42 research outputs found
Joint approach combining damage and paleoseismology observations constrains the 1714 A.D. Bhutan earthquake at magnitude 8±0.5
International audienceThe region of Bhutan is thought to be the only segment of the Himalayas not having experienced a major earthquake over the past half millennium. A proposed explanation for this apparent seismic gap is partial accommodation of the India-Asia convergence further south across the Shillong Plateau, yet the seismic behavior of the Himalayan megathrust in Bhutan is unknown. Here we present historical documents from the region reporting on an earthquake in 1714âA.D. and geological evidence of surface rupture to constrain the latest large event in this area. We compute various earthquake scenarios using empirical scaling relationships relating magnitude with intensity, source location and rupture geometry. Our results constrain the 1714âA.D. earthquake to have ruptured the megathrust in Bhutan, most likely during a M7.5â8.5 event. This finding reclassifies the apparent seismic gap to a former information gap and implies that the entire Himalayan arc has a high level of earthquake potential
Effet des précurseurs de monoxyde d'azote sur la fonction vasculaire et la performance à l'exercice
Primary and secondary prevention of cardiovascular diseases is a major public health concern. Cardiovascular prevention is mainly underpinned by the control of cardiovascular risks. Among them, arterial hypertension (30% of adults in France) and sedentarity (40% of french population) represents two main targets in cardiovascular prevention. Endothelial function as well as exercise tolerance and performance (fitness status) are used as powerful markers of cardiovascular morbidity-mortality.A normal vasomotor endothelial function allows to regulate vascular tone. By synthesising vasoactive substances, vascular endothelium continuously maintains an optimal balance between vasodilation and vasoconstriction to match oxygen and energetic substrate supply to the demand. Endothelial function is plastic, and is increased for instance by physical activity and decreased with age. Endothelial dysfunction is essentially characterized by the production of less vasodilation substances, inducing an increase in blood pressure, arterial stiffness and leading to blood-tissue exchanges alterations. Degrees of endothelial dysfunction is considered as a cardiovascular risk marker.One major vasoactive substance is nitric oxide (NO), which is produced by NO-synthase (NOS) in endothelium, and is a mediator of smooth muscle cells relaxation. This major endogen synthesis can be complemented by NO synthesis from simple reduction of nitrite to NO. Several mechanisms are provided to explain a decrease in NO endothelial synthesis, including decrease of enzymatic activity (NOS) and/or an inadequate substrate or cofactor bioavailability. This decrease in NO bioavailability can be offset, either by NOS activity optimization, or increase NO bioavailability at a vascular level. Although the effects of NO precursor supplementation on health and exercise performance have been extensively studied, results are somehow controversial, mainly due to methodological discrepancies. Thus, the real interest of these types of interventions stays unclear.Thought this thesis work, we were interested to physiological effect in healthy subjects of different interventions which may increase NO bioavailability at vascular level. Focusing on food supplement consumption, we differentiated two NO precursor, two supplementation modalities, and two populations.We have assessed effect of increasing NO bioavailability by acute or chronic supplementation of both NOS-dependent (L-arginine, L-citrulline) and/or NOS-independent (nitrate) pathways, with or without simultaneous training program, in young and older healthy subjects, on vascular function and exercise performances.In healthy young individuals, NO precursor intake increase endothelial function assessed by post-ischemic vasodilation, without effect neither on arterial pressure and fitness nor on exercise performances. However, nitrate and citrulline supplementation increase exercise training effect on maximal strength and strength endurance. In healthy older adults, chronic intake of nitrate and citrulline reduce arterial pressure and improve maximal aerobic power by decrease of submaximal VO2 and heart rate.Depuis de nombreuses annĂ©es, la prĂ©vention primaire et secondaire des atteintes cardiovasculaires chez lâhomme est devenue un vĂ©ritable enjeu de santĂ© publique. Lâaxe principal de cette prĂ©vention est lâidentification et le contrĂŽle des facteurs de risques cardiovasculaires. Parmis eux, lâhypertension artĂ©rielle (30% des adultes en France) et la sĂ©dentaritĂ© (40% de la population française) sont des acteurs majoritaiement dans la pathogĂ©nĂ©se des maladies cardiovasculaires. La fonction endothĂ©liale ainsi que la tolĂ©rance et la performance Ă lâexercice, sont utilisĂ©es comme de puissants marqueurs de morbi-mortalitĂ© cardiovasculaires.Une fonction vasomotrice endothĂ©liale normale permet de contrĂŽler le tonus vasculaire, dâoptimiser la circulation sanguine et participe au contrĂŽle dâapports en oxygĂšne et substrats Ă©nergĂ©tiques adaptĂ©s aux besoins tissulaires. Par la production de substances vasoactives, lâendothĂ©lium vasculaire assure en permanence un Ă©quilibre entre vasodilatation et vasoconstriction. La fonction endothĂ©liale est plastique, sâamĂ©liorant par exemple avec lâactivitĂ© physique et sâaltĂ©rant avec lâĂąge. La dysfonction endothĂ©liale de son cĂŽtĂ©, se caractĂ©rise essentiellement par une moindre sĂ©crĂ©tion de substances vasodilatatrices participant Ă lâĂ©lĂ©vation de la pression artĂ©rielle, une augmentation de la rigiditĂ© artĂ©rielle et Ă une altĂ©ration des Ă©changes sang-tissus.Lâune des substances vasodilatatrices majeures est le monoxyde dâazote (NO) synthĂ©tisĂ© au niveau de lâendothĂ©lium, par la NO-synthase endothĂ©liale (eNOS), et dont la diffusion vers les cellules musculaires lisses sous-jacentes, entraine leurs relĂąchements. Cette synthĂšse endogĂšne majeure est complĂ©tĂ©e par une synthĂšse de NO Ă partir dâune simple rĂ©duction du nitrite circulant en NO. Les mĂ©canismes proposĂ©s pour expliquer la baisse de la synthĂšse endothĂ©liale de NO incluent une diminution de lâactivitĂ© enzymatique (eNOS) et/ou une insuffisance en substrats et cofacteurs disponibles pour celle-ci. Cette diminution de la biodisponibilitĂ© en NO peut ĂȘtre compensĂ©e, soit par optimisation de lâactivitĂ© de la NOS, soit par un apport de NO au niveau vasculaire. Bien que la littĂ©rature ait largement Ă©tudiĂ© lâeffet de prĂ©curseur de NO sur la santĂ© et la performance Ă lâexercice, les rĂ©sultats restent trĂšs contrastĂ©s, notamment du fait de questions mĂ©thodologiques, et lâintĂ©rĂȘt rĂ©el de ce type dâintervention reste Ă clarifier.Au cours de ce travail de thĂšse, nous nous sommes intĂ©ressĂ©s Ă lâeffet de diffĂ©rentes interventions capables dâaugmenter la biodisponibilitĂ© en NO au niveau vasculaire, chez le sujet sain. En se focalisant sur lâingestion de complĂ©ments alimentaires, nous avons diffĂ©renciĂ© deux types de prĂ©curseurs de NO et deux modalitĂ©s de supplĂ©mentation (aiguĂ« et chronique). Nous avons Ă©valuĂ© lâeffet de lâaugmentation de la biodisponibilitĂ© en NO en supplĂ©mentant les voies NOS-dĂ©pendantes (L-arginine, L-citrulline) et/ou NOS-indĂ©pendantes (nitrate) de façon aigĂŒe ou chronique, avec ou sans programme dâentraĂźnement Ă lâeffort simultanĂ©, chez des sujets sains jeunes ou ĂągĂ©s, sur la fonction vasculaire et les performances Ă lâeffort.Chez le sujet jeune en bonne santĂ©, il apparait que lâingestion de prĂ©curseurs de NO amĂ©liore la fonction endothĂ©liale Ă©valuĂ©e par la vasodilatation post-ischĂ©mique, sans impacter ni la pression et la rigiditĂ© artĂ©rielle, ni la performance Ă lâexercice. En revanche, la supplĂ©mentation en nitrate et citrulline optimise les effets de lâentrainement sur la force maximale et lâendurance de force. Chez le sujet ĂągĂ©, la prise chronique de nitrate et citrulline rĂ©duit la pression artĂ©rielle et amĂ©liore la puissance maximal aerobie en diminuant la VO2 et la frĂ©quence cardiaque sous maximale
DĂ©formation HolocĂšne de lâHimalaya du Bhoutan. Apport de la gĂ©omorphologie et de la palĂ©osismologie.
The Himalayan arc is one of the most of active intra-continental orogen in the world. Geological explorations of the Himalayas since the late 19th century have emphasized a 2500-km-long roughly cylindrical structure, with striking continuity of main units and thrust faults. However recent geophysical and geological investigations have revealed lateral variations (present-day convergence rates, gravimetry, seismicity, morphology, exhumation rates, and crustal structures).Over the las centuries, several major earthquakes (Mw > 7.5) have struck the arc and the dramatic effects of the Gorkha earthquake sequence in 2015 point to the important societal dimension. However, both the maximum size and the occurence probability of such earthquakes are still debated. While the kingdom of Bhutan is a key area in the understanding of the whole Himaayan arc, the country is still poorly documented. Long considered as a 350-km-long seismic gap, a single historical account reports a devastating earthquake in AD 1713.The first part of this thesis focuses on the quantification of vertical deformation along a N-S transect, from the southern-most thrust (The Main Frontal Thrust) to the High Himalaya. In the past three years we have carried out three fieldwork campains during which we sampled different deformation features such as (1) alluvial terraces along the front in order to quantify and the spatial and temporal variation of the Holocene uplift, (2) watershed basins in order to quantify the short term denudation rate ( 7.5) ont affectĂ© lâHimalaya et le lourd bilan humain du sĂ©isme de Gorkha en 2015 indique un aspect sociĂ©tal important. Cependant, la taille maximale et la probabilitĂ© dâoccurrence de ces mĂ©ga-sĂ©ismes sont toujours matiĂšre Ă dĂ©bat. Or, bien quâĂ©tant une zone charniĂšre le long de lâarc, le royaume du Bhoutan reste pas ou peu documentĂ©. Longtemps considĂ©rĂ© comme une zone asismique de 350 km de long, un seul Ă©crit historique rapporte lâoccurrence dâun sĂ©isme dĂ©vastateur en 1713.Lâobjectif de ce travail de thĂšse est de quantifier la dĂ©formation, Ă diffĂ©rentes Ă©chelles spatiale et temporelle, de lâHimalaya du Bhoutan Ă travers des Ă©tudes morphotectonique et palĂ©osismologique. Un premier volet vise Ă quantifier les mouvements verticaux le long dâun profil N-S allant de la structure la plus frontale (le Main Frontal Thrust) Ă la haute chaĂźne. Trois campagnes de terrain ont Ă©tĂ© rĂ©alisĂ©es permettant lâĂ©chantillonnage de (1) de terrasses alluviales le long du front permettant de quantifier et dâĂ©tudier les variations du soulĂšvement frontal HolocĂšne, (2) de bassins versants pour lâĂ©tude de la dĂ©nudation court-terme (< 20 ka) dĂ©rivĂ©e des cosmonuclĂ©ides (10Be) et (3) de terrasses alluviales dans le Moyen-Pays pour quantifier la dĂ©nudation Ă une Ă©chelle de temps un peu plus longue (< 50 ka).Le second volet de cette Ă©tude porte sur diffĂ©rentes Ă©tudes palĂ©osismologiques le long du front ouest et centre Bhoutanais. Trois campagnes de terrain ont permis dâinvestiguer six sites diffĂ©rents. La datation et la modĂ©lisation de charbons dĂ©tritiques a permis de mettre en Ă©vidence lâoccurrence de cinq sĂ©ismes majeurs durant les derniers 2700 ans. Ces rĂ©sultats montrent que le Bhoutan ne peut pas ĂȘtre considĂ©rĂ© comme une zone asismique. A une Ă©chelle rĂ©gionale, lâoccurrence de sĂ©ismes majeurs au Bhoutan participe au dĂ©bat dâun sĂ©isme de magnitude 9 le long de lâarc Himalayen
Holocene deformation in the Bhutan Himalaya from geomorphic and paleoseismologic study
La chaĂźne Himalayenne est l'un des exemples les plus spectaculaires de dĂ©formation active Ă la surface de notre planĂšte. Au cours des derniers siĂšcles, de nombreux sĂ©ismes majeurs (Mw â» 7.5) ont affectĂ© cette zone et le lourd bilan humain du sĂ©isme de Gorkha en 2015 a une nouvelle fois rappelĂ© lâimportance de parvenir Ă mieux estimer lâalĂ©a sismique de cette rĂ©gion. Bien que les structures lithologiques et tectoniques semblent montrer au premier ordre une cylindricitĂ© le long des 2500 km de l'arc Himalayen, de nombreuses Ă©tudes, menĂ©es principalement au NĂ©pal, ont permis de mettre en Ă©vidence des variations latĂ©rales structurales, thermochronologiques, morphologiques, gravimĂ©triques, sismologiques ou gĂ©odĂ©siques. Le rĂŽle de ces variations latĂ©rales sur la segmentation sismique reste cependant mal contraint. La taille maximale et la probabilitĂ© dâoccurrence de ces mĂ©ga-sĂ©ismes sont donc toujours matiĂšre Ă dĂ©bat.Ainsi, le comportement sismique de lâHimalaya du Bhoutan reste Ă©nigmatique. Pour certains les faibles taux de sismicitĂ© observĂ©s actuellement font de ce royaume une zone asismique de 350 km de long. Pour dâautres, Ă lâinstar de lâHimalaya du NĂ©pal, la faible sismicitĂ© observĂ©e est associĂ© Ă une forte accumulation de contrainte susceptible de gĂ©nĂ©rer des sĂ©ismes majeurs. L'objectif de ce travail de thĂšse est dâamĂ©liorer notre connaissance de cette rĂ©gion en quantifiant la dĂ©formation Ă diffĂ©rentes Ă©chelles spatiales et temporelles via des Ă©tudes morphotectoniques et palĂ©osismologiques.La premiĂšre partie de cette thĂšse vise Ă quantifier les mouvements verticaux Ă lâouest Bhutan et le long du Main Frontal Thrust, structure la plus frontale situĂ©e au sud Bhoutan. Trois campagnes de terrain ont Ă©tĂ© rĂ©alisĂ©es permettant l'Ă©chantillonnage (1) de terrasses alluviales le long du front afin de quantifier et d'Ă©tudier les variations du soulĂšvement HolocĂšne, (2) de bassins versants pour l'Ă©tude de la dĂ©nudation court-terme (âș 20 ka) dĂ©rivĂ©e des cosmonuclĂ©ides (10Be) et (3) de terrasses alluviales dans le Moyen-Pays pour quantifier lâincision HolocĂšne. Les vitesses verticales obtenues au front sont comparables Ă celle proposĂ©es le long du reste de lâarc himalayen, suggĂ©rant une cinĂ©matique relativement simple. Par contre, nos rĂ©sultats indiquent une variation de la gĂ©omĂ©trie du chevauchement himalayen (Main Himalayan Thrust) entre lâest NĂ©pal et lâouest Bhoutan. La seconde partie porte sur plusieurs Ă©tudes palĂ©osismologiques le long du front ouest et centre Bhoutanais. Six sites diffĂ©rents ont Ă©tĂ© Ă©tudiĂ©s au cours de trois campagnes de terrain. La datation et la modĂ©lisation de charbons dĂ©tritiques a permis de mettre en Ă©vidence l'occurrence dâau moins cinq sĂ©ismes majeurs durant les derniers 2700 ans, faisant du Bhoutan une zone sismiquement aussi active que le NĂ©pal. A une Ă©chelle rĂ©gionale, cette Ă©tude apporte donc de nouvelles contraintes et contribue au dĂ©bat sur la possibilitĂ© dâoccurrence d'un sĂ©isme de magnitude 9 le long de l'arc Himalayen.The Himalayan arc is one of the most active intra-continental mountain belts in the world. Over the last centuries, several major earthquakes (Mw â» 7.5) have struck this arc. The dramatic effects of the Gorkha earthquake sequence in 2015 pointed once again the crucial need to improve seismic hazard assessment of this area. Geological explorations of the Himalayas since the late 19th century have emphasized a 2500-km-long roughly cylindrical structure, with striking continuity of main units and thrust faults. However recent geophysical and geological investigations have revealed lateral variations. The relationship between these variations and earthquakes segmentation along the arc remains poorly constraint. The maximum size and the occurrence probability of such earthquakes are still a matter of debate.For instance, the seismic behavior of Bhutan remains enigmatic. The present-day low seismicity rate observed in this area can reflect two opposite fault behaviors: an aseismic creeping zone or a zone of stress accumulation for future great earthquakes as the others parts of Himalayas. The main objective of this thesis is to bring new constraints on the deformation of the Bhutan Himalayas, at different space- and time-scales, through morphotectonic and paleoseismological approaches.The first part of this thesis focuses on the vertical deformation assessment along a N-S transect in western Bhutan and along the Main Frontal Thrust, which is the southern-most thrust in southern Bhutan. In the past three years, we have carried out three fieldwork campaigns to sample (1) frontal terraces to assess Holocene uplift rates, (2) watershed basins to quantify short term denudation rates (âș 20 ky) derived from cosmonuclides 10Be and (3) hinterland alluvial terraces to quantify the Holocene incision rate. Frontal Holocene uplift rates obtained in Bhutan are consistent with those obtained in the others parts of Himalayas. Furthermore, our results reveal a variation in the geometry of the Main Himalayan Thrust between eastern Nepal and western Bhutan. The second part focuses on several paleoseismic studies along the west and central bhutanese Himalayan front. Different sites were investigated during three fieldwork campaigns. Detritic charcoals sampling and modeling suggest the occurrence of at least five surface-rupturing earthquakes during the last ~2700 years. These results demonstrate that the present-day low seismicity rate observed in Bhutan is not representative of the seismic activity at longer time scale. At regional scale, they also take part of a broader discussion on the probability of occurrence of a magnitude 9 earthquake along the Himalayan arc
assessment of no precursors suppplement on exercise physiological response
Depuis de nombreuses annĂ©es, la prĂ©vention primaire et secondaire des atteintes cardiovasculaires chez lâhomme est devenue un vĂ©ritable enjeu de santĂ© publique. Lâaxe principal de cette prĂ©vention est lâidentification et le contrĂŽle des facteurs de risques cardiovasculaires. Parmis eux, lâhypertension artĂ©rielle (30% des adultes en France) et la sĂ©dentaritĂ© (40% de la population française) sont des acteurs majoritaiement dans la pathogĂ©nĂ©se des maladies cardiovasculaires. La fonction endothĂ©liale ainsi que la tolĂ©rance et la performance Ă lâexercice, sont utilisĂ©es comme de puissants marqueurs de morbi-mortalitĂ© cardiovasculaires.Une fonction vasomotrice endothĂ©liale normale permet de contrĂŽler le tonus vasculaire, dâoptimiser la circulation sanguine et participe au contrĂŽle dâapports en oxygĂšne et substrats Ă©nergĂ©tiques adaptĂ©s aux besoins tissulaires. Par la production de substances vasoactives, lâendothĂ©lium vasculaire assure en permanence un Ă©quilibre entre vasodilatation et vasoconstriction. La fonction endothĂ©liale est plastique, sâamĂ©liorant par exemple avec lâactivitĂ© physique et sâaltĂ©rant avec lâĂąge. La dysfonction endothĂ©liale de son cĂŽtĂ©, se caractĂ©rise essentiellement par une moindre sĂ©crĂ©tion de substances vasodilatatrices participant Ă lâĂ©lĂ©vation de la pression artĂ©rielle, une augmentation de la rigiditĂ© artĂ©rielle et Ă une altĂ©ration des Ă©changes sang-tissus.Lâune des substances vasodilatatrices majeures est le monoxyde dâazote (NO) synthĂ©tisĂ© au niveau de lâendothĂ©lium, par la NO-synthase endothĂ©liale (eNOS), et dont la diffusion vers les cellules musculaires lisses sous-jacentes, entraine leurs relĂąchements. Cette synthĂšse endogĂšne majeure est complĂ©tĂ©e par une synthĂšse de NO Ă partir dâune simple rĂ©duction du nitrite circulant en NO. Les mĂ©canismes proposĂ©s pour expliquer la baisse de la synthĂšse endothĂ©liale de NO incluent une diminution de lâactivitĂ© enzymatique (eNOS) et/ou une insuffisance en substrats et cofacteurs disponibles pour celle-ci. Cette diminution de la biodisponibilitĂ© en NO peut ĂȘtre compensĂ©e, soit par optimisation de lâactivitĂ© de la NOS, soit par un apport de NO au niveau vasculaire. Bien que la littĂ©rature ait largement Ă©tudiĂ© lâeffet de prĂ©curseur de NO sur la santĂ© et la performance Ă lâexercice, les rĂ©sultats restent trĂšs contrastĂ©s, notamment du fait de questions mĂ©thodologiques, et lâintĂ©rĂȘt rĂ©el de ce type dâintervention reste Ă clarifier.Au cours de ce travail de thĂšse, nous nous sommes intĂ©ressĂ©s Ă lâeffet de diffĂ©rentes interventions capables dâaugmenter la biodisponibilitĂ© en NO au niveau vasculaire, chez le sujet sain. En se focalisant sur lâingestion de complĂ©ments alimentaires, nous avons diffĂ©renciĂ© deux types de prĂ©curseurs de NO et deux modalitĂ©s de supplĂ©mentation (aiguĂ« et chronique). Nous avons Ă©valuĂ© lâeffet de lâaugmentation de la biodisponibilitĂ© en NO en supplĂ©mentant les voies NOS-dĂ©pendantes (L-arginine, L-citrulline) et/ou NOS-indĂ©pendantes (nitrate) de façon aigĂŒe ou chronique, avec ou sans programme dâentraĂźnement Ă lâeffort simultanĂ©, chez des sujets sains jeunes ou ĂągĂ©s, sur la fonction vasculaire et les performances Ă lâeffort.Chez le sujet jeune en bonne santĂ©, il apparait que lâingestion de prĂ©curseurs de NO amĂ©liore la fonction endothĂ©liale Ă©valuĂ©e par la vasodilatation post-ischĂ©mique, sans impacter ni la pression et la rigiditĂ© artĂ©rielle, ni la performance Ă lâexercice. En revanche, la supplĂ©mentation en nitrate et citrulline optimise les effets de lâentrainement sur la force maximale et lâendurance de force. Chez le sujet ĂągĂ©, la prise chronique de nitrate et citrulline rĂ©duit la pression artĂ©rielle et amĂ©liore la puissance maximal aerobie en diminuant la VO2 et la frĂ©quence cardiaque sous maximale.Primary and secondary prevention of cardiovascular diseases is a major public health concern. Cardiovascular prevention is mainly underpinned by the control of cardiovascular risks. Among them, arterial hypertension (30% of adults in France) and sedentarity (40% of french population) represents two main targets in cardiovascular prevention. Endothelial function as well as exercise tolerance and performance (fitness status) are used as powerful markers of cardiovascular morbidity-mortality.A normal vasomotor endothelial function allows to regulate vascular tone. By synthesising vasoactive substances, vascular endothelium continuously maintains an optimal balance between vasodilation and vasoconstriction to match oxygen and energetic substrate supply to the demand. Endothelial function is plastic, and is increased for instance by physical activity and decreased with age. Endothelial dysfunction is essentially characterized by the production of less vasodilation substances, inducing an increase in blood pressure, arterial stiffness and leading to blood-tissue exchanges alterations. Degrees of endothelial dysfunction is considered as a cardiovascular risk marker.One major vasoactive substance is nitric oxide (NO), which is produced by NO-synthase (NOS) in endothelium, and is a mediator of smooth muscle cells relaxation. This major endogen synthesis can be complemented by NO synthesis from simple reduction of nitrite to NO. Several mechanisms are provided to explain a decrease in NO endothelial synthesis, including decrease of enzymatic activity (NOS) and/or an inadequate substrate or cofactor bioavailability. This decrease in NO bioavailability can be offset, either by NOS activity optimization, or increase NO bioavailability at a vascular level. Although the effects of NO precursor supplementation on health and exercise performance have been extensively studied, results are somehow controversial, mainly due to methodological discrepancies. Thus, the real interest of these types of interventions stays unclear.Thought this thesis work, we were interested to physiological effect in healthy subjects of different interventions which may increase NO bioavailability at vascular level. Focusing on food supplement consumption, we differentiated two NO precursor, two supplementation modalities, and two populations.We have assessed effect of increasing NO bioavailability by acute or chronic supplementation of both NOS-dependent (L-arginine, L-citrulline) and/or NOS-independent (nitrate) pathways, with or without simultaneous training program, in young and older healthy subjects, on vascular function and exercise performances.In healthy young individuals, NO precursor intake increase endothelial function assessed by post-ischemic vasodilation, without effect neither on arterial pressure and fitness nor on exercise performances. However, nitrate and citrulline supplementation increase exercise training effect on maximal strength and strength endurance. In healthy older adults, chronic intake of nitrate and citrulline reduce arterial pressure and improve maximal aerobic power by decrease of submaximal VO2 and heart rate
Topographic disequilibrium, landscape dynamics and active tectonics: an example from the Bhutan Himalaya
International audienceThe quantification of active tectonics from geomorphological and morphometric approaches commonly implies that erosion and tectonics have reached a certain balance. Such equilibrium conditions are however rare in nature, as questioned and documented by recent theoretical studies indicating that drainage basins may be perpetually rearranging even though tectonic and climatic conditions remain constant. Here, we document these drainage dynamics in the Bhutan Himalaya, where evidence for out-of-equilibrium morphologies have for long been noticed, from major (> 1 km high) river knickpoints and from high-altitude low-relief regions in the mountain hinterland. To further characterize these morphologies and their dynamics, we perform field observations and a detailed quantitative morphometric analysis using Ï plots and Gilbert metrics of drainages over various spatial scales, from major Himalayan rivers to their tributaries draining the low-relief regions. We first find that the river network is highly dynamic and unstable, with much evidence of divide migration and river captures. The landscape response to these dynamics is relatively rapid. Our results do not support the idea of a general wave of incision propagating upstream, as expected from most previous interpretations. Also, the specific spatial organization in which all major knickpoints and low-relief regions are located along a longitudinal band in the Bhutan hinterland, whatever their spatial scale and the dimensions of the associated drainage basins, calls for a common local supporting mechanism most probably related to active tectonic uplift. From there, we discuss possible interpretations of the observed landscape in Bhutan. Our results emphasize the need for a precise documentation of landscape dynamics and disequilibrium over various spatial scales as a first step in morpho-tectonic studies of active landscapes
Seismic analysis of the detachment and impact phases of a rockfall and application for estimating rockfall volume and freeâfall height
International audienceWe analyzed 21 rockfalls that occurred in limestone cliffs of the Chartreuse Massif (French Alps). These rockfalls were detected both by Terrestrial Laser Scanning or photogrammetry and by a local seismological network. The combination of these methods allowed us to study relations between rockfall properties (location of detachment and impacts areas, volume, geometry, propagation) and the induced seismic signal. We observed events with different propagation modes (sliding, mass flow, free-fall) that could be determined from Digital Elevation Models. We focused on events that experienced a free-fall after their detachment. We analyzed the first parts of the seismic signals corresponding to the detachment phase and to the first impact. The detachment phase has a smaller amplitude than the impact phase, and its amplitude and duration increasewith rockfall volume. By measuring the time delay between the detachment phase and the first impact, we can estimate the free-fall height. We found a relation Es=aEpbbetween the potential energy of a rockfall Ep and the seismic energy Esgenerated during the first impact, with parameters a=10-8and b=1.55 and with a correlation coefficient RÂČ=0.98. We can thus estimate both the potential energy of a block and its free-fall height from the seismic signals. By combining these results, we obtain an accurate estimate of the rockfall volume. This relation was then tested on different geological settings and for larger volumes using Yosemite and Mount Granier rockfalls. We also compared our results with a data set of controlled releases of single blocks (Hibert et al., 2017) in order to investigate smaller volumes
Synergetic Effect of NO Precursor Supplementation and Exercise Training
International audienceIntroduction: Nitric oxide (NO) precursor supplementation has been shown to increase NO bioavailability and can potentially improve vascular function and exercise performance. It remains unclear whether the combination of NO precursor supplementation and exercise training has synergic effects on exercise performance. This study aims to assess the effect of chronic nitrate and citrulline intake on exercise training adaptations in healthy young individuals.Methods: In this randomized, double-bind trial, 24 healthy young (12 females) subjects performed vascular function assessment (blood pressure, pulse wave velocity, postischemia vasodilation, and cerebrovascular reactivity) and both local (submaximal isometric unilateral knee extension) and whole-body (incremental cycling) exercise tests to exhaustion before and after a 2-month exercise training program and daily intake of a placebo or a nitrate-rich salad and citrulline (N + C, 520 mg nitrate and 6 g citrulline) drink. Prefrontal cortex and quadriceps oxygenation was monitored continuously during exercise by near-infrared spectroscopy.Results: N + C supplementation had no effect on vascular function and muscle and cerebral oxygenation during both local and whole-body exercise. N + C supplementation induced a significantly larger increase in maximal knee extensor strength (+5.1 ± 3.5 vs +0.2 ± 5.5 kg, P = 0.008) as well as a trend toward a larger increase in knee extensor endurance (+35.2 ± 26.1 vs +24.0 ± 10.4 contractions, P = 0.092) than placebo, but no effect on exercise training-induced maximal aerobic performance improvement.Conclusion: These results suggest that chronic nitrate and citrulline supplementation enhances the effect of exercise training on quadriceps muscle function in healthy active young individuals, but this does not translate into improved maximal aerobic performances
Synergetic Effect of NO Precursor Supplementation and Exercise Training
International audienceIntroduction: Nitric oxide (NO) precursor supplementation has been shown to increase NO bioavailability and can potentially improve vascular function and exercise performance. It remains unclear whether the combination of NO precursor supplementation and exercise training has synergic effects on exercise performance. This study aims to assess the effect of chronic nitrate and citrulline intake on exercise training adaptations in healthy young individuals.Methods: In this randomized, double-bind trial, 24 healthy young (12 females) subjects performed vascular function assessment (blood pressure, pulse wave velocity, postischemia vasodilation, and cerebrovascular reactivity) and both local (submaximal isometric unilateral knee extension) and whole-body (incremental cycling) exercise tests to exhaustion before and after a 2-month exercise training program and daily intake of a placebo or a nitrate-rich salad and citrulline (N + C, 520 mg nitrate and 6 g citrulline) drink. Prefrontal cortex and quadriceps oxygenation was monitored continuously during exercise by near-infrared spectroscopy.Results: N + C supplementation had no effect on vascular function and muscle and cerebral oxygenation during both local and whole-body exercise. N + C supplementation induced a significantly larger increase in maximal knee extensor strength (+5.1 ± 3.5 vs +0.2 ± 5.5 kg, P = 0.008) as well as a trend toward a larger increase in knee extensor endurance (+35.2 ± 26.1 vs +24.0 ± 10.4 contractions, P = 0.092) than placebo, but no effect on exercise training-induced maximal aerobic performance improvement.Conclusion: These results suggest that chronic nitrate and citrulline supplementation enhances the effect of exercise training on quadriceps muscle function in healthy active young individuals, but this does not translate into improved maximal aerobic performances