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Статті в журналах з теми "Constant load exercise"
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Hussain, S. N., R. L. Pardy, and J. A. Dempsey. "Mechanical impedance as determinant of inspiratory neural drive during exercise in humans." Journal of Applied Physiology 59, no. 2 (August 1, 1985): 365–75. http://dx.doi.org/10.1152/jappl.1985.59.2.365.
Повний текст джерелаАнотація:
Five healthy males exercised progressively with small 2-min increments in work load. We measured inspiratory drive (occlusion pressure, P0.1), pulmonary resistance (RL), dynamic pulmonary compliance (Cdyn), transdiaphragmatic pressure (Pdi), and diaphragmatic electromyogram (EMGdi). Minute ventilation (VE), mean inspiratory flow rate (VT/TI), and P0.1 all increased exponentially with increased work load, but P0.1 increased at a faster rate than did VT/TI or VE. Thus effective impedance (P0.1/VT/TI) rose throughout exercise. The increasing P0.1 was mostly due to augmented Pdi and coincided with increased EMGdi during this initial portion of inspiration. We found no consistent change in RL or Cdyn throughout exercise. With He breathing (80% He-20% O2), RL was reduced at all work loads; P0.1 fell in comparison with air-breathing values and VE, VT, and VT/TI rose in moderate and heavy work; and P0.1/VT/TI was unchanged with increasing exercise loads. Step reductions in gas density at a constant work load of any intensity showed an immediate reduction in the rate of rise of EMGdi and Pdi followed by increased VT/TI, breathing frequency, and hypocapnia. These changes were maintained during prolonged periods of unloading and were immediately reversible on return to air breathing. These data are consistent with the existence of a reflex effect on the magnitude of inspiratory neural drive during exercise that is sensitive to the load presented by the normal mechanical time constant of the respiratory system. This “load” is a significant determinant of the hyperpneic response and thus of the maintenance of normocapnia during exercise.
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Marino, F. E. "The limitations of the constant load and self-paced exercise models of exercise physiology." Comparative Exercise Physiology 8, no. 1 (January 1, 2012): 3–9. http://dx.doi.org/10.3920/cep11012.
Повний текст джерелаАнотація:
The fundamental tenets of exercise physiology are to describe energy transformations during physical work and make predictions about physical performance during different conditions. Historically, the most popular method to observe such responses during exercise has been the constant load or fixed intensity protocol based largely on the assumption that there is a threshold response of the organism under given conditions. However, constant load exercise does not fully allow for randomness or variability as the biological system is overridden by a predetermined externally imposed load which cannot be altered. Conversely, in self-regulated (paced) exercise there is almost an immediate reduction in power output and muscle recruitment upon commencing exercise. This observation suggests the existence of a neural inhibitory command processes. This difference in regulation demonstrates the inherent importance of variability in the biological system; for in tightly controlled energy expenditure, as is the case during constant load exercise, sensory cues cannot be fully integrated to provide a more appropriate response to the given task. The collective evidence from conventional constant load versus self-regulated exercise studies suggest that energy transformations are indeed different so that the inherent biological variability accounts for the different results achieved by the two experimental paradigms.
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Gairola, Anjuli, Thariana Salazar, Ruth Georges, and Kristen Betterman. "Session RPE During A Constant Load Submaximal Treadmill Exercise." Medicine & Science in Sports & Exercise 52, no. 7S (July 2020): 631. http://dx.doi.org/10.1249/01.mss.0000681164.21004.45.
Повний текст джерела
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Yamazaki, F., N. Fujii, R. Sone, and H. Ikegami. "Responses of sweating and body temperature to sinusoidal exercise in physically trained men." Journal of Applied Physiology 80, no. 2 (February 1, 1996): 491–95. http://dx.doi.org/10.1152/jappl.1996.80.2.491.
Повний текст джерелаАнотація:
The effect of physical training on the dynamic responses of sweating to transient exercise is still controversial. We determined the phase response and amplitude response (delta) of sweating rate and body temperature to sinusoidal exercise in physically trained and untrained subjects. Eight trained and seven untrained male subjects exercised on a cycle ergometer with a constant load for 30 min; for the next 28 min, they exercised with a sinusoidal load. The sinusoidal load variation ranged from approximately 10 to 60% of peak O2 uptake with a 4-min period. The ambient temperature and the relative humidity during exercise were 25 degrees C and 35%, respectively. There was no difference between the groups in the phase lags of esophageal temperature (Tes) and mean skin temperature (Tsk), whereas the phase lags of sweating rates for the chest and forearm were significantly shorter in the trained group (P < 0.05). The delta of Tes and Tsk per 1 W of exercise load in the trained group was significantly smaller than that in the untrained group (both, P < 0.05), whereas there was no difference between the groups in the delta of sweating rate for the chest and forearm. We conclude that subjects who have undergone long-term physical training show prompter dynamic characteristics of sweating response compared with untrained subjects and have a higher capacity to maintain constant body temperature during exercise at transient load.
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WELTMAN, ARTHUR, JUDY Y. WELTMAN, CHRISTOPHER J. WOMACK, SHALA E. DAVIS, JEFFREY L. BLUMER, GLENN A. GAESSER, and MARK L. HARTMAN. "Exercise training decreases the growth hormone (GH) response to acute constant-load exercise." Medicine & Science in Sports & Exercise 29, no. 5 (May 1997): 669–76. http://dx.doi.org/10.1097/00005768-199705000-00013.
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Pepin, Véronique, Didier Saey, Claude H. Côté, Pierre LeBlanc, and François Maltais. "Susceptibility to Muscle Fatigue and Lung Mechanics in Chronic Obstructive Pulmonary Disease." Clinical & Investigative Medicine 30, no. 3 (June 1, 2007): 27. http://dx.doi.org/10.25011/cim.v30i3.1721.
Повний текст джерелаАнотація:
Background: Contractile fatigue of the quadriceps occurs in a significant proportion of patients with COPD after constant-load cycling exercise. Dynamic hyperinflation, by altering cardiac output during exercise, could contribute to fatigue susceptibility in this population. The purpose of this study was to compare operational lung volumes during constant workrate exercise between COPD patients who do and those who do not develop contractile fatigue of the quadriceps (fatiguers vs non-fatiguers).
Methods: Sixty-two patients with COPD (FEV1: 46±16%) completed a constant-load cycling test at 80% of the peak workrate achieved during progressive cycle ergometry. Ventilatory parameters were monitored breath-by-breath, while inspiratory capacity maneuvers were obtained every other minute during constant-load cycling. Quadriceps twitch force was measured with magnetic stimulation of the femoral nerve before and after the test. Muscle fatigue was defined as a post-exercise reduction in quadriceps twitch force of more than 15% of the resting value.
Results: Forty patients (65%) developed muscle fatigue after constant-load cycling. No significant differences were found between fatiguers and non-fatiguers with respect to age, body mass index, resting lung function, peak oxygen consumption, and endurance time to constant-load exercise. Change in inspiratory capacity from rest to end-exercise (DIC) was similar between both subgroups (DIC: 0.56±0.32L vs 0.56±0.47L for fatiguers and non-fatiguers respectively, P=0.99).
Conclusion: Susceptibility to muscle fatigue could not be predicted by exercise duration or by the degree of dynamic hyperinflation in patients with COPD.
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Friden, J., P. N. Sfakianos, and A. R. Hargens. "Muscle soreness and intramuscular fluid pressure: comparison between eccentric and concentric load." Journal of Applied Physiology 61, no. 6 (December 1, 1986): 2175–79. http://dx.doi.org/10.1152/jappl.1986.61.6.2175.
Повний текст джерелаАнотація:
This study investigates the dynamic and resting intramuscular pressures associated with eccentric and concentric exercise of muscles in a low-compliance compartment. The left and righ leg anterior compartments of eight healthy males (ages 22–32 yr) were exercised by either concentric or eccentric contractions of the same load (400 submaximal contractions at constant rate, 20/min for 20 min at a load corresponding to 15% of individual maximal dorsiflexion torque). Tissue fluid pressures were measured with the slit-catheter technique before, during, and after the exercise. Average peak intramuscular pressure generated during eccentric exercise (236 mmHg) was significantly greater than during concentric exercise (157 mmHg, P less than 0.001). Peak isometric contraction pressure in the eccentrically exercised compartment was significantly higher both within 20 min postexercise and on the second postexercise day (P less than 0.001). Resting pressure 2 days postexercise was significantly higher on the eccentrically exercised side (10.5 mmHg) compared with the concentrically exercised (4.4 mmHg, P less than 0.05). The ability to sustain tension during postexercise isometric contractions was impaired on the “eccentric” side. Soreness was exclusively experienced in the eccentrically exercised muscles. We conclude that eccentric exercise causes significant intramuscular pressure elevation in the anterior compartment, not seen following concentric exercise, and that this may be one of the factors associated with development of delayed muscle soreness in a tight compartment.
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Takahashi, Shinji, Tomonori Chiba, Hiroaki Ishii, and Takahiko Nishijima. "Validity of Expired Gas Simulation Model during Constant Load Exercise." International Journal of Sport and Health Science 1, no. 1 (2003): 119–28. http://dx.doi.org/10.5432/ijshs.1.119.
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Yano, Tokuo, Yasuhito Kumazaki, and Katsumi Asano. "Kinetics of Mixed Venous CO2 Pressure in Constant-Load Exercise." Applied Human Science 14, no. 3 (1995): 155–56. http://dx.doi.org/10.2114/ahs.14.155.
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Milanese, Manlio, Riccardo Saporiti, Stefano Bartolini, Riccardo Pellegrino, Michele Baroffio, Vito Brusasco, and Emanuele Crimi. "Bronchodilator effects of exercise hyperpnea and albuterol in mild-to-moderate asthma." Journal of Applied Physiology 107, no. 2 (August 2009): 494–99. http://dx.doi.org/10.1152/japplphysiol.00302.2009.
Повний текст джерелаАнотація:
In asthmatic patients, either bronchodilatation or bronchoconstriction may develop during exercise. In 18 patients with mild-to-moderate asthma, we conducted two studies with the aims to 1) quantify the bronchodilator effect of hyperpnea induced by incremental-load maximum exercise compared with effects of inhaled albuterol ( study 1, n = 10) and 2) determine the time course of changes in airway caliber during prolonged constant-load exercise ( study 2, n = 8). In both studies, it was also investigated whether the bronchodilator effects of exercise hyperpnea and albuterol are additive. Changes in airway caliber were measured by changes in partial forced expiratory flow. In study 1, incremental-load exercise was associated with a bronchodilatation that was ∼60% of the maximal bronchodilatation obtainable with 1,500 μg of albuterol. In study 2, constant-load exercise was associated with an initial moderate bronchodilatation and a late airway renarrowing. In both studies, premedication with inhaled albuterol (400 μg) promoted sustained bronchodilatation during exercise, which was additive to that caused by exercise hyperpnea. In conclusion, in mild-to-moderate asthmatic individuals, hyperpnea at peak exercise was associated with a potent yet not complete bronchodilatation. During constant-load exercise, a transient bronchodilatation was followed by airway renarrowing, suggesting prevalence of constrictor over dilator effects of hyperpnea. Finally, the bronchodilator effect of hyperpnea was additive to that of albuterol.
Дисертації з теми "Constant load exercise"
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Odendal, Elsabe. "Pulmonary function and acid-base balance high intensity constant-load exercise." Master's thesis, University of Cape Town, 1993. http://hdl.handle.net/11427/27123.
Повний текст джерелаАнотація:
The possibility that an inadequate response of the pulmonary system might limit high intensity exercise in man has received increasing attention over the past few years. However, very few scientific investigations have focused systematically on pulmonary function during high intensity constant-load exercise. Furthermore, many studies have examined only one part of the pulmonary system during exercise and some have not included blood gas measurements as a measure of the adequacy of pulmonary function. The studies reported in this thesis were designed to investigate the possible failure of the gas exchanging and pump functions of the pulmonary system during high intensity constant-load exercise. In particular, the aim was to determine the extent to which the pulmonary system might be a factor causing fatigue during this form of exercise.
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Burnley, Mark. "Effects of prior exercise on the on-transient oxygen uptake kinetics of constant-load exercise." Thesis, University of Brighton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392874.
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Wagner, Holly A. "Determining optimal load for a constant-load cycle ergometer test relative to isotonic leg strength." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-01242009-063426/.
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Fritsch, LeaAnn Thompson. "Effects of chronic suboptimal energy intake on constant-load exercise in young women." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-09182008-063227/.
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Rieger, Brian W. "Physiological and Metabolic Responses to Constant-Load Exercise on an Inclined Stepper and Treadmill." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36647.
Повний текст джерелаАнотація:
This study evaluated oxygen uptake (VO2), heart rate (HR), and lactate [HLa] responses between the treadmill (TM) and the CardiosquatTM 1650 LETM inclined stepper by StairMasterTM (SM) during constant-load exercise. The slow component of VO2 (SC) was a central variable assessed during exercise. Twenty-two healthy college-aged (18-30) subjects completed an incremental TM and SM exercise test to establish a workload equivalent to 70% VO2peak. Following each incremental test, a 20-minute constant-load exercise bout was performed . Incremental and instant-load exercise bouts were separated by at least 48 hours. The order of the tests were randomized. VO2, HR, and [HLa] were evaluated at 5, 10, 15, and 20-minutes of exercise. Expired gases were analyzed using a Med Graphics CPX/D metabolic cart.
Blood samples were analyzed immediately for lactate concentration with an automated lactate analyzer (Yellow Springs Instrument Model 1500 Sport ). A two-way ANOVA with repeated measures was performed on the rate of change between the treadmill and stepper for VO2, HR, and [HLa]. No significant differences were found for any of the response variables (P>0.05). These results suggest at that the same relative workload, the SM does not elicit a more pronounced SC than the TM.
Based on these findings, the SM appears to be an appropriate modality of exercise for various clinical populations.Master of Science
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Naouar, Neïla. "Oxygénation musculaire, EMG et fonction ventilatoire chez des sportifs porteurs d'hémoglobinopathie durant un exercice physique." Electronic Thesis or Diss., Amiens, 2021. http://www.theses.fr/2021AMIE0025.
Повний текст джерелаАнотація:
L'objectif de cette thèse était triple 1)- Etudier la fonction ventilatoire durant un exercice incrémental maximal et un exercice sous-maximal prolongé chez des sportifs porteurs de trait drépanocytaire (PTD) 2)- Etudier la performance de la fonction ventilatoire durant un exercice à charge constante chez des sujets ayant une β-thalassémie mineure, 3)- Evaluer l'adaptation physiologique durant un effort sous-maximal prolongé chez des sportifs atteints de drépanocytose hétérozygote. La première étude a montré que l'exercice incrémental maximal et l'exercice à charge constante induisent une fatigue spirométrique, de la force et de l'endurance des muscles respiratoires chez les sujets porteurs de trait drépanocytaire. L'exercice rectangulaire affecte de façon importante la force et l'endurance musculaire respiratoire que l'exercice triangulaire. La deuxième étude a montré par ailleurs, une altération de la performance de la fonction ventilatoire après la réalisation d'un exercice sous-maximal prolongé chez les sujets ayant une β-thalassémie mineure. Ainsi, une diminution importante de l'endurance des muscles respiratoires a été constatée chez ces individus pathologiques en réponse à l'exercice à charge constante par rapport aux sujets sains. Ces résultats confirment que les sujets ayant des hémoglobinopathies n'ont pas la capacité de maintenir des niveaux élevés de ventilation pendant un exercice physique intense. Ensuite, lors de la troisième étude, la détermination de la PMA a permis d'affirmer que la forme hétérozygote de la drépanocytose n'est pas un facteur limitant de l'aptitude physique aérobie maximale. L'adaptation à un effort sous-maximal, évaluée par la phase rapide est parfaitement normale chez les sujets ayant un trait drépanocytaire. Par contre, l'amplitude de la composante lente de VO2, plus élevée chez les PTD suggère que ces individus pathologiques se caractérisent par une mauvaise tolérance à l'effort. Cette élévation était corrélée avec l'HbO2 et HHb qui étaient stables durant l'effort. Cette stabilité confirme la génération du mécanisme de remodelage vasculaire chez les PTD en réponse à des problèmes hémorhéologiques produits par l'effort. Une augmentation précoce du RMS et une diminution linéaire de 25,63% de MPF corrélée avec HHb, ont été constatées durant l'effort chez les individus pathologiques par rapport aux sujets sans hémoglobinopathie, affirmant que la baisse de déformabilité des globules rouges dont sont signalés généralement les sujets porteurs de trait drépanocytaire bouleverse de façon accrue la microcirculation musculaire qui pourrait être responsable de la composante lente de VO2. Ces résultats montrent que les sujets ayant une hémoglobinopathie pourraient avoir une fonction ventilatoire moins performante durant un effort physique intense que les sujets sains. Également, ces individus pourraient avoir une fatigue musculaire périphérique plus importante que les sujets à hémoglobine normale et une oxygénation musculaire stable durant un exercice rectangulaire. Ils présentent une capacité aérobie et une tolérance à l'effort d'endurance, inférieures aux sujets sains durant un effort sous-maximalThe aim of this thesis was threefold 1)- To study the ventilatory function during a maximal incremental exercise and a prolonged submaximal exercise in athletes with sickle cell trait (SCT), 2)- To study the performance of the ventilatory function during a constant load exercise in subjects with minor β-thalassemia, 3)- Evaluate the physiological adaptation during prolonged submaximal exercise in athletes with heterozygous sickle cell disease. The first study showed that maximal incremental exercise and constant load exercise induce spirometric fatigue, and decreased strength and endurance of the respiratory muscles in subjects with sickle cell trait. Rectangular exercise significantly affects respiratory muscle strength and endurance than triangular exercise. The second study was showed an impairment of the performance of ventilatory function after performing prolonged submaximal exercise in subjects with minor β-thalassemia. Thus, a significant decrease in the endurance of the respiratory muscles was observed in these pathological individuals in response to constant load exercise compared to healthy subjects. These results confirm that hemoglobinopathic subjects do not have the ability to maintain high levels of ventilation during intense physical exercise. Then, in the third study, the determination of the MAP confirmed that the heterozygous form of sickle cell disease is not a limiting factor in maximal aerobic physical fitness. Adaptation to submaximal effort, assessed by the rapid phase, is perfectly normal in subjects with sickle cell trait. In contrast, the amplitude of the slow component of VO2, which is higher in SCT, suggests that these pathological individuals are characterized by weak tolerance to exercise. This rise was correlated with HbO2 and HHb which were satble during exercise. This stability confirms the generation of the vascular remodeling mechanism in SCT in response to hemorheological problems produced by exercise. An precocious increase in RMS and a 25.63% linear decrease in MPF correlated with HHb, were observed during exercise in pathologic individuals compared to subjects without hemoglobinopathy, affirming that the decrease in erythrocyte deformabilities which are generally reported in subjects with sickle cell trait disrupts the muscular microcirculation in an increased manner which could be responsible for the slow component of VO2. These results show that subjects with hemoglobinopathy could have a less efficient ventilatory function during intense physical exertion than healthy subjects. Also, these individuals might have more significant peripheral muscle fatigue than subjects with normal hemoglobin and stable muscle oxygenation during rectangular exercise. They exhibit aerobic capacity and tolerance to endurance effort inferior than healthy subjects during submaximal effort
Книги з теми "Constant load exercise"
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Burnley, Mark. Effects of prior exercise on the on-transient oxygen uptake kinetics of constant-load exercise. 2002.
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Rowland, Thomas W. Cardiovascular function. Oxford University Press, 2013. http://dx.doi.org/10.1093/med/9780199232482.003.0019.
Повний текст джерелаАнотація:
While the critical nature of blood perfusion during exercise is well recognized, many questions remain incompletely answered. What are the mechanisms by which circulation of blood is increased during exercise? By what means is circulatory flow tightly linked to tissue metabolic demands? What limits increases in circulatory flow during exhaustive exercise? By what mechanism does repeated exercise (i.e. fitness training) improve cardiovascular capacity? And—germane to the present discussion—are the answers to any or all of these questions diff erent in children than adults? Chapter 19 considers these issues, summarizing available information in the paediatric population from the perspectives of three different exercise models: progressive treadmill or cycle ergometer exercise to exhaustion, sustained constant-load submaximal exercise (cardiovascular drift ), and isometric or resistance exercise.
Частини книг з теми "Constant load exercise"
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Osawa, Takuya, Ryotaro Kime, Masako Fujioka, Takuya Osada, Norio Murase, and Toshihito Katsumura. "O2 Saturation in the Intercostal Space During Moderate and Heavy Constant-Load Exercise." In Oxygen Transport to Tissue XXXV, 143–48. New York, NY: Springer New York, 2013. http://dx.doi.org/10.1007/978-1-4614-7411-1_20.
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Varray, Alain, Valérie Barthe, Jacques Mercier, Pierre Wintrebert, Bernard Albat, André Thévenet, and Christian Préfaut. "Cardiorespiratory Adaptations of Heart Transplant Patients During a Constant Work Load Exercise at the Ventilatory Threshold." In Adapted Physical Activity, 193–200. Tokyo: Springer Japan, 1994. http://dx.doi.org/10.1007/978-4-431-68272-1_31.
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Yoshida, Takayoshi, and Brian J. Whipp. "Dynamics of the Pulmonary O2 Uptake to Blood Flow Ratio $$\left( {{\rm{\dot VO}}_{\rm{2}} {\rm{/\dot Q}}} \right)$$ During and Following Constant-Load Exercise." In Advances in Experimental Medicine and Biology, 207–11. Boston, MA: Springer US, 1995. http://dx.doi.org/10.1007/978-1-4615-1933-1_39.
Повний текст джерелаТези доповідей конференцій з теми "Constant load exercise"
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Costa, M. V., L. A. Pereira, R. S. Oliveira, R. E. Pedro, T. V. Camata, Taufik Abrão, M. A. O. C. Brunetto, and L. R. Altimari. "Fourier and wavelet spectral analysis of EMG signals in maximal constant load dynamic exercise." In 2010 32nd Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC 2010). IEEE, 2010. http://dx.doi.org/10.1109/iembs.2010.5626474.
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Camata, T. V., J. L. Dantas, T. Abrão, M. A. O. C. Brunetto, A. C. Moraes, and L. R. Altimari. "Fourier and wavelet spectral analysis of EMG signals in supramaximal constant load dynamic exercise." In 2010 32nd Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC 2010). IEEE, 2010. http://dx.doi.org/10.1109/iembs.2010.5626743.
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Minville, C., F. Maltais, and D. Saey. "Dynamic Hyperinflation in Patients with Chronic Obstructive Pulmonary Disease: Comparison of Incremental and Constant Load Cycle Exercise Tests." In American Thoracic Society 2009 International Conference, May 15-20, 2009 • San Diego, California. American Thoracic Society, 2009. http://dx.doi.org/10.1164/ajrccm-conference.2009.179.1_meetingabstracts.a1553.
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Kanezaki, Masashi. "Olfactory stimulation of TRPM8 agonist lessen the perception of dyspnea induced by constant load exercise in never-smokers." In Annual Congress 2015. European Respiratory Society, 2015. http://dx.doi.org/10.1183/13993003.congress-2015.pa3719.
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Maximiano, António, Guilherme Vaz, and Jule Scharnke. "CFD Verification and Validation Study for a Captive Bullet Entry in Calm Water." In ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/omae2017-61666.
Повний текст джерелаАнотація:
As a step towards complex impact loads cases, e.g. lifeboat drop tests or ship/platform slamming in waves, a verification and validation (V&V) study is carried out with an open-usage community based CFD code ReFRESCO for a simple impact load test case: a captive axisymmetric generic lifeboat shape (bullet) that penetrates the water surface at a constant velocity and angle of attack. The quantities of interest are the body fixed longitudinal force FX, vertical force FZ, and pitch moment MYY. The influence of the iterative convergence level, domain size and free surface modelling are investigated. Seven different grids and four time steps were used to assess the grid and time step sensitivity, in a total of 28 calculations. For the tested grids and time steps it was found that the results are more sensitive to the grid resolution than to the time step. The pressure distribution on the hull is correlated with the trends observed in the loads, and the relation between between relative and static pressure is found to be important for the calculated loads. An experimental test campaign was previously carried out by MARIN, and its results are used to validate the simulations performed. A very good match between experiments and simulations is found. A V&V study is performed for the quantities of interest at nine different time instants covering the impact phase. The numerical uncertainties are obtained from a solution verification procedure [1]. The experimental uncertainties are estimated, and a validation exercise carried out according to the ASME standards [2]. The outcome of the validation exercise is an estimated 95 % confidence interval for the modelling error, δM. For FX the modelling error is below 15 N, for 8 out of 9 time instants. For FZ the modelling error is below 14 N, except at the time instants where, due to vibrations in the experimental setup, a larger value (up to 23 N) is found. For MYY the modelling error is under 5N m. These results provide confidence in ReFRESCO for the simulation of free surface impact flows.
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Mneimneh, Farah, Nesreen Ghaddar, Kamel Ghali, Charbel Moussalem, and Ibrahim Omeis. "A Comparative Study on the Effectiveness of Evaporative and Phase Change Material Cooling Vests for People With Paraplegia." In ASME 2021 Heat Transfer Summer Conference collocated with the ASME 2021 15th International Conference on Energy Sustainability. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/ht2021-60491.
Повний текст джерелаАнотація:
Abstract Personal cooling vests to alleviate thermal strain in persons with thoracic spinal cord injury (SCI), named paraplegia, were tested. Mainly, phase change material (PCM) cooling vests were the most frequent type applied at different exercises and ambient conditions. Published results of PCM cooling vests indicated its significant effect in reducing body core temperature for persons having more than 50% of their trunk skin as sensate. Nevertheless, preferences of persons with SCI obtained from subjective voting during experimental studies revealed that the use of PCM cooling vests caused additional burden weight on the body and sometimes restricted the movement. It is of interest to investigate the effect of an alternative personal evaporative cooling vest (ECV), characterized by light weight and practical use without hindering body movement of persons with SCI. In this study, it is aimed to compare the effect of ECV on the physiological and psychological responses of persons with SCI compared to that of PCM cooling vests under the same ambient conditions and metabolic rates. The research methodology included human subject experiments for persons with mid-thoracic (T4-T8) and low-thoracic (T9-T12) injury where the sensate skin of the trunk is at least 50% of its area. Thirteen participants were recruited to perform an arm-crank exercise at a constant load of 30 W for 30-min while using ECV inside a controlled climatic chamber of hot conditions (30°C, 4 0% RH). Measurements of body core and skin temperatures as well as thermal comfort and sensation, perceived exertion and skin wettedness were done. Furthermore, Multi-way ANOVA test was conducted to analyse the results of three tests: no vest (NV), with ECV, and with PCM. Findings of mid- and low-thoracic groups showed similar effectiveness of ECV compared to PCM cooling vest in reducing core temperature, yet the change in perceived exertion was better with the use of ECV due to its light weight.
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Schneider, Michael, Jens Dickhoff, Karsten Kusterer, Wilfried Visser, Eike Stumpf, Jan-Philipp Hofmann, and Dieter Bohn. "Development of a Gas Turbine Concept for Electric Power Generation in a Commercial Hybrid Electric Aircraft." In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-92065.
Повний текст джерелаАнотація:
Abstract Civil aviation is growing 4.7% per annum. Alternative propulsion systems are necessary to reduce emissions causing global warming. The electrification of aircraft propulsion systems has the potential to use renewable energy and reduce the environmental footprint of aviation. At present, full electric flight appears to be feasible for small aircraft only, due to the power density of batteries which is approximately 45-times lower than that of kerosene. Hybrid electric concepts may present a bridging technology towards more electrified aviation for short/mid-range aircraft. The hybrid concept combines the benefits of electrical power with conventional turboshaft engine technology. Within the framework of the ‘HyFly’ project (supported by the German Luftfahrtforschungsprogramm LuFo V-3), a hybrid electric concept for a short/mid-range 19 PAX aircraft is studied. In this paper the results of a preliminary design exercise of the gas turbine used in this concept is presented. Conventional aircraft gas turbines deliver maximum power only at take-off for a short period of time. At this power setting temperature and stress levels are at the extreme and dominate overall engine life consumption. In the HyFly concept, the gas turbine inlet temperature is kept constant during the entire flight. The engine is not driven into the extreme take-off power setting, resulting in a significant increase of engine life. The constant power setting also offers the opportunity to optimize efficiency especially around the base load point. For take-off and an emergency power rating, extra power is provided by batteries. In this paper, a survey of existing engine technology is presented considering suitability for the concept. The impact of improvement of component efficiencies, increase in cycle pressure ratio and turbine inlet temperature, relative to the state-of-the-art, is analyzed using a B&B-AGEMA in-house gas turbine simulation tool. In addition, a weight model is presented for preliminary estimation of engine mass. Finally, requirements for the individual gas turbine sub-component design and performance are defined. This will build the basis for further component design.
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Szolwinski, Matthew P., G. Harish, and Thomas N. Farris. "Comparison of Fretting Fatigue Crack Nucleation Experiments to Multiaxial Fatigue Theory Life Predictions." In ASME 1997 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/imece1997-0745.
Повний текст джерелаАнотація:
Abstract Fretting is associated with microslip at the interface of contacts experiencing oscillatory loads. One consequence of fretting is the formation and subsequent growth of cracks at the edge of contact, a phenomenon known as fretting fatigue. Fretting fatigue is an important high cycle fatigue failure mechanism in aircraft structural lap joints and turbine blade/disk contacts. A well-characterized, integrated fretting test system has been developed in which both normal and cyclic tangential fretting loads are applied and monitored in conjunction with a bulk load on the specimen. The experimental data includes histories of the three applied forces and a detailed record of the evolution of interfacial friction coefficient, as driven by the surface microslip. The experimental system has been exercised to observe fretting crack nucleation and growth under a wide range of loading conditions in the context of a statistically-designed test matrix. An extensive multiaxial fatigue analysis based on the stress-strain cycle experienced by each point of the bodies subjected to the fretting loads reveals that the critical location for crack formation is the trailing edge of contact, consistent with observations made in the laboratory. The resulting stress-strain cycles are coupled with strain-life theory and literature values of uniaxial fatigue constants to predict fretting fatigue crack nucleation. The data collected for 2024-T351 aluminum alloy correlates very well with this prediction.
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Swan, Colby C., and Hyung-Joo Kim. "Multi-Scale Micro-Mechanical Poroelastic Modeling of Fluid Flow in Cortical Bone." In ASME 2004 International Mechanical Engineering Congress and Exposition. ASMEDC, 2004. http://dx.doi.org/10.1115/imece2004-61002.
Повний текст джерелаАнотація:
To explore the potential role that load-induced fluid flow plays as a mechano-transduction mechanism in bone adaptation, a lacunar-canalicular scale bone poroelasticity model is developed and exercised. The model uses micromechanics to homogenize the pericanalicular bone matrix, a system of straight circular cylinders in the bone matrix through which bone fluids can flow, as a locally anisotropic poroelastic medium. In this work, a simplified two-dimensional model of a periodic array of lacunae and their surrounding systems of canaliculi is developed and exercised to quantify local fluid flow characteristics in the vicinity of a single lacuna. When the cortical bone model is loaded, microscale stress and strain concentrations occur in the vicinity of individual lacunae and give rise to microscale spatial variations in the pore fluid pressure field. Consequently, loading of cortical bone can induce fluid flow in the canaliculi and exchange of fluid between canaliculi and lacunae. For realistic bone morphology parameters, and a range of loading frequencies, fluid pressures and fluid-solid shear stresses in the canalicular bone are computed and the associated energy dissipation in the models compared to that measured in physical in vitro experiments on human cortical bone. For realistic volume fractions of canaliculi, deformation-induced fluid flow is found to have a much larger characteristic time constant than deformation-induced flow in the Haversian system.
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Janosik, Lesley A., and Stephen F. Duffy. "A Viscoplastic Constitutive Theory for Monolithic Ceramics — II." In ASME 1999 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/99-gt-266.
Повний текст джерелаАнотація:
This paper, which is the second of two in a series, exercises the viscoplastic constitutive model developed by the authors in the previous article (Janosik and Duffy, 1998). The model accounts for time-dependent phenomena (e.g., creep, rate sensitivity, and stress relaxation) in monolithic ceramics. Additionally, the formulation exhibits a sensitivity to hydrostatic stress, and allows different behavior in tension and compression. Here, the constitutive equations formulated for the flow law (i.e., the Strain rate) and the evolutionary law have been incorporated into computer algorithms for predicting the multiaxial inelastic (creep) response of a given homogeneous state of stress. Numerically simulated examples illustrate the model’s ability to capture the time-dependent phenomena suggested above. For each imposed service (load) history considered, creep curves and viscoplastic flow surfaces are examined to demonstrate the model’s ability to capture the inelastic creep deformation response. No attempt is made here to assess the accuracy of the model in comparison to experiment. A quantitative assessment is reserved for a later date, after the material constants have been suitably characterized for a specific ceramic material.
Звіти організацій з теми "Constant load exercise"
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Brosh, Arieh, David Robertshaw, Yoav Aharoni, Zvi Holzer, Mario Gutman, and Amichai Arieli. Estimation of Energy Expenditure of Free Living and Growing Domesticated Ruminants by Heart Rate Measurement. United States Department of Agriculture, April 2002. http://dx.doi.org/10.32747/2002.7580685.bard.
Повний текст джерелаАнотація:
Research objectives were: 1) To study the effect of diet energy density, level of exercise, thermal conditions and reproductive state on cardiovascular function as it relates to oxygen (O2) mobilization. 2) To validate the use of heart rate (HR) to predict energy expenditure (EE) of ruminants, by measuring and calculating the energy balance components at different productive and reproductive states. 3) To validate the use of HR to identify changes in the metabolizable energy (ME) and ME intake (MEI) of grazing ruminants. Background: The development of an effective method for the measurement of EE is essential for understanding the management of both grazing and confined feedlot animals. The use of HR as a method of estimating EE in free-ranging large ruminants has been limited by the availability of suitable field monitoring equipment and by the absence of empirical understanding of the relationship between cardiac function and metabolic rate. Recent developments in microelectronics provide a good opportunity to use small HR devices to monitor free-range animals. The estimation of O2 uptake (VO2) of animals from their HR has to be based upon a consistent relationship between HR and VO2. The question as to whether, or to what extent, feeding level, environmental conditions and reproductive state affect such a relationship is still unanswered. Studies on the basic physiology of O2 mobilization (in USA) and field and feedlot-based investigations (in Israel) covered a , variety of conditions in order to investigate the possibilities of using HR to estimate EE. In USA the physiological studies conducted using animals with implanted flow probes, show that: I) although stroke volume decreases during intense exercise, VO2 per one heart beat per kgBW0.75 (O2 Pulse, O2P) actually increases and measurement of EE by HR and constant O2P may underestimate VO2unless the slope of the regression relating to heart rate and VO2 is also determined, 2) alterations in VO2 associated with the level of feeding and the effects of feeding itself have no effect on O2P, 3) both pregnancy and lactation may increase blood volume, especially lactation; but they have no effect on O2P, 4) ambient temperature in the range of 15 to 25°C in the resting animal has no effect on O2P, and 5) severe heat stress, induced by exercise, elevates body temperature to a sufficient extent that 14% of cardiac output may be required to dissipate the heat generated by exercise rather than for O2 transport. However, this is an unusual situation and its affect on EE estimation in a freely grazing animal, especially when heart rate is monitored over several days, is minor. In Israel three experiments were carried out in the hot summer to define changes in O2P attributable to changes in the time of day or In the heat load. The animals used were lambs and young calves in the growing phase and highly yielding dairy cows. In the growing animals the time of day, or the heat load, affected HR and VO2, but had no effect on O2P. On the other hand, the O2P measured in lactating cows was affected by the heat load; this is similar to the finding in the USA study of sheep. Energy balance trials were conducted to compare MEI recovery by the retained energy (RE) and by EE as measured by HR and O2P. The trial hypothesis was that if HR reliably estimated EE, the MEI proportion to (EE+RE) would not be significantly different from 1.0. Beef cows along a year of their reproductive cycle and growing lambs were used. The MEI recoveries of both trials were not significantly different from 1.0, 1.062+0.026 and 0.957+0.024 respectively. The cows' reproductive state did not affect the O2P, which is similar to the finding in the USA study. Pasture ME content and animal variables such as HR, VO2, O2P and EE of cows on grazing and in confinement were measured throughout three years under twenty-nine combinations of herbage quality and cows' reproductive state. In twelve grazing states, individual faecal output (FO) was measured and MEI was calculated. Regression analyses of the EE and RE dependent on MEI were highly significant (P<0.001). The predicted values of EE at zero intake (78 kcal/kgBW0.75), were similar to those estimated by NRC (1984). The EE at maintenance condition of the grazing cows (EE=MEI, 125 kcal/kgBW0.75) which are in the range of 96.1 to 125.5 as presented by NRC (1996 pp 6-7) for beef cows. Average daily HR and EE were significantly increased by lactation, P<0.001 and P<0.02 respectively. Grazing ME significantly increased HR and EE, P<0.001 and P<0.00l respectively. In contradiction to the finding in confined ewes and cows, the O2P of the grazing cows was significantly affected by the combined treatments (P<0.00l ); this effect was significantly related to the diet ME (P<0.00l ) and consequently to the MEI (P<0.03). Grazing significantly increased O2P compared to confinement. So, when EE of grazing animals during a certain season of the year is estimated using the HR method, the O2P must be re measured whenever grazing ME changes. A high correlation (R2>0.96) of group average EE and of HR dependency on MEI was also found in confined cows, which were fed six different diets and in growing lambs on three diets. In conclusion, the studies conducted in USA and in Israel investigated in depth the physiological mechanisms of cardiovascular and O2 mobilization, and went on to investigate a wide variety of ruminant species, ages, reproductive states, diets ME, time of intake and time of day, and compared these variables under grazing and confinement conditions. From these combined studies we can conclude that EE can be determined from HR measurements during several days, multiplied by O2P measured over a short period of time (10-15 min). The study showed that RE could be determined during the growing phase without slaughtering. In the near future the development microelectronic devices will enable wide use of the HR method to determine EE and energy balance. It will open new scopes of physiological and agricultural research with minimizes strain on animals. The method also has a high potential as a tool for herd management.
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Avellán, Leopoldo, Zulima Leal Calderon, and Giulia Lotti. Why do some Development Projects Disburse Funds Faster than Others. Inter-American Development Bank, November 2021. http://dx.doi.org/10.18235/0003839.
Повний текст джерелаАнотація:
The timely disbursement of funds is a necessary condition for the success of international development projects. Disbursements track the progress of projects in completing the products that ultimately will deliver the projects desired outcomes. Moreover, in a world with pressing needs for external financing, project disbursements are an important source of external liquidity for recipient countries. However, some projects start disbursing faster than others and at relatively larger amounts. Hence learning why some projects disburse faster than others is important to understand not only which projects are more likely to achieve development outcomes sooner, but also to assess their value as providers of external liquidity in times of distress. As it has become evident over the past year with the COVID-19 pandemic, multilateral lending has played a crucial role in helping emerging countries face the larger financing needs originated by the crisis. In 2020, Inter-American Development Bank (IDB) disbursements increased 49% over 2019, reaching $13.4 billion, more than doubling the baseline disbursement projection. This paper assesses which observable characteristics of investment loans offered by the IDB are associated with faster disbursements. The results indicate substantial heterogeneity across countries, sectors, and loan modalities. All else constant, results-based loans and loans in the social sector are more likely to disburse within 2 years after being approved. Projects in countries where it takes longer to meet at least some of the clauses to start disbursing are less likely to start disbursing 2 years after approval. Projects that are expected to have longer execution times disburse at slower speeds within 24 months after approval. Overall, country factors seem to play a more relevant role than sectorial factors in explaining the probability that a project will disburse funds quickly. These and other findings in the paper can inform future programming exercises and help optimize the disbursement processes.