during 14 weeks (3 sessions/week). Before and after training, peak oxygen uptake, isokinetic torque and body composition were assessed. Muscle biopsies were also obtained from vastus lateralis (VLat) and deltoid (Del) muscle in order to evaluate enzymatic activities, fibre type composition and area, microvascular network and satellite cell (SC) content. Among specific adaptations, we observed a significant increase in peak oxygen uptake (VO2 peak), CS and HAD activities as well as an improvement of LC/PF index in VLat after endurance training. We also found a significant increase in maximal isokinetic torque and muscle cross sectional area assessed by MRI after upper body resistance training. However, at the cellular level, this hypertrophy was not observed in Del. Our training program also induced non specific adaptations, such as a significant improvement in leg maximal isokinetic torque or a significant hypertrophy of type IIA fibres in Vlat after endurance training. After resistance training, a significant enhancement of VO2 peak during arm cranking and an increase in CS activity in Del was also observed. In response to training, the number of satellite cells per fibre increased in both muscles, mainly through a significant increase in the number of SC associated to type II fibres. The training program also improved body composition and blood lipid profile, which opens up future investigations using this training design, for example in subjects with metabolic syndromeST ETIENNE-BU Sciences (422182103) / SudocSudocFranceF

Sprint Interval Training: What are the Clinical Implications and Precautions?

Sprint Interval Training: What are the Clinical Implications and Precautions

The effect of wave-induced turbulence on intertidal mudflats: Impact of boat traffic and wind

Semi-diurnal and fortnightly surveys were carried out to quantify the effects of wind- and navigation-induced highenergy events on bed sediments above intertidal mudflats. The mudflats are located in the upper fluvial part (Oissel mudflat) and at the mouth (Vasiere Nord mudflat) of the macrotidal Seine estuary. Instantaneous flow velocities and mudflat bed elevation were measured at a high frequency and high resolution with an acoustic doppler velocimeter (ADV) and an ALTUS altimeter, respectively. Suspended particulate matter concentrations were estimated by calibrating the ADV acoustic backscattered intensity with bed sediments collected at the study sites. Turbulent bed shear stress values were estimated by the turbulent kinetic energy method, using velocity variances filtered from the wave contribution. Wave shear stress and maximum wave–current shear stress values were calculated with the wave–current interaction (WCI) model, which is based on the bed roughness length, wave orbital velocities and the wave period (TS). In the fluvial part of the estuary, boat passages occurred unevenly during the surveys and were characterized by long waves (TS450 s) induced by the drawdown effect and by short boat-waves (TSo10 s). Boat waves generated large bottom shear stress values of 0.5Nm-2 for 2–5 min periods and, in burst of several seconds, larger bottom shear stress values up to 1Nm-2. At the mouth of the estuary, west south-west wind events generated short waves (TSo10 s) of HS values ranging from 0.1 to 0.3 m. In shallow-water environment (water depth o1.5 m), these waves produced bottom shear stress values between 1 and 2Nm-2. Wave–current shear stress values are one order of magnitude larger than the current-induced shear stress and indicate that navigation and wind are the dominant hydrodynamic forcing parameters above the two mudflats. Bed elevation and SPM concentration time series showed that these high energy events induced erosion processes of up to several centimetres. Critical erosion shear stress (tce) values were determined from the SPM concentration and bed elevation measurements. Rough tce values were found above 0.2Nm-2 for the Oissel mudflat and about 1Nm-2 for the Vasiere Nord mudflat. These results demonstrate the advantages of combining the measurement of instantaneous velocity and bed elevation to determine in situ the erosion and deposition processes as a function of bottom shear stress variations

Controlling factors of rhythmic sedimentation processes on a macrotidal estuarine mudflat. Role of the turbidity maximum, the Seine estuary, France

The aim of this study is to analyse and to quantify the fine particles transfer (i.e. 7.1 m). Then, deposition of SPM from the turbidity maximum becomes important, allowing fine particles to settle on the mudflat, where the current velocities are low (< 0.4 m s− 1). On tides of lower range (< 7.1 m) bed elevation levels suggest that erosion of the mudflat surface dominates, however dewatering processes also occur in the soft mud deposits resulting in compaction. During periods of wave activity and periods of increasing river discharge, the mudflat surface experiences rapid erosion. These periods of erosion (sudden or progressive) imply a transfer of fine-grained material from the mudflat surface back into the TM.The long term (∼ 22 months), high frequency (1 measurement every 10 min) and high resolution (0.6 mm) dataset obtained from the altimeter allows quantification of the volume of material exchanged between the intertidal area and the estuarine standing stock of SPM. The maximum of deposition on the studied mudflat during the study was of 27 cm, with highest deposition occurring after the periods of highest river flow and implying that between 25 and 40% of the maximum estimated mass of SPM held within the estuarine TM (300,000–500,000 T) had been temporarily deposited on the mudflat. Likewise following periods of resuspension by wave activity, bed elevations reduced by an order of ∼ 1 cm, suggesting a release of between 1–1.5% of the TM load from the mudflat back into suspension.The study shows that lateral exchanges of sediment between the intertidal reaches of the estuary and the water column are an important part of the sediment budget, and that the supply of sediment available for deposition (i.e. the TM) has a causal relationship with sedimentation rates experienced by intertidal mudflats

Invited Letter to Editor in response to: Constitutional thinness: body fat metabolism and skeletal muscle are important factors

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