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Vianna, Jeferson M., Francisco Z. Werneck, Emerson F. Coelho, Vinicius O. Damasceno y Victor M. Reis. "Oxygen Uptake and Heart Rate Kinetics after Different Types of Resistance Exercise". Journal of Human Kinetics 42, n.º 1 (1 de octubre de 2014): 235–44. http://dx.doi.org/10.2478/hukin-2014-0077.
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Abstract Oxygen uptake (VO2) and heart rate (HR) kinetics after exercise are important indicators of fitness and cardiovascular health. However, these variables have been little investigated in resistance exercise (RE). The current study compared post-exercise kinetics of VO2 and the HR among different types of REs. The study included 14 males (age: 26.5±5.4 years, body mass: 80.1±11.4 kg, body height: 1.77±0.07 m, fat content: 11.3±4.6%) with RE experience. Dynamic muscle strength was measured using one repetition maximum (1RM) with regard to the half-squat, bench press, pull-down, and triceps pushdown exercises. The participants performed a maximum number of repetitions at 80% of 1RM for each exercise, separated by a recovery period of 60 minutes. VO2 was measured using ergospirometry. VO2 and HR kinetics were assessed using the time constant of the recovery curves, and excess oxygen consumption (EPOC) was calculated afterward. Significant differences were not observed across the exercises with regard to VO2 kinetics. However, the half-squat exercise elicited a greater EPOC than the bench press and triceps pushdown exercises (p<.05). HR kinetics was slower for the half-squat exercise than for the other exercises (p<.05). These findings confirm that the type of RE influences both the cardiac autonomic response post-exercise and EPOC, but not VO2 kinetics
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McCreary, C. R., P. D. Chilibeck, G. D. Marsh, D. H. Paterson, D. A. Cunningham y R. T. Thompson. "Kinetics of pulmonary oxygen uptake and muscle phosphates during moderate-intensity calf exercise". Journal of Applied Physiology 81, n.º 3 (1 de septiembre de 1996): 1331–38. http://dx.doi.org/10.1152/jappl.1996.81.3.1331.
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The purpose of this study is to directly compare the dynamic responses of phosphocreatine (PCr) and P(i) to those oxygen uptake (VO2) measured at the lung during transitions to and from moderate-intensity exercise. Changes in PCr and P(i) were measured by 31P-nuclear magnetic resonance spectroscopy, and changes in VO2 were measured breath by breath by mass spectroscopy during transitions to and from moderate-intensity square-wave ankle plantar flexion exercise in 11 subjects (7 men and 4 women; mean age 27 yr). Three repeated transitions were averaged for improvement in signal-to-noise ratio of phosphate data, and 12 transitions were averaged for VO2 measurements. Averaged transitions were fit with a monoexponential curve for determination of the time constant (tau) of the responses. Mean tau values for on transients of PCr, P(i), and phrase 2 VO2 were 47.0, 57.7, and 44.5 s, respectively, whereas means tau values for off transients were 44.8, 42.1, and 33.4 s, respectively. There were no significant differences between tau values for phosphate- and VO2-measured transients or on and off transients. The similarity of on and off kinetics supports linear first-order respiratory control models. Measurement of phase 2 pulmonary VO2 kinetics to and from moderate-intensity small-muscle-mass exercise reflect muscle phosphate kinetics (and muscle oxygen consumption).
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Reddy, Madhuri G., Stephanie A. Pelligra, Alexis A. Thompson y Robert I. Liem. "Decreased Fitness Is Associated with Abnormal Cardiopulmonary Response to Maximal Exercise in Pediatric Sickle Cell Anemia." Blood 120, n.º 21 (16 de noviembre de 2012): 2109. http://dx.doi.org/10.1182/blood.v120.21.2109.2109.
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Abstract Abstract 2109 The clinical burden of sickle cell anemia (SCA) has a tremendous impact on physical functioning, including cardiopulmonary fitness, among affected individuals. However, the physiologic basis of exercise limitation remains poorly understood in this population. The objective of our study was to characterize the cardiopulmonary response to maximal exercise and to delineate the physiologic mechanisms responsible for decreased fitness among children and young adults with SCA. Methods: We prospectively performed maximal cardiopulmonary exercise testing (CPET) on 60 subjects with SCA (hemoglobin SS or S/β0 thalassemia) and 20 controls without SCA or sickle cell trait matched for race and gender. CPET was completed using a graded, symptom-limited cycle ergometry protocol with breath-by-breath, gas exchange analysis and pre/post spirometry. The primary outcome of fitness was defined by weight-adjusted, peak oxygen consumption (peak VO2). Slopes for determining oxygen uptake kinetics and ventilatory efficiency were calculated using 10-second averages of data points. We used the V-slope method to determine ventilatory threshold. Bivariate comparisons of continuous data were performed using Student's t-test for independent samples (IBM, SPSS V20). We used multivariate analysis to derive a model for determining independent contributors to peak VO2 in subjects. Results: There was no difference in gender distribution among subjects and controls, but subjects were older (15.1 ± 3.44 vs. 13.2 ±2.9 years, p = 0.03) and had lower hemoglobin (8.8 ±1.3 vs. 12.8 ±1.5 g/dL, p < 0.0001). All subjects met criteria for a maximal test as defined by a respiratory exchange ratio (RER) ≥ 1.1, and in all, testing was terminated due to excessive fatigue. No major adverse events occurred during CPET in any subject. Only 1/60 (1.7%) subjects developed vaso-occlusive pain requiring hospitalization in the 2-week follow-up period after testing. Nearly all of the major indicators of CPET performance and gas exchange were adversely affected in our subjects. Compared to controls, subjects demonstrated significantly lower mean peak VO2 (26.9 ±6.9 vs. 40.6 ±8.2 mL/kg/min, p < 0.0001), even after adjustment for age and hemoglobin. Average total test time (5.6 ±1.3 vs. 7.8 ±2.2 min, p = 0.012) and peak work rate (108 ±37 vs. 151 ±57 watts, p = 0.011) were similarly reduced as was ventilatory threshold (1.01 ±0.29 vs. 1.34 ±0.34 L/min, p < 0.0001), indicating earlier transition to anaerobic metabolism during exercise. Heart rate reserve, the difference between achieved maximal and baseline heart rates, was significantly lower (99 ±14 vs. 111 ±15, p = 0.002) in subjects. Slopes calculated using minute ventilation (VE), expired CO2 (VCO2), VO2 and work rate also indicated significantly reduced ventilatory efficiency (ΔVE/ΔVCO2), oxygen delivery (ΔVO2/ΔWR) and oxygen uptake (ΔVO2/ΔVE) kinetics in subjects versus controls. To examine the physiologic contributors to peak VO2 in subjects with SCA alone, we developed a multivariate model that included age, baseline hemoglobin, heart rate reserve, maximal VE, pre-exercise forced expiratory volume in 1 second, and ventilatory threshold. This model explained 67% of the variability observed in peak VO2 in subjects, with age, maximal VE and ventilatory threshold retaining independent contributions to peak VO2 and ventilatory threshold making the largest contribution with an non-standardized β coefficient of 11.9 (SE ±3.2), p < 0.0001. Conclusions: Maximal CPET is safe in children and young adults with SCA, suggesting that acute exercise challenge is well tolerated in this population even at high levels of exercise intensity and physical exertion. When compared to their peers, children and young adults with SCA demonstrate significantly reduced fitness levels. Exercise limitation in SCA may be attributed to complex derangements in the cardiopulmonary and metabolic responses to exercise that are independent of anemia. Our findings highlight the need to develop targeted exercise training strategies aimed at improving fitness in this population and to assess its impact on overall disease severity. Disclosures: No relevant conflicts of interest to declare.
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Jones, M. T., R. E. Rawson y D. Robertshaw. "Determination of maximal oxygen consumption in exercising pregnant sheep". Journal of Applied Physiology 73, n.º 1 (1 de julio de 1992): 234–39. http://dx.doi.org/10.1152/jappl.1992.73.1.234.
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Previous work with pregnant ewes has shown that acute bouts of exercise may cause changes in plasma hormone concentrations, blood flow distribution, and maternal and fetal temperatures. However, most of these studies do not quantify the chosen exercise intensity through measurement of oxygen consumption (VO2). Therefore the purpose of this study was to statistically model the VO2 response of pregnant sheep to treadmill (TM) exercise to determine the exercise intensities (% maximal VO2) of previous studies. Ewes with either single (n = 9) or twin (n = 5) fetuses were studied from 100 to 130 days of gestation. After 1–2 wk of TM habituation, maximal VO2 (VO2max) was determined by measurements of VO2 (open flow-through method) and blood lactate concentration. VO2 was measured as a function of TM incline (0, 3, 5, and 7 degree) and speed (0.8–3.4 m/s). VO2max averaged 57 +/- 7 (SD) ml.min-1.kg-1, and peak lactate concentration during exercise averaged 22 +/- 2 mmol/l. The relationship between VO2 (ml.min-1.kg-1) and incline (INC) and speed (SP) [VO2 = 0.70(INC) + 13.95(SP) + 1.07(INC x SP) - 1.18] was linear (r2 = 0.94). Our findings suggest that most previous research used exercise intensities less than 60% VO2max and indicate the need for further research that examines the effect of exercise during pregnancy at levels greater than 60% VO2max.
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Paterson, D. H., D. A. Cunningham, J. G. Pickering, M. A. Babcock y D. R. Boughner. "Oxygen uptake kinetics in cardiac transplant recipients". Journal of Applied Physiology 77, n.º 4 (1 de octubre de 1994): 1935–40. http://dx.doi.org/10.1152/jappl.1994.77.4.1935.
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Our purpose was to examine the gas exchange response to exercise in heart transplant (HT) patients and to characterize the O2 uptake kinetics (tau VO2) during successive square-wave on-transients from loadless cycling to moderate exercise. We hypothesized that with a slow heart rate response (and O2 transport limitation) O2 kinetics would be slowed but that with a repeated exercise initiated while the heart rate remained elevated the tau VO2 would be faster. Six male HT patients performed two ramp-function tests to determine peak O2 uptake (1.32 +/- 0.23 l/min) and ventilation threshold (1.02 +/- 0.16 l/min). Patients subsequently completed two repeats of a square-wave forcing function and repeated this on 2 days. Alveolar gas exchange was measured breath by breath. A monoexponential fit of signal-averaged data of the first exercise on-transient (between days) yielded a significantly slower tau VO2 in HT subjects than in healthy men (mean age 47 yr; n = 8) (77 +/- 26 vs. 45 +/- 4 s). With successive exercise (2nd transition) initiated while HR remained elevated the tau VO2 of HT patients was 46 +/- 17 s. The faster O2 kinetics of the second transition suggests that O2 delivery was enhanced and therefore that the tau VO2 may reflect bioenergetic processes controlling the rate of oxidative metabolism.
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Coast, J. R., S. A. Rasmussen, K. M. Krause, J. A. O'Kroy, R. A. Loy y J. Rhodes. "Ventilatory work and oxygen consumption during exercise and hyperventilation". Journal of Applied Physiology 74, n.º 2 (1 de febrero de 1993): 793–98. http://dx.doi.org/10.1152/jappl.1993.74.2.793.
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The work of breathing (WB), and thus the energy requirement of the respiratory muscles, is increased any time minute ventilation (VE) is elevated, by either exercise or voluntary hyperventilation. Respiratory muscle O2 consumption (VRMO2) in humans has generally been estimated by having subjects breathe at a level comparable to that during exercise while the change in O2 consumption (VO2) is measured. The difference between VO2 at rest and during hyperventilation is attributed to the respiratory muscles and is assumed to be similar to VRMO2 during exercise at the same VE. However, it has been suggested that WB differs between exercise and hyperventilation and that WB during exercise is lower than during hyperventilation at the same VE. In this study we measured WB during exercise and hyperventilation and from these measurements estimated VRMO2. WB, VE, and VO2 were measured in five male subjects during rest and during exercise or hyperventilation at levels of VE ranging from 30 to 130 l/min. VE/WB relationship was determined for both hyperventilation and exercise. Multiple regression analysis showed that the shape of the two curves was different (P < 0.0001), with WB at high levels of VE being < or = 25% higher in hyperventilation than in exercise. In a second study in which frequency, tidal volume, and duty cycle were controlled as well as VE, there was no difference in WB between exercise and hyperventilation. VO2 was significantly correlated with WB, and the estimated VRMO2 did not increase as a fraction of total VO2 as exercise intensity rose.(ABSTRACT TRUNCATED AT 250 WORDS)
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Barstow, T. J., S. Buchthal, S. Zanconato y D. M. Cooper. "Muscle energetics and pulmonary oxygen uptake kinetics during moderate exercise". Journal of Applied Physiology 77, n.º 4 (1 de octubre de 1994): 1742–49. http://dx.doi.org/10.1152/jappl.1994.77.4.1742.
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The present study tested whether, during moderate exercise, 1) the dynamic responses of ADP and changes in free energy of ATP hydrolysis (delta GATP) were similar to those of phosphocreatine [PCr; as would be expected for a simple controller of muscle respiration (QO2)] and 2) the rise in pulmonary O2 uptake (VO2) during cycle exercise would reflect the rise in muscle QO2 indicated by the calf PCr kinetics. The responses of PCr, Pi, ADP, and delta GATP were measured from the calf in five subjects during supine treadle exercise using 31P-magnetic resonance spectroscopy and compared with those for VO2, measured breath by breath during upright cycle exercise. The time constants for delta GATP [24.2 +/- 14.2 (SE) s] were not significantly different from those for PCr (26.3 +/- 17.3 s) and Pi (30.7 +/- 22.5 s) (P > 0.05). The time constants for phase 2 VO2 (29.9 +/- 16.8 s) were also similar to those of PCr. In contrast, the dynamics of ADP were distorted from those of PCr due to dynamic changes in pH. These results are consistent with mechanisms of respiratory control that feature substrate control by PCr or thermodynamic control through changes in delta GATP. However, these results are not consistent with substrate control by ADP in a simple fashion. Furthermore, the similarity of time constants for phase 2 VO2 and muscle PCr suggests that phase 2 VO2 kinetics reflect those of muscle QO2 in healthy subjects during moderate exercise.
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Cooper, D. M., C. Berry, N. Lamarra y K. Wasserman. "Kinetics of oxygen uptake and heart rate at onset of exercise in children". Journal of Applied Physiology 59, n.º 1 (1 de julio de 1985): 211–17. http://dx.doi.org/10.1152/jappl.1985.59.1.211.
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Requirements for cellular homeostasis appear to be unchanged between childhood and maturity. We hypothesized, therefore, that the kinetics of O2 uptake (VO2) in the transition from rest to exercise would be the same in young children as in teenagers. To test this, VO2 and heart rate kinetics from rest to constant work rate (75% of the subject's anaerobic threshold) in 10 children (5 boys and 5 girls) aged 7–10 yr were compared with values found in 10 teenagers (5 boys and 5 girls) aged 15–18 yr. Gas exchange was measured breath to breath, and phases I and II of the transition and phase III (steady-state exercise) were evaluated from multiple transitions in each child. Phase I (the VO2 at 20 s of exercise expressed as percent rest-to-steady-state exercise VO2) was not significantly correlated with age or weight [mean value 42.5 +/- 8.9% (SD)] nor was the phase II time constant for VO2 [mean 27.3 +/- 4.7 (SD) s]. The older girls had significantly slower kinetics than the other children but were also found to be less fit. When the teenagers exercised at work rates well below 75% of their anaerobic threshold, phase I VO2 represented a higher proportion of the overall response, but the phase II kinetics were unchanged. The temporal coupling between the cellular production of mechanical work at the onset of exercise and the uptake of environmental O2 appears to be controlled throughout growth in children.
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Barstow, T. J. y P. A. Mole. "Linear and nonlinear characteristics of oxygen uptake kinetics during heavy exercise". Journal of Applied Physiology 71, n.º 6 (1 de diciembre de 1991): 2099–106. http://dx.doi.org/10.1152/jappl.1991.71.6.2099.
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We assessed the linearity of oxygen uptake (VO2) kinetics for several work intensities in four trained cyclists. VO2 was measured breath by breath during transitions from 33 W (baseline) to work rates requiring 38, 54, 85, and 100% of maximal aerobic capacity (VO2max). Each subject repeated each work rate four times over 8 test days. In every case, three phases (phases 1, 2, and 3) of the VO2 response could be identified. VO2 during phase 2 was fit by one of two models: model 1, a double exponential where both terms begin together close to the start of phase 2, and model 2, a double exponential where each of the exponential terms begins independently with separate time delays. VO2 rose linearly for the two lower work rates (slope 11 ml.min-1 W-1) but increased to a greater asymptote for the two heavier work rates. In all four subjects, for the two lighter work rates the double-exponential regression reduced to a single value for the time constant (average across subjects 16.1 +/- 7.7 s), indicating a truly monoexponential response. In addition, one of the responses to the heaviest work rate was monoexponential. For the remaining seven biexponential responses to the two heaviest work rates, model 2 produced a significantly better fit to the responses (P less than 0.05), with a mean time delay for the slow component of 105 +/- 46 s.(ABSTRACT TRUNCATED AT 250 WORDS)
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Zanconato, S., D. M. Cooper y Y. Armon. "Oxygen cost and oxygen uptake dynamics and recovery with 1 min of exercise in children and adults". Journal of Applied Physiology 71, n.º 3 (1 de septiembre de 1991): 993–98. http://dx.doi.org/10.1152/jappl.1991.71.3.993.
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To test the hypothesis that O2 uptake (VO2) dynamics are different in adults and children, we examined the response to and recovery from short bursts of exercise in 10 children (7–11 yr) and 13 adults (26–42 yr). Each subject performed 1 min of cycle ergometer exercise at 50% of the anaerobic threshold (AT), 80% AT, and 50% of the difference between the AT and the maximal O2 uptake (VO2max) and 100 and 125% VO2max. Gas exchange was measured breath by breath. The cumulative O2 cost [the integral of VO2 (over baseline) through exercise and 10 min of recovery (ml O2/J)] was independent of work intensity in both children and adults. In above-AT exercise, O2 cost was significantly higher in children [0.25 +/- 0.05 (SD) ml/J] than in adults (0.18 +/- 0.02 ml/J, P less than 0.01). Recovery dynamics of VO2 in above-AT exercise [measured as the time constant (tau VO2) of the best-fit single exponential] were independent of work intensity in children and adults. Recovery tau VO2 was the same in both groups except at 125% VO2max, where tau VO2 was significantly smaller in children (35.5 +/- 5.9 s) than in adults (46.3 +/- 4 s, P less than 0.001). VO2 responses (i.e., time course, kinetics) to short bursts of exercise are, surprisingly, largely independent of work rate (power output) in both adults and children. In children, certain features of the VO2 response to high-intensity exercise are, to a small but significant degree, different from those in adults, indicating an underlying process of physiological maturation.
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Haidet, G. C. "Dynamic exercise in senescent beagles: oxygen consumption and hemodynamic responses". American Journal of Physiology-Heart and Circulatory Physiology 257, n.º 5 (1 de noviembre de 1989): H1428—H1437. http://dx.doi.org/10.1152/ajpheart.1989.257.5.h1428.
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Seven senescent beagles and seven younger mature beagles were studied at rest, as well as during maximal and submaximal exercise on a motor-driven treadmill. Maximal exercise capacity was significantly (P less than 0.05) reduced, and maximal total body O2 consumption (VO2 max) was 31% lower in senescent beagles. VO2 was also significantly reduced in old dogs, when directly compared at the same relative workloads in old and younger mature dogs. However, VO2 was very similar in both groups during each of the absolute levels of directly comparable exercise. The observed age-related reduction in VO2 max was associated with a significant 25% reduction in maximal cardiac output (CO) in senescent beagles, and with an 11% reduction in maximal arteriovenous O2 difference. CO was also significantly reduced in old dogs at the same relative levels of submaximal exercise evaluated. Combined effects of reductions in stroke volume and in heart rate both contributed to the observed reductions in CO observed in senescent dogs during maximal exercise, as well as during relative levels of submaximal exercise. However, CO responses at each absolute level of submaximal exercise were similar in senescent and younger mature beagles, and the relationship between CO and VO2 was also similar in both groups. Increases in stroke volume significantly contributed to observed increases in CO beginning at the same relative level of exercise in both old and young dogs. Results of this study demonstrate that significant age-related changes in VO2max and in other associated hemodynamic parameters occur during maximal exercise. Many of these changes are also apparent when relative levels of submaximal exercise are directly compared in senescent and in younger mature beagles. However, most hemodynamic responses during absolute levels of exercise are similar in both groups, unless these parameters reflect the relative workload performed, indicating that these responses are appropriate for each absolute level of work that can be performed in the senescent dogs.
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Poole, D. C., W. Schaffartzik, D. R. Knight, T. Derion, B. Kennedy, H. J. Guy, R. Prediletto y P. D. Wagner. "Contribution of excising legs to the slow component of oxygen uptake kinetics in humans". Journal of Applied Physiology 71, n.º 4 (1 de octubre de 1991): 1245–60. http://dx.doi.org/10.1152/jappl.1991.71.4.1245.
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Rates of performing work that engender a sustained lactic acidosis evidence a slow component of pulmonary O2 uptake (VO2) kinetics. This slow component delays or obviates the attainment of a stable VO2 and elevates VO2 above that predicted from considerations of work rate. The mechanistic basis for this slow component is obscure. Competing hypotheses depend on its origin within either the exercising limbs or the rest of the body. To resolve this question, six healthy males performed light nonfatiguing [approximately 50% maximal O2 uptake (VO2max)] and severe fatiguing cycle ergometry, and simultaneous measurements were made of pulmonary VO2 and leg blood flow by thermodilution. Blood was sampled 1) from the femoral vein for O2 and CO2 pressures and O2 content, lactate, pH, epinephrine, norepinephrine, and potassium concentrations, and temperature and 2) from the radial artery for O2 and CO2 pressures, O2 content, lactate concentration, and pH. Two-leg VO2 was thus calculated as the product of 2 X blood flow and arteriovenous O2 difference. Blood pressure was measured in the radial artery and femoral vein. During light exercise, both pulmonary and leg VO2 remained stable from minute 3 to the end of exercise (26 min). In contrast, during severe exercise [295 +/- 10 (SE) W], pulmonary VO2 increased 19.8 +/- 2.4% (P less than 0.05) from minute 3 to fatigue (occurring on average at 20.8 min). Over the same period, leg VO2 increased by 24.2 +/- 5.2% (P less than 0.05). Increases of leg and pulmonary VO2 were highly correlated (r = 0.911), and augmented leg VO2 could account for 86% of the rise in pulmonary VO2.(ABSTRACT TRUNCATED AT 250 WORDS)
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Stathokostas, Liza, John M. Kowalchuk, Robert J. Petrella y Donald H. Paterson. "Moderate and heavy oxygen uptake kinetics in postmenopausal women". Applied Physiology, Nutrition, and Metabolism 34, n.º 6 (diciembre de 2009): 1065–72. http://dx.doi.org/10.1139/h09-107.
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The lack of estrogen in postmenopausal women not using hormone replacement therapy (HRT), compared with those using HRT, may reduce submaximal blood flow during exercise and result in an oxygen delivery limitation constraining oxygen uptake (VO2) kinetics. The adaptation of pulmonary VO2 (VO2p) during the transition to exercise in older women was examined in this study. Thirty-one healthy postmenopausal women (mean age, 61 ± 6 years), 15 not using HRT and 16 using HRT, performed repeated exercise transitions (6 min) on a cycle, to work rates corresponding to 80% of estimated ventilatory threshold (moderate-intensity exercise) and to Δ50 (heavy-intensity exercise). There was no difference in moderate-intensity τVO2p between non-HRT (40 ± 9 s) and HRT (41 ± 9 s) women. Similarly, there was no difference in heavy-intensity τVO2p between non-HRT (44 ± 8 s) and HRT (45 ± 8 s) women. Thus, HRT did not affect the slowing of VO2 kinetics of older women.
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De Blasi, R. A., M. Ferrari, A. Natali, G. Conti, A. Mega y A. Gasparetto. "Noninvasive measurement of forearm blood flow and oxygen consumption by near-infrared spectroscopy". Journal of Applied Physiology 76, n.º 3 (1 de marzo de 1994): 1388–93. http://dx.doi.org/10.1152/jappl.1994.76.3.1388.
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We applied near-infrared spectroscopy (NIRS) for the simultaneous measurement of forearm blood flow (FBF) and oxygen consumption (VO2) in the human by inducing a 50-mmHg venous occlusion. Eleven healthy subjects were studied both at rest and after hand exercise during vascular occlusion. FBF was also measured by strain-gauge plethysmography. FBF measured by NIRS was 1.9 +/- 0.8 ml.100 ml-1.min-1 at rest and 8.2 +/- 2.9 ml.100 ml-1.min-1 after hand exercise. These values showed a correlation (r = 0.94) with those obtained by the plethysmography. VO2 values were 4.6 +/- 1.3 microM O2 x 100 ml-1.min-1 at rest and 24.9 +/- 11.2 microM O2 x 100 ml-1.min-1 after hand exercise. The scatter of the FBF and VO2 values showed a good correlation between the two variables (r = 0.93). The results demonstrate that NIRS provides the particular advantage of obtaining the contemporary evaluation of blood flow and VO2, allowing correlation of these two variables by a single maneuver without discomfort for the subject.
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Barstow, T. J. y P. A. Mole. "Simulation of pulmonary O2 uptake during exercise transients in humans". Journal of Applied Physiology 63, n.º 6 (1 de diciembre de 1987): 2253–61. http://dx.doi.org/10.1152/jappl.1987.63.6.2253.
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Computer simulation of blood flow and O2 consumption (QO2) of leg muscles and of blood flow through other vascular compartments was made to estimate the potential effects of circulatory adjustments to moderate leg exercise on pulmonary O2 uptake (VO2) kinetics in humans. The model revealed a biphasic rise in pulmonary VO2 after the onset of constant-load exercise. The length of the first phase represented a circulatory transit time from the contracting muscles to the lung. The duration and magnitude of rise in VO2 during phase 1 were determined solely by the rate of rise in venous return and by the venous volume separating the muscle from the lung gas exchange sites. The second phase of VO2 represented increased muscle metabolism (QO2) of exercise. With the use of a single-exponential model for muscle QO2 and physiological estimates of other model parameters, phase 2 VO2 could be well described as a first-order exponential whose time constant was within 2 s of that for muscle QO2. The use of unphysiological estimates for certain parameters led to responses for VO2 during phase 2 that were qualitatively different from QO2. It is concluded that 1) the normal response of VO2 in humans to step increases in muscle work contains two components or phases, the first determined by cardiovascular phenomena and the second primarily reflecting muscle metabolism and 2) the kinetics of VO2 during phase 2 can be used to estimate the kinetics of muscle QO2. The simulation results are consistent with previously published profiles of VO2 kinetics for square-wave transients.
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KORZENIEWSKI, Bernard y Jerzy A. ZOLADZ. "Factors determining the oxygen consumption rate (V.o2) on-kinetics in skeletal muscles". Biochemical Journal 379, n.º 3 (1 de mayo de 2004): 703–10. http://dx.doi.org/10.1042/bj20031740.
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Using a computer model of oxidative phosphorylation developed previously [Korzeniewski and Mazat (1996) Biochem. J. 319, 143–148; Korzeniewski and Zoladz (2001) Biophys. Chem. 92, 17–34], we analyse the effect of several factors on the oxygen-uptake kinetics, especially on the oxygen consumption rate (Vo2) and half-transition time t1/2, at the onset of exercise in skeletal muscles. Computer simulations demonstrate that an increase in the total creatine pool [PCr±Cr] (where Cr stands for creatine and PCr for phosphocreatine) and in glycolytic ATP supply lengthen the half-transition time, whereas increase in mitochondrial content, in parallel activation of ATP supply and ATP usage, in oxygen concentration, in proton leak, in resting energy demand, in resting cytosolic pH and in initial alkalization decrease this parameter. Theoretical studies show that a decrease in the activity of creatine kinase (CK) [displacement of this enzyme from equilibrium during on-transient (rest-to-work transition)] accelerates the first stage of the Vo2 on-transient, but slows down the second stage of this transient. It is also demonstrated that a prior exercise terminated a few minutes before the principal exercise shortens the transition time. Finally, it is shown that at a given ATP demand, and under conditions where CK works near the thermodynamic equilibrium, the half-transition time of Vo2 kinetics is determined by the amount of PCr that has to be transformed into Cr during rest-to-work transition; therefore any factor that diminishes the difference in [PCr] between rest and work at a given energy demand will accelerate the Vo2 on-kinetics. Our conclusions agree with the general idea formulated originally by Easterby [(1981) Biochem. J. 199, 155–161] that changes in metabolite concentrations determine the transition times between different steady states in metabolic systems.
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Chilibeck, P. D., D. H. Paterson, W. D. Smith y D. A. Cunningham. "Cardiorespiratory kinetics during exercise of different muscle groups and mass in old and young". Journal of Applied Physiology 81, n.º 3 (1 de septiembre de 1996): 1388–94. http://dx.doi.org/10.1152/jappl.1996.81.3.1388.
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The purpose was to compare cardiorespiratory kinetics during exercise of different muscle groups (double-leg cycling vs treadmill walking and single-leg ankle plantar flexion) in old and young subjects. Oxygen uptake (VO2) during exercise transitions was measured breath by breath, and the phase 2 portion of the response was fit by a monoexponential for determination of the time constant (tau) of VO2. Two separate studies were performed: in study 1, 12 old (age 66.7 yr) and 16 young (aged 26.3 yr) subjects were compared during cycling and ankle plantar flexion exercise, and in the study 2, five old (aged 69.6 yr) and five young (24.4 yr) subjects were compared during cycling and treadmill walking. VO2 transients during square-wave cycling exercise were significantly slower in the old compared with the young groups. In contrast, VO2 kinetics did not differ between old and young groups during plantar flexion exercise. Heart rate (HR) kinetics followed the same pattern, with tau HR being significantly slower in the old vs young groups during transitions to cycling but not to plantar flexion. In study 2 tau VO2 and tau HR during on-transients to treadmill square-wave exercise were significantly slower in the old group compared with the young group, but tau VO2 was significantly faster during treadmill exercise than during cycling in the old group. The differences with aging between the modes of exercise may be related to the muscle mass involved and the circulatory demands. On the other hand, slowed VO2 kinetics with age appear to occur in a mode (cycling) in which the muscles are not accustomed to the activity, whereas in a mode of normal activity (walking) and with the muscle groups (plantar flexors) accustomed to the activity, VO2 kinetics are not slowed to the same degree with age.
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Molina, Renato y Benedito Sérgio Denadai. "Muscle damage slows oxygen uptake kinetics during moderate-intensity exercise performed at high pedal rate". Applied Physiology, Nutrition, and Metabolism 36, n.º 6 (diciembre de 2011): 848–55. http://dx.doi.org/10.1139/h11-109.
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This study aimed to investigate the dependence of oxygen uptake (VO2) kinetics on pedal cadence during moderate-intensity exercise following exercise-induced muscle damage (EIMD). Twenty untrained males were randomly assigned to a 50 revolution per minute (rpm) (age, 23.3 ± 1.8 years; VO2max, 38.9 ± 2.8 mL·kg–1·min–1) or 100 rpm group (age, 24.4 ± 3.5 years, VO2max, 42.9 ± 4.3 mL·kg–1·min–1). Participants completed “step” tests to moderate-intensity exercise from an unloaded baseline on a cycle ergometer before (baseline) and at 24 and 48 h after muscle-damaging exercise (10 sets of 10 eccentric contractions performed on an isokinetic dynamometer with a 2-min rest between each set). Pedal cadence was kept constant throughout each cycling trial (50 or 100 rpm). There were no changes in phase II pulmonary VO2 kinetics following EIMD for the 50 rpm group (baseline = 35 ± 4 s; 24 h = 35 ± 7 s; and 48 h = 36 ± 9 s). However, the phase II VO2 was significantly greater at 24 h (59 ± 27 s) compared with baseline (39 ± 6 s) and 48 h (40 ± 9 s) for the 100 rpm group. It is concluded that the effects of EIMD on phase II VO2 kinetics during moderate-intensity cycling exercise is dependent on pedal cadence. The slower VO2 kinetics after muscle damage suggests that type II fibers are involved during transition to moderate-intensity exercise at high pedal cadence.
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Chilibeck, Philip D., Donald H. Paterson, Robert J. Petrella y David A. Cunningham. "The Influence of Age and Cardiorespiratory Fitness on Kinetics of Oxygen Uptake". Canadian Journal of Applied Physiology 21, n.º 3 (1 de junio de 1996): 185–96. http://dx.doi.org/10.1139/h96-015.
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The purpose of this study was to determine the influences of ageing and cardiorespiratory fitness on kinetics of VO2 during the transition to exercise of moderate intensity. Subjects performed three transitions to and from a 6-minute square wave constant load, at an intensity corresponding to 90% of ventilatory threshold (VET), to determine VO2 kinetics. The young group had a significantly faster time constant of VO2 (τVO2). τVO2 was significantly correlated with VO2max for both young and old groups; however, the slope of the τVO2 - VO2max regression equation was steeper for the old group, indicating that fit older subjects had VO2 kinetics that approached those of fit young. A multiple linear regression indicated that relative fitness was the strongest significant predictor of τVO2, followed by sex and age. Although VO2 kinetics are definitely slowed with age, relative levels of cardiorespiratory fitness also have a great influence on the dynamic response of VO2. Key words: VO2max, ventilatory threshold, heart rate kinetics
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Lyons, Scott, Mark Richardson, Phillip Bishop, Joe Smith, Hank Heath y Judy Giesen. "Excess post-exercise oxygen consumption in untrained males: effects of intermittent durations of arm ergometry". Applied Physiology, Nutrition, and Metabolism 31, n.º 3 (1 de junio de 2006): 196–201. http://dx.doi.org/10.1139/h05-017.
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The purpose of this study was to investigate excess post-exercise oxygen consumption (EPOC) following a continuous 30 min bout of upper-body exercise (UBE) compared with 3 consecutive 10 min bouts of UBE. Ten male subjects (age (mean ± standard deviation), 25.7 ± 5.83 years; arm VO2 peak, 2.2 ± 0.25 L·min-1), on separate days (48 h between trials) and in counterbalanced order, performed a continuous 30 min bout of arm exercise at 60% of arm VO2 peak and 3 separate 10 min bouts of arm exercise at 60% of arm VO2 peak. Subjects reported to the laboratory rested and after a 12 h fast. Each test was preceded by a 30 min baseline test to determine resting metabolic rate. Post-exercise VO2 was continuously monitored until baseline was re-established. Results showed that the combined magnitude of the EPOCs from the intermittent exercise sessions was significantly (p > .05) greater (4.47 ± 1.58 L O2) than that elicited from the continuous exercise session (1.54 ± 1.25 L O2). These data indicate that separating a continuous 30 min arm exercise into 3 equal 10 min arm exercises will elicit a small but significantly higher EPOC, and thus result in greater post-exercise energy expenditure. This could be beneficial for those unable to perform lower-body exercise (LBE), or for those with limited exercise capacities.Key words: upper-body exercise, EPOC, magnitude, recovery.
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Mertens, Luc, Tony Reybrouck, Benedicte Eyskens, Wim Daenen y Marc Gewillig. "Slow Kinetics of Oxygen Uptake in Patients with a Fontan-Type Circulation". Pediatric Exercise Science 15, n.º 2 (mayo de 2003): 146–55. http://dx.doi.org/10.1123/pes.15.2.146.
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Peak oxygen consumption and anaerobic threshold are both decreased in patients with a Fontan-type circulation. This study wanted to evaluate oxygen uptake kinetics at the onset and at the end of of a steady-state low-level exercise. The delay in cardiorespiratory response was evaluated by calculating the oxygen deficit at the onset of exercise and the recovery half-time at the end. Twelve patients with Fontan circulation (aged 11.4 − SD 5.1 year; 5.2 − 1.9 year after surgery) and 26 normal controls of comparable age (11.3 − 2.2 year) were submitted to a constant-load exercise test of six minutes on a treadmill (speed 5 km/h, inclination 4%). Gas exchange was measured using a breath-by-breath technique. The normalized oxygen deficit was calculated by subtracting the oxygen uptake (VO2) values measured at the onset of exercise from the steady-state VO2 obtained at the end of exercise. These differences were cumulated and expressed as a percentage of the cumulated oxygen cost for the 6 min exercise test. The half-time recovery time was defined as the time to reach 50% of the end exercise VO2 value. The normalized oxygen deficit was significantly higher in Fontan-patients compared to the control group (10.2 − 4.6% vs. 6.1 − 1.3%; p < .001). Also the recovery half-time was significantly higher in the patient group compared to the control group (74.2 − 25.6 s vs. 51.2 − 10.8 s; p < .05). A blunted heart rate response was present in the patients during the first two minutes of exercise, indicating that a slowed cardiac output response could explain the decreased oxygen kinetics in Fontan-patients.
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Jones, J. H., K. E. Longworth, A. Lindholm, K. E. Conley, R. H. Karas, S. R. Kayar y C. R. Taylor. "Oxygen transport during exercise in large mammals. I. Adaptive variation in oxygen demand". Journal of Applied Physiology 67, n.º 2 (1 de agosto de 1989): 862–70. http://dx.doi.org/10.1152/jappl.1989.67.2.862.
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This study investigated mechanisms used by horses and steers to increase O2 uptake and delivery (VO2) from resting to maximal rates and identified the mechanisms that enable horses to achieve higher maximal rates of O2 consumption (VO2max) than steers. VO2 and circulatory variables were measured while Standardbred trotting horses and steers (450-kg body mass) stood quietly and ran on a treadmill at speeds up to those eliciting VO2max. As VO2 increased in both species, heart rate and circulating hemoglobin (Hb) concentration increased, thereby increasing O2 delivery by the circulation, while cardiac stroke volume remained unchanged. At VO2max arterial PCO2 increased from its resting value in horses but was unchanged in steers, and arterial PO2 decreased in both species. Although the horses hypoventilated and were hypoxemic at VO2max, no significant decrease in arterial Hb saturation occurred. VO2max of the horses was 2.6 times higher than that of the steers and was associated with a 100% larger cardiac output, 100% larger stroke volume, and 40% higher Hb concentration, whereas heart rates at VO2max were identical in the two species. The higher cardiac output of the horses at VO2max resulted from a 1.2-fold higher mean arterial pressure and 1.6-fold lower peripheral tissue resistance (associated with a larger skeletal muscle capillary bed). Both the magnitude of the difference in VO2max between horses and steers and the mechanisms used to achieve it are the same as observed in smaller pairs of mammalian species with large variation in aerobic capacity.
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Hughson, R. L., J. E. Cochrane y G. C. Butler. "Faster O2 uptake kinetics at onset of supine exercise with than without lower body negative pressure". Journal of Applied Physiology 75, n.º 5 (1 de noviembre de 1993): 1962–67. http://dx.doi.org/10.1152/jappl.1993.75.5.1962.
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The kinetics of oxygen uptake (VO2) were observed at the onset of submaximal cycling exercise in seven men and one woman [mean age 22.6 +/- 0.9 (SE) yr] in the upright and supine positions and the supine position with -40 mmHg lower body negative pressure (LBNP). There was no significant difference for peak VO2 and ventilatory threshold between the supine (3,081 +/- 133 and 1,954 +/- 138 ml/min, respectively) and the supine + LBNP positions (3,062 +/- 152 and 1,973 +/- 122 ml/min); however, both were reduced compared with upright exercise (3,483 +/- 200 and 2,353 +/- 125 ml/min). Kinetic analysis applied to six repetitions by each subject indicated a slowing from a mean total lag time (time required to achieve 63% of the difference in VO2 between baseline and new steady state) of 36.3 +/- 2.7 s in upright exercise to 44.1 +/- 3.5 s in the supine position. However, total lag time for the supine + LBNP position (36.0 +/- 2.8 s) did not differ from upright exercise but was significantly faster than supine exercise. These data have been interpreted in support of an O2 transport limitation to VO2 kinetics at the onset of supine exercise that is countered by LBNP, likely through a more rapid increase in perfusion to the exercising muscle at these submaximal work rates.
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Vollestad, N. K., J. Wesche y O. M. Sejersted. "Gradual increase in leg oxygen uptake during repeated submaximal contractions in humans". Journal of Applied Physiology 68, n.º 3 (1 de marzo de 1990): 1150–56. http://dx.doi.org/10.1152/jappl.1990.68.3.1150.
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We examine whether muscle oxygen consumption (VO2) increases gradually during repeated submaximal isometric contractions. Six subjects made two-legged isometric quadriceps contractions at 30% maximal voluntary contraction for 6 s with 4 s of rest between until exhaustion (58 +/- 8 min). Blood samples were taken from the femoral vein and artery, and blood velocity was recorded by ultrasound-Doppler technique in the femoral artery. Blood flow was calculated from velocity and artery diameter values. Leg VO2 increased sixfold within the 1st min of exercise. A further doubling of the VO2 was seen during the remainder of the exercise, reaching 307 +/- 22 ml/min at exhaustion. This latter increase was due to a 54% increase in blood flow and a 34% increase in oxygen extraction. After 20 min of recovery VO2 was still 75% higher than preexercise values. The results show a twofold increase in energy demand of the working muscle during repeated constant-force isometric contractions. The increased energy cost of contraction is probably localized at the cellular level, and it parallels fatigue determined as decreased force-generating capacity.
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Harms, C. A. y J. M. Stager. "Low chemoresponsiveness and inadequate hyperventilation contribute to exercise-induced hypoxemia". Journal of Applied Physiology 79, n.º 2 (1 de agosto de 1995): 575–80. http://dx.doi.org/10.1152/jappl.1995.79.2.575.
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Is inadequate hyperventilation a cause of the exercise-induced hypoxemia observed in some athletes during intense exercise? If so, is this related to low chemoresponsiveness? To test the hypothesis that exercise-induced hypoxemia, inadequate hyperventilation, and chemoresponsiveness are related, 36 nonsmoking healthy men were divided into hypoxemic (Hyp; n = 13) or normoxemic (Nor; n = 15) groups based on arterial oxygen saturation (SaO2; Hyp < or = 90%, Nor > 92%) observed during maximum O2 uptake (VO2max). Men with intermediate SaO2 values (n = 8) were only included in correlation analysis. Ventilatory parameters were collected at rest, during a treadmill maximal oxygen consumption (VO2max) test, and during a 5-min run at 90% VO2max. Chemoresponsiveness at rest was assessed via hypoxic ventilatory response (HVR) and hypercapnic ventilatory response (HCVR). VO2max was not significantly different between Nor and Hyp. SaO2 was 93.8 +/- 0.9% (Nor) and 87.7 +/- 2.0% (Hyp) at VO2max. End-tidal PO2 and the ratio of minute ventilation to oxygen consumption (VE/VO2) were lower while PETCO2 was higher for Hyp (P < or = 0.01). End-tidal PO2, end-tidal PCO2, and VE/VO2 correlated (P < or = 0.05) to SaO2 (r = 0.84, r = -0.70, r = 0.72, respectively), suggesting that differences in oxygenation were due to differences in ventilation. HVR and HCVR were significantly lower for Hyp. HVR was related to VE/VO2 (r = 0.43), and HCVR was related to the ratio of VE to CO2 production at VO2max (r = 0.61)
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van Erck, Emmanuelle, Dominique-Marie Votion, Didier Serteyn y Tatiana Art. "Evaluation of oxygen consumption during field exercise tests in Standardbred trotters". Equine and Comparative Exercise Physiology 4, n.º 1 (febrero de 2007): 43–49. http://dx.doi.org/10.1017/s1478061507776466.
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AbstractReasons for performing the study: In human exercise physiology, the current gold standard for evaluating aerobic capacity is the measurement of oxygen consumption (VO2) and maximal oxygen uptake (VO2max). The evaluation of VO2 in horses is performed in some laboratories equipped with a treadmill but has only been exceptionally reported in field conditions because of the lack of adapted equipment. Objectives: The aim of this study was (1) to assess the feasibility of VO2 measurement on the track using a recently validated portable breath-by-breath gas analyser system adapted to horses (Cosmed K4b2® and Equimask®), (2) to compare these results with those obtained during a treadmill exercise test and (3) to study correlations between VO2 and physiological parameters usually measured in field condition such as heart rate (HR), lactataemia (LA) and the speed at which HR equals 200 beats per minute (bpm) (V200) or LA 4 mmol l− 1 (VLA4). Methods: Five healthy Standardbred trotters in training were submitted to two stepwise incremental exercise tests, one driven on the racetrack and the other on a high-speed treadmill with a 4% incline. Speed (v), HR, ventilatory parameters and VO2 were continuously recorded throughout the duration of the tests and LA was evaluated after each step. Results: All horses completed the test satisfactorily after an initial acclimatization to the mask. There were marked individual differences in ventilatory strategy, and breathing frequency (Rf) at the higher levels of exercise was noticeably low. The VCO2 measurements were incoherent. There were no significant differences between track and treadmill maximal data obtained during the last step [VO2peak (track: 139.9 ± 8.9 ml kg− 1 min− 1; treadmill: 139.9 ± 13.4 ml kg− 1 min− 1), LAmax (track: 6.5 ± 1.6 mmol l− 1; treadmill: 7.3 ± 3.0 mmol l− 1), HRmax (track: 229 ± 6.2 bpm; treadmill: 222 ± 13 bpm)], although the maximal speed required to reach similar workloads was significantly higher on the track (11.9 ± 0.6 m s− 1vs. 9.7 ± 0.4 m s− 1). The correlation between VO2 and HR (r = 0.87; P < 0.001) and VO2 and LA (r = 0.75; P < 0.0001) during both tests was good but no correlation was found between VO2peak and HRmax, LAmax, V200 or VLA4. Conclusions: This is the first report of a practical portable system to measure VO2 and ventilation continuously during high-speed field exercise tests. However, current mask design markedly influences ventilation and could have prohibited the attainment of VO2max. Furthermore, consistent VCO2 measurements should be implemented by the manufacturers. Potential relevance: Continuous breath-by-breath ventilation and VO2 measurements can be recorded in horses in the field at submaximal levels. With necessary adaptations to the system entailed, this study opens new perspectives in the analysis of physiological and metabolic mechanisms of exercise in the equine species in genuine track conditions.
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Bauerle, O. y M. Younes. "Role of ventilatory response to exercise in determining exercise capacity in COPD". Journal of Applied Physiology 79, n.º 6 (1 de diciembre de 1995): 1870–77. http://dx.doi.org/10.1152/jappl.1995.79.6.1870.
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The progression of chronic obstructive pulmonary disease (COPD) is generally associated with decreased exercise capacity. Differences in forced expired volume in 1 s (FEV1) among patients account for only a fraction of the variability in maximal oxygen consumption (VO2max). We hypothesized that variability in ventilatory response to exercise and in inspiratory mechanics and body mass index contributes importantly to variability in VO2max in this disease. We analyzed the files of 53 patients with established diagnosis of COPD who underwent a recent symptom-limited exercise test. We used inspiratory capacity and maximum inspiratory flow as measures of variability in inspiratory mechanics. The minute ventilation (VE) at the subject's VO2max was divided by the predicted in a normal subject at the same VO2 to obtain a ratio (VE,max/VE,pred). The ventilatory response during exercise provided the best correlation with peak VO2 (r = 0.62). FEV1 and inspiratory capacity also correlated with peak oxygen consumption but not as well as the ventilatory response (r = 0.49 and r = 0.46, respectively). Maximum inspiratory flow and body mass index showed only weak positive correlations (r = 0.23, not significant). The stepwise analysis generated the following equation: VO2max (%predicted) = (77.26 x VE,pred/VE,max) + [0.45 x FEV1 (%predicted)] - 23.66; r = 0.76, P < 0.001. We conclude that variability in the ventilatory response during exercise is one of the main determinants of variability in exercise capacity in COPD patients.
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Nagashima, K., H. Nose, T. Yoshida, T. Kawabata, Y. Oda, A. Yorimoto, O. Uemura y T. Morimoto. "Relationship between atrial natriuretic peptide and plasma volume during graded exercise with water immersion". Journal of Applied Physiology 78, n.º 1 (1 de enero de 1995): 217–24. http://dx.doi.org/10.1152/jappl.1995.78.1.217.
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To assess the relationship between atrial natriuretic peptide (ANP) and the reduction in plasma volume (PV) during exercise, we measured changes in PV and ANP in seven male volunteers during treadmill exercise in air (AE) and with water immersion (WE) together with time control studies of rest in air and in water. Blood samples were collected from a catheter in the antecubital vein at exercise intensities of 32, 49, 65, and 78% of peak oxygen consumption (VO2). Plasma ANP in AE increased significantly from the resting value [15 +/- 1 (SE) pg/ml] only at 78% of peak VO2 (29 +/- 5 pg/ml), whereas ANP in WE increased significantly at exercise levels of > 49% of peak VO2 and reached 68 +/- 9 pg/ml at 78% of peak VO2. Although PV in AE and WE decreased significantly with VO2 of > 49% of peak VO2 (P < 0.01), the decrease from the resting value in WE was significantly greater than that in AE of > 65% of peak VO2 (P < 0.01) and the decreases at 78% of peak VO2 were -9.7 +/- 0.8 and -6.1 +/- 1.7%, respectively. The difference in the decrease in PV between AE and WE at corresponding VO2 correlated strongly with that in the increase in ANP (r = -0.97; P < 0.01). These results are consistent with the hypothesis that ANP may be involved in the fluid shift from the intra- to extravascular space during exercise.
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Liguzinski, Piotr y Bernard Korzeniewski. "Oxygen delivery by blood determines the maximal Vo2 and work rate during whole body exercise in humans: in silico studies". American Journal of Physiology-Heart and Circulatory Physiology 293, n.º 1 (julio de 2007): H343—H353. http://dx.doi.org/10.1152/ajpheart.01371.2006.
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It has been proposed by Saltin ( J Exp Biol 115: 345–354, 1985) that oxygen delivery by blood is limiting for maximal work and oxygen consumption in humans during whole body exercise but not during single-muscle exercise. To test this prediction quantitatively, we developed a static (steady-state) computer model of oxygen transport to and within human skeletal muscle during single-muscle (quadriceps) exercise and whole body (cycling) exercise. The main system fluxes, namely cardiac output and oxygen consumption by muscle, are described as a function of the “primary” parameter: work rate. The model is broadly validated by comparison of computer simulations with various experimental data. In silico studies show that, when all other parameters and system properties are kept constant, an increase in the working muscle mass from 2.5 kg (single quadriceps) to 15 kg (two legs) causes, at some critical work intensity, a drop in oxygen concentration in muscle cells to (very near) zero, and therefore oxygen supply by blood limits maximal oxygen consumption and oxidative ATP production. Therefore, the maximal oxygen consumption per muscle mass is significantly higher during single-muscle exercise than during whole body exercise. The effect is brought about by a distribution of a limited amount of oxygen transported by blood in a greater working muscle mass during whole body exercise.
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Patti, Alessandro, Daniel Neunhaeuserer, Sara Ortolan, Fausto Roman, Andrea Gasperetti, Francesca Battista, Caterina Di Bella et al. "A clinical evaluation of VO2 kinetics in kidney transplant recipients". European Journal of Applied Physiology 121, n.º 7 (3 de abril de 2021): 2005–13. http://dx.doi.org/10.1007/s00421-021-04672-x.
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Abstract Purpose Aerobic exercise capacity is reduced in patients with chronic kidney disease, partly due to alterations at the muscular and microvascular level. This study evaluated oxygen uptake (VO2) kinetics as indicator of muscular oxidative metabolism in a population of Kidney Transplant Recipients (KTRs). Methods Two groups of KTRs enrolled 3 (n = 21) and 12 months (n = 14) after transplantation and a control group of healthy young adults (n = 16) underwent cardiopulmonary exercise testing on cycle-ergometer. The protocol consisted in two subsequent constant, moderate-load exercise phases with a final incremental test until exhaustion. Results The time constant of VO2 kinetics was slower in KTRs at 3 and 12 months after transplantation compared to controls (50.4 ± 13.1 s and 43.8 ± 11.6 s vs 28.9 ± 8.4 s, respectively; P < 0.01). Peak VO2 was lower in KTRs evaluated 3 months after transplantation compared to patients evaluated after 1 year (21.3 ± 4.3 and 26.4 ± 8.0 mL/kg/min; P = 0.04). Blood haemoglobin (Hb) concentration was higher in KTRs evaluated at 12 months (12.8 ± 1.7 vs 14.6 ± 1.7 g/dL; P < 0.01). Among KTRs, τ showed a moderate negative correlation with Peak VO2 (ρ = − 0.52) and Oxygen uptake efficiency slope (OUES) (r = − 0.57) while no significant correlation with Hb and peak heart rate. Conclusions KTRs show slower VO2 kinetics compared to healthy controls. Hb and peak VO2 seem to improve during the first year after transplantation. VO2 kinetics were significantly associated with indices of cardiorespiratory fitness, but less with central determinants of aerobic capacity, thus suggesting a potential usefulness of adding this index of muscular oxidative metabolism to functional evaluation in KTRs.
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Gaesser, G. A., S. A. Ward, V. C. Baum y B. J. Whipp. "Effects of infused epinephrine on slow phase of O2 uptake kinetics during heavy exercise in humans". Journal of Applied Physiology 77, n.º 5 (1 de noviembre de 1994): 2413–19. http://dx.doi.org/10.1152/jappl.1994.77.5.2413.
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We tested the hypothesis that infused epinephrine (Epi) would augment the slow phase of oxygen uptake (VO2) during heavy exercise. Six normal healthy males initially performed a ramp test on a cycle ergometer to estimate the lactate threshold (LT) and determine peak VO2. Each subject then performed two 20-min constant-load tests at a power output calculated to elicit a VO2 equal to estimated LT + 0.2(peak VO2--estimated LT) under control conditions throughout and with an intravenous infusion of Epi from minutes 10 to 20 at a rate of 100 ng.kg-1.min-1. Pulmonary gas exchange variables were determined breath by breath. Arterialized venous blood was repeatedly sampled from the dorsum of the heated hand. Epi infusion elevated (P < 0.05) plasma Epi concentration (i.e., from 420 +/- 130 pg/ml at minute 10 to 2,190 +/- 410 pg/ml at minute 20) but had no effect on plasma norepinephrine or K+ concentrations. Concentrations of blood lactate and pyruvate were increased, pH was decreased, and base excess became more negative by infusion of Epi (P < 0.05). Epi infusion increased (P < 0.05) CO2 production and the respiratory exchange ratio but had no effect on ventilation or VO2. VO2 increased (P < 0.05) to the same extent in both control (3.14 +/- 0.12 l/min at minute 10, 3.28 +/- 0.12 l/min at minute 20) and Epi infusion (3.10 +/- 0.11 l/min at minute 10, 3.25 +/- 0.11 l/min at minute 20) trials. We therefore concluded that neither Epi nor its associated humoral consequences contribute significantly to the slow phase of VO2 kinetics during heavy exercise.
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Kooyman, G. L. y P. J. Ponganis. "Emperor penguin oxygen consumption, heart rate and plasma lactate levels during graded swimming exercise." Journal of Experimental Biology 195, n.º 1 (1 de octubre de 1994): 199–209. http://dx.doi.org/10.1242/jeb.195.1.199.
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Oxygen consumption (VO2), heart rate and blood chemistry were measured in four emperor penguins, Aptenodytes forsteri (Gray), during graded swimming exercise. The maximum VO2 obtained, 52 ml O2 kg-1 min-1, was 7.8 times the measured resting VO2 of 6.7 ml O2 kg-1 min-1 and 9.1 times the predicted resting VO2. As the swimming effort rose, a linear increase in surface and submerged heart rates (fH) occurred. The highest average maximum surface and submersion heart rates of any bird were 213 and 210 beats min-1, respectively. No increase in plasma lactate concentrations occurred until VO2 was greater than 25 ml O2 kg-1 min-1. At the highest VO2 values measured, plasma lactate concentration reached 9.4 mmol l-1. In comparison with other animals of approximately the same mass, the aerobic capacity of the emperor penguin is less than those of the emu and dog but about the same as those of the seal, sea lion and domestic goat. For aquatic animals, a low aerobic capacity seems to be consistent with the needs of parsimonious oxygen utilization while breath-holding.
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Lai, Nicola, Melita M. Nasca, Marco A. Silva, Fatima T. Silva, Brian J. Whipp y Marco E. Cabrera. "Influence of exercise intensity on pulmonary oxygen uptake kinetics at the onset of exercise and recovery in male adolescents". Applied Physiology, Nutrition, and Metabolism 33, n.º 1 (febrero de 2008): 107–17. http://dx.doi.org/10.1139/h07-154.
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The dynamics of the pulmonary oxygen uptake (VO2) responses to square-wave changes in work rate can provide insight into bioenergetic processes sustaining and limiting exercise performance. The dynamic responses at the onset of exercise and during recovery have been investigated systematically and are well characterized at all intensities in adults; however, they have not been investigated completely in adolescents. We investigated whether adolescents display a slow component in their VO2 on- and off-kinetic responses to heavy- and very heavy-intensity exercise, as demonstrated in adults. Healthy African American male adolescents (n = 9, 14–17 years old) performed square-wave transitions on a cycle ergometer (from and to a baseline work rate of 20 W) to work rates of moderate (M), heavy (H), and very heavy (VH) intensity. In all subjects, the VO2 on-kinetics were best described with a single exponential at moderate intensity (τ1, on = 36 ± 11 s) and a double exponential at heavy (τ1, on = 29 ± 9 s; τ2, on = 197 ± 92 s) and very heavy (τ1, on = 36 ± 9 s; τ2, on = 302 ± 14 s) intensities. In contrast, the VO2 off-kinetics were best described with a single exponential at moderate (τ1, off = 48 ± 9 s) and heavy (τ1, off = 53 ± 7 s) intensities and a double exponential at very heavy (τ1, off = 51 ± 3 s; τ2, off = 471 ± 54 s) intensity. In summary, adolescents consistently displayed a slow component during heavy exercise (on- but not off- transition) and very heavy exercise (on- and off-transitions). Although the overall response dynamics in adolescents were similar to those previously observed in adults, their specific characterizations were different, particularly the lack of symmetry between the on- and off-responses.
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Vanoverschelde, J. J., B. Essamri, R. Vanbutsele, A. d'Hondt, J. R. Cosyns, J. R. Detry y J. A. Melin. "Contribution of left ventricular diastolic function to exercise capacity in normal subjects". Journal of Applied Physiology 74, n.º 5 (1 de mayo de 1993): 2225–33. http://dx.doi.org/10.1152/jappl.1993.74.5.2225.
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Previous studies have established that most of the heterogeneity in exercise capacity seen with sedentariness, aging, or physical training can be accounted for by individual differences in the maximal rate of total body oxygen consumption (VO2 max) during dynamic exercise. However, the factors that limit VO2 max in normal subjects remain disputed. To test the hypothesis that differences in left ventricular diastolic performance contribute to the heterogeneity of VO2 max seen in healthy subjects, 57 normal sedentary volunteers (36 +/- 13 yr, range 20–76 yr) and 9 endurance athletes (37 +/- 8 yr, range 26–51 yr) were studied. Aerobic capacity was estimated as VO2 max during a multistage dynamic cycle exercise protocol, whereas resting left ventricular systolic and diastolic function was assessed by two-dimensional and Doppler echocardiography. The relationship of the left ventricular functional indexes with VO2 max was investigated by stepwise multiple regression analysis. VO2 max ranged from 25 to 58 ml.kg-1 x min-1 in sedentary subjects and from 44 to 60 ml.kg-1 x min-1 in athletes. With univariate analysis, significant correlations were observed between VO2 max and age (r = -0.60), maximal heart rate (r = 0.48), maximal work load (r = 0.80), left ventricular volumes at both end diastole (r = 0.51) and end systole (r = 0.62), peak early transmitral filling velocities (r = 0.80), and the ratio of early to late transmitral filling velocities (r = 0.87).
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Hughson, R. L. y M. D. Inman. "Oxygen uptake kinetics from ramp work tests: variability of single test values". Journal of Applied Physiology 61, n.º 1 (1 de julio de 1986): 373–76. http://dx.doi.org/10.1152/jappl.1986.61.1.373.
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The variability in the estimation of the mean response time (MRT) of O2 uptake (VO2) kinetics from single ramp work rate exercise tests was examined in six repetitions by five fit subjects. Work rate increased at 50 W/min from a base line of 25 W to a work rate of 120% ventilatory threshold. Breath-by-breath data were analyzed by linear regression from 2 min after the onset of the ramp to the 120% work rate. Individual subjects showed approximately twofold differences in estimates of MRT; the coefficient of variation from individuals ranged from 18.5 to 29.3%. The MRT obtained as the mean from the individual repetitions did not differ from the MRT obtained from pooled within-subject data. Analysis of variance on the individual MRT estimates showed 53.9% of the variability was attributable to the slope of the regression, whereas only 2.4% could be attributed to baseline VO2. It was concluded that several repetitions of the ramp work rate tests should be pooled prior to estimation of kinetics parameters.
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Connelly, T. P., L. M. Sheldahl, F. E. Tristani, S. G. Levandoski, R. K. Kalkhoff, M. D. Hoffman y J. H. Kalbfleisch. "Effect of increased central blood volume with water immersion on plasma catecholamines during exercise". Journal of Applied Physiology 69, n.º 2 (1 de agosto de 1990): 651–56. http://dx.doi.org/10.1152/jappl.1990.69.2.651.
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To examine the influence of an increase in central blood volume with head-out water immersion (WI) on the sympathoadrenal response to graded dynamic exercise, nine healthy men underwent upright leg cycle exercise on land and with WI. Plasma norepinephrine and epinephrine concentrations were used as indexes of overall sympathoadrenal activity. Oxygen consumption (VO2), heart rate, systolic blood pressure, and plasma concentrations of norepinephrine, epinephrine, and lactate were determined at work loads corresponding to approximately 40, 60, 80, and 100% peak VO2. Peak VO2 did not differ on land and with WI. Plasma norepinephrine concentration was reduced (P less than 0.05) at 80 and 100% peak VO2 with WI and on land, respectively. Plasma epinephrine and lactate concentrations were similar on land and with WI at the three submaximal work stages, but both were reduced (P less than 0.05) at peak exertion with WI. Heart rate was lower (P less than 0.05) at the three highest work intensities with WI. These results suggest that the central shift in blood volume with WI reduces the sympathoadrenal response to high-intensity dynamic exercise.
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Shykoff, B. E., L. E. Farhi, A. J. Olszowka, D. R. Pendergast, M. A. Rokitka, C. G. Eisenhardt y R. A. Morin. "Cardiovascular response to submaximal exercise in sustained microgravity". Journal of Applied Physiology 81, n.º 1 (1 de julio de 1996): 26–32. http://dx.doi.org/10.1152/jappl.1996.81.1.26.
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Cardiac output (Q), heart rate (HR), blood pressure, and oxygen consumption (VO2) were measured repeatedly both at rest and at two levels of exercise in six subjects during microgravity exposure. Exercise was at 30 and 60% of the workload producing the individual's maximal VO2 in 1 G. Three of the subjects were on a 9-day flight, Spacelab Life Sciences-1, and three were on a 15-day flight, Spacelab Life Sciences-2. We found no temporal differences during the flights. Thus we have combined all microgravity measurements to compare in-flight values with erect or supine control values. At rest, Q in flight was 126% of Q erect (P < 0.01) but was not different from Q supine, and HR in flight was 81% of HR erect (P < 0.01) and 91% of HR supine (P < 0.05). Thus resting stroke volume (SV) in flight was 155% of SV erect (P < 0.01) and 109% SV supine (P < 0.05). Resting mean arterial blood pressure and diastolic pressure were lower in flight than erect (P < 0.05). Exercise values were considered as functions of VO2. The increase in Q with VO2 in flight was less than that at 1 G (slope 3.5 vs. 6.1 x min-1.l-1.min-1). SV in flight fell with increasing VO2, whereas SV erect rose and SV supine remained constant. The blood pressure response to exercise was not different in flight from erect or supine. We conclude that true microgravity causes a cardiovascular response different from that seen during any of its putative simulations.
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Mueller, P. J., M. T. Jones, R. E. Rawson, P. J. van Soest y H. F. Hintz. "Effect of increasing work rate on metabolic responses of the donkey (Equus asinus)". Journal of Applied Physiology 77, n.º 3 (1 de septiembre de 1994): 1431–38. http://dx.doi.org/10.1152/jappl.1994.77.3.1431.
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Oxygen consumption (VO2) and concentration of venous blood metabolites were measured in donkeys trained to run and to pull loads on a treadmill. VO2 in two donkeys running at maximal speed on a 9.8% slope was 110 +/- 2 ml.min-1.kg-1, approximately 22 times preexercise VO2. Average heart rate at maximal VO2 (VO2max) was 223 +/- 2 beats/min, five times the preexercise heart rate. Blood lactate increased 14-fold, and blood glucose did not change (P > 0.05). Animals running up a 4% incline and incremental draft loading of five donkeys walking on the level were also studied. The total energy cost of walking unloaded was 2.86 +/- 0.06 J.m-1.kg live wt-1. During low- to medium-intensity draft work for 25 min, glucose fell below preexercise values (P < 0.05), whereas plasma hematocrit and cortisol increased (P < 0.05). Blood lactate remained unchanged up to approximately 40% VO2 max but increased 170% at approximately 60% VO2max. The responses in donkeys are similar to those of exercising horses except for the rapid decline in blood glucose observed during low-intensity exercise and the lower lactate levels at both the high-intensity exercise and the apparent anaerobic threshold.
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Cunningham, D. A., C. M. St Croix, D. H. Paterson, F. Özyener y B. J. Whipp. "The Off-Transient Pulmonary Oxygen Uptake (VO2 ) Kinetics Following Attainment of a Particular VO2 During Heavy-Intensity Exercise in Humans". Experimental Physiology 85, n.º 3 (mayo de 2000): 339–47. http://dx.doi.org/10.1111/j.1469-445x.2000.01919.x.
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Wasserman, K. "Coupling of external to cellular respiration during exercise: the wisdom of the body revisited". American Journal of Physiology-Endocrinology and Metabolism 266, n.º 4 (1 de abril de 1994): E519—E539. http://dx.doi.org/10.1152/ajpendo.1994.266.4.e519.
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The changes in cellular respiration needed to increase energy output during exercise are intimately and predictably linked to external respiration through the circulation. This review addresses the mechanisms by which lactate accumulation might influence O2 uptake (VO2) and CO2 output (VCO2) kinetics. Respiratory homeostasis (a steady state with respect to VO2 and VCO2) is achieved by 3-4 min for work rates not associated with an increase in arterial lactate. When blood lactate increases significantly above rest for constant work rate exercise, VO2 characteristically increases past 3 min (slow component) at a rate proportional to the lactate concentration increase. The development of a similar slow component in VCO2 is not evident. The divergence of VCO2 from VO2 increase can be accounted for by extra CO2 release from the cell as HCO3- buffers lactic acid. Thus the slow component of aerobic CO2 production (parallel to VO2) is masked by the increase in buffer VCO2. This CO2, and the consumption of extracellular HCO3- by the lactate-producing cells, shifts the oxyhemoglobin dissociation curve rightward (Bohr effect). The exercise lactic acidosis has been observed to occur after the minimal capillary PO2 is reached. Thus the lactic acidosis serves to facilitate oxyhemoglobin dissociation and O2 transport to the muscle cells without a further decrease in end-capillary PO2. From these observations, it is hypothesized that simultaneously measured dynamic changes in VO2 and VCO2 might be useful to infer the aerobic and anaerobic contributions to exercise bioenergetics for a specific work task.
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Walton, M. y B. D. Anderson. "The aerobic cost of saltatory locomotion in the fowler's toad (Bufo woodhousei fowleri)". Journal of Experimental Biology 136, n.º 1 (1 de mayo de 1988): 273–88. http://dx.doi.org/10.1242/jeb.136.1.273.
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Studies of kangaroos suggest that hopping provides energy savings during locomotion at high speeds, although studies of small mammals suggest that hopping is no more economical than running. To obtain comparative data on anurans, we exercised Fowler's toads (Bufo woodhousei fowleri, 25.8 g) on treadmills at speeds ranging from 0.09 to 0.63 km h-1 while measuring oxygen consumption (VO2), endurance or hop kinematics. The toads walked at slow speeds and hopped at fast speeds. Steady-state VO2 (VO2,ss) increased linearly with speed to a maximum (VO2, max) of 1.17 ml O2 g-1 h-1 at 0.27 km h-1 and was nine times the average pre-exercise VO2. The maximum rate of oxygen consumption during treadmill exercise was comparable to VO2,max previously reported for less natural exercise regimes. At speeds greater than or equal to 0.27 km h-1, VO2,ss was independent of speed. At speeds less than or equal to 0.36 km h-1, toads moved for over 1h, but endurance decreased sharply at higher speeds. Hop rate, hop length, hop height and angle of take-off increased with speed. Hopping in B.w. fowleri was not less costly than running in other animals of similar body size and was inefficient at converting metabolic to mechanical energy. The present study suggests that hopping in toads, as in small mammals, is not economical during sustained locomotion and is most important during short bursts of high-intensity activity.
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Rampinini, Ermanno, Aldo Sassi, Andrea Morelli, Stefano Mazzoni, Maurizio Fanchini y Aaron J. Coutts. "Repeated-sprint ability in professional and amateur soccer players". Applied Physiology, Nutrition, and Metabolism 34, n.º 6 (diciembre de 2009): 1048–54. http://dx.doi.org/10.1139/h09-111.
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This study investigated the repeated-sprint ability (RSA) physiological responses to a standardized, high-intensity, intermittent running test (HIT), maximal oxygen uptake (VO2 max), and oxygen uptake (VO2) kinetics in male soccer players (professional (N = 12) and amateur (N = 11)) of different playing standards. The relationships between each of these factors and RSA performance were determined. Mean RSA time (RSAmean) and RSA decrement were related to the physiological responses to HIT (blood lactate concentration ([La–]), r = 0.66 and 0.77; blood bicarbonate concentration ([HCO3–]), r = –0.71 and –0.75; and blood hydrogen ion concentration ([H+]),r = 0.61 and 0.73; all p < 0.05), VO2 max (r = –0.45 and –0.65, p < 0.05), and time constant (τ) in VO2 kinetics (r = 0.62 and 0.62, p < 0.05). VO2 max was not different between playing standards (58.5 ± 4.0 vs. 56.3 ± 4.5 mL·kg–1·min–1; p = 0.227); however, the professional players demonstrated better RSAmean (7.17 ± 0.09 vs. 7.41 ± 0.19 s; p = 0.001), lower [La–] (5.7 ± 1.5 vs. 8.2 ± 2.2 mmol·L–1; p = 0.004), lower [H+] (46.5 ± 5.3 vs. 52.2 ± 3.4 mmol·L–1; p = 0.007), and higher [HCO3–] (20.1 ± 2.1 vs. 17.7 ± 1.7 mmol·L–1; p = 0.006) after the HIT, and a shorter τ in VO2 kinetics (27.2 ± 3.5 vs. 32.3 ± 6.0 s; p = 0.019). These results show that RSA performance, the physiological response to the HIT, and τ differentiate between professional- and amateur-standard soccer players. Our results also show that RSA performance is related to VO2 max, τ, and selected physiological responses to a standardized, high-intensity, intermittent exercise.
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Rivera, A. M., A. E. Pels, S. P. Sady, M. A. Sady, E. M. Cullinane y P. D. Thompson. "Physiological factors associated with the lower maximal oxygen consumption of master runners". Journal of Applied Physiology 66, n.º 2 (1 de febrero de 1989): 949–54. http://dx.doi.org/10.1152/jappl.1989.66.2.949.
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We examined the hemodynamic factors associated with the lower maximal O2 consumption (VO2max) in older formerly elite distance runners. Heart rate and VO2 were measured during submaximal and maximal treadmill exercise in 11 master [66 +/- 8 (SD) yr] and 11 young (32 +/- 5 yr) male runners. Cardiac output was determined using acetylene rebreathing at 30, 50, 70, and 85% VO2max. Maximal cardiac output was estimated using submaximal stroke volume and maximal heart rate. VO2max was 36% lower in master runners (45.0 +/- 6.9 vs. 70.4 +/- 8.0 ml.kg-1.min-1, P less than or equal to 0.05), because of both a lower maximal cardiac output (18.2 +/- 3.5 vs. 25.4 +/- 1.7 l.min-1) and arteriovenous O2 difference (16.6 +/- 1.6 vs. 18.7 +/- 1.4 ml O2.100 ml blood-1, P less than or equal to 0.05). Reduced maximal heart rate (154.4 +/- 17.4 vs. 185 +/- 5.8 beats.min-1) and stroke volume (117.1 +/- 16.1 vs. 137.2 +/- 8.7 ml.beat-1) contributed to the lower cardiac output in the older athletes (P less than or equal 0.05). These data indicate that VO2max is lower in master runners because of a diminished capacity to deliver and extract O2 during exercise.
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Carter, Helen, Andrew M. Jones, Thomas J. Barstow, Mark Burnley, Craig A. Williams y Jonathan H. Doust. "Oxygen uptake kinetics in treadmill running and cycle ergometry: a comparison". Journal of Applied Physiology 89, n.º 3 (1 de septiembre de 2000): 899–907. http://dx.doi.org/10.1152/jappl.2000.89.3.899.
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The purpose of the present study was to comprehensively examine oxygen consumption (V˙o 2) kinetics during running and cycling through mathematical modeling of the breath-by-breath gas exchange responses to moderate and heavy exercise. After determination of the lactate threshold (LT) and maximal oxygen consumption (V˙o 2 max) in both cycling and running exercise, seven subjects (age 26.6 ± 5.1 yr) completed a series of “square-wave” rest-to-exercise transitions at running speeds and cycling power outputs that corresponded to 80% LT and 25, 50, and 75%Δ (Δ being the difference between LT andV˙o 2 max).V˙o 2 responses were fit with either a two- (<LT) or three-phase ( >LT) exponential model. The parameters of theV˙o 2 kinetic response were similar between exercise modes, except for the V˙o 2 slow component, which was significantly ( P < 0.05) greater for cycling than for running at 50 and 75%Δ (334 ± 183 and 430 ± 159 ml/min vs. 205 ± 84 and 302 ± 154 ml/min, respectively). We speculate that the differences between the modes are related to the higher intramuscular tension development in heavy cycle exercise and the higher eccentric exercise component in running. This may cause a relatively greater recruitment of the less efficient type II muscle fibers in cycling.
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Cleland, Sarah Margaret, Juan Manuel Murias, John Michael Kowalchuk y Donald Hugh Paterson. "Effects of prior heavy-intensity exercise on oxygen uptake and muscle deoxygenation kinetics of a subsequent heavy-intensity cycling and knee-extension exercise". Applied Physiology, Nutrition, and Metabolism 37, n.º 1 (febrero de 2012): 138–48. http://dx.doi.org/10.1139/h11-143.
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This study examined the effects of prior heavy-intensity exercise on the adjustment of pulmonary oxygen uptake (VO2p) and muscle deoxygenation Δ[HHb] during the transition to subsequent heavy-intensity cycling (CE) or knee-extension (KE) exercise. Nine young adults (aged 24 ± 5 years) performed 4 repetitions of repeated bouts of heavy-intensity exercise separated by light-intensity CE and KE, which included 6 min of baseline exercise, a 6-min step of heavy-intensity exercise (H1), 6-min recovery, and a 6-min step of heavy-intensity exercise (H2). Exercise was performed at 50 r·min–1 or contractions per minute per leg. Oxygen uptake (VO2) mean response time was ∼20% faster (p < 0.05) during H2 compared with H1 in both modalities. Phase 2 time constants (τ) were not different between heavy bouts of CE (H1, 29.6 ± 6.5 s; H2, 28.0 ± 4.6 s) or KE exercise (H1, 31.6 ± 6.7 s; H2, 29.8 ± 5.6 s). The VO2 slow component amplitude was lower (p < 0.05) in H2 in both modalities (CE, 0.19 ± 0.06 L·min–1; KE, 0.12 ± 0.07 L·min–1) compared with H1 (CE, 0.29 ± 0.09 L·min–1; KE, 0.18 ± 0.07 L·min–1), with the contribution of the slow component to the total VO2 response reduced (p < 0.05) in H2 during both exercise modes. The effective τHHb was similar between bouts for CE (H1, 18.2 ± 3.0 s; H2, 18.0 ± 3.6 s) and KE exercise (H1, 26.0 ± 7.0 s; H2, 24.0 ± 5.8 s). The ΔHHb slow component was reduced during H2 in both CE and KE (p < 0.05). In conclusion, phase 2 VO2p was unchanged with priming exercise; however, a faster mean response time of VO2p during the heavy-intensity exercise preceded by a priming heavy-intensity exercise was attributed to a smaller slow component and reduced muscle deoxygenation indicative of improved muscle O2 delivery during the second bout of exercise.
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Barnas, G. M., M. Gleeson y W. Rautenberg. "Respiratory and cardiovascular responses of the exercising chicken to spinal cord cooling at different ambient temperatures. I. Cardiovascular responses and blood gases". Journal of Experimental Biology 114, n.º 1 (1 de enero de 1985): 415–26. http://dx.doi.org/10.1242/jeb.114.1.415.
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We measured oxygen consumption (VO2), heart rate (HR), stroke volume (SV), cardiac output (CO) and mean arterial blood pressure (MBPa) of chickens during 15 min treadmill exercise at 0.5 ms-1 and 0.8 ms-1 at thermoneutral (23 degrees C), low (9 degrees C) and high (34 degrees C) ambient temperature (Ta); the vertebral canal was cooled to 34 degrees C during the middle 5 min of each exercise period. PO2, PCO2, pH and oxygen content (CO2) of the arterial and mixed venous blood were also measured. VO2 during exercise was not significantly affected by Ta. Spinal cord cooling produced definite increases in VO2, CO and SV during 0.5 ms-1 exercise at 9 degrees C; otherwise, effects of spinal cord cooling were not significant. HR, SV and CO were all linearly related to VO2; these relationships were unaffected by spinal cord cooling or Ta. Blood pressure did not increase during exercise. PaCO2 and P-vCO2 did not increase significantly during exercise. The arterial-venous CO2 difference was increased by exercise only at 34 degrees C. The chickens generally hyperventilated at 34 degrees C Ta compared to the other Ta values. No consistent effect on blood gases or on pH and CO2 of the blood could be attributed to spinal cord cooling.
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Chad, K. E. y B. M. Quigley. "Exercise intensity: effect on postexercise O2 uptake in trained and untrained women". Journal of Applied Physiology 70, n.º 4 (1 de abril de 1991): 1713–19. http://dx.doi.org/10.1152/jappl.1991.70.4.1713.
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Despite many reports of long-lasting elevation of metabolism after exercise, little is known regarding the effects of exercise intensity and duration on this phenomenon. This study examined the effect of a constant duration (30 min) of cycle ergometer exercise at varied intensity levels [50 and 70% of maximal O2 consumption (VO2max)] on 3-h recovery of oxygen uptake (VO2). VO2 and respiratory exchange ratios were measured by open-circuit spirometry in five trained female cyclists (age 25 +/- 1.7 yr) and five untrained females (age 27 +/- 0.8 yr). Postexercise VO2 measured at intervals for 3 h after exercise was greater (P less than 0.01) after exercise at 50% VO2max in trained (0.40 +/- 0.01 l/min) and untrained subjects (0.39 +/- 0.01 l/min) than after 70% VO2max in (0.31 +/- 0.02 l/min) and untrained subjects (0.29 +/- 0.02 l/min). The lower respiratory exchange ratio values (P less than 0.01) after 50% VO2max in trained (0.78 +/- 0.01) and untrained subjects (0.80 +/- 0.01) compared with 70% VO2max in trained (0.81 +/- 0.01) and untrained subjects (0.83 +/- 0.01) suggest that an increase in fat metabolism may be implicated in the long-term elevation of metabolism after exercise. This was supported by the greater estimated fatty acid oxidation (P less than 0.05) after 50% VO2max in trained (147 +/- 4 mg/min) and untrained subjects (133 +/- 9 mg/min) compared with 70% VO2max in trained (101 +/- 6 mg/min) and untrained subjects (85 +/- 7 mg/min).
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Olschewski, H. y K. Bruck. "Thermoregulatory, cardiovascular, and muscular factors related to exercise after precooling". Journal of Applied Physiology 64, n.º 2 (1 de febrero de 1988): 803–11. http://dx.doi.org/10.1152/jappl.1988.64.2.803.
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The effect of slightly lowered body temperature on endurance time and possibly related physiological factors was studied in seven male volunteers exercising on a cycle ergometer at an ambient temperature (Ta) of 18 degrees C. Work load was increased to 40% in a stepwise manner (phase I, min 0–16) followed by a period at 80% of peak oxygen consumption (VO2) sustained to exhaustion. On one day, exercise was preceded by a double cold exposure (precooling test, PRET), resulting in a 204-kJ/m2 negative heat storage and a 4 and 0.2 degrees C lower mean skin and core temperature at the start of exercise compared with the control test (CONT). Core temperature dropped further during exercise in PRET. Endurance time at 80% of peak VO2 was increased by 12% (P less than 0.05) in PRET. Heart rate (HR) was decreased throughout PRET (P less than 0.05); oxygen pulse and arteriovenous O2 difference were significantly increased in phase I of PRET, whereas the PRET-CONT differences in stroke volume and cardiac output were not significant. In phase II of PRET (min 16–28, heavy exercise) sweat rate (SR) and heat conductivity, indicating forearm blood flow, were lower (-39%, P less than 0.001; -37%). Pedal rate (PR) was 9% lower (P less than 0.01) in phase II of PRET. At the termination of exercise, PRET-CONT differences in HR, SR, and PR had disappeared.
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Regensteiner, Judith G., Timothy A. Bauer, Jane E. B. Reusch, Suzanne L. Brandenburg, Jeffrey M. Sippel, Andria M. Vogelsong, Susan Smith, Eugene E. Wolfel, Robert H. Eckel y William R. Hiatt. "Abnormal oxygen uptake kinetic responses in women with type II diabetes mellitus". Journal of Applied Physiology 85, n.º 1 (1 de julio de 1998): 310–17. http://dx.doi.org/10.1152/jappl.1998.85.1.310.
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Persons with type II diabetes mellitus (DM), even without cardiovascular complications have a decreased maximal oxygen consumption (V˙o2 max) and submaximal oxygen consumption (V˙o2) during graded exercise compared with healthy controls. We evaluated the hypothesis that change in the rate ofV˙o2in response to the onset of constant-load exercise (measured byV˙o2-uptake kinetics) was slowed in persons with type II DM. Ten premenopausal women with uncomplicated type II DM, 10 overweight, nondiabetic women, and 10 lean, nondiabetic women had aV˙o2 maxtest. On two separate occasions, subjects performed 7-min bouts of constant-load bicycle exercise at workloads below and above the lactate threshold to enable measurements of V˙o2kinetics and heart rate kinetics (measuring rate of heart rate rise).V˙o2 maxwas reduced in subjects with type II DM compared with both lean and overweight controls ( P < 0.05). Subjects with type II DM had slowerV˙o2and heart rate kinetics than did controls at constant workloads below the lactate threshold. The data suggest a notable abnormality in the cardiopulmonary response at the onset of exercise in people with type II DM. The findings may reflect impaired cardiac responses to exercise, although an additional defect in skeletal muscle oxygen diffusion or mitochondrial oxygen utilization is also possible.
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Oliveira, Diogo R., Lio F. Gonçalves, António M. Reis, Ricardo J. Fernandes, Nuno D. Garrido y Victor M. Reis. "The oxygen uptake slow component at submaximal intensities in breaststroke swimming". Journal of Human Kinetics 51, n.º 1 (1 de junio de 2016): 165–73. http://dx.doi.org/10.1515/hukin-2015-0179.
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Abstract The present work proposed to study the oxygen uptake slow component (VO2 SC) of breaststroke swimmers at four different intensities of submaximal exercise, via mathematical modeling of a multi-exponential function. The slow component (SC) was also assessed with two different fixed interval methods and the three methods were compared. Twelve male swimmers performed a test comprising four submaximal 300 m bouts at different intensities where all expired gases were collected breath by breath. Multi-exponential modeling showed values above 450 ml·min−1 of the SC in the two last bouts of exercise (those with intensities above the lactate threshold). A significant effect of the method that was used to calculate the VO2 SC was revealed. Higher mean values were observed when using mathematical modeling compared with the fixed interval 3rd min method (F=7.111; p=0.012; η2=0.587); furthermore, differences were detected among the two fixed interval methods. No significant relationship was found between the SC determined by any method and the blood lactate measured at each of the four exercise intensities. In addition, no significant association between the SC and peak oxygen uptake was found. It was concluded that in trained breaststroke swimmers, the presence of the VO2 SC may be observed at intensities above that corresponding to the 3.5 mM-1 threshold. Moreover, mathematical modeling of the oxygen uptake on-kinetics tended to show a higher slow component as compared to fixed interval methods.