Reactive oxygen species (ROS) have been linked with both depressed Na + ,K + -pump activity and skeletal muscle fatigue. This study investigated N -acetylcysteine (NAC) effects on muscle Na + ,K + ...-pump activity and potassium (K + ) regulation during prolonged, submaximal endurance exercise. Eight well-trained subjects participated in a double-blind,
randomised, crossover design, receiving either NAC or saline (CON) intravenous infusion at 125 mg kg â1 h â1 for 15 min, then 25 mg kg â1 h â1 for 20 min prior to and throughout exercise. Subjects cycled for 45 min at 71%
, then continued at 92%
until fatigue. Vastus lateralis muscle biopsies were taken before exercise, at 45 min and fatigue and analysed for maximal
in vitro Na + ,K + -pump activity (K + -stimulated 3-O-methyfluorescein phosphatase; 3-O-MFPase). Arterialized venous blood was sampled throughout exercise and analysed
for plasma K + and other electrolytes. Time to fatigue at 92%
was reproducible in preliminary trials ( c.v. 5.6 ± 0.6%) and was prolonged with NAC by 23.8 ± 8.3% (NAC 6.3 ± 0.5 versus CON 5.2 ± 0.6 min, P < 0.05). Maximal 3-O-MFPase activity decreased from rest by 21.6 ± 2.8% at 45 min and by 23.9 ± 2.3% at fatigue ( P < 0.05). NAC attenuated the percentage decline in maximal 3-O-MFPase activity (%Îactivity) at 45 min ( P < 0.05) but not at fatigue. When expressed relative to work done, the %Îactivity-to-work ratio was attenuated by NAC at 45
min and fatigue ( P < 0.005). The rise in plasma K + during exercise and the ÎK + -to-work ratio at fatigue were attenuated by NAC ( P < 0.05). These results confirm that the antioxidant NAC attenuates muscle fatigue, in part via improved K + regulation, and point to a role for ROS in muscle fatigue.
Prolonged exhaustive submaximal exercise in humans induces marked metabolic changes, but little is known about effects on muscle Na+-K+-ATPase activity and sarcoplasmic reticulum Ca2+ regulation. We ...therefore investigated whether these processes were impaired during cycling exercise at 74.3 +/- 1.2% maximal O2 uptake (mean +/- SE) continued until fatigue in eight healthy subjects (maximal O2 uptake of 3.93 +/- 0.69 l/min). A vastus lateralis muscle biopsy was taken at rest, at 10 and 45 min of exercise, and at fatigue. Muscle was analyzed for in vitro Na+-K+-ATPase activity maximal K+-stimulated 3-O-methylfluorescein phosphatase (3-O-MFPase) activity, Na+-K+-ATPase content (3Houabain binding sites), sarcoplasmic reticulum Ca2+ release rate induced by 4 chloro-m-cresol, and Ca2+ uptake rate. Cycling time to fatigue was 72.18 +/- 6.46 min. Muscle 3-O-MFPase activity (nmol.min(-1).g protein(-1)) fell from rest by 6.6 +/- 2.1% at 10 min (P <0.05), by 10.7 +/- 2.3% at 45 min (P <0.01), and by 12.6 +/- 1.6% at fatigue (P <0.01), whereas 3Houabain binding site content was unchanged. Ca2+ release (mmol.min(-1).g protein(-1)) declined from rest by 10.0 +/- 3.8% at 45 min (P <0.05) and by 17.9 +/- 4.1% at fatigue (P < 0.01), whereas Ca2+ uptake rate fell from rest by 23.8 +/- 12.2% at fatigue (P=0.05). However, the decline in muscle 3-O-MFPase activity, Ca2+ uptake, and Ca2+ release were variable and not significantly correlated with time to fatigue. Thus prolonged exhaustive exercise impaired each of the maximal in vitro Na+-K+-ATPase activity, Ca2+ release, and Ca2+ uptake rates. This suggests that acutely downregulated muscle Na+, K+, and Ca2+ transport processes may be important factors in fatigue during prolonged exercise in humans.
Background and purpose: The purpose of this study was to assess the structural and functional properties of common beech forest ecosystems in Croatia across a wide macro-climatic gradient ...(Mediterranean, Alpine and Continental) and to gain insight into the ways they adapt to progressing short-term climatic extremes and anomalies.
Material and Methods: Research was undertaken by integration of the expert based, country scale typological delineation of 13 beech ecosystem types, climatic and topographic grids and indices of ecosystem performances such as the JRC FAPAR (Fraction of Absorbed Photosynthetically Active Radiation).
Results: This study reveals preferential environmental conditions for beech ecosystem types together with limiting conditions in three margins of the beech distribution area: highest altitudinal zone, south-eastern continental Pannonian zone and the Mediterranean. The results show that the common beech can adapt to a very wide range of environmental conditions: annual mean temperatures from 2.1oC to 13.5oC, annual precipitation from 739 mm to 3444 mm, and altitudinal range from 20.3 m up to 1576 m above sea level. FAPAR reveals some new insight into the adaptive potential and response mechanisms of the common beech to emerging climate change.
Conclusion: The common beech has great potential to adapt to increasing spring warming by a preterm shift of phenology onset and retain relatively stable productivity during the phenology peak in July and August, unrelated to external climatic forcing. These findings indicate that the flexibility of phenological timing, especially during springtime, present one of the important mechanisms of adaptation and resilience of the common beech.
Alkalosis enhances human exercise performance, and reduces K + loss in contracting rat muscle. We investigated alkalosis effects on K + regulation, ionic regulation and fatigue during intense ...exercise in nine untrained volunteers. Concentric finger flexions
were conducted at 75% peak work rate (â¼3 W) until fatigue, under alkalosis (Alk, NaHCO 3 , 0.3 g kg â1 ) and control (Con, CaCO 3 ) conditions, 1 month apart in a randomised, double-blind, crossover design. Deep antecubital venous (v) and radial arterial
(a) blood was drawn at rest, during exercise and recovery, to determine arterio-venous differences for electrolytes, fluid
shifts, acidâbase and gas exchange. Finger flexion exercise barely perturbed arterial plasma ions and acidâbase status, but
induced marked arterio-venous changes. Alk elevated HCO 3 â and P CO 2 , and lowered H + ( P < 0.05). Time to fatigue increased substantially during Alk (25 ± 8%, P < 0.05), whilst both K + a and K + v were reduced ( P < 0.01) and K + a-v during exercise tended to be greater ( P = 0.056, n = 8). Muscle K + efflux at fatigue was greater in Alk (21.2 ± 7.6 µmol min â1 , 32 ± 7%, P < 0.05, n = 6), but peak K + uptake rate was elevated during recovery (15 ± 7%, P < 0.05) suggesting increased muscle Na + ,K + -ATPase activity. Alk induced greater Na + a , Cl â v , muscle Cl â influx and muscle lactate concentration (Lac â ) efflux during exercise and recovery ( P < 0.05). The lower circulating K + and greater muscle K + uptake, Na + delivery and Cl â uptake with Alk, are all consistent with preservation of membrane excitability during exercise. This suggests that lesser
exercise-induced membrane depolarization may be an important mechanism underlying enhanced exercise performance with Alk.
Thus Alk was associated with improved regulation of K + , Na + , Cl â and Lac â .
Background and purpose: The purpose of this study was to assess the structural and functional properties of common beech forest ecosystems in Croatia across a wide macro-climatic gradient ...(Mediterranean, Alpine and Continental) and to gain insight into the ways they adapt to progressing short-term climatic extremes and anomalies.
Material and Methods: Research was undertaken by integration of the expert based, country scale typological delineation of 13 beech ecosystem types, climatic and topographic grids and indices of ecosystem performances such as the JRC FAPAR (Fraction of Absorbed Photosynthetically Active Radiation).
Results: This study reveals preferential environmental conditions for beech ecosystem types together with limiting conditions in three margins of the beech distribution area: highest altitudinal zone, south-eastern continental Pannonian zone and the Mediterranean. The results show that the common beech can adapt to a very wide range of environmental conditions: annual mean temperatures from 2.1oC to 13.5oC, annual precipitation from 739 mm to 3444 mm, and altitudinal range from 20.3 m up to 1576 m above sea level. FAPAR reveals some new insight into the adaptive potential and response mechanisms of the common beech to emerging climate change.
Conclusion: The common beech has great potential to adapt to increasing spring warming by a preterm shift of phenology onset and retain relatively stable productivity during the phenology peak in July and August, unrelated to external climatic forcing. These findings indicate that the flexibility of phenological timing, especially during springtime, present one of the important mechanisms of adaptation and resilience of the common beech.
The production of reactive oxygen species in skeletal muscle is linked with muscle fatigue. This study investigated whether the antioxidant compound N-acetylcysteine (NAC) augments time to fatigue ...during prolonged, submaximal cycling exercise. Seven men completed a double-blind, crossover study, receiving NAC or placebo before and during cycling exercise, comprising 45 min at 70% of peak oxygen consumption (Vo2 peak) and then to fatigue at 90% Vo2 peak. NAC was intravenously infused at 125 mg.kg-1.h-1 for 15 min and then 25 mg.kg-1.h-1 for 20 min before and throughout exercise, which was continued until fatigue. Arterialized venous blood was analyzed for NAC concentration, hematology, and plasma electrolytes. NAC induced no serious adverse reactions and did not affect hematology, acid-base status, or plasma electrolytes. Time to fatigue was reproducible in preliminary trials (coefficient of variation 7.4 +/- 1.2%) and was not augmented by NAC (NAC 14.6 +/- 4.5 min; control 12.8 +/- 5.4 min). However, time to fatigue during NAC trials was correlated with Vo2 peak (r = 0.78; P < 0.05), suggesting that NAC effects on performance may be dependent on training status. The rise in plasma K+ concentration at fatigue was attenuated by NAC (P < 0.05). The ratio of rise in K+ concentration to work and the percentage change in time to fatigue tended to be inversely related (r = -0.71; P < 0.07). Further research is required to clarify a possible training status-dependent effect of NAC on muscle performance and K+ regulation.
In the elements of structures with a limited resource during operation, significant cyclic stresses can occur, reaching and exceeding the yield strength; the results of an experimental study of the ...effect of the magnitude of preliminary plastic deformations on the strength and durability of structural alloys under low-cycle loading can be of undoubted interest for practice. The use of experimental planning methods in the study of the influence of the maximum cycle stresses and the magnitude of the preliminary permanent deformation on the low-cycle fatigue of 03Kh13AG19 chromium-manganese steel at T = 4.2 K under pulsating tension showed that these methods can be successfully used.
•We analyzed the responses of forests to extreme droughts and rainy conditions.•We performed the regional scale approach on 11 bioclimates across Croatia.•We use JRC FAPAR spatial datasets at monthly ...intervals from 1998 to 2005.•Indices of resilience at annual and intra-annual scale were applied.•Various response strategies based on seasonal phenology were discovered.
Croatia is positioned in the transitional zone of South-eastern Europe and the Mediterranean, a region with frequent occurrence of severe droughts and dry spells, which makes it particularly vulnerable to the impact of climate change. It distends across three main European biogeographical regions – Continental, Alpine and Mediterranean – and therefore has a very high level of forest diversity comprised of 11 out of 14 European forest types. This makes it very convenient to study the exposure of main European forest types to extreme climatic events in the southern limits of their species distribution range. This study provides an assessment of responses of forest vegetation under episodes of climatic anomalies consisting of the most severe historical dry and warm spells in 2000 and 2003, together with the extremely rainy season in 2005 across Croatian territory. The question of interest in this study was to reveal how the existing forest types across the territorial gradient respond to highly expressed extreme climatic variations and to infer some clues about related adaptive strategies. The regional scale approach was applied which previously performed structural delineation of forest cover into eleven main forest groups or bioclimates and were examined considering functional differences. Responses of eleven bioclimatic types were analyzed by time series (1998–2005) of monthly FAPAR (The Fraction of Absorbed Photosynthetic Active Radiation) coverage with a spatial resolution of 1.2km, freely available from JRC FAPAR project. To quantify and differentiate the vegetation response in the considered years we adopted indices of resilience (resistance, recovery, resilience and relative resilience). We also provided a modified approach by applying these indices on a seasonal scale to examine the relationship between variations of phenology and ecosystem responses. The results confirmed the modification of seasonality of photosynthetic activity in relation to the altitudinal and spatial gradient. At the intra-seasonal scale, we distinguished specific opportunistic behavior of the common beech and oak forest types to alternating climatic conditions. Beech forest types show a very high ability to shift their phenology to earlier spring warming as a consequence of global warming. However, continental and Mediterranean oak forest types and in particular Aleppo pine and holm oak forests showed a higher increase of FAPAR during rainy events. The revealed capability of some tree species to better exploit rainfall in very wet periodic episodes has to be further evaluated in drawing conclusions about the overall resilience of forests under future climate change scenarios.
Metallurgy, mechanical engineering, energy, agriculture, food industry, energy, electronics, rocket and space technology – this is a far from complete list of areas of the national economy in which ...liquid cryogenic products (cryoproducts). The production volumes of such products and the scale of their use are constantly increasing. This is due to the fact that cryogenic temperatures (below 120 K) provide unique opportunities for the implementation of such physical phenomena and processes that do not manifest themselves under normal conditions, but are used very effectively in science and technology. The solution of fundamental scientific problems and applied problems of both promising and current importance is determined by the level of development of cryogenic technology and the degree of its practical application. The continuous expansion of the scale of production of liquid cryogenic products has led in recent years to a significant increase in the volume of production of systems for their storage and transportation. These systems, as a rule, are welded shell structures in execution, they are operated in difficult conditions of temperature and force effects. The share of their production in the total output of cryogenic engineering products is very significant, and the operating conditions are the most stressful in comparison with other types of cryogenic structures. For the manufacture of cryogenic shell structures, expensive non-ferrous alloys and special steels are used, the degree of consumption of which, taking into account the sufficient material consumption of such structures and the expanding scale of their production, is constantly increasing. Therefore, one of the most urgent for cryogenic mechanical engineering at present is the problem of reducing the material consumption of shell structures and increasing their reliability and durability. It is obvious that a solution to this problem for cryogenic engineering products can be achieved by improving the methods of their strength calculations based on taking into account the specific hardening effect of low temperature on structural alloys. The phenomenon of low-cycle fatigue of metals is associated with elastoplastic deformation of their macrovolumes. The kinetics of elastoplastic deformation processes under cyclic loading depends on the loading conditions and material properties, and the nature of these processes and their intensity have a decisive influence on the features of material destruction. If the accumulation of deformation is small, then the destruction, as a rule, is of a fatigue nature; quasi-static fracture (similar in appearance to fracture during static tests for short-term strength) occurs after the realization of the ultimate plasticity of the material. The task of assessing the bearing capacity and durability under cyclic loading conditions is extremely important. Under cyclic loading, a number of specific phenomena and factors that are difficult to take into account analytically arise, which are primarily associated with the development of fatigue damage, with the need to assess the cyclic and structural instability of materials 1. Since such studies are very laborious and expensive, the problem of minimizing such experiments is currently urgent. In this paper, we investigate the possibility of using mathematical planning methods for experimental studies at cryogenic temperatures. Experiment planning is usually understood as the procedure for choosing the volume and conditions of testing necessary and sufficient to solve the problem with the required accuracy.
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