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2. Chronic hypobaric hypoxia increases isolated rat fast-twitch and slow-twitch limb muscle force and fatigue
- Creator:
- El-Khoury, R., Bradford, A., and O´Halloran, K. D.
- Type:
- article, články, model:article, and TEXT
- Subject:
- Fyziologie člověka a srovnávací fyziologie, fyziologie člověka, human physiology, hypoxia, skeletal muscle, fatigue, 14, and 612
- Language:
- English
- Description:
- Chronic hypoxia alters respiratory muscle force and fatigue, effects that could be attributed to hypoxia and/or increased activation due to hyperventilation. We hypothesized that chronic hypoxia is associated with phenotypic change in non-respiratory muscles and therefore we tested the hypothesis that chronic hypobaric hypoxia increases limb muscle force and fatigue. Adult male Wistar rats were exposed to normoxia or hypobaric hypoxia (PB=450 mm Hg) for 6 weeks. At the end of the treatment period, soleus (SOL) and extensor digitorum longus (EDL) muscles were removed under pentobarbitone anaesthesia and strips were mounted for isometric force determination in Krebs solution in standard water-jacketed organ baths at 25 °C. Isometric twitch and tetanic force, contractile kinetics, forcefrequency relationship and fatigue characteristics were determined in response to electrical field stimulation. Chronic hypoxia increased specific force in SOL and EDL compared to age-matched normoxic controls. Furthermore, chronic hypoxia decreased endurance in both limb muscles. We conclude that hypoxia elicits functional plasticity in limb muscles perhaps due to oxidative stress. Our results may have implications for respiratory disorders that are characterized by prolonged hypoxia such as chronic obstructive pulmonary disease (COPD)., R. El-Khoury, A. Bradford, K. D. O´Halloran., and Obsahuje seznam literatury
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
3. Determination of the fatigue strength of a railway vehicle node using the probability approach
- Creator:
- Václavík, Jaroslav, Marek, Pavel, Chvojan, Jan, and Kepka, Miloslav
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- railway, wagon, probability, fatigue, service life, Goodman diagram, and SBRA
- Language:
- English
- Description:
- This paper presents a case study for the strength demonstration of a railway wagon welded node using the probability approach. The design variables were taken from the existing standardization for railway vehicles. The fatigue damage summation method for proving the satisfactory service life as well as the Goodman diagram method for verification of the unlimited service life was used for the node examination. The probability estimation was made using the Monte Carlo SBRA method with the help of the Anthill software. and Obsahuje seznam literatury
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
4. Does cardiovascular autonomic dysfunction contribute to fatigue in myasthenia gravis?
- Creator:
- Elsais, Ahmed, Kerty, Emilia, Russell, Kristoffer, and Toska, Karin
- Format:
- počítač and online zdroj
- Type:
- model:article and TEXT
- Subject:
- myasthenia gravis, fatigue, autonomic disturbance, cardiovascular response, and acetylcholine esterase inhibitors
- Language:
- English
- Description:
- Myasthenia gravis (MG) is an autoimmune disease characterized by fatigable muscle weakness. Despite full spontaneous or pharmacological remission some MG patients still complain of physical and mental fatigue. Fatigue has been related to autonomic dysregulation. The aim of this study was to assess autonomic responses in a group of MG patients in complete remission but complaining of persistent fatigue. Seventeen wellregulated but persistently fatigued MG patients and 17 individually matched controls underwent echocardiography assessing systolic and diastolic heart function. Beat to beat cardiovascular responses at rest and to 30o head-up tilt, tilt-back, and 2-min static handgrip contraction were recorded. Fatigued MG patients had a statistically significant higher resting HR than their matched controls (p=0.03). The difference in resting heart rate between MG patients not using acetylcholine esterase inhibitors (AChEi) and their matched controls was even more pronounced (p=0.007). The autonomic cardiovascular adjustments to head-up tilt, tilt-back and handgrip contraction were not statistically significant different between patients and controls. We found a higher resting heart rate in all wellregulated but fatigued MG patients compared with controls. The difference was more pronounced between patients not taking AChEi compared to their matched controls. This finding may reflect a disturbed resting sympathovagal balance and this might be a contributing factor to the fatigue symptoms.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
5. Effect of pedaling rates and myosin heavy chain composition in the vastus lateralis muscle on the power generating capability during incremental cycling in humans
- Creator:
- Majerczak, Joanna, Szkutnik, Z., Duda, K., Komorowska, M., Kolodziejski, L., Karasinski, J., and Zoladz, J. A.
- Format:
- print, bez média, and svazek
- Type:
- article, články, model:article, and TEXT
- Subject:
- Biochemie. Molekulární biologie. Biofyzika, fyziologie, únava, kyslík, physiology, fatigue, oxygen, cycling, myosin heavy chain isoforms, muscle fatigue, 2, and 577
- Language:
- English
- Description:
- a_1 In this study, we have determined power output reached at maximal oxygen uptake during incremental cycling exercise (PI,max) performed at low and at high pedaling rates in nineteen untrained men with various myosin heavy chain composition (MyHC) in the vastus lateralis muscle. On separate days, subjects performed two incremental exercise tests until exhaustion at 60 rev . min-1 and at 120 rev . min-1. In the studied group of subjects PI,max reached during cycling at 60 rev . min-1 was significantly higher (p=0.0001) than that at 120 rev . min-1 (287±29 vs. 215±42 W, respectively for 60 and 120 rev . min-1). For further comparisons, two groups of subjects (n=6, each) were selected according to MyHC composition in the vastus lateralis muscle: group H with higher MyHC II content (56.8±2.79 %) and group L with lower MyHC II content in this muscle (28.6±5.8 %). PI,max reached during cycling performed at 60 rev . min-1 in group H was significantly lower than in group L (p=0.03). However, during cycling at 120 rev . min-1, there was no significant difference in PI,max reached by both groups of subjects (p=0.38). Moreover, oxygen uptake (VO2), blood hydrogen ion [H+], plasma lactate [La-] and ammonia [NH3] concentrations determined at the four highest power outputs completed during the incremental cycling performed at 60 as well as 120 rev . min-1, in the group H were significantly higher than in group L. We have concluded that during an incremental exercise performed at low pedaling rates the subjects with lower content of MyHC II in the vastus lateralis muscle possess greater power generating capabilities than the subjects with higher content of MyHC II. Surprisingly, at high pedaling rate, power generating capabilities in the subjects with higher MyHC II content in the vastus lateralis muscle did not differ from those found in the subjects with lower content of MyHC II in this muscle., a_2 We have concluded that during an incremental exercise performed at low pedaling rates the subjects with lower content of MyHC II in the vastus lateralis muscle possess greater power generating capabilities than the subjects with higher content of MyHC II. Surprisingly, at high pedaling rate, power generating capabilities in the subjects with higher MyHC II content in the vastus lateralis muscle did not differ from those found in the subjects with lower content of MyHC II in this muscle, despite higher blood [H+], [La-] and [NH3] concentrations. This indicates that at high pedaling rates the subjects with higher percentage of MyHC II in the vastus lateralis muscle perform relatively better than the subjects with lower percentage of MyHC II in this muscle., J. Majerczak, Z. Szkutnik, K. Duda, M. Komorowska, I. Kolodziejski, J. Karasinski, J. A. Zoladz., and Obsahuje bibliografii a bibliografické odkazy
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
6. New test approach and evaluation of dynamic and thermal parameters of elastomers
- Creator:
- Pešek, Luděk, Vaněk, František, Procházka, Pavel, Bula, Vítězslav, and Cibulka, Jan
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- rubber, dynamic, tests, identification, fatigue, and thermo-mechanics
- Language:
- English
- Description:
- The new test approach for evaluation of thermo-visco-elastic parameters of elastomers is designed, realized and discussed herein. The main attention is devoted to a kinematically excited rubber beam specimen under transient resonant sweep excitation. Mechanical material characteristics, i.e. Young modulus and loss angle, are identified from analytical formulas of frequency function based on measured dynamic loading and response signals. Heat material constants were estimated indirectly by numerical thermo-mechanical FE model and matching numerical and experimental results. The 'sweep' regime tests serve for estimation of thermal and mechanical dependences. Long-term fatigue tests with cyclic resonant loading enable analysis of material degradation, such as hardening and permanent deformations. and Obsahuje seznam literatury
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
7. Physical exercise-induced cardiovascular adjustments are modulated by muscarinic cholinoceptors within the ventromedial hypothalamic nucleus
- Creator:
- Wanner, S. P., Guimarães, J. B., Pires, W., La Guardia, R. B., Haibara, A. S., Marubayashi, U., Coimbra, C. C., and Lima, N. R. V.
- Format:
- Type:
- article, články, model:article, and TEXT
- Subject:
- Fyziologie člověka a srovnávací fyziologie, acetylcholin, únava, acetylcholine, fatigue, hypothalamus, methylatropine, 14, and 612
- Language:
- English
- Description:
- The effects of blocking ventromedial hypothalamic nucleus (VMH) muscarinic cholinoceptors on cardiovascular responses were investigated in running rats. Animals were anesthetized with pentobarbital sodium and fitted with bilateral cannulae into the VMH. After recovering from surgery, the rats were familiarized to running on a treadmill. The animals then had a polyethylene catheter implanted into the left carotid artery to measure blood pressure. Tail skin temperature (Ttail), heart rate, and systolic, diastolic and mean arterial pressure were measured after bilateral injections of 0.2 μl of 5 × 10−9 mol methylatropine or 0.15 M NaCl solution into the hypothalamus. Cholinergic blockade of the VMH reduced time to fatigue by 31% and modified the temporal profile of cardiovascular and Ttail adjustments without altering their maximal responses. Mean arterial pressure peak was achieved earlier in methylatropine-treated rats, which also showed a 2-min delay in induction of tail skin vasodilation, suggesting a higher sympathetic tonus to peripheral vessels. In conclusion, muscarinic cholinoceptors within the VMH are involved in a neuronal pathway that controls exercise-induced cardiovascular adjustments. Furthermore, blocking of cholinergic transmission increases sympathetic outflow during the initial minutes of exercise, and this higher sympathetic activity may be responsible for the decreased performance., S. P. Wanner ... [et al.]., and Obsahuje bibliografii a bibliografické odkazy
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
8. Simulation of voltage dip event in fixed-speed wind turbines: fatigue evaluation
- Creator:
- Veluri, Badrinath, Santos-Martin, David, and Jensen, Henrik Myhre
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- voltage dip, electro-mechanical model, drivetrain, induction generator, rainflow count, and fatigue
- Language:
- English
- Description:
- Grid code modifications require the in service fixed speed wind turbines to ride-through grid faults. Voltage dips due to electrical grid faults generate transients of the generator electromagnetic torque. These transients result in significant stresses and vibrations affecting the fatigue life of the components. An electro-mechanical model was built to simulate the grid faults that excite the asynchronous generator with poorly damped stator flux oscillations. These oscillations cause transients of the generator electromagnetic torque. This article focuses in estimating the resulting significant stresses transients affecting the fatigue life of drivetrain system due to voltage dips. A rainflow cycle counting method was developed to evaluate the fatigue life of the mechanical system. The methodology analyses the stress history and estimates the mean and amplitudes of the counted cycles, and time of duration to calculate the accumulated damage occurred during the voltage dip event. and Obsahuje seznam literatury
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
9. The cost of sleep-related road traffic accidents in the Czech Republic
- Creator:
- Honců, Marek
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- road transport safety, road traffic accidents, accident costs, human life value, fatigue, sleepiness, and microsleep
- Language:
- English
- Description:
- The road traffic accidents (RTA) cause large dainage on human health and life, material and environmental damages. The human resource losses represent the main component of the social costs of RTA. These total costs are estimated at per cents of GDP. The severity and effects of the sleep-related RTA are similar to the alcohol-related RTA. According to foreign studies they comprise 1 to 25% of all accidents. In the Czech Republic these data are not available, the amount of social costs of the sleep-related RTA can be estimated at billions of CZK yearly.
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
10. The effects of head cooling on endurance and neuroendocrine responses to exercise in warm conditions
- Creator:
- Ansley, L., Marvin, G., Sharma, A., Kendall, M. J., Jones, D. A., and Bridge, M. W.
- Format:
- print, bez média, and svazek
- Type:
- article, články, model:article, and TEXT
- Subject:
- Fyziologie člověka a srovnávací fyziologie, fyziologie, hypertermie, tělesná cvičení, únava, physiology, hyperthermia, exercises, fatigue, prolactin, head cooling, 14, and 612
- Language:
- English
- Description:
- The present study investigated the effects of head cooling during endurance cycling on performance and the serotonergic neuroendocrine response to exercise in the heat. Subjects exercised at 75 % VO2max to volitional fatigue on a cycle ergometer at an ambient temperature of 29±1.0 °C, with a relative humidity of approximately 50 %. Head cooling resulted in a 51 % (p<0.01) improvement in exercise time to fatigue and Borg Scale ratings of perceived exertion were significantly lower throughout the exercise period with cooling (p<0.01). There were no indications of peripheral mechanisms of fatigue either with, or without, head cooling, indicating the importance of central mechanisms. Exercise in the heat caused the release of prolactin in response to the rise in rectal temperature. Head cooling largely abolished the prolactin response while having no effect on rectal temperature. Tympanic temperature and sinus skin temperature were reduced by head cooling and remained low throughout the exercise. It is suggested that there is a co-ordinated response to exercise involving thermoregulation, neuroendocrine secretion and behavioural adaptations that may originate in the hypothalamus or associated areas of the brain. Our results are consistent with the effects of head cooling being mediated by both direct cooling of the brain and modified cerebral artery blood flow, but an action of peripheral thermoreceptors cannot be excluded., L. Ansley, G. Marvin, A. Sharma, M. J. Kendall, D. A. Jones, M. W. Bridge., and Obsahuje bibliografii a bibliografické odkazy
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public