Ammonium and nitrate in soil and upland rice yield as affected by cover crops and their desiccation time

The objective of this work was to evaluate the effect of cover crops and their desiccation times on upland rice yield and on the levels of nitrate and ammonium in a no-tillage soil. The experiment was carried out in a randomized blocks, with split plots and three replicates. Cover crops (plots) were sowed in the off-season (March 2009). In November 2009, at 30, 20, 10 and 0 days before rice sowing (split plots), herbicide was applied on the cover crops (fallow, Panicum maximum, Urochloa ruziziensis, U. brizantha and millet). Straw and soil were sampled (0 - 10 cm) at the sowing day, and after 7, 14, 21, 28 and 35 days. Straws from millet and fallow were degraded more rapidly and provided the lowest level of nitrate in the soil. Urochloa ruziziensis, U. brizantha and P. maximum produced higher amounts of dry matter, and provided the highest levels of nitrate in the soil. Millet provides the lowest nitrate/ammonium ratio and the highest upland rice yield. Desiccations carried out at 30 and 20 days before sowing had the largest levels of nitrate in the soil at the sowing date. Nitrogen content and forms in the soil are affected by cover crops and their desiccation times.

Influence of the world's most challenging mountain ultra-marathon on energy cost and running mechanics

PURPOSE: To examine the effects of the world's most challenging mountain ultra-marathon (Tor des Géants(®) 2012) on the energy cost of three types of locomotion (cycling, level and uphill running) and running kinematics. METHODS: Before (pre-) and immediately after (post-) the competition, a group of ten male experienced ultra-marathon runners performed in random order three submaximal 4-min exercise trials: cycling at a power of 1.5 W kg(-1) body mass; level running at 9 km h(-1) and uphill running at 6 km h(-1) at an inclination of +15 % on a motorized treadmill. Two video cameras recorded running mechanics at different sampling rates. RESULTS: Between pre- and post-, the uphill-running energy cost decreased by 13.8 % (P = 0.004); no change was noted in the energy cost of level running or cycling (NS). There was an increase in contact time (+10.3 %, P = 0.019) and duty factor (+8.1 %, P = 0.001) and a decrease in swing time (-6.4 %, P = 0.008) in the uphill-running condition. CONCLUSION: After this extreme mountain ultra-marathon, the subjects modified only their uphill-running patterns for a more economical step mechanics.

Combining hypoxic methods for peak performance.

New methods and devices for pursuing performance enhancement through altitude training were developed in Scandinavia and the USA in the early 1990s. At present, several forms of hypoxic training and/or altitude exposure exist: traditional 'live high-train high' (LHTH), contemporary 'live high-train low' (LHTL), intermittent hypoxic exposure during rest (IHE) and intermittent hypoxic exposure during continuous session (IHT). Although substantial differences exist between these methods of hypoxic training and/or exposure, all have the same goal: to induce an improvement in athletic performance at sea level. They are also used for preparation for competition at altitude and/or for the acclimatization of mountaineers. The underlying mechanisms behind the effects of hypoxic training are widely debated. Although the popular view is that altitude training may lead to an increase in haematological capacity, this may not be the main, or the only, factor involved in the improvement of performance. Other central (such as ventilatory, haemodynamic or neural adaptation) or peripheral (such as muscle buffering capacity or economy) factors play an important role. LHTL was shown to be an efficient method. The optimal altitude for living high has been defined as being 2200-2500 m to provide an optimal erythropoietic effect and up to 3100 m for non-haematological parameters. The optimal duration at altitude appears to be 4 weeks for inducing accelerated erythropoiesis whereas <3 weeks (i.e. 18 days) are long enough for beneficial changes in economy, muscle buffering capacity, the hypoxic ventilatory response or Na(+)/K(+)-ATPase activity. One critical point is the daily dose of altitude. A natural altitude of 2500 m for 20-22 h/day (in fact, travelling down to the valley only for training) appears sufficient to increase erythropoiesis and improve sea-level performance. 'Longer is better' as regards haematological changes since additional benefits have been shown as hypoxic exposure increases beyond 16 h/day. The minimum daily dose for stimulating erythropoiesis seems to be 12 h/day. For non-haematological changes, the implementation of a much shorter duration of exposure seems possible. Athletes could take advantage of IHT, which seems more beneficial than IHE in performance enhancement. The intensity of hypoxic exercise might play a role on adaptations at the molecular level in skeletal muscle tissue. There is clear evidence that intense exercise at high altitude stimulates to a greater extent muscle adaptations for both aerobic and anaerobic exercises and limits the decrease in power. So although IHT induces no increase in VO(2max) due to the low 'altitude dose', improvement in athletic performance is likely to happen with high-intensity exercise (i.e. above the ventilatory threshold) due to an increase in mitochondrial efficiency and pH/lactate regulation. We propose a new combination of hypoxic method (which we suggest naming Living High-Training Low and High, interspersed; LHTLHi) combining LHTL (five nights at 3000 m and two nights at sea level) with training at sea level except for a few (2.3 per week) IHT sessions of supra-threshold training. This review also provides a rationale on how to combine the different hypoxic methods and suggests advances in both their implementation and their periodization during the yearly training programme of athletes competing in endurance, glycolytic or intermittent sports.

Evaluation des risques liés aux nanomatériaux pour la population générale et pour l'environnement : rapport d'expertise collective

Une expertise collective sur l'évaluation des risques liés aux nanomatériaux pour la population générale et pour l'environnement a identifié plusieurs centaines de produits de grande consommation contenant des nanomatériaux, présents dans notre quotidien : textiles, cosmétiques, alimentaires, équipements sportifs, matériaux de construction... Des études nouvelles suggèrent la possibilité de risques pour la santé et pour l'environnement de certains produits. Face à cette situation d'incertitude, l'Afsset recommande d'agir sans attendre au nom du principe de précaution et de 1) Rendre obligatoire la traçabilité des nanomatériaux. Cela passe par une obligation de déclaration par les industriels, 2) la mise en place un étiquetage clair qui mentionne la présence de nanomatériaux dans les produits et informe sur la possibilité de relargage à l'usage, 3) d'aller jusqu'à l'interdiction de certains usages des nanomatériaux pour lesquels l'utilité est faible par rapport aux dangers potentiels, 4) l'harmonisation des cadres réglementaires français et européens pour généraliser les meilleures pratiques : déclaration, autorisation, substitution. En particulier, une révision de REACh s'impose pour prendre en compte les nanomatériaux manufacturés de manière spécifique et quel que soit leur tonnage. L'expertise fait également des recommandations pour construire une méthode renouvelée d'évaluation des risques sanitaires qui soit adaptée aux spécificités des nanomatériaux. Pour cela l'Afsset a testé les méthodologies classiques d'évaluation des risques sur 4 produits particuliers et courants : la chaussette antibactérienne (nanoparticules d'argent), le ciment autonettoyant et le lait solaire (nanoparticules de dioxyde de titane), la silice alimentaire à l'état nanométrique. Ces 4 produits représentent bien les voies d'exposition de l'homme (cutanée, inhalation, ingestion) et la possibilité de dispersion environnementale. Ces travaux font apparaître une urgence à faire progresser les connaissances sur les expositions et les dangers potentiels des nanomatériaux. Aujourd'hui, seuls 2% des études publiées sur les nanomatériaux concernent leurs risques pour la santé et l'environnement. Le premier effort devra porter sur la normalisation des caractéristiques des nanomatériaux. Les priorités de la recherche devront cibler la toxicologie, l'écotoxicologie et la mesure des expositions. Enfin, l'Afsset prévoit de s'autosaisir pour définir en 2 ans, avec son groupe de travail, un outil simplifié d'évaluation des risques. Il s'agit d'une grille de cotation des risques qui permet de catégoriser les produits en plusieurs gammes de risques. Face à ce chantier considérable, une mise en réseau entre les organismes européens et internationaux pour se partager le travail est nécessaire. Elle a commencé autour de l'OCDE qui coordonne des travaux d'évaluation des risques et de l'ISO qui travaille à la mise en place de nouvelles normes. [Auteurs]

Ruzigrass affecting soil-phosphorus availability

The objective of this work was to evaluate the effectiveness of ruzigrass (Urochloaruziziensis) in enhancing soil-P availability in areas fertilized with soluble or reactive rock phosphates. The area had been cropped for five years under no-till, in a system involving soybean, triticale/black-oat, and pearl millet. Previously to the five-year cultivation period, corrective phosphorus fertilization was applied once on soil surface, at 0.0 and 80 kg ha-1 P2O5, as triple superphosphate or Arad rock phosphate. After this five-year period, plots received the same corrective P fertilization as before and ruzigrass was introduced to the cropping system in the stead of the other cover crops. Soil samples were taken (0-10 cm) after ruzigrass cultivation and subjected to soil-P fractionation. Soybean was grown thereafter without P application to seed furrow. Phosphorus availability in plots with ruzigrass was compared to the ones with spontaneous vegetation for two years. Ruzigrass cultivation increased inorganic (resin-extracted) and organic (NaHCO3) soil P, as well as P concentration in soybean leaves, regardless of the P source. However, soybean yield did not increase significantly due to ruzigrass introduction to the cropping system. Soil-P availability did not differ between soluble and reactive P sources. Ruzigrass increases soil-P availability, especially where corrective P fertilization is performed.

Alteration of neuromuscular function in squash

The alteration in neuromuscular function of knee extensor muscles was characterised after a squash match in 10 trained players. Maximal voluntary contraction (MVC) and surface EMG activity of vastus lateralis (VL) and vastus medialis (VM) muscles were measured before and immediately after a 1-h squash match. M-wave and twitch contractile properties were analysed following single stimuli. MVC declined (280.5+/-46.8 vs. 233.6+/-35.4 Nm, -16%; P<0.001) after the exercise and this was accompanied by an impairment of central activation, as attested by decline in voluntary activation (76.7+/-10.4 vs. 71.3+/-9.6%, -7%; P<0.05) and raw EMG activity of the two vastii (-17%; P<0.05), whereas RMS/M decrease was lesser (VL: -5%; NS and VM: -12%; P=0.10). In the fatigued state, no significant changes in M-wave amplitude (VL: -9%; VM: -5%) or duration were observed. Following exercise, the single twitch was characterised by lower peak torque (-20%; P<0.001) as well as shorter half-relaxation time (-13%; P<0.001) and reduced maximal rate of twitch tension development (-23%; P<0.001) and relaxation (-17%; P<0.05). A 1-h squash match play caused peripheral fatigue by impairing excitation-contraction coupling, whereas sarcolemmal excitability seems well preserved. Our results also emphasise the role of central activation failure as a possible mechanism contributing to the torque loss observed in knee extensors. Physical conditioners should consider these effects when defining their training programs for squash players.

Comparison of plantar pressure distribution in adolescent runners at low vs. high running velocity

This study aimed to compare foot plantar pressure distribution while jogging and running in highly trained adolescent runners. Eleven participants performed two constant-velocity running trials either at jogging (11.2 ± 0.9 km/h) or running (17.8 ± 1.4 km/h) pace on a treadmill. Contact area (CA in cm(2)), maximum force (F(max) in N), peak pressure (PP in kPa), contact time (CT in ms), and relative load (force time integral in each individual region divided by the force time integral for the total plantar foot surface, in %) were measured in nine regions of the right foot using an in-shoe plantar pressure device. Under the whole foot, CA, F(max) and PP were lower in jogging than in running (-1.2% [p<0.05], -12.3% [p<0.001] and -15.1% [p<0.01] respectively) whereas CT was higher (+20.1%; p<0.001). Interestingly, we found an increase in relative load under the medial and central forefoot regions while jogging (+6.7% and +3.7%, respectively; [p<0.05]), while the relative load under the lesser toes (-8.4%; p<0.05) was reduced. In order to prevent overloading of the metatarsals in adolescent runners, excessive mileage at jogging pace should be avoided.

Ventilation, Oxidative Stress, and Nitric Oxide in Hypobaric versus Normobaric Hypoxia.

PURPOSE: Slight differences in physiological responses and nitric oxide (NO) have been reported at rest between hypobaric hypoxia (HH) and normobaric hypoxia (NH) during short exposure.Our study reports NO and oxidative stress at rest and physiological responses during moderate exercise in HH versus NH. METHODS: Ten subjects were randomly exposed for 24 h to HH (3000 m; FIO2, 20.9%; BP, 530 ± 6 mm Hg) or to NH (FIO2, 14.7%; BP, 720 ± 1 mm Hg). Before and every 8 h during the hypoxic exposures, pulse oxygen saturation (SpO2), HR, and gas exchanges were measured during a 6-min submaximal cycling exercise. At rest, the partial pressure of exhaled NO, blood nitrate and nitrite (NOx), plasma levels of oxidative stress, and pH levels were additionally measured. RESULTS: During exercise, minute ventilation was lower in HH compared with NH (-13% after 8 h, P < 0.05). End-tidal CO2 pressure was lower (P < 0.01) than PRE both in HH and NH but decreased less in HH than that in NH (-25% vs -37%, P < 0.05).At rest, exhaled NO and NOx decreased in HH (-46% and -36% after 24 h, respectively, P < 0.05) whereas stable in NH. By contrast, oxidative stress was higher in HH than that in NH after 24 h (P < 0.05). The plasma pH level was stable in HH but increased in NH (P < 0.01). When compared with prenormoxic values, SpO2, HR, oxygen consumption, breathing frequency, and end-tidal O2 pressure showed similar changes in HH and NH. CONCLUSION: Lower ventilatory responses to a similar hypoxic stimulus during rest and exercise in HH versus NH were sustained for 24 h and associated with lower plasma pH level, exaggerated oxidative stress, and impaired NO bioavailability.

LRCW.NET: A web site with a virtual laboratory for the study of coarse and cooking wares in the Late Antique Mediterranean

This contribution presents the LRCW.net a website with a virtual laboratory intranet devoted to the study of coarse and cooking wares in the late Antique Mediterranean. It is designed as a public website with a virtual laboratory intranet. There, all institutions and researchers interested in the subject can work together towards a specific purpose such as the creation of an on-line ‘encyclopedia’ for these categories of ceramics. The LRCW.net website and the associated virtual laboratory are just a small part of a wider initiative that aims to create an on-line Encyclopedia for Ancient Ceramics in the Mediterranean.

Inter-limb coordination and energy cost in swimming.

OBJECTIVES: This study investigated the relationship between inter-arm coordination and the energy cost of locomotion in front crawl and breaststroke and explored swimmers' flexibility in adapting their motor organization away from their preferred movement pattern. DESIGN: Nine front-crawlers performed three 300-m in front crawl and 8 breaststrokers performed three 200-m in breaststroke at constant submaximal intensity and with 5-min rests. Each trial was performed randomly in a different coordination pattern: freely chosen, 'maximal glide' and 'minimal glide'. Two underwater cameras videotaped frontal and side views to analyze speed, stroke rate, stroke length and inter-limb coordination. METHODS: In front crawl, inter-arm coordination was quantified by the index of coordination (IdC) and the leg beat kicks were counted. In breaststroke, four time gaps quantified the arm to leg coordination (i.e., time between leg and arm propulsions; time between beginning, 90° flexion and end of arm and leg recoveries). The energy cost of locomotion was calculated from gas exchanges and blood lactate concentration. RESULTS: In both front crawl and breaststroke, the freely chosen coordination corresponded to glide pattern and showed the lowest energy cost (12.8 and 17.1Jkg(-1)m(-1), respectively). Both front-crawlers and breaststrokers were able to reach 'maximal glide' condition (respectively, +35% and +28%) but not 'minimal glide' condition for front crawl. CONCLUSIONS: The freely chosen pattern appeared more economic because more trained. When coordination was constrained, the swimmers had higher coordination flexibility in breaststroke than in front crawl, suggesting that breaststroke coordination was easier to regulate by changing glide time.