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1.
Dose-related elevations in venous pH with citrate ingestion do not alter 40-km cycling time-trial performance 总被引:1,自引:0,他引:1
Elske J. Schabort G. Wilson Timothy D. Noakes 《European journal of applied physiology》2000,83(4-5):320-327
The purpose of the current investigation was to determine whether sodium citrate enhances endurance cycling performance and,
if so, what dosage(s) produces this effect. Eight trained [peak power output: 362 (48) W; power:weight: 5.1 (0.4) W · kg−1, mean (SD)] male cyclists were requested to complete four, 40-km time-trials, each separated by 3–7 days, on their own bicycles,
mounted on a Kingcycle ergometer. To mimic the stochastic nature of cycle road races, the time-trials included four 500-m,
four 1-km and two 2-km sprints. The experimental conditions involved the ingestion of three dosages of sodium citrate dissolved
in 400 ml water: 0.2 g · kg−1, 0.4 g · kg−1 and 0.6 g · kg−1 body mass (b.m.) and a placebo (calcium carbonate, 0.1 g · kg−1 b.m.). Subjects were asked to complete both the sprints and total distance in the fastest time possible. Venous blood samples
were collected before, as well as at 10-km intervals during the trials for the analysis of plasma lactate and glucose concentrations
and for the measurement of blood pH and PCO2 levels. Immediately before, as well as during exercise, pH was significantly higher in the group ingesting the highest citrate
dose (range 7.36–7.45) compared to the placebo (range 7.31–7.39) and the two lower citrate dosages. Despite this, no significant
differences in power output (P=0.886) or time taken to complete the 40 km (P=0.754) were measured between the four trials. The average performance times (in min:s, with SD in parentheses) and average
power output (in W) for the 40-km time-trials were: 58:46 (5:06) [265 (62) W], 60:24 (6:07) [251 (59) W], 61:47 (5:07) [243
(44) W] and 60:02 (5.05) [255 (55) W] for the 0.2, 0.4, 0.6 g · kg−1 b.m. sodium citrate and placebo trials, respectively. There were also no significant differences measured between treatments
in terms of time, power output, speed or heart rate during the 500-m, 1-km and 2-km sprints. The ingestion of increasing sodium
citrate dosages before exercise produced dose-dependent changes in pH, base excess and HCO−
3 concentrations before and during the 40-km time-trial. However, these changes influenced neither the time-trial time nor
the sprinting performance times.
Accepted: 7 June 2000 相似文献
2.
Eight males were recruited to examine the effect of branched-chain amino acid (BCAA) supplementation on exercise capacity in a glycogen-depleted state in a warm environment. Following a exercise and dietary regimen designed to reduce glycogen availability, subjects returned to the laboratory the following morning and remained seated for 2 h, before cycling to volitional exhaustion at 50% O2 peak in a warm environment [30.0 (0.2)°C; mean (SD)]. Four 250 ml aliquots of a 12 g l–1 BCAA solution or placebo were ingested at 30 min intervals prior to exercise, with an additional 150 ml consumed every 15 min throughout exercise. BCAA ingestion had no effect on exercise capacity [placebo 103.9 (26.9) min; BCAA 111.0 (29.2) min; P=0.129). No difference in heart rate (P=0.345), core temperature (P=0.628), or weighted mean skin temperature (P=0.114) was apparent between trials. Ingestion of the BCAA solution produced a marked increase in plasma BCAA immediately prior to exercise [+1126 (158) mol l–1; P<0.001) with this difference maintained throughout. Consequently, a significant reduction in the plasma concentration ratio of free tryptophan to BCAA was observed during the BCAA trial when compared to the placebo (P<0.001). Plasma ammonia concentration was significantly elevated during exercise throughout the BCAA trial (P<0.001), with no change from rest apparent during the placebo trial (P=0.608). Blood glucose (P=0.114) and lactate (P=0.836) concentrations were not different between trials. Ingestion of a BCAA solution prior to, and during, prolonged exercise in glycogen-depleted subjects did not influence exercise capacity in a warm environment. 相似文献
3.
Effects of carbohydrate feedings on plasma free tryptophan and branched-chain amino acids during prolonged cycling 总被引:3,自引:0,他引:3
J. Mark Davis Stephen P. Bailey Jeffrey A. Woods Floyd J. Galiano Marc T. Hamilton William P. Bartoli 《European journal of applied physiology》1992,65(6):513-519
Summary Brain serotonin (5-hydroxytryptamine, 5-HT) has been suggested to be involved in central fatigue during prolonged exercise. Changes in the ratio of plasma free tryptophan (free Trp) to branched-chain amino acids (BCAA) are associated with altered brain 5-HT synthesis. The purposes of this study were to describe systematically the effects of prolonged exercise on changes in plasma free Trp and BCAA and to examine the effects of carbohydrate (CHO) feedings on these same variables. Eight well-trained men [
max = 57.8 (SE 4.1) ml kg–1 min–1] cycled for up to 255 min at a power output corresponding toVO2 at lactate threshold (approximately 68%VO2max) on three occasions separated by at least 1 week. Subjects drank 5 ml kg–1 body wt–1 of either a water placebo, or a liquid beverage containing a moderate (6% CHO) or high (12% CHO) concentration of carbohydrate beginning at min 14 of exercise and every 30 min thereafter. Exercise time to fatigue was shorter in subjects receiving placebo [190 (SE 4) min] as compared to 6% CHO [235 (SE 10) min] and 12% CHO [234 (SE 9) min] (P<0.05). Glucose and insulin decreased in the placebo group, and free Trp, free-Trp/BCAA, and free fatty acids increased approximately five- to sevenfold (P < 0.05). These changes were attenuated in a dose-related manner by the carbohydrate drinks. Plasma free Trp and plasma free fatty acids were highly correlated (r=0.86,P<0.001). Plasma BCAA did not change in the placebo group, but decreased slightly in those receiving 6% CHO and 12% CHO (P<0.05). No differences in heart rate,
, plasma volume and respiratory exchange ratio were found. The results indicate that free Trp and free Trp/BCAA increase progressively during prolonged cycling to fatigue. This response was attenuated by CHO feedings. Changes in plasma free fatty acids probably play a prominent role in these responses. 相似文献
4.
Game sport and training require repeated high intensity bursts. This study examined differences between high intensity, intermittent
work in two phases of the menstrual cycle. Six physically active young women (age 19–29) performed 10 6-s sprints on a cycle
ergometer in both the mid-follicular (FP) (days 6–10) and late-luteal phases (LP) (days 20–24) of the menstrual cycle. Work,
power, oxygen intake
parameters, and capillarized blood lactate were measured. Data are analyzed using the Friedman and Wilcoxon matched pairs
tests. There was no difference between menstrual phases in peak 6-s power (6.8(0.6) W kg−1 in FP, 6.9(0.6) W kg−1 in LP), the drop off in work (1.2(3.5) J kg−1 in FP and 1.0(2.7) J kg−1 in LP), or in the sprint
(23.7 (1.5) mL kg−1 min−1 in LP and 24.3(2.4) mL kg−1 min−1 in FP). Capillarized blood lactate was also similar in both phases of the menstrual cycle both at 1 min (9.2 (2.7) mmol L−1 in FP, 9.2 (3.1) mmol L−1) and at 3 min (9.0 (2.2) mmol L−1 in FP, 9.2 (2.2) mmol L−1 in LP). However, the average 6-s work was greater in the LP (39.3 (3.4) J kg−1) than during the FP (38.3 (3.1) J kg−1) (P=0.023). The recovery
was also greater in the LP than the FP (26.3 (2.4) mL kg−1 min−1 in LP, 25.0 (2.6) mL kg−1 min−1 in FP, P=0.023). Average work over a series of sprints and the
consumed between sprints may be slightly greater during the LP than the FP of the menstrual cycle. 相似文献
5.
Short-term maximum intensity performance, absolute and related to body mass, is lower in children than adolescents. The underlying
mechanisms are not clear. We analysed Wingate Anaerobic Test (WAnT) performance and metabolism in ten boys (mean (SD); age
11.8 (0.5) years, height 1.51 (0.05) m, body mass 36.9 (2.5) kg, muscle mass 13.0 (1.0) kg) and 10 adolescents (16.3 (0.7)
years, 1.81 (0.05) m, 67.3 (4.1) kg, 28.2 (1.7) kg). Related to body mass, power of flywheel acceleration (6.0 (1.6) vs. 8.1
(1.1) W kg−1), peak power (10.8 (0.7) vs. 11.5 (0.6) W kg−1), average power (7.9 (0.5) vs. 8.9 (0.7) W kg−1), minimum power (6.1 (0.7) vs. 6.9 (0.9) W kg−1) and anaerobic lactic energy (687.6 (75.6) vs. 798.2 (43.0) J kg−1) were lower (P < 0.05) in boys than in adolescents. Related to muscle mass the change in lactate (0.69 (0.08) vs. 0.69 (0.04) mmol kgMM−1 s−1) and PCr (0.60 (0.17) vs. 0.52 (0.10) mmol kgMM−1 s−1) were not different. The corresponding oxygen uptake (1.34 (0.13) vs. 1.09 (0.13) ml kgMM−1 s−1), total metabolic rate (132.4 (12.6) vs. 119.7 (8.5) W kgMM−1) and PP (30.5 (2.6) vs. 27.5 (1.7 W) kgMM−1) were higher (P < 0.01) in boys than in adolescents. The results reflect a lower relative muscle mass combined with no differences in muscular
anaerobic but fascilitated aerobic metabolism in boys. Compared with adolescents, boys’ performance seemed to be significantly
impaired by flywheel inertia but supported by identical brake force related to body mass. 相似文献
6.
Johnson NA Stannard SR Chapman PG Thompson MW 《European journal of applied physiology》2006,98(1):62-70
This study assessed the effect of altered carbohydrate (CHO) availability on self-selected work rate during prolonged time-trial cycling. Eight endurance-trained men undertook two experimental cycling time-trials after glycogen-depleting exercise and 2 days of: (a) high (9.3 ± 0 g CHO kg−1 day−1) (HC) and (b) low CHO intakes (0.6 ± 0.1 g CHO kg−1 day−1) (LC), via a double-blinded crossover design. All feedback regarding performance was removed during both exercise trials. Self-selected external power output was not different during the first 2 h of exercise between experimental conditions (P > 0.05), despite reported sensations of increased tiredness before and during exercise, significantly reduced whole body CHO oxidation (P < 0.05), plasma lactate concentrations (P < 0.05) and earlier onset of fatigue during exercise in LC versus HC. Perceived exertion was not different throughout exercise between conditions (P > 0.05). Mean power output declined significantly in LC versus HC (P < 0.05) after ∼ 2 h of exercise, and was associated with significant reductions in cadence, heart rate and plasma glucose concentration (P < 0.05). These results demonstrate that when compared with time-trial cycling performed after a HC diet, reduced CHO availability does not initially alter self-selected work rate in endurance athletes who are deceived of their CHO status prior to exercise. This finding suggests that reduced work rate during exercise following lowered CHO intake may, in part, be a consequence of the subject’s awareness of dietary CHO restriction rather than solely a physiologically mediated action. Further research is required to distinguish the influence of circulating glucose and peripheral glycogen availability on pacing strategy during prolonged exercise. 相似文献
7.
M. E. Pearce D. A. Cunningham A. P. Donner P. A. Rechnitzer G. M. Fullerton J. H. Howard 《European journal of applied physiology》1983,52(1):115-119
Summary Oxygen uptake-velocity regression equations were developed for floor and level treadmill walking by having two groups of men,
aged 19–29 years (n=20) and 55–66 years (n=22), walk at four self-selected paces, from “rather slowly” to “as fast as possible”. A two-variable quadratric model relating
VO2 (ml·kg−1·min−1) to velocity (m·s−1) was adopted for prediction purposes. However, age and fatness significantly (p<0.05) interacted with treadmill walking speed, while age alone significantly interacted with floor speed. In addition, a
significant difference was found between the energy cost of floor and treadmill walking. For example at the normal walking
speed of 1.33 m·s−1, the energy cost for the treadmill (age 55–66 years) was 10.58 ml·kg−1·min−1 and for the floor, 11.04 ml·kg−1·min−1 (p<0.05). Four quadratic equations are therefore presented, one each for floor and treadmill in each of the two age-groups.
The percent variance explained was between 87 and 95% for each of these equations.
Supported by a grant from the Ontario Ministry of Health (DM449) 相似文献
8.
The plasma levels and milk excretion of eprinomectin were determined in goats following topical application at doses of 0.5 mg kg−1 and 1.0 mg kg−1. The area under the concentration–time curve (AUC) was 2 times lower for 0.5 mg kg−1 (8.24 ± 3.50 ng day−1 ml−1) than for 1.0 mg kg−1 (15.68 ± 8.84 ng day−1 ml−1), suggesting that the pharmacokinetics of eprinomectin in goats is dose independent. The bioavailability of eprinomectin
in lactating compared with non-lactating goats is low. This is probably due to the physiological status of dairy animals,
which present a marked decrease in body fat. Comparison of the eprinomectin concentrations in the milk and plasma demonstrated
a parallel disposition of the drug with a milk-to-plasma ratio of 0.10–0.25. The amount of drug recovered in the milk was
0.3–0.5% of the total administered dose. In all cases, the maximum level of residue in milk remained below the maximum acceptable
level of 30 ng ml−1 permitted in lactating cattle.
Received: 16 April 2000 / Accepted: 6 September 2000 相似文献
9.
Bailey DM Williams C Betts JA Thompson D Hurst TL 《European journal of applied physiology》2011,111(6):925-936
There is no consensus regarding the effects of mixed antioxidant vitamin C and/or vitamin E supplementation on oxidative stress
responses to exercise and restoration of muscle function. Thirty-eight men were randomly assigned to receive either placebo
group (n = 18) or mixed antioxidant (primarily vitamin C & E) supplements (n = 20) in a double-blind manner. After 6 weeks, participants performed 90 min of intermittent shuttle-running. Peak isometric
torque of the knee flexors/extensors and range of motion at this joint were determined before and after exercise, with recovery
of these variables tracked for up to 168 h post-exercise. Antioxidant supplementation elevated pre-exercise plasma vitamin
C (93 ± 8 μmol l−1) and vitamin E (11 ± 3 μmol l−1) concentrations relative to baseline (P < 0.001) and the placebo group (P ≤ 0.02). Exercise reduced peak isometric torque (i.e. 9–19% relative to baseline; P ≤ 0.001), which persisted for the first 48 h of recovery with no difference between treatment groups. In contrast, changes
in the urine concentration of F2-isoprostanes responded differently to each treatment (P = 0.04), with a tendency for higher concentrations after 48 h of recovery in the supplemented group (6.2 ± 6.1 vs. 3.7 ± 3.4 ng ml−1). Vitamin C & E supplementation also affected serum cortisol concentrations, with an attenuated increase from baseline to
the peak values reached after 1 h of recovery compared with the placebo group (P = 0.02) and serum interleukin-6 concentrations were higher after 1 h of recovery in the antioxidant group (11.3 ± 3.4 pg ml−1) than the placebo group (6.2 ± 3.8 pg ml−1; P = 0.05). Combined vitamin C & E supplementation neither reduced markers of oxidative stress or inflammation nor did it facilitate
recovery of muscle function after exercise-induced muscle damage. 相似文献
10.
Carbohydrate supplementation during prolonged cycling exercise spares muscle glycogen but does not affect intramyocellular lipid use 总被引:1,自引:0,他引:1
Stellingwerff T Boon H Gijsen AP Stegen JH Kuipers H van Loon LJ 《Pflügers Archiv : European journal of physiology》2007,454(4):635-647
Using contemporary stable-isotope methodology and fluorescence microscopy, we assessed the impact of carbohydrate supplementation
on whole-body and fiber-type-specific intramyocellular triacylglycerol (IMTG) and glycogen use during prolonged endurance
exercise. Ten endurance-trained male subjects were studied twice during 3 h of cycling at 63 ± 4% of maximal O2 uptake with either glucose ingestion (CHO trial; 0.7 g CHO kg−1 h−1) or without (CON placebo trial; water only). Continuous infusions with [U-13C] palmitate and [6,6-2H2] glucose were applied to quantify plasma free fatty acids (FFA) and glucose oxidation rates and to estimate intramyocellular
lipid and glycogen use. Before and after exercise, muscle biopsy samples were taken to quantify fiber-type-specific IMTG and
glycogen content. Plasma glucose rate of appearance (R
a) and carbohydrate oxidation rates were substantially greater in the CHO vs CON trial. Carbohydrate supplementation resulted
in a lower muscle glycogen use during the first hour of exercise in the CHO vs CON trial, resulting in a 38 ± 19 and 57 ± 22%
decreased utilization in type I and II muscle-fiber glycogen content, respectively. In the CHO trial, both plasma FFA R
a and subsequent plasma FFA concentrations were lower, resulting in a 34 ± 12% reduction in plasma FFA oxidation rates during
exercise (P < 0.05). Carbohydrate intake did not augment IMTG utilization, as fluorescence microscopy revealed a 76 ± 21 and 78 ± 22%
reduction in type I muscle-fiber lipid content in the CHO and CON trial, respectively. We conclude that carbohydrate supplementation
during prolonged cycling exercise does not modulate IMTG use but spares muscle glycogen use during the initial stages of exercise
in endurance-trained men. 相似文献
11.
Roger A. Fielding William J. Evans Virginia A. Hughes Lyle L. Moldawer Bruce R. Bistrian 《European journal of applied physiology》1986,55(5):482-485
Summary Alpha-ketoisocaproic acid (KIC) is the product of the transamination of the indispensable amino acid leucine, which is the
first step in the complete degradation of leucine. To determine the effects of intense exercise on muscle and blood levels
of KIC, 7 male volunteers performed cycle exercise to exhaustion. After pedaling at an intensity of 90 W for 3 min, the load
was increased by 60 W every 3 min until volitional fatigue. Muscle biopsies were obtained prior to and immediately after exercise
and rapidly frozen for later determination of KIC. During exercise, blood lactate levels increased as expected, while plasma
KIC levels did not change. Following exercise, plasma KIC levels rose significantly with peak values occurring 15 min after
exercise and did not return to pre-exercise values until 60 min after exercise. In contrast, muscle KIC levels increased during
exercise from a pre-exercise mean of 49.4±4.1 Μmol · kg−1 wet wt to 78.1±6.5 Μmol · kg−1 after exercise, an average increase of 48% (P<0.05). These data indicate that during intense exercise, leucine transamination in muscle may continue at a faster rate than
the decarboxylation of KIC. In addition, plasma levels of KIC did not reflect the intracellular accumulation of KIC during
exercise, suggesting a delay in the diffusion of KIC from muscle. 相似文献
12.
F. Schena F. Guerrini P. Tregnaghi B. Kayser 《European journal of applied physiology》1992,65(5):394-398
Summary To investigate the influence of a branched-chain amino acid (BCAA) supplementation on chronic hypoxia-related loss of body mass and muscle loss, 16 subjects [age 35.8 (SD 5.6) years] participating in a 21-day trek at a mean altitude of 3,255 (SD 458) m, were divided in two age-, sex- and fitness-matched groups and took either a dietary supplementation of BCAA (5.76, 2.88 and 2.88 g per day of leucine, isoleucine and valine, respectively) or a placebo (PLAC) in a controlled double-blind manner. Daily energy intake at altitude decreased by 4% in both groups compared with sea level. After altitude exposure both groups showed a significant loss of body mass, 1.7% and 2.8% for BCAA and PLAC, respectively. Fat mass had decreased significantly by 11.7% for BCAA and 10.3% for PLAC, whereas BCAA showed a significantly increased lean mass of 1.5%, as opposed to no change in PLAC. Arm muscle cross-sectional area tended to increase in BCAA, whereas there was a significant decrease of 6.8% in PLAC (P<0.05 between groups). The same tendency, although not significant, was observed for the thigh muscle cross-sectional area. On the whole it seemed that PLAC had been catabolizing whereas BCAA had been synthesizing muscle tissue. Single jump height from a squatted position showed a similar tendency to increase in both groups. Lower limb maximal power decreased less in BCAA than in PLAC (2.4% vs 7.8%, P<0.05). We concluded that BCAA supplementation may prevent muscle loss during chronic hypobaric hypoxia. 相似文献
13.
Melo X Santa-Clara H Almeida JP Carnero EA Sardinha LB Bruno PM Fernhall B 《European journal of applied physiology》2011,111(5):839-849
This study compared the validity of reported equations as predictors of peak VO2 in 8–10-year-old children. Participants (90 boys and girls aged 8–10 years) performed the multistage-shuttle-run-test (MSRT)
and peak VO2 was measured in field using a portable gas analyser. The equations that estimated peak VO2 from the MSRT performance were chosen according to the age range of this study. As follows, the FITNESSGRAM reports and the
equations of Leger et al. (Can J Appl Sport Sci 5: 77–84, 1988), Barnett et al. (Pediatr Exerc Sci 5:42–50, 1993), Matsuzaka et al. (Pediatr Exerc Sci 16:113–125, 2004) and Fernhall et al. (Am J Ment Retard 102:602–612, 1998) were used to estimate the peak VO2 and compared with the directly measured value. The equation of Leger et al. (Can J Appl Sport Sci 5: 77–84, 1988) provided a mean difference (d) of 4.7 ml kg−1 min−1 and a 1.0 slope. The equation of Matsuzaka et al. (Pediatr Exerc Sci 16:113–125, 2004)(a) using maximal speed (MS) showed a higher d (5.4) than the remaining using total laps d (4.2). The equation of Barnett et al. (Pediatr Exerc Sci 5:42–50, 1993)(a) that includes triceps skinfold and MS showed the highest d (6.1) but the smallest range (24.1) and slope (0.6). Data from the FITNESSGRAM had the smallest d (1.8 ml kg−1 min−1), but also had the highest range between limits of agreement (28.6 ml kg−1 min−1) and a 1.2 slope. The lowest slope (0.4) and range (22.2 ml kg−1 min−1) were observed using the equation of Fernhall et al. (Am J Ment Retard 102:602–612, 1998). Log transformation of the data revealed that the equations of Matsuzaka et al. (Pediatr Exerc Sci 16:113–125, 2004)(a) (1.1*/÷1.25) and Fernhall et al. (Am J Ment Retard 102:602–612, 1998) (1.17*/÷1.25) showed the closest agreement among all, but they still yield unsatisfactory accuracy. 相似文献
14.
Finn JP Ebert TR Withers RT Carey MF Mackay M Phillips JW Febbraio MA 《European journal of applied physiology》2001,84(3):238-243
This double blind study investigated the effect of oral creatine supplementation (CrS) on 4 × 20 s of maximal sprinting on
an air-braked cycle ergometer. Each sprint was separated by 20 s of recovery. A group of 16 triathletes [mean age 26.6 (SD 5.1) years.
mean body mass 77.0 (SD 5.8) kg, mean body fat 12.9 (SD 4.6)%, maximal oxygen uptake 4.86 (SD 0.7) l · min−1] performed an initial 4 × 20 s trial after a muscle biopsy sample had been taken at rest. The subjects were then matched
on their total intramuscular creatine content (TCr) before being randomly assigned to groups to take by mouth either a creatine
supplement (CRE) or a placebo (CON) before a second 4 × 20 s trial. A muscle biopsy sample was also taken immediately before
this second trial. The CrS of 100 g comprised 4 × 5 g for 5 days. The initial mean TCr were 112.5 (SD 8.7) and 112.5 (SD 10.7) mmol · kg−1 dry mass for CRE and CON, respectively. After creatine loading and placebo ingestion respectively, CRE [128.7 (SD 11.8) mmol ·
kg−1 dry mass] had a greater (P=0.01) TCr than CON [112.0 (SD 10.0) mmol · kg−1 dry mass]. While the increase in free creatine for CRE was statistically significant (P=0.034), this was not so for the changes in phosphocreatine content [trial 1: 75.7 (SD 6.9), trial 2: 84.7 (SD 11.0) mmol ·
kg−1 dry mass, P=0.091]. There were no significant differences between CRE and CON for citrate synthase activity (P=0.163). There was a tendency towards improved performance in terms of 1 s peak power (in watts P=0.07; in watts per kilogram P=0.05), 5 s peak power (in watts P=0.08) and fatigue index (P=0.08) after CrS for sprint 1 of the second trial. However, there was no improvement for mean power (in watts P=0.15; in watts per kilogram P=0.1) in sprint 1 or for any performance values in subsequent sprints. Our results suggest that, while CrS elevates the intramuscular
stores of free creatine, this does not have an ergogenic effect on 4 × 20 s all-out cycle sprints with intervening 20-s rest
periods.
Accepted: 2 October 2000 相似文献
15.
Bélanger P Fillion Y Couturier K Gauthier MS Lavoie JM 《European journal of applied physiology》2003,89(1):8-13
The purpose of the present study was to assess the effects of exogenously increasing the circulating levels of glucagon on
the metabolic responses to exercise in rats. A total of six groups of rats were infused (iv) either with glucagon (20 or 50 ng·kg−1·min−1) or saline (0.9% NaCl), either in the resting state or during a bout of running exercise (45 min, 26 m·min−1, 0% grade). Blood samples were taken at the end of the 45-min experiment. Animals infused with glucagon at 50 ng·kg−1·min−1 showed significantly (P<0.01) higher mean plasma glucagon concentrations than animals infused with saline or glucagon at 20 ng·kg−1·min−1. In addition, exercise resulted in significantly (P<0.05) higher mean plasma glucagon concentrations, compared to rest, in all groups. In spite of these differences in glucagon
concentrations, there were no significant (P>0.05) effects of exercise and glucagon infusion on mean hepatic glycogen, plasma glucose, insulin, C-peptide, β-hydroxybutyrate,
or catecholamine concentrations. Although exercise resulted in a significant (P<0.01) increase in plasma glycerol and free fatty acid concentrations and a significant (P<0.05) decrease in glycogen in the soleus muscle, these responses were not affected by the glucagon infusion. These results suggest that the liver is non-responsive
to physiological hyperglucagonemia in a short-term (45 min) exercise situation.
Electronic Publication 相似文献
16.
Laurent CM Meyers MC Robinson CA Green JM 《European journal of applied physiology》2007,100(6):645-651
The 30-s Wingate anaerobic test (30-WAT) is the most widely accepted protocol for measuring anaerobic response, despite documented
physical side effects. Abbreviation of the 30-WAT without loss of data could enhance subject compliance while maintaining
test applicability. The intent of this study was to quantify the validity of the 20-s Wingate anaerobic test (20-WAT) versus
the traditional 30-WAT. Fifty males (mean ± SEM; age = 20.5 ± 0.3 years; Ht = 1.6 ± 0.01 m; Wt = 75.5 ± 2.6 kg) were randomly
selected to either a validation (N = 35) or cross-validation group (N = 15) and completed a 20-WAT and 30-WAT in double blind, random order on separate days to determine peak power (PP; W kg−1), mean power (MP; W kg−1), and fatigue index (FI; %). Utilizing power outputs (relative to body mass) recorded during each second of both protocols,
a non-linear regression equation (Y
20WAT+10 = 31.4697 e−0.5[ln(X
second/1174.3961)/2.63692]; r
2 = 0.97; SEE = 0.56 W kg−1) successfully predicted (error ∼10%) the final 10 s of power outputs in the cross-validation population. There were no significant
differences between MP and FI between the 20-WAT that included the predicted 10 s of power outputs (20-WAT+10) and the 30-WAT.
When derived data were subjected to Bland–Altman analyses, the majority of plots (93%) fell within the limits of agreement
(±2SD). Therefore, when compared to the 30-WAT, the 20-WAT may be considered a valid alternative when used with the predictive
non-linear regression equation to derive the final power output values. 相似文献
17.
Antti Mero Anne Leikas Juha Knuutinen Juha J. Hulmi Vuokko Kovanen 《European journal of applied physiology》2009,105(2):215-223
We examined the acute effects of a 1-h strength training session (STS) on plasma amino acid concentration following orally
ingestion of leucine, branched-chain amino acids (BCAAs) or glutamine in nine physically active men who participated in double-blinded
and randomised experiments. The subjects took placebo, leucine, BCAAs, or glutamine capsules (50 mg/kg) in either rest (REST)
or STS condition. Blood samples were taken before and at 30, 60, 90, and 120 min after the beginning of the treatment and
they were assayed for plasma amino acids with HPLC. Following both leucine and BCAA ingestion the peak concentration of leucine
was similar at rest (524 ± 46 and 530 ± 29 nmol/ml, respectively) and similar after STS (398 ± 43 and 387 ± 46 nmol/ml, respectively)
but the rest and STS concentrations differed from each other (P < 0.01–0.001). The modelled polynomial data for the leucine treatment showed that the peak concentration of leucine occurred
at 67 min at rest and at 90 min in STS (difference between REST and STS: P = 0.012). For the BCAA treatment the polynomial data showed that the peak concentration of leucine occurred at 72 min at rest
and at 78 min in STS (P = 0.067). The peak concentration of glutamine was similar in both rest and STS condition and occurred at 60 min at rest and
at 57 min in STS. In conclusion, 1-h of STS slows the increase in the peak concentration of plasma leucine similarly after
oral ingestion of leucine or BCAAs but after oral ingestion of glutamine it has no slowing effect on glutamine concentration. 相似文献
18.
Gotshalk LA Kraemer WJ Mendonca MA Vingren JL Kenny AM Spiering BA Hatfield DL Fragala MS Volek JS 《European journal of applied physiology》2008,102(2):223-231
Muscle power and strength decrease with age leading to reduced independence and increased health risk from falls. Creatine
supplementation can increase muscle power and strength. The purpose of this study was to examine the effects of 7 days of
creatine supplementation on body composition, muscular strength, and lower-body motor functional performance in older women.
Thirty 58–71 year old women performed three test sessions (T1–T3) each separated by one week. Each session consisted of one
repetition maximum tests for bench press and leg press, and isometric hand-grip, tandem gait, upper-body ergometer, and lower-body
ergometer tests. Following T2, subjects were assigned to a creatine monohydrate (0.3 g kg body mass−1 for 7 days) (CR: 63.31 ± 1.22 year, 160.00 ± 1.58 cm, 67.11 ± 4.38 kg) or a placebo (PL: 62.98 ± 1.11 year, 162.25 ± 2.09 cm,
67.84 ± 3.90 kg) supplementation group. CR significantly (P < 0.05) increased bench press (1.7 ± 0.4 kg), leg press (5.2 ± 1.8 kg), body mass (0.49 ± 0.04 kg) and fat free mass (0.52 ± 0.05)
and decreased completion time on the functional tandem gait tests from T2–T3. No significant changes were found for PL on
any of the measured variables. No adverse side-effects were reported by either group. Short-term creatine supplementation
resulted in an increase in strength, power, and lower-body motor functional performance in older women without any adverse
side effects 相似文献
19.
Zehnder M Christ ER Ith M Acheson KJ Pouteau E Kreis R Trepp R Diem P Boesch C Décombaz J 《European journal of applied physiology》2006,98(4):341-354
Intramyocellular lipids (IMCL) and muscle glycogen provide local energy during exercise (EX). The objective of this study was to clarify the role of high versus low IMCL levels at equal initial muscle glycogen on fuel selection during EX. After 3 h of depleting exercise, 11 endurance-trained males consumed in a crossover design a high-carbohydrate (7 g kg−1 day−1) low-fat (0.5 g kg−1 day−1) diet (HC) for 2.5 days or the same diet with 3 g kg−1 day−1 more fat provided during the last 1.5 days of diet (four meals; HCF). Respiratory exchange, thigh muscle substrate breakdown by magnetic resonance spectroscopy, and plasma FFA oxidation ([1-13C]palmitate) were measured during EX (3 h, 50% W
max). Pre-EX IMCL concentrations were 55% higher after HCF. IMCL utilization during EX in HCF was threefold greater compared with HC (P < 0.001) and was correlated with aerobic power and highly correlated (P < 0.001) with initial content. Glycogen values and decrements during EX were similar. Whole-body fat oxidation (Fatox) was similar overall and plasma FFA oxidation smaller (P < 0.05) during the first EX hour after HCF. Myocellular fuels contributed 8% more to whole-body energy demands after HCF (P < 0.05) due to IMCL breakdown (27% Fatox). After EX, when both IMCL and glycogen concentrations were again similar across trials, a simulated 20-km time-trial showed no difference in performance between diets. In conclusion, IMCL concentrations can be increased during a glycogen loading diet by consuming additional fat for the last 1.5 days. During subsequent exercise, IMCL decrease in proportion to their initial content, partly in exchange for peripheral fatty acids. 相似文献
20.
Cathcart AJ Murgatroyd SR McNab A Whyte LJ Easton C 《European journal of applied physiology》2011,111(9):2051-2061
Laboratory-based studies have demonstrated that adding protein (PRO) to a carbohydrate (CHO) supplement can improve thermoregulatory
capacity, exercise performance and recovery. However, no study has investigated these effects in a competitive sporting context.
This study assessed the effects of combined CHO–PRO supplementation on physiological responses and exercise performance during
8 days of strenuous competition in a hot environment. Twenty-eight cyclists participating in the TransAlp mountain bike race
were randomly assigned to fitness-matched placebo (PLA 76 g L−1 CHO) or CHO–PRO (18 g L−1 PRO, 72 g L−1 CHO) groups. Participants were given enough supplements to allow ad libitum consumption. Physiological and anthropometric
variables were recorded pre- and post-exercise. Body mass decreased significantly from race stage 1 to 8 in the PLA group
(−0.75 ± 0.22 kg, P = 0.01) but did not change in the CHO–PRO group (0.42 ± 0.42 kg, P = 0.35). Creatine kinase concentration and muscle soreness were substantially elevated during the race, but were not different
between groups (P = 0.82, P = 0.44, respectively). Urine osmolality was significantly higher in the CHO–PRO versus the PLA group (P = 0.04) and the rise in tympanic temperature from pre- to post-exercise was significantly less in CHO–PRO versus PLA (P = 0.01). The CHO–PRO group also completed the 8 stages significantly quicker than the PLA group (2,277 ± 127 vs. 2,592 ± 68 min,
respectively, P = 0.02). CHO–PRO supplementation therefore appears to prevent body mass loss, enhance thermoregulatory capacity and improve
competitive exercise performance despite no effect on muscle damage. 相似文献