ABSTRACT
We hypothesized that blockade of alpha(1)-adrenergic receptors would prevent the rise in peripheral vascular resistance that normally occurs during acclimatization. Sixteen eumenorrheic women were studied at sea level (SL) and at 4,300 m (days 3 and 10). Volunteers were randomly assigned to take the selective alpha(1)-blocker prazosin or placebo. Venous compliance, forearm vascular resistance, and blood flow were measured using plethysmography. Venous compliance fell by day 3 in all subjects (1.39 +/- 0.30 vs. 1.62 +/- 0.43 ml. Delta 30 mmHg(-1) x 100 ml tissue(-1) x min(-1) at SL, means +/- SD). Altitude interacted with prazosin treatment (P < 0.0001) such that compliance returned to SL values by day 10 in the prazosin-treated group (1.68 +/- 0.19) but not in the placebo-treated group (1.20 +/- 0.10, P < 0.05). By day 3 at 4,300 m, all women had significant falls in resistance (35.2 +/- 13.2 vs. 54.5 +/- 16.1 mmHg x ml(-1) x min(-1) at SL) and rises in blood flow (2.5 +/- 1.0 vs. 1.6 +/- 0.5 ml. 100 ml tissue(-1) x min(-1) at SL). By day 10, resistance and flow returned toward SL, but this return was less in the prazosin-treated group (resistance: 39.8 +/- 4.6 mmHg x ml(-1) x min(-1) with prazosin vs. 58.5 +/- 9.8 mmHg x ml(-1) x min(-1) with placebo; flow: 1.9 +/- 0.7 ml. 100 ml tissue(-1) x min(-1) with prazosin vs. 2.3 +/- 0.3 ml x 100 ml tissue(-1) x min(-1) with placebo, P < 0.05). Lower resistance related to higher circulating epinephrine in both groups (r = -0.50, P < 0.0001). Higher circulating norepinephrine related to lower venous compliance in the placebo-treated group (r = -0.42, P < 0.05). We conclude that alpha(1)-adrenergic stimulation modulates peripheral vascular changes during acclimatization.
Subject(s)
Acclimatization/drug effects , Acclimatization/physiology , Adrenergic alpha-Antagonists/pharmacology , Altitude , Prazosin/pharmacology , Adult , Blood Pressure/drug effects , Blood Pressure/physiology , Epinephrine/blood , Female , Forearm/physiology , Humans , Norepinephrine/blood , Plethysmography , Regional Blood Flow/drug effects , Regional Blood Flow/physiology , Vascular Resistance/drug effects , Vascular Resistance/physiology , Veins/physiologyABSTRACT
Because the ovarian steroid hormones, progesterone and estrogen, have higher blood levels in the luteal (L) than in the follicular (F) phase of the menstrual cycle, and because of their known effects on ventilation and hematopoiesis, we hypothesized that less hypoxemia and less erythropoiesis would occur in the L than the F phase of the cycle after arrival at altitude. We examined erythropoiesis with menstrual cycle phase in 16 women (age 22.6 +/- 0.6 yr). At sea level, 11 of 16 women were studied during both menstrual cycle phases, and, where comparison within women was available, cycle phase did not alter erythropoietin (n = 5), reticulocyte count (n = 10), and red cell volume (n = 9). When all 16 women were taken for 11 days to 4,300-m altitude (barometric pressure = 462 mmHg), paired comparisons within women showed no differences in ovarian hormone concentrations at sea level vs. altitude on menstrual cycle day 3 or 10 for either the F (n = 11) or the L (n = 5) phase groups. Arterial oxygen saturation did not differ between the F and L groups at altitude. There were no differences by cycle phase on day 11 at 4,300 m for erythropoietin [22.9 +/- 4.7 (L) vs. 18.8 +/- 3.4 mU/ml (F)], percent reticulocytes [1.9 +/- 0.1 (L) vs. 2.1 +/- 0.3% (F)], hemoglobin [13.5 +/- 0.3 (L) vs. 13.7 +/- 0.3 g/100 ml (F)], percent hematocrit [40.6 +/- 1.4 (L) vs. 40.7 +/- 1.0% (F)], red cell volume [31.1 +/- 3.6 (L) vs. 33.0 +/- 1.6 ml/kg (F)], and blood ferritin [8.9 +/- 1.7 (L) vs. 10.2 +/- 0.9 microg/l (F)]. Blood level of erythropoietin was related (r = 0.77) to arterial oxygen saturation but not to the levels of progesterone or estradiol. We conclude that erythropoiesis was not altered by menstrual cycle phase during the first days at 4,300-m altitude.
Subject(s)
Altitude , Erythropoiesis/physiology , Menstrual Cycle/physiology , Adult , Arteries , Estradiol/blood , Female , Follicular Phase/physiology , Humans , Luteal Phase/physiology , Oxygen/blood , Partial Pressure , Progesterone/blood , Respiration , Time FactorsABSTRACT
Interleukin-6 (IL-6), an important cytokine involved in a number of biological processes, is consistently elevated during periods of stress. The mechanisms responsible for the induction of IL-6 under these conditions remain uncertain. This study examined the effect of alpha-adrenergic blockade on the IL-6 response to acute and chronic high-altitude exposure in women both at rest and during exercise. Sixteen healthy, eumenorrheic women (aged 23.2 +/- 1.4 yr) participated in the study. Subjects received either alpha-adrenergic blockade (prazosin, 3 mg/day) or a placebo in a double-blinded, randomized fashion. Subjects participated in submaximal exercise tests at sea level and on days 1 and 12 at altitude (4,300 m). Resting plasma and 24-h urine samples were collected throughout the duration of the study. At sea level, no differences were found at rest for plasma IL-6 between groups (1.5 +/- 0.2 and 1.2 +/- 0.3 pg/ml for placebo and blocked groups, respectively). On acute ascent to altitude, IL-6 levels increased significantly in both groups compared with sea-level values (57 and 84% for placebo and blocked groups, respectively). After 12 days of acclimatization, IL-6 levels remained elevated for placebo subjects; however, they returned to sea-level values in the blocked group. alpha-Adrenergic blockade significantly lowered the IL-6 response to exercise both at sea level (46%) and at altitude (42%) compared with placebo. A significant correlation (P = 0.004) between resting IL-6 and urinary norepinephrine excretion rates was found over the course of time while at altitude. In conclusion, the results indicate a role for alpha-adrenergic regulation of the IL-6 response to the stress of both short-term moderate-intensity exercise and hypoxia.
Subject(s)
Adrenergic alpha-Antagonists/pharmacology , Altitude , Exercise/physiology , Interleukin-6/biosynthesis , Adrenergic alpha-Agonists/pharmacology , Adult , Anaerobic Threshold/physiology , Catecholamines/urine , Female , Humans , Male , Menstrual Cycle/physiology , Ovary/metabolism , Oxygen Consumption/physiology , Phenylephrine/pharmacologyABSTRACT
Women living at low altitudes or acclimatized to high altitudes have greater effective ventilation in the luteal (L) compared with follicular (F) menstrual cycle phase and compared with men. We hypothesized that ventilatory acclimatization to high altitude would occur more quickly and to a greater degree in 1) women in their L compared with women in their F menstrual cycle phase, and 2) in women compared with men. Studies were conducted on 22 eumenorrheic, unacclimatized, sea-level (SL) residents. Indexes of ventilatory acclimatization [resting ventilatory parameters, hypoxic ventilatory response, hypercapnic ventilatory response (HCVR)] were measured in 14 women in the F phase and in 8 other women in the L phase of their menstrual cycle, both at SL and again during a 12-day residence at 4,300 m. At SL only, ventilatory studies were also completed in both menstrual cycle phases in 12 subjects (i.e., within-subject comparison). In these subjects, SL alveolar ventilation (expressed as end-tidal PCO(2)) was greater in the L vs. F phase. Yet the comparison between L- and F-phase groups found similar levels of resting end-tidal PCO(2), hypoxic ventilatory response parameter A, HCVR slope, and HCVR parameter B, both at SL and 4,300 m. Moreover, these indexes of ventilatory acclimatization were not significantly different from those previously measured in men. Thus female lowlanders rapidly ascending to 4,300 m in either the L or F menstrual cycle phase have similar levels of alveolar ventilation and a time course for ventilatory acclimatization that is nearly identical to that reported in male lowlanders.
Subject(s)
Acclimatization/physiology , Altitude , Blood Gas Analysis , Carbon Dioxide/blood , Female , Follicular Phase/physiology , Humans , Luteal Phase/physiology , Male , Menstrual Cycle/physiology , Oxygen Consumption/physiology , Respiratory Function Tests , Respiratory Mechanics/physiology , Sex CharacteristicsABSTRACT
After short-term exposure to high altitude (HA), men appear to be less sensitive to insulin than at sea level (SL). We hypothesized that the same would be true in women, that reduced insulin sensitivity would be directly related to the rise in plasma epinephrine concentrations at altitude, and that the addition of alpha-adrenergic blockade would potentiate the reduction. To test the hypotheses, 12 women consumed a high-carbohydrate meal at SL and after 16 h at simulated 4,300-m elevation (HA). Subjects were studied twice at each elevation: once with prazosin (Prz), an alpha(1)-adrenergic antagonist, and once with placebo (Pla). Mathematical models were used to assess insulin resistance based on fasting [homeostasis model assessment of insulin resistance (HOMA-IR)] and postprandial [composite model insulin sensitivity index (C-ISI)] glucose and insulin concentrations. Relative to SL-Pla (HOMA-IR: 1.86 +/- 0.35), insulin resistance was greater in HA-Pla (3.00 +/- 0.45; P < 0.05), SL-Prz (3.46 +/- 0.51; P < 0.01), and HA-Prz (2.82 +/- 0.43; P < 0.05). Insulin sensitivity was reduced in HA-Pla (C-ISI: 4.41 +/- 1.03; P < 0.01), SL-Prz (5.73 +/- 1.01; P < 0.05), and HA-Prz (4.18 +/- 0.99; P < 0.01) relative to SL-Pla (8.02 +/- 0.92). Plasma epinephrine was significantly elevated in HA-Pla (0.57 +/- 0.08 ng/ml; P < 0.01), SL-Prz (0.42 +/- 0.07; P < 0.05), and HA-Prz (0.82 +/- 0.07; P < 0.01) relative to SL-Pla (0.28 +/- 0.04), but correlations with HOMA-IR, HOMA-beta-cell function, and C-ISI were weak. In women, short-term exposure to simulated HA reduced insulin sensitivity compared with SL. The change does not appear to be directly mediated by a concurrent rise in plasma epinephrine concentrations.
Subject(s)
Altitude Sickness/physiopathology , Altitude , Blood Glucose/metabolism , Insulin/metabolism , Prazosin/pharmacology , Receptors, Adrenergic, alpha-1/physiology , Adrenergic alpha-1 Receptor Antagonists , Adult , Altitude Sickness/blood , C-Peptide/blood , Dietary Carbohydrates , Epinephrine/pharmacology , Fasting , Female , Homeostasis , Humans , Insulin/blood , Insulin Resistance/physiology , Insulin Secretion , Male , Models, Biological , Placebos , Reference Values , Sex Characteristics , Time FactorsABSTRACT
We examined the effect of recombinant human growth hormone (rhGH) and/or recombinant human insulin-like growth factor-I (rhIGF-l) on regional fat loss in postmenopausal women undergoing a weight loss regimen of diet plus exercise. Twenty-seven women aged 59-79 years, 20-40% above ideal body weight, completed a 12-week program consisting of resistance training 2 days/week and walking 3 days/week, while consuming a diet that was 500 kcal/day less than that required for weight maintenance. Participants were randomly assigned in a double-blind fashion to receive rhGH (0.025 mg/kg BW/day; n = 7), rhIGF-I (0.015 mg/kg BW/day; n = 7), rhGH + rhIGF-I (n = 6), or placebo (PL; n = 7). Regional and whole body fat mass were determined by dual X-ray absorptiometry. Body fat distribution was assessed by the ratios of trunk fat-to-limb fat (TrF/LimbF) and trunk fat-to-total fat (TrF/TotF). Limb and trunk fat decreased in all groups (p < 0.01). For both ratios of fat distribution, the rhGH treated group experienced an enhanced loss of truncal compared to peripheral fat (p < 0.01), with no significant change for those administered rhIGF-I or PL. There was no association between change in fat distribution and indices of cardiovascular disease risk as determined by serum lipidilipoprotein levels and maximal aerobic capacity. These results suggest that administration of rhGH facilitates a decrease in central compared to peripheral fat in older women undertaking a weight loss program that combines exercise and moderate caloric restriction, although no beneficial effects are conferred to lipid/lipoprotein profiles. Further, the effect of rhGH is not enhanced by combining rhGH with rhIGF-I administration. In addition, rhIGF-I does not augment the loss of trunk fat when administered alone.
Subject(s)
Energy Intake , Exercise , Fats/metabolism , Growth Hormone/pharmacology , Postmenopause/metabolism , Weight Loss , Aged , Double-Blind Method , Estrogen Replacement Therapy , Female , Humans , Middle AgedABSTRACT
The activity of the hypothalamic-GH-insulin-like growth factor I (hypothalamic-GH-IGF-I) axis declines with age, and some of the catabolic changes of aging have been attributed to the somatopause. The purpose of this investigation was to determine the impact of 1 yr of IGF-I hormone replacement therapy on body composition, bone density, and psychological parameters in healthy, nonobese, postmenopausal women over 60 yr of age. Subjects (n = 16, 70.6 +/- 2.0 yr, 71.8 +/- 2.8 kg) were randomly assigned to either the self-injection IGF-I (15 microg/kg twice daily) or placebo group and were studied at baseline, at 6 months, and at 1 yr of treatment. There were no significant differences between the IGF-I and placebo groups in any of the measured variables at baseline. Fasting blood IGF-I levels were significantly elevated above baseline values (65.6 +/- 11.9 ng/mL) at 6 months (330.0 +/- 52.8) and 12 months (297.7 +/- 40.8) in the IGF-I treated group but did not change in the placebo subjects. Circulating levels of IGF-binding protein-1 and -3 were unaffected by the IGF-I treatment. Bone mineral density of the forearm, lumbar spine, hip, and whole body [as measured by dual-energy x-ray absorptiometry (DXA)] did not change in either group. Similarly, there was no difference in DXA-measured lean mass, fat mass, or percent body fat throughout the treatment intervention. Muscle strength values (grip, bench press, leg press), blood lipid parameters (cholesterol, high-density lipoprotein, low-density lipoprotein, triglycerides), and measures of postmeal glucose disposal were not altered by IGF-I treatment, although postmeal insulin levels were lower in the IGF-I subjects at 12 months. IGF-I did not affect bone turnover markers (osteocalcin and type I collagen N-teleopeptide), but subjects who were taking estrogen had significantly lower turnover markers than subjects who were not on estrogen at baseline, 6 months, and 12 months. Finally, the psychological measures of mood and memory were also not altered by the intervention. Despite the initial intent to recruit additional subjects, the study was discontinued after 16 subjects completed the protocol, because the preliminary analyses above indicated that no changes were occurring in any outcome variables, regardless of treatment regimen. Therefore, we conclude that 1 yr of IGF-I treatment, at a dose sufficient to elevate circulating IGF-I to young normal values, is not an effective means to alter body composition or blood parameters nor improve bone density, strength, mood, or memory in older women.
Subject(s)
Body Composition/drug effects , Bone Density/drug effects , Insulin-Like Growth Factor I/administration & dosage , Postmenopause/physiology , Postmenopause/psychology , Affect/drug effects , Drug Administration Schedule , Female , Humans , Insulin-Like Growth Factor I/analysis , Insulin-Like Growth Factor I/pharmacology , Memory/drug effects , Middle Aged , Postmenopause/blood , Treatment FailureABSTRACT
We have previously documented the importance of the sympathetic nervous system in acclimatizing to high altitude in men. The purpose of this investigation was to determine the extent to which alpha-adrenergic blockade affects the sympathoadrenal responses to exercise during acute high-altitude exposure in women. Twelve eumenorrheic women (24.7 +/- 1.3 yr, 70.6 +/- 2.6 kg) were studied at sea level and on day 2 of high-altitude exposure (4,300-m hypobaric chamber) in either their follicular or luteal phase. Subjects performed two graded-exercise tests at sea level (on separate days) on a bicycle ergometer after 3 days of taking either a placebo or an alpha-blocker (3 mg/day prazosin). Subjects also performed two similar exercise tests while at altitude. Effectiveness of blockade was determined by phenylephrine challenge. At sea level, plasma norepinephrine levels during exercise were 48% greater when subjects were alpha-blocked compared with their placebo trial. This difference was only 25% when subjects were studied at altitude. Plasma norepinephrine values were significantly elevated at altitude compared with sea level but to a greater extent for the placebo ( upward arrow 59%) vs. blocked ( upward arrow 35%) trial. A more dramatic effect of both altitude ( upward arrow 104% placebo vs. 95% blocked) and blockade ( upward arrow 50% sea level vs. 44% altitude) was observed for plasma epinephrine levels during exercise. No phase differences were observed across any condition studied. It was concluded that alpha-adrenergic blockade 1) resulted in a compensatory sympathoadrenal response during exercise at sea level and altitude, and 2) this effect was more pronounced for plasma epinephrine.
Subject(s)
Adrenergic beta-Antagonists/pharmacology , Altitude , Epinephrine/blood , Exercise/physiology , Norepinephrine/blood , Adrenergic alpha-Agonists/pharmacology , Adrenergic alpha-Antagonists/pharmacology , Adult , Double-Blind Method , Epinephrine/urine , Exercise Test , Female , Humans , Norepinephrine/urine , Oxygen Consumption/physiology , Phenylephrine/pharmacology , Prazosin/pharmacology , Time FactorsABSTRACT
BACKGROUND: Studies were conducted to determine the effect of altitude exposure on intraocular pressure (IOP) and any relationship with the severity of acute mountain sickness (AMS). HYPOTHESES: a) IOP is decreased during exposure to 4300 m altitude; b) there is a positive correlation between IOP and AMS; and c) there is a correlation between changes in urinary catecholamines and IOP. METHODS: IOP (noncontact tonometry) was measured in 11 resting males during acute simulated altitude (446 mmHg, < 2 h, hypobaric chamber), during altitude acclimatization (15 d at 4300 m), and in 6 of the 11 volunteers during re-exposure in the chamber after 8 d at sea level (Study A). In a second study (Study B) of 12 females, IOP (contact tonometry) and 24-h urinary catecholamines were measured during a 50-h chamber exposure (446 mmHg). AMS severity was assessed using the Environmental Symptoms Questionnaire (ESQ-C). RESULTS: IOP decreased 25% after 2 d at altitude and returned toward sea level values by 15 d (Study A). IOP was reduced 13% after 5 h of exposure followed by return toward sea level values (Study B). Significant correlation was found between the sea level IOP and ESQ-C (Study A); significant correlation was found between the reduction in IOP and the ESQ-C and urinary epinephrine concentrations (Study B). CONCLUSIONS: Altitude exposure resulted in a reduction in IOP that occurred within hours and recovered during acclimatization. This reduction may be related to increases in epinephrine concentration. Measurement of IOP before and during altitude exposure may provide an objective method of assessing an individual's response to hypoxic stress.
Subject(s)
Acclimatization , Altitude , Intraocular Pressure , Adult , Altitude Sickness/physiopathology , Analysis of Variance , Atmospheric Pressure , Catecholamines/urine , Female , Humans , Male , Tonometry, Ocular/methodsABSTRACT
The purpose of this investigation was to determine the sympathoadrenal response to exercise in women after acclimatization to high altitude. Sixteen eumenorrheic women (age, 23.6 +/- 1.2 years; weight, 56.2 +/- 4.3 kg) were studied at sea level and after 10 days of high-altitude exposure (4,300 m) in either the follicular (n = 11) or luteal (n = 5) phase. Subjects performed two 45-minute submaximal steady-state exercise tests (50% and 65% peak O2 consumption [VO2 peak]) at sea level on a bicycle ergometer. Exercise tests were also performed on day 10 of altitude exposure (50% VO2 peak at sea level). As compared with rest, plasma epinephrine levels increased 36% in response to exercise at 50% VO2 peak at sea level, with no differences found between cycle phases. This increase was significantly greater (increase 44%) during exercise at 65% VO2 peak. At altitude, the epinephrine response was identical to that found for 65% VO2 peak exercise at sea level (increase 44%), with no differences found between phase assignments. The plasma norepinephrine response differed from that for epinephrine such that the increase with exercise at altitude (increase 61%) was significantly greater compared with 65% Vo2 peak exercise at sea level (increase 49%). Again, no phase differences were observed. It is concluded that the sympathoadrenal response to exercise (1) did not differ between cycle phases across any condition and (2) was similar to that found previously in men, and (3) the relative exercise intensity is the primary factor responsible for the epinephrine response to exercise, whereas altitude had an additive effect on the norepinephrine response to exercise.
Subject(s)
Adrenal Glands/physiology , Altitude , Exercise/physiology , Sympathetic Nervous System/physiology , Adult , Epinephrine/blood , Female , Follicular Phase/blood , Follicular Phase/physiology , Heart Rate/physiology , Humans , Lactic Acid/blood , Luteal Phase/blood , Luteal Phase/physiology , Norepinephrine/blood , Oxygen Consumption/physiology , RespirationABSTRACT
To evaluate the effects of endurance training on the expression of monocarboxylate transporters (MCT) in human vastus lateralis muscle, we compared the amounts of MCT1 and MCT4 in total muscle preparations (MU) and sarcolemma-enriched (SL) and mitochondria-enriched (MI) fractions before and after training. To determine if changes in muscle lactate release and oxidation were associated with training-induced changes in MCT expression, we correlated band densities in Western blots to lactate kinetics determined in vivo. Nine weeks of leg cycle endurance training [75% peak oxygen consumption (VO(2 peak))] increased muscle citrate synthase activity (+75%, P < 0.05) and percentage of type I myosin heavy chain (+50%, P < 0.05); percentage of MU lactate dehydrogenase-5 (M4) isozyme decreased (-12%, P < 0.05). MCT1 was detected in SL and MI fractions, and MCT4 was localized to the SL. Muscle MCT1 contents were consistent among subjects both before and after training; in contrast, MCT4 contents showed large interindividual variations. MCT1 amounts significantly increased in MU, SL, and MI after training (+90%, +60%, and +78%, respectively), whereas SL but not MU MCT4 content increased after training (+47%, P < 0.05). Mitochondrial MCT1 content was negatively correlated to net leg lactate release at rest (r = -0.85, P < 0.02). Sarcolemmal MCT1 and MCT4 contents correlated positively to net leg lactate release at 5 min of exercise at 65% VO(2 peak) (r = 0.76, P < 0.03 and r = 0. 86, P < 0.01, respectively). Results support the conclusions that 1) endurance training increases expression of MCT1 in muscle because of insertion of MCT1 into both sarcolemmal and mitochondrial membranes, 2) training has variable effects on sarcolemmal MCT4, and 3) both MCT1 and MCT4 participate in the cell-cell lactate shuttle, whereas MCT1 facilitates operation of the intracellular lactate shuttle.
Subject(s)
Carrier Proteins/physiology , L-Lactate Dehydrogenase/physiology , Muscle Proteins , Muscle, Skeletal/physiology , Physical Endurance/physiology , Physical Fitness/physiology , Adult , Amino Acid Sequence , Anaerobic Threshold/physiology , Blotting, Western , Carrier Proteins/metabolism , Humans , Isoenzymes , L-Lactate Dehydrogenase/metabolism , Lactic Acid/metabolism , Male , Mitochondria, Muscle/enzymology , Mitochondria, Muscle/metabolism , Molecular Sequence Data , Monocarboxylic Acid Transporters , Muscle, Skeletal/enzymology , Myosin Heavy Chains/metabolism , Oxidation-Reduction , Prostaglandin-Endoperoxide Synthases/biosynthesis , Subcellular Fractions/metabolismABSTRACT
The hypothesis that endurance training increases gluconeogenesis (GNG) during rest and exercise was evaluated. We determined glucose turnover with [6,6-(2)H]glucose and lactate incorporation into glucose by use of [3-(13)C]lactate during 1 h of cycle ergometry at two intensities [45 and 65% peak O(2) consumption (VO(2 peak))] before and after training [65% pretraining VO(2 peak)], same absolute workload (ABT), and 65% posttraining VO(2 peak), same relative intensity (RLT). Nine males (178.1 +/- 2.5 cm, 81.8 +/- 3.3 kg, 27.4 +/- 2.0 yr) trained for 9 wk on a cycle ergometer 5 times/wk for 1 h at 75% VO(2 peak). The power output that elicited 66.0 +/- 1.1% of VO(2 peak) pretraining elicited 54.0 +/- 1.7% posttraining. Rest and exercise arterial glucose concentrations were similar before and after training, regardless of exercise intensity. Arterial lactate concentration during exercise was significantly greater than at rest before and after training. Compared with 65% pretraining, arterial lactate concentration decreased at ABT (4.75 +/- 0.4 mM, 65% pretraining; 2.78 +/- 0.3 mM, ABT) and RLT (3.76 +/- 0.46 mM) (P < 0.05). At rest after training, the percentage of glucose rate of appearance (R(a)) from GNG more than doubled (1.98 +/- 0.5% pretraining; 5.45 +/- 1.3% posttraining), as did the rate of GNG (0.11 +/- 0.03 mg x kg(-1) x min(-1) pretraining, 0.24 +/- 0.06 mg x kg(-1) x min(-1) posttraining). During exercise after training, %glucose R(a) from GNG increased significantly at ABT (2.3 +/- 0.8% at 65% pre- vs. 7.6 +/- 2.1% posttraining) and RLT (6.1 +/- 1.5%), whereas GNG increased almost threefold (P < 0.05) at ABT (0.24 +/- 0.08 mg x kg(-1) x min(-1) 65% pre-, and 0.71 +/- 0.18 mg x kg(-1) x min(-1) posttraining) and RLT (0.75 +/- 0.26 mg x kg(-1) x min(-1)). We conclude that endurance training increases gluconeogenesis twofold at rest and threefold during exercise at given absolute and relative exercise intensities.
Subject(s)
Exercise/physiology , Gluconeogenesis , Physical Endurance , Rest , Adult , Arteries , Blood Glucose/metabolism , Humans , Kinetics , Lactic Acid/blood , Male , Oxygen ConsumptionABSTRACT
To evaluate the hypothesis that exposure to high altitude would reduce blood glucose and total carbohydrate utilization relative to sea level (SL), 16 young women were studied over four 12-day periods: at 50% of peak O(2) consumption in different menstrual cycle phases (SL-50), at 65% of peak O(2) consumption at SL (SL-65), and at 4,300 m (HA). After 10 days in each condition, blood glucose rate of disappearance (R(d)) and respiratory exchange ratio were measured at rest and during 45 min of exercise. Glucose R(d) during exercise at HA (4.71 +/- 0.30 mg. kg(-1). min(-1)) was not different from SL exercise at the same absolute intensity (SL-50 = 5.03 mg. kg(-1). min(-1)) but was lower at the same relative intensity (SL-65 = 6.22 mg. kg(-1). min(-1), P < 0.01). There were no differences, however, when glucose R(d) was corrected for energy expended (kcal/min) during exercise. Respiratory exchange ratios followed the same pattern, except carbohydrate oxidation remained lower (-23.2%, P < 0.01) at HA than at SL when corrected for energy expended. In women, unlike in men, carbohydrate utilization decreased at HA. Relative abundance of estrogen and progesterone in women may partially explain the sex differences in fuel utilization at HA, but subtle differences between menstrual cycle phases at SL had no physiologically relevant effects.
Subject(s)
Altitude , Carbohydrate Metabolism , Exercise/physiology , Adult , Basal Metabolism , Blood Glucose/metabolism , Catecholamines/blood , Female , Humans , Hydrocortisone/blood , Insulin/blood , Lactic Acid/blood , Male , Menstrual Cycle/blood , Menstrual Cycle/physiology , Oxidation-Reduction , Oxygen Consumption , Pulmonary Gas Exchange , Sex CharacteristicsABSTRACT
To test the hypotheses that prolonged exposure to moderately high altitude increases the energy requirement of adequately fed women and that the sole cause of the increase is an elevation in basal metabolic rate (BMR), we studied 16 healthy women [21.7 +/- 0.5 (SD) yr; 167.4 +/- 1.1 cm; 62.2 +/- 1.0 kg]. Studies were conducted over 12 days at sea level (SL) and at 4,300 m [high altitude (HA)]. To test that menstrual cycle phase has an effect on energetics at HA, we monitored menstrual cycle in all women, and most women (n = 11) were studied in the same phase at SL and HA. Daily energy intake at HA was increased to respond to increases in BMR and to maintain body weight and body composition. Mean BMR for the group rose 6.9% above SL by day 3 at HA and fell to SL values by day 6. Total energy requirement remained elevated 6% at HA [ approximately 670 kJ/day (160 kcal/day) above that at SL], but the small and transient increase in BMR could not explain all of this increase, giving rise to an apparent "energy requirement excess." The transient nature of the rise in BMR may have been due to the fitness level of the subjects. The response to altitude was not affected by menstrual cycle phase. The energy requirement excess is at present unexplained.
Subject(s)
Altitude , Energy Intake/physiology , Energy Metabolism/physiology , Adult , Basal Metabolism/physiology , Body Composition , Body Weight , Catecholamines/analysis , Female , Follicular Phase/physiology , Humans , Luteal Phase/physiology , Nitrogen/analysis , Oxygen Consumption , Time Factors , Water-Electrolyte BalanceABSTRACT
In previous gender comparisons of muscle performance, men and women rarely have been closely matched, absolute force has not been equalized, and rates of fatigue and early recovery have not been determined. We compared adductor pollicis muscle performance at a similar absolute force development in healthy men and women (both n=9) matched for adductor pollicis maximal voluntary contraction (MVC) force (132 +/- 5 N for women and 136 +/- 4 N for men, mean +/- SE, P > 0.05). Subjects repeated static contractions at a target force of approximately 50% of MVC force of rested muscle (68 +/- 3 N or 51.9 +/- 1.0% MVC for women and 72 +/- 2 N or 53.0 +/- 2.0% MVC for men, P > 0.05) for 5 s followed by 5 s rest until exhaustion, i. e. inability to maintain the target force for 5 s. MVC force was measured following each minute of exercise, at exhaustion, and after each minute for 3 min of passive recovery. For women compared with men: MVC force fell less after 1 min of exercise (to 93 +/- 1% vs. 80 +/- 3% of MVC force of rested muscle, respectively, P < 0.05); MVC force (N min-1) fell approximately 2-fold slower (P < 0.05); and endurance time to exhaustion was nearly two times longer (14.7 +/- 1. 6 min vs. 7.9 +/- 0.7 min, P < 0.05). After declining to a similar level of MVC force of rested muscle at exhaustion (56 +/- 1% for women and 56 +/- 3% for men), MVC force rose faster in women than in men (to 71 +/- 2% vs. 65 +/- 3% of MVC force of rested muscle, respectively; P < 0.05) during the first minute of recovery. The findings are consistent with the hypothesis that slower adductor pollicis muscle fatigue in women is linked with differences between men and women both in impairment of force generating capacity, per se, and in rates of recovery between contractions.
Subject(s)
Muscle Contraction/physiology , Muscle Fatigue/physiology , Muscle, Skeletal/physiology , Sex Characteristics , Adult , Electric Stimulation , Exercise Test , Female , Humans , Male , Thumb/physiology , Transducers, PressureABSTRACT
We evaluated the hypotheses that endurance training decreases arterial lactate concentration ([lactate](a)) during continuous exercise by decreasing net lactate release () and appearance rates (R(a)) and increasing metabolic clearance rate (MCR). Measurements were made at two intensities before [45 and 65% peak O(2) consumption (VO(2 peak))] and after training [65% pretraining VO(2 peak), same absolute workload (ABT), and 65% posttraining VO(2 peak), same relative intensity (RLT)]. Nine men (27.4 +/- 2.0 yr) trained for 9 wk on a cycle ergometer, 5 times/wk at 75% VO(2 peak). Compared with the 65% VO(2 peak) pretraining condition (4.75 +/- 0.4 mM), [lactate](a) decreased at ABT (41%) and RLT (21%) (P < 0.05). decreased at ABT but not at RLT. Leg lactate uptake and oxidation were unchanged at ABT but increased at RLT. MCR was unchanged at ABT but increased at RLT. We conclude that 1) active skeletal muscle is not solely responsible for elevated [lactate](a); and 2) training increases leg lactate clearance, decreases whole body and leg lactate production at a given moderate-intensity power output, and increases both whole body and leg lactate clearance at a high relative power output.
Subject(s)
Lactic Acid/metabolism , Muscle, Skeletal/metabolism , Physical Endurance/physiology , Physical Fitness/physiology , Adult , Algorithms , Body Composition/physiology , Diet , Exercise Test , Hemodynamics/physiology , Humans , Kinetics , Leg/physiology , Male , Regional Blood Flow/physiologyABSTRACT
Travel to terrestrial altitudes greater than 2500 m, for more than 2 to 3 days, results in acute and long-term physiologic adaptations with the potential to profoundly affect the requirements for some nutrients. This article discusses the evidence for these increased requirements and makes recommendations regarding appropriate intakes at high altitude. Discussion of nutrients includes energy and the food components that supply it (i.e., protein, carbohydrate, and fat), water, vitamins, and minerals. Because the anorexia associated with high altitude exposure may limit the intake of adequate nutrients, a food and water regimen, or "doctrine," is proposed and described.
Subject(s)
Altitude , Exercise/physiology , Mountaineering/physiology , Nutritional Requirements , Diet , Energy Metabolism , Humans , Micronutrients/metabolism , Water/physiologyABSTRACT
We evaluated the hypotheses that alterations in glucose disposal rate (R(d)) due to endurance training are the result of changed net glucose uptake by active muscle and that blood glucose is shunted to working muscle during exercise requiring high relative power output. We studied leg net glucose uptake during 1 h of cycle ergometry at two intensities before training [45 and 65% of peak rate of oxygen consumption (VO(2 peak))] and after training [65% pretraining VO(2 peak), same absolute workload (ABT), and 65% posttraining VO(2 peak), same relative workload (RLT)]. Nine male subjects (178.1 +/- 2.5 cm, 81.8 +/- 3.3 kg, 27.4 +/- 2.0 yr) were tested before and after 9 wk of cycle ergometer training, five times a week at 75% VO(2 peak). The power output that elicited 66.0 +/- 1.1% of VO(2 peak) before training elicited 54.0 +/- 1.7% after training. Whole body glucose R(d) decreased posttraining at ABT (5.45 +/- 0.31 mg. kg(-1). min(-1) at 65% pretraining to 4.36 +/- 0.44 mg. kg(-1). min(-1)) but not at RLT (5.94 +/- 0.47 mg. kg(-1). min(-1)). Net glucose uptake was attenuated posttraining at ABT (1.87 +/- 0.42 mmol/min at 65% pretraining and 0.54 +/- 0.33 mmol/min) but not at RLT (2.25 +/- 0. 81 mmol/min). The decrease in leg net glucose uptake at ABT was of similar magnitude as the drop in glucose R(d) and thus could explain dampened glucose flux after training. Glycogen degradation also decreased posttraining at ABT but not RLT. Leg net glucose uptake accounted for 61% of blood glucose flux before training and 81% after training at the same relative (65% VO(2 peak)) workload and only 38% after training at ABT. We conclude that 1) alterations in active muscle glucose uptake with training determine changes in whole body glucose kinetics; 2) muscle glucose uptake decreases for a given, moderate intensity task after training; and 3) hard exercise (65% VO(2 peak)) promotes a glucose shunt from inactive tissues to active muscle.
Subject(s)
Glucose/metabolism , Muscle, Skeletal/metabolism , Physical Education and Training , Physical Endurance/physiology , Adult , Arteries , Blood Glucose/analysis , Glucagon/blood , Glycogen/metabolism , Humans , Insulin/blood , Kinetics , Leg , Male , Oxygen Consumption/physiology , Pulmonary Gas Exchange/physiologyABSTRACT
PURPOSE: The purpose of this study was to compare postprandial glycemic, insulinemic, and physiologic responses to a pre-exercise meal calculated to have a low glycemic index (LGI) with one calculated to have a moderately high glycemic index (HGI); each meal provided three foods totaling 1.5 g carbohydrate/kg body weight. METHODS: After an overnight fast, 10 trained cyclists consumed one of the test meals or water 30 min before cycling 2 h at 70% of maximum oxygen uptake (VO2max), followed by cycling to exhaustion at 100% of VO2max. RESULTS: Plasma insulin levels were significantly lower (P < 0.05) after LGI than after HGI through 20 min of exercise. Significantly higher (P < 0.05) respiratory exchange ratios were observed after HGI than after LGI until 2 h of exercise. At that time plasma glucose levels were significantly higher and ratings of perceived exertion lower (P < 0.05) after LGI compared with after HGI. Time to exhaustion was 59% longer after LGI (206.5+/-43.5 s) than after HGI (129.5+/-22.8 s). CONCLUSIONS: These results suggest a pre-exercise LGI may positively affect maximal performance following sustained exercise. The LGI maintained higher plasma glucose levels at the end of 2 h of strenuous exercise than the HGI, which may have better supported subsequent maximal effort.
Subject(s)
Blood Glucose/analysis , Dietary Carbohydrates/metabolism , Exercise/physiology , Physical Endurance/physiology , Adult , Bicycling , Blood Glucose/metabolism , Humans , Male , Oxygen Consumption , Postprandial PeriodABSTRACT
To evaluate the hypothesis that endurance training increases intramuscular triglyceride (IMTG) oxidation, we studied leg net free fatty acid (FFA) and glycerol exchange during 1 h of cycle ergometry at two intensities before training [45 and 65% of peak rate of oxygen consumption (V(O2) peak)] and after training [65% pretraining V(O2) peak, same absolute workload (ABT), and 65% posttraining V(O2) peak, same relative intensity (RLT)]. Nine male subjects (178.1 +/- 2.5 cm, 81.8 +/- 3.3 kg, 27.4 +/- 2.0 yr) were tested before and after 9 wk of cycle ergometer training, five times per week at 75% V(O2) peak. The power output that elicited 66.1 +/- 1.1% of V(O2) peak before training elicited 54.0 +/- 1.7% after training due to a 14.6 +/- 3.1% increase in V(O2) peak. Training significantly (P < 0.05) decreased pulmonary respiratory exchange ratio (RER) values at ABT (0.96 +/- 0.01 at 65% pre- vs. 0.93 +/- 0.01 posttraining) but not RLT (0.95 +/- 0.01). After training, leg respiratory quotient (RQ) was not significantly different at either ABT (0.98 +/- 0.02 pre- vs. 0.98 +/- 0.03 posttraining) or RLT (1.01 +/- 0.02). Net FFA uptake was increased at RLT but not ABT after training. FFA fractional extraction was not significantly different after training or at any exercise intensity. Net glycerol release, and therefore IMTG lipolysis calculated from three times net glycerol release, did not change from rest to exercise or at ABT but decreased at the same RLT after training. Muscle biopsies revealed minor muscle triglyceride changes during exercise. Simultaneous measurements of leg RQ, net FFA uptake, and glycerol release by working legs indicated no change in leg FFA oxidation, FFA uptake, or IMTG lipolysis during leg cycling exercise that elicits 65% pre- and 54% posttraining V(O2) peak. Training increases working muscle FFA uptake at 65% V(O2) peak, but high RER and RQ values at all work intensities indicate that FFA and IMTG are of secondary importance as fuels in moderate and greater-intensity exercise.