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ABSTRACT: Sildenafil improves oxygen delivery and maximal exercise capacity at very high altitudes (≥ 4,350 m), but it is unknown whether sildenafil improves these variables and longer-duration exercise performance at moderate and high altitudes where competitions are more common. The purpose of this study was to determine the effects of sildenafil on cardiovascular hemodynamics, arterial oxygen saturation (SaO(2)), peak exercise capacity (W (peak)), and 15-km time trial performance in endurance-trained subjects at simulated moderate (MA; ~2,100 m, 16.2% F(I)O(2)) and high (HA; ~3,900 m, 12.8% F(I)O(2)) altitudes. Eleven men and ten women completed two HA W (peak) trials after ingesting placebo or 50 mg sildenafil. Subjects then completed four exercise trials (30 min at 55% of altitude-specific W (peak) + 15-km time trial) at MA and HA after ingesting placebo or 50 mg sildenafil. All trials were performed in randomized, counterbalanced, and double-blind fashion. Sildenafil had little influence on cardiovascular hemodynamics at MA or HA, but did result in higher SaO(2) values (+3%, p < 0.05) compared to placebo during steady state and time trial exercise at HA. W (peak) at HA was 19% lower than SL (p < 0.001) and was not significantly affected by sildenafil. Similarly, the significantly slower time trial performance at MA (28.1 ± 0.5 min, p = 0.016) and HA (30.3 ± 0.6 min, p < 0.001) compared to SL (27.5 ± 0.6 min) was unaffected by sildenafil. We conclude that sildenafil is unlikely to exert beneficial effects at altitudes <4,000 m for a majority of the population.
Arbeitsphysiologie 03/2011; 111(12):3031-40. · 2.15 Impact Factor
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ABSTRACT: Sildenafil improves maximal exercise capacity at high altitudes (∼4350-5800 m) by reducing pulmonary arterial pressure and enhancing oxygen delivery, but the effects on exercise performance at less severe altitudes are less clear.
To determine the effects of sildenafil on cardiovascular hemodynamics (heart rate, stroke volume, and cardiac output), arterial oxygen saturation (SaO2), and 6-km time-trial performance of endurance-trained men and women at a simulated altitude of ∼3900 m.
Twenty men and 15 women, endurance-trained, completed one experimental exercise trial (30 min at 55% of altitude-specific capacity +6-km time trial) at sea level (SL) and two trials at simulated high altitude (HA) while breathing hypoxic gas (12.8% FIo2) after ingestion of either placebo or 50 mg sildenafil in double-blind, randomized, and counterbalanced fashion.
Maximal exercise capacity and SaO2 were significantly reduced at HA compared to SL (18%-23%), but sildenafil did not significantly improve cardiovascular hemodynamics or time-trial performance in either men or women compared to placebo and only improved SaO2 in women (4%). One male subject (5% of male subjects, 2.8% of all subjects) exhibited a meaningful 36-s improvement in time-trial performance with sildenafil compared to placebo.
In this group of endurance trained men and women, sildenafil had very little influence on cardiovascular hemodynamics, SaO2, and 6-km time-trial performance at a simulated altitude of ∼3900 m. It appears that a very small percentage of endurance-trained men and women derive meaningful improvements in aerobic performance from sildenafil at a simulated altitude of ∼3900 m.
High altitude medicine & biology 01/2011; 12(3):215-22. · 1.58 Impact Factor
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ABSTRACT: We combined tracer and arteriovenous (a-v) balance techniques to evaluate the effects of exercise and endurance training on leg triacylglyceride turnover as assessed by glycerol exchange. Measurements on an exercising leg were taken to be a surrogate for working skeletal muscle. Eight men completed 9 wk of endurance training [5 days/wk, 1 h/day, 75% peak oxygen consumption (Vo(2peak))], with leg glycerol turnover determined during two pretraining trials [45 and 65% Vo(2peak) (45% Pre and 65% Pre, respectively)] and two posttraining trials [65% of pretraining Vo(2peak) (ABT) and 65% of posttraining Vo(2peak) (RLT)] using [(2)H(5)]glycerol infusion, femoral a-v sampling, and measurement of leg blood flow. Endurance training increased Vo(2peak) by 15% (45.2 +/- 1.2 to 52.0 +/- 1.8 mlxkg(-1)xmin(-1), P < 0.05). At rest, there was tracer-measured leg glycerol uptake (41 +/- 8 and 52 +/- 15 micromol/min for pre- and posttraining, respectively) even in the presence of small, but significant, net leg glycerol release (-68 +/- 19 and -50 +/- 13 micromol/min, respectively; P < 0.05 vs. zero). Furthermore, while there was no significant net leg glycerol exchange during any of the exercise bouts, there was substantial tracer-measured leg glycerol turnover during exercise (i.e., simultaneous leg muscle uptake and leg release) (uptake, release: 45% Pre, 194 +/- 41, 214 +/- 33; 65% Pre, 217 +/- 79, 201 +/- 84; ABT, 275 +/- 76, 312 +/- 87; RLT, 282 +/- 83, 424 +/- 75 micromol/min; all P < 0.05 vs. corresponding rest). Leg glycerol turnover was unaffected by exercise intensity or endurance training. In summary, simultaneous leg glycerol uptake and release (indicative of leg triacylglyceride turnover) occurs despite small or negligible net leg glycerol exchange, and furthermore, leg glycerol turnover can be substantially augmented during exercise.
AJP Endocrinology and Metabolism 11/2007; 293(4):E950-7. · 4.75 Impact Factor
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ABSTRACT: To evaluate the contribution of working muscle to whole body lipid oxidation, we examined the effects of exercise intensity and endurance training (9 wk, 5 days/wk, 1 h, 75% Vo(2 peak)) on whole body and leg free fatty acid (FFA) kinetics in eight male subjects (26 +/- 1 yr, means +/- SE). Two pretraining trials [45 and 65% Vo(2 max) (45UT, 65UT)] and two posttraining trials [65% of pretraining Vo(2 peak) (ABT), and 65% of posttraining Vo(2 peak) (RLT)] were performed using [1-(13)C]palmitate infusion and femoral arteriovenous sampling. Training increased Vo(2 peak) by 15% (45.2 +/- 1.2 to 52.0 +/- 1.8 ml.kg(-1).min(-1), P < 0.05). Muscle FFA fractional extraction was lower during exercise (EX) compared with rest regardless of workload or training status ( approximately 20 vs. 48%, P < 0.05). Two-leg net FFA balance increased from net release at rest ( approximately -36 micromol/min) to net uptake during EX for 45UT (179 +/- 75), ABT (236 +/- 63), and RLT (136 +/- 110) (P < 0.05), but not 65UT (51 +/- 127). Leg FFA tracer measured uptake was higher during EX than rest for all trials and greater during posttraining in RLT (716 +/- 173 micromol/min) compared with pretraining (45UT 450 +/- 80, 65UT 461 +/- 72, P < 0.05). Leg muscle lipid oxidation increased with training in ABT (730 +/- 163 micromol/min) vs. 65UT (187 +/- 94, P < 0.05). Leg muscle lipid oxidation represented approximately 62 and 30% of whole body lipid oxidation at lower and higher relative intensities, respectively. In summary, training can increase working muscle tracer measured FFA uptake and lipid oxidation for a given power output, but both before and after training the association between whole body and leg lipid metabolism is reduced as exercise intensity increases.
AJP Endocrinology and Metabolism 01/2007; 292(1):E107-16. · 4.75 Impact Factor
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ABSTRACT: We evaluated the hypothesis that net leg total FFA, LDL-C, and TG uptake and HDL-C release during moderate-intensity cycling exercise would be increased following endurance training. Eight sedentary men (26 +/- 1 yr, 77.4 +/- 3.7 kg) were studied in the postprandial state during 90 min of rest and 60 min of exercise twice before (45% and 65% V(O2 peak)) and twice after 9 wk of endurance training (55% and 65% posttraining V(O2 peak)). Measurements across an exercising leg were taken to be a surrogate for active skeletal muscle. To determine limb lipid exchange, femoral arterial and venous blood samples drawn simultaneously at rest and during exercise were analyzed for total and individual FFA (e.g., palmitate, oleate), LDL-C, HDL-C, and TG concentrations, and limb blood flow was determined by thermodilution. The transition from rest to exercise resulted in a shift from net leg total FFA release (-44 +/- 16 micromol/min) to uptake (193 +/- 49 micromol/min) that was unaffected by either exercise intensity or endurance training. The relative net leg release and uptake of individual FFA closely resembled their relative abundances in the plasma with approximately 21 and 41% of net leg total FFA uptake during exercise accounted for by palmitate and oleate, respectively. Endurance training resulted in significant changes in arterial concentrations of HDL-C (49 +/- 5 vs. 52 +/- 5 mg/dl, pre vs. post) and LDL-C (82 +/- 9 vs. 76 +/- 9 mg/dl, pre vs. post), but there was no net TG or LDL-C uptake or HDL-C release across the resting or active leg before or after endurance training. In conclusion, endurance training favorably affects blood lipoprotein profiles, even in young, healthy normolipidemic men, but muscle contractions per se have little effect on net leg LDL-C, or TG uptake or HDL-C release during moderate-intensity cycling exercise. Therefore, the favorable effects of physical activity on the lipid profiles of young, healthy normolipidemic men in the postprandial state are not attributable to changes in HDL-C or LDL-C exchange across active skeletal muscle.
AJP Endocrinology and Metabolism 10/2006; 291(3):E656-65. · 4.75 Impact Factor
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ABSTRACT: To investigate the effects of prolonged hypoxia and antioxidant supplementation on ventilatory threshold (VT) during high-altitude (HA) exposure (4300 m).
Sixteen physically fit males (25 +/- 5 yr; 77.8 +/- 8.5 kg) performed an incremental test to maximal exertion on a cycle ergometer at sea level (SL). Subjects were then matched on VO2peak, ventilatory chemosensitivity, and body mass and assigned to either a placebo (PL) or antioxidant (AO) supplement group in a randomized, double-blind manner. PL or AO (12 mg of beta-carotene, 180 mg of alpha-tocopherol acetate, 500 mg of ascorbic acid, 100 mug of selenium, and 30 mg of zinc daily) were taken 21 d prior to and for 14 d at HA. During HA, subjects participated in an exercise program designed to achieve an energy deficit of approximately 1400 kcal.d(-1). VT was reassessed on the second and ninth days at HA (HA2, HA9).
Peak power output (Wpeak) and VO2peak decreased (28%) in both groups upon acute altitude exposure (HA2) and were unchanged with acclimatization and exercise (HA9). Power output at VT (WVT) decreased from SL to HA2 by 41% in PL, but only 32% in AO (P < 0.05). WVT increased in PL only during acclimatization (P < 0.05) and matched AO at HA9. Similar results were found when VT was expressed in terms of % Wpeak and % VO2peak.
VT decreases upon acute HA exposure but improves with acclimatization. Prior AO supplementation improves VT upon acute, but not chronic altitude exposure.
Medicine & Science in Sports & Exercise 08/2006; 38(8):1425-31. · 4.43 Impact Factor
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Medicine & Science in Sports & Exercise 04/2006; 38(5):S526. · 4.43 Impact Factor
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Todd A Hagobian, Kevin A Jacobs,
Andrew W Subudhi,
Jill A Fattor,
Paul B Rock,
Stephen R Muza,
Charles S Fulco,
Barry Braun,
Ann Grediagin,
Robert S Mazzeo,
Allen Cymerman,
Anne L Friedlander
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ABSTRACT: This study tested the hypothesis that antioxidant supplementation would attenuate plasma cytokine (IL-6, tumor necrosis factor (TNF)-alpha), and C-reactive protein (CRP) concentrations at rest and in response to exercise at 4300-m elevation.
A total of 17 recreationally trained men were matched and assigned to an antioxidant (N = 9) or placebo (N = 8) group in a double-blinded fashion. At sea level (SL), energy expenditure was controlled and subjects were weight stable. Then, 3 wk before and throughout high altitude (HA), an antioxidant supplement (10,000 IU beta-carotene, 200 IU alpha-tocopherol acetate, 250 mg ascorbic acid, 50 microg selenium, 15 mg zinc) or placebo was given twice daily. At HA, energy expenditure increased approximately 750 kcal.d(-1) and energy intake decreased approximately 550 kcal.d, resulting in a caloric deficit of approximately 1200-1500 kcal.d(-1). At SL and HA day 1 (HA1) and day HA13, subjects exercised at 55% of VO2peak until they expended approximately 1500 kcal. Blood samples were taken at rest, end of exercise, and 2, 4, and 20 h after exercise.
No differences were seen between groups in plasma IL-6, CRP, or TNF-alpha at rest or in response to exercise. For both groups, plasma IL-6 concentration was significantly higher at the end of exercise, 2, 4, and 20 h after exercise at HA1 compared with SL and HA13. Plasma CRP concentration was significantly elevated 20 h postexercise for both groups on HA1 compared to SL and HA13. TNF-alpha did not differ at rest or in response to exercise.
Plasma IL-6 and CRP concentrations were elevated following exercise at high altitude on day 1, and antioxidant supplementation did not attenuate the rise in plasma IL-6 and CRP concentrations associated with hypoxia, exercise, and caloric deficit.
Medicine & Science in Sports & Exercise 03/2006; 38(2):276-85. · 4.43 Impact Factor
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ABSTRACT: We evaluated the hypothesis that fatty acid reesterification would be increased during rest and exercise in the midluteal menstrual cycle phase and during oral contraceptive use, when ovarian hormone concentrations are high, compared with the early follicular phase. Subjects were eight moderately active, weight-stable, eumenorrheic women (24.8 +/- 1.2 yr, peak oxygen consumption = 42.0 +/- 2.3 ml.kg(-1).min(-1)) who had not taken oral contraceptives for at least 6 mo. Plasma free fatty acid (FFA) kinetics were assessed in the 3-h postprandial state by continuous infusion of [1-(13)C]palmitate and [1,1,2,3,3-(2)H]glycerol during 90 min of rest and 60 min of exercise at 45% and 65% peak oxygen consumption in the early follicular and midluteal menstrual cycle phases and during the inactive- and high-dose phases following 4 mo of oral contraceptive use. Plasma FFA rates of appearance, disappearance, and oxidation increased significantly from rest to exercise with no differences noted between menstrual cycle or oral contraceptive phases or exercise intensities. Compared with either menstrual cycle phase, oral contraceptive use resulted in an increase in plasma-derived fatty acid reesterification and a decrease in the proportion of plasma FFA rate of disappearance that was oxidized at rest and during exercise. Endogenous and exogenous synthetic ovarian hormones do not exert a measurable influence on plasma FFA turnover or oxidation at rest or during moderate-intensity exercise in the 3-h postprandial state when carbohydrate use predominates. The increase in whole body lipolytic rate during exercise noted previously with oral contraceptive use is not matched by an increase in fatty acid oxidation and results in an increase in reesterification. Synthetic ovarian hormones contained in oral contraceptives increase lipolytic rate, but fatty acid oxidation during exercise is determined by exercise intensity and its metabolic and endocrine consequences.
Journal of Applied Physiology 06/2005; 98(5):1720-31. · 3.75 Impact Factor
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ABSTRACT: An emerging technique used for the study of metabolic regulation is the elevation of lactate concentration with a sodium-lactate infusion, the lactate clamp (LC). However, hematological and acid-base properties affected by the infusion of hypertonic solutions containing the osmotically active strong ions sodium (Na(+)) and lactate (Lac(-)) are a concern for clinical and research applications of LC. In the present study, we characterized the hematological and plasma acid-base changes during rest and prolonged, light- to moderate-intensity (55% Vo(2 peak)) exercise with and without LC. During the control (Con) trial, subjects were administered an isotonic, isovolumetric saline infusion. During LC, plasma lactate concentration ([Lac(-)]) was elevated to 4 meq/l during rest and to 4-7 meq/l during exercise. During LC at rest, there were rapid and transient changes in plasma, erythrocyte, and blood volumes. LC resulted in decreased plasma [H(+)] (from 39.6 to 29.6 neq/l) at the end of exercise while plasma [HCO(3)(-)] increased from 26 to 32.9 meq/l. Increased plasma strong ion difference [SID], due to increased [Na(+)], was the primary contributor to decreased [H(+)] and increased [HCO(3)(-)]. A decrease in plasma total weak acid concentration also contributed to these changes, whereas Pco(2) contributed little. The infusion of hypertonic LC caused only minor volume, acid-base, and CO(2) storage responses. We conclude that an LC infusion is appropriate for studies of metabolic regulation.
Journal of Applied Physiology 04/2005; 98(3):856-65. · 3.75 Impact Factor
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ABSTRACT: This two-part study tested the hypotheses that the use of a new cooling device, purported to extract heat from the body core through the palm of the hand, would (a) attenuate core temperature rise during submaximal exercise in the heat, thereby suppressing exercise-associated metabolic changes, and (b) facilitate a higher sustained workload, thus shortening the completion time of a time-trial performance test.
In Study 1, 8 male triathletes (age 27.9 +/- 2.0 yrs, mass 77.2 +/- 3.1 kg, VO2peak 59.0 +/- 4.1 ml x min(-1) x kg(-1)) cycled for 1 hr at the same absolute workload (approximately 60% VO2peak) in a heated room (31.9 +/- 0.1 degrees C, 24 +/- 1% humidity) on two occasions counterbalanced for cooling (C) or noncooling (NC). In Study 2, 8 similar subjects (age 26.9 +/- 2.0 yrs, mass 75.2 +/- 3.7 kg, VO2peak 54.1 +/- 3.1 ml x min(-1) x kg(-1)) performed two 30-km cycling time-trial performance tests under the same conditions (C(T), NC(T)).
In Study 1, cooling attenuated the rise in tympanic temperature (T(TY)) (1.2 +/- 0.2 vs. 1.8 +/- 0.2 degrees C; p < 0.01) and lowered mean oxygen consumption (VO2, 2.4 +/- 0.1 vs. 2.7 +/- 0.1 L x min(-1); p < 0.05) and blood lactate (1.7 +/- 0.2 vs. 2.2 +/- 0.2 mmol x L(-1); p < 0.01) during exercise. There were no significant differences in respiratory exchange ratio (RER), blood glucose, heart rate (HR), face temperature (T(F)), or back temperature (T(B)) between NC and C. In Study 2, time to complete 30 km was 6 +/- 1% less with cooling than without cooling (60.9 +/- 2.0 vs. 64.9 +/- 2.6 min; p < 0.01). During the last 20% of C(T), subjects sustained a workload that was 14 +/- 5% (p = 0.06) higher than NC(T) at the same T(TY) and HR.
Heat extraction through the hand during cycle ergometer exercise in the heat can (a) lower T(TY), lactate concentration, and VO2 during a submaximal set-workload test and (b) reduce the time it takes to complete a 30-km time-trial test.
Canadian journal of applied physiology = Revue canadienne de physiologie appliquée 03/2005; 30(1):87-104. · 1.30 Impact Factor
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ABSTRACT: Catecholamine release is known to be regulated by feedforward and feedback mechanisms. Norepinephrine (NE) and epinephrine (Epi) concentrations rise in response to stresses, such as exercise, that challenge blood glucose homeostasis. The purpose of this study was to assess the hypothesis that the lactate anion is involved in feedback control of catecholamine concentration. Six healthy active men (26 +/- 2 yr, 82 +/- 2 kg, 50.7 +/- 2.1 ml.kg(-1).min(-1)) were studied on five occasions after an overnight fast. Plasma concentrations of NE and Epi were determined during 90 min of rest and 90 min of exercise at 55% of peak O2 consumption (VO2 peak) two times with exogenous lactate infusion (lactate clamp, LC) and two times without LC (CON). The blood lactate profile ( approximately 4 mM) of a preliminary trial at 65% VO2 peak (65%) was matched during the subsequent LC trials. In resting men, plasma NE concentration was not different between trials, but during exercise all conditions were different with 65% > CON > LC (65%: 2,115 +/- 166 pg/ml, CON: 1,573 +/- 153 pg/ml, LC: 930 +/- 174 pg/ml, P < 0.05). Plasma Epi concentrations at rest were different between conditions, with LC less than 65% and CON (65%: 68 +/- 9 pg/ml, CON: 59 +/- 7 pg/ml, LC: 38 +/- 10 pg/ml, P < 0.05). During exercise, Epi concentration showed the same trend (65%: 262 +/- 37 pg/ml, CON: 190 +/- 34 pg/ml, LC: 113.2 +/- 23 pg/ml, P < 0.05). In conclusion, lactate attenuates the catecholamine response during moderate-intensity exercise, likely by feedback inhibition.
AJP Endocrinology and Metabolism 01/2005; 288(1):E143-7. · 4.75 Impact Factor
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ABSTRACT: Hypobaric hypoxia and heightened metabolic rate increase free radical production.
We tested the hypothesis that antioxidant supplementation would reduce oxidative stress associated with increased energy expenditure (negative energy balance) at high altitude (HA 4300 m).
For 12 d at sea level (SL), 18 active men were fed a weight-stabilizing diet. Testing included fasting blood and 24-h urine samples to assess antioxidant status [plasma alpha-tocopherol, beta-carotene, lipid hydroperoxides (LPO), and urinary 8-hydroxydeoxyguanosine (8-OHdG)] and a prolonged submaximal (55% Vo2peak) oxidative stress index test (OSI) to evaluate exercise-induced oxidative stress (plasma LPO, whole blood reduced and oxidized glutathione, glutathione peroxidase, and urinary 8-OHdG). Subjects were then matched and randomly assigned to either a placebo or antioxidant supplement group for a double-blinded trial. Supplementation (20,000 IU of beta-carotene, 400 IU alpha-tocopherol acetate, 500 mg ascorbic acid, 100 microg selenium, and 30 mg zinc, or placebo) was begun 3 wk prior to and throughout a 14-d HA intervention. At HA, subjects' daily energy intake and expenditure were adjusted to achieve a caloric deficit of approximately 1400 kcal. Fasting blood and 24-h urine samples were collected throughout HA and the OSI test was repeated on HA day 1 and day 13.
Resting LPO concentrations increased and urinary 8-OHdG concentrations decreased over HA with no effect of supplementation. Prolonged submaximal exercise was not associated with increased concentrations of oxidative stress markers at SL or HA.
Antioxidant supplementation did not significantly affect markers of oxidative stress associated with increased energy expenditure at HA.
Aviation Space and Environmental Medicine 11/2004; 75(10):881-8. · 0.88 Impact Factor
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ABSTRACT: We examined the effects of menstrual cycle phase and oral contraceptive (OC) use on triglyceride mobilization during 90 min of rest and 60 min of leg ergometry exercise at 45 and 65% peak O(2) uptake (Vo(2 peak)) in eight moderately physically active, eumenorrheic women (24.8 +/- 1.2 yr). Subjects were tested during the follicular phase (FP) and the luteal phase (LP) before OC use and during the inactive phase (IP) and high-dose phase (HP) after 4 complete mo of OC use. Glycerol rate of appearance (R(a)), a measure of triglyceride mobilization, was determined in a 3-h postabsorptive state using a primed constant infusion of [1,1,2,3,3-(2)H]glycerol. Before OC use (BOC), there were no significant differences between FP and LP in any of the variables studied. Dietary composition, exercise patterns, plasma glycerol concentrations, growth hormone concentrations, and exercise respiratory exchange ratio did not change with OC use. However, 4 mo of OC use significantly (P < 0.05) increased glycerol R(a) in HP during exercise at 45% Vo(2 peak) (6.2 +/- 0.2, 6.5 +/- 0.4, and 7.7 +/- 1.1 micromol.kg(-1).min(-1) for BOC, IP, and HP, respectively) and in IP and HP at 65% Vo(2 peak) (6.6 +/- 0.1, 8.2 +/- 0.6, and 8.1 +/- 0.7 micromol.kg(-1).min(-1) for BOC, IP, and HP, respectively). Plasma cortisol concentrations were significantly higher with OC use at rest and during exercise at 45 and 65% Vo(2 peak). In summary, although fluctuations of endogenous ovarian steroids have little effect on triglyceride mobilization, the synthetic ovarian steroids found in OCs increase triglyceride mobilization and plasma cortisol concentrations in exercising women. We conclude that the hierarchy of effects of ovarian steroids and their analogs on triglyceride mobilization in exercising women is as follows: energy flux > OC use > recent carbohydrate nutrition, menstrual cycle effects.
Journal of Applied Physiology 08/2004; 97(1):302-9. · 3.75 Impact Factor
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Medicine & Science in Sports & Exercise 04/2004; 36(5):S108-S109. · 4.43 Impact Factor
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ABSTRACT: The number of individuals with spinal cord injury (SCI) participating in sports at recreational and elite levels is on the rise. However, loss of autonomic nervous system function below the lesion can compromise thermoregulatory capacity and increase the risk of heat stress relative to able-bodied (AB) individuals.
To test the hypotheses that exercise in a heated environment would increase tympanic temperature (TTY) more in individuals with SCI than AB individuals, and that foot cooling using a new device would attenuate the rise in TTY during exercise in both groups.
Six subjects with SCI (lesions C5-T5) and six AB controls were tested in a heated environment (means +/- SEM, temperature = 31.8 +/- 0.2 degrees C, humidity = 26 +/- 1%) for 45 min at 66% +/- 5 of arm cranking VO2peak and 30 min of recovery on two separate occasions with foot cooling (FC) or no foot cooling (NC) in randomized order.
During exercise and recovery in both trials, SCI TTY was elevated above baseline (P < 0.001) but more so in the NC versus FC trial (1.6 +/- 0.2 degrees C vs 1.0 +/- 0.2 degrees C, respectively, P < 0.005). Within the AB group, TTY was elevated above baseline for both trials (P < 0.001) with peak increases of 0.5 +/- 0.2 degrees C and 0.3 +/- 0.2 degrees C for NC and FC, respectively. TTY, face, and back temperature were higher in both SCI trials compared with AB trials (P < 0.05). Heart rate during exercise and recovery was lower in the SCI FC versus SCI NC (P < 0.05).
These results suggest that extraction of heat through the foot may provide an effective way to manipulate tympanic temperature in individuals with SCI, especially during exercise in the heat.
Medicine & Science in Sports & Exercise 03/2004; 36(3):411-7. · 4.43 Impact Factor
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ABSTRACT: To test the hypothesis that lactate plays a central role in the distribution of carbohydrate (CHO) potential energy for oxidation and glucose production (GP), we performed a lactate clamp (LC) procedure during rest and moderate intensity exercise. Blood [lactate] was clamped at approximately 4 mM by exogenous lactate infusion. Subjects performed 90 min exercise trials at 65 % of the peak rate of oxygen consumption (V(O(2))(,peak); 65 %), 55 % V(O(2))(,peak) (55 %) and 55 % V(O(2))(,peak) with lactate clamped to the blood [lactate] that was measured at 65 % V(O(2))(,peak) (55 %-LC). Lactate and glucose rates of appearance (R(a)), disappearance (R(d)) and oxidation (R(ox)) were measured with a combination of [3-(13)C]lactate, H(13)CO(3)(-), and [6,6-(2)H(2)]glucose tracers. During rest and exercise, lactate R(a) and R(d) were increased at 55 %-LC compared to 55 %. Glucose R(a) and R(d) were decreased during 55 %-LC compared to 55 %. Lactate R(ox) was increased by LC during exercise (55 %: 6.52 +/- 0.65 and 55 %-LC: 10.01 +/- 0.68 mg kg(-1) min(-1)) which was concurrent with a decrease in glucose oxidation (55 %: 7.64 +/- 0.4 and 55 %-LC: 4.35 +/- 0.31 mg kg(-1) min(-1)). With LC, incorporation of (13)C from tracer lactate into blood glucose (L GNG) increased while both GP and calculated hepatic glycogenolysis (GLY) decreased. Therefore, increased blood [lactate] during moderate intensity exercise increased lactate oxidation, spared blood glucose and decreased glucose production. Further, exogenous lactate infusion did not affect rating of perceived exertion (RPE) during exercise. These results demonstrate that lactate is a useful carbohydrate in times of increased energy demand.
The Journal of Physiology 12/2002; 544(Pt 3):963-75. · 4.72 Impact Factor
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ABSTRACT: To evaluate the hypothesis that precursor supply limits gluconeogenesis (GNG) during exercise, we examined training-induced changes in glucose kinetics [rates of appearance (R(a)) and disappearance (R(d))], oxidation (R(ox)), and recycling (R(r)) with an exogenous lactate infusion to 3.5-4.0 mM during rest and to pretraining 65% peak O(2) consumption (VO(2 peak)) levels during exercise. Control and clamped trials (LC) were performed at rest pre- (P(R)R, P(R)R-LC) and posttraining (P(O)R, P(O)R-LC) and during exercise pre- (P(R)E(X)) and posttraining at absolute (P(O)A(B), P(O)A(B)-LC) and relative (P(O)R(L), P(O)R(L)-LC) intensities. Glucose R(r) was not different in any rest or exercise condition. Glucose R(a) did not differ as a result of LC. Glucose R(ox) was significantly decreased with LC at P(O)R (0.38 +/- 0.03 vs. 0.56 +/- 0.04 mg. kg(-1). min(-1)) and P(O)A(B) (3.82 +/- 0.51 vs. 5.0 +/- 0.62 mg. kg(-1). min(-1)). Percent glucose R(d) oxidized decreased with all LC except P(O)R(L)-LC (P(R)R, 32%; P(R)R-LC, 22%; P(O)R, 27%; P(O)R-LC, 20%; P(O)A(B), 95%; P(O)A(B)-LC, 77%), which resulted in a significant increase in oxidation from alternative carbohydrate (CHO) sources at rest and P(O)A(B). We conclude that 1) increased arterial [lactate] did not increase glucose R(r) measured during rest or exercise after training, 2) glucose disposal or production did not change with increased precursor supply, and 3) infusion of exogenous CHO in the form of lactate resulted in the decrease of glucose R(ox).
AJP Endocrinology and Metabolism 12/2002; 283(5):E889-98. · 4.75 Impact Factor
