Glucose feedings and exercise in rats: glycogen use, hormone responses, and performance

1990 ◽  
Vol 69 (3) ◽  
pp. 989-994 ◽  
Author(s):  
C. A. Slentz ◽  
J. M. Davis ◽  
D. L. Settles ◽  
R. R. Pate ◽  
S. J. Settles
Keyword(s):  
Plasma Glucose ◽  
Glucose Solution ◽  
Endurance Performance ◽  
Time To Exhaustion ◽  
O2 Consumption ◽  
Exercise Time ◽  
Time Points ◽  
Hormone Responses ◽  
Glycogen Utilization ◽  
And Performance

This study compared the effects of glucose feeding and water on endurance performance, glycogen utilization, and endocrine responses to exhaustive running in rats. Forty-eight trained rats ran at approximately 70% peak O2 consumption (VO2) while receiving, via gavage, 1 ml of an 18% glucose solution or water every 30 min. Glucose- (GF) and water-fed rats (WF) were pair matched and killed at rest, at 25 or 50% of their previously determined run time to exhaustion, or at exhaustion. Run times to exhaustion were 4.6 +/- 1.0 and 3.0 +/- 0.9 h in GF and WF rats, respectively. In WF rats, plasma glucose declined continuously from a resting value of 7.4 +/- 0.5 to 1.8 +/- 0.5 mM at exhaustion and was lower than in GF rats at all exercise time points. In GF rats, glucose was maintained at 7.4 +/- 0.5 mM for 3 h before dropping to 3.9 +/- 0.6 mM at exhaustion. In both groups, liver and muscle glycogen decreased dramatically during the 1st h and changed only slightly thereafter. During the 3rd h, glycogen levels were maintained in GF rats but continued to decrease in WF rats (P less than 0.05). Insulin decreased during exercise and was not significantly different between groups. Glucagon, epinephrine, norepinephrine, and corticosterone increased to a greater extent in WF than in GF rats during the first 3 h of exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Failure of Low Dose Carbohydrate Feeding to Attenuate Glucoregulatory Hormone Responses and Improve Endurance Performance

1991 ◽  
Vol 1 (4) ◽  
pp. 338-352 ◽  
Author(s):  
William A. Burgess ◽  
J. Mark Davis ◽  
William P. Bartoli ◽  
Jeffrey A. Woods
Keyword(s):  
Plasma Glucose ◽  
Perceived Exertion ◽  
Low Dose ◽  
Endurance Performance ◽  
Moderate Intensity ◽  
Carbohydrate Feeding ◽  
Glucoregulatory Hormones ◽  
Flavored Water ◽  
Hormone Responses ◽  
And Performance

The effects of ingesting a low dose of CHO on plasma glucose, glucoregulatory hormone responses, and performance during prolonged cycling were investigated. Nine male subjects cycled for 165 min at ≈67% peakfollowed by a two-stage performance ride to exhaustion on two occasions in the laboratory. Every 20 min during exercise, subjects consumed either a flavored water placebo (P) or a dilute carbohydrate beverage (C). Blood samples were collected immediately before, every 20 min throughout, and immediately after exercise. Plasma was analyzed for glucose, lactate, free fatty acids (FFA), and various glucoregulatory hormones., RER, heart rate, perceived exertion, and exercise performance were also measured. Lactate, FFA, epinephrine, norepinephrine, ACTH, cortisol, and glucagon increased with exercise whereas glucose and insulin decreased (p≤05). Except for a small difference in glucose at 158 min of exercise and at exhaustion, no significant differences were found between drinks for any of the variabfes studied (p≥ 05). Ingestion of 13 g carbohydrate per hour is not sufficient to maintain plasma glucose, attenuate the glucoregulatory hormone response, and improve performance during prolonged moderate intensity cycling.

scholarly journals The Physiological Effects of Amino Acids Arginine and Citrulline: Is There a Basis for Development of a Beverage to Promote Endurance Performance? A Narrative Review of Orally Administered Supplements

Beverages ◽  
2020 ◽  
Vol 6 (1) ◽  
pp. 11 ◽  
Author(s):  
Hollie Speer ◽  
Nathan M. D’Cunha ◽  
Michael J. Davies ◽  
Andrew J. McKune ◽  
Nenad Naumovski
Keyword(s):  
Synergistic Effects ◽  
Endurance Performance ◽  
Performance Outcomes ◽  
Time To Exhaustion ◽  
No Production ◽  
Full Potential ◽  
Physiological Effects ◽  
And Performance ◽  
Physiological Benefits ◽  
Endothelial Nitric Oxide

Nutritional and ergogenic aid supplementation is prevalent within athletic or general fitness populations, and is only continuing to gain momentum. Taken in isolation or as a combination, amino acid (AA) supplementation has the potential to increase endurance performance among other benefits. L-Arginine (L-Arg) and L-Citrulline (L-Cit) are two AAs proposed to increase endothelial nitric oxide (NO) synthesis, with potential additional physiological benefits, and therefore may contribute to enhanced performance outcomes such as increased power output, or time to exhaustion. However, the appropriate dose for promoting physiological and performance benefits of these AAs, and their potential synergistic effects remains to be determined. Therefore, the aim of this review was to evaluate the varied concentrations used in the current literature, assess the effects of L-Arg and L-Cit in combination on physiological responses and endurance performance, and consider if there is a fundamental basis for providing these supplements in the form of a beverage. A total of six studies were considered eligible for the review which utilized a range of 3–8 g of the AA constituents. The findings support the notion that supplementing with a combination of L-Arg and L-Cit may increase NO production, enhance vasodilation, and therefore increase performance capacity in athletes. A beverage as a carrier for the two AAs is worth considering; however, there remains limited research assessing these outcomes across a consistent range of concentrations in order to see their full potential.

Intravenous versus Oral Rehydration during a Brief Period: Stress Hormone Responses to Subsequent Exhaustive Exercise in the Heat

2000 ◽  
Vol 10 (4) ◽  
pp. 361-374 ◽  
Author(s):  
Douglas J. Casa ◽  
Carl M. Maresh ◽  
Lawrence E. Armstrong ◽  
Stavros A. Kavouras ◽  
Jorge A. Herrera-Soto ◽  
...  
Keyword(s):  
Body Weight ◽  
Body Fat ◽  
Exhaustive Exercise ◽  
Time To Exhaustion ◽  
Stress Hormone ◽  
Plasma Acth ◽  
Exercise Time ◽  
Oral Rehydration ◽  
Hydration State ◽  
Hormone Responses

The purpose of this study was to determine if intravenous fluid rehydration, versus oral rehydration. during a brief period (20 min) differentially affects plasma ACTH, cortisol, and norepinephrine concentrations during subsequent exhaustive exercise in the heat. Following dehydration (DHY) to −4% of body weight, 8 nonacclimated highly trained males (age = 23.5 ± 1.2 years, V̇O2peak = 61.4±0.8 ml · kg · min−1, % body fat = 13.5±0.6%) cycled to exhaustion at 74% V̇O2peak in 36.8 °C on three different occasions. These included: (a) no fluid (NF), where no fluid was provided during the rehydration period; (b) DRINK, where oral rehydration (0.45% NaCl) was provided equal to 50% of the prior DHY; and (c) IV, where intravenous infusion (0.45% NaCl) was provided equal to 50%’ of the prior DHY. Exercise time to exhaustion was not different p = .07) between the DRINK (34.86 ±4.01) and IV (29.48 ± 3.50) trials, but both were significantly p < .05) longer than the NF (18.95 ± 2.73) trial. No differences (p > .05) were found for any of the hormone measures among trials. The endocrine responses at exhaustion were similar regardless of hydration state and mode of rehydration, but rehydration prolonged the exercise time to exhaustion.

Dissociation of changes in VO2 max, muscle QO2, and performance with training in rats

1989 ◽  
Vol 66 (4) ◽  
pp. 1620-1625 ◽  
Author(s):  
M. I. Lambert ◽  
T. D. Noakes
Keyword(s):  
Time Course ◽  
Matched Control ◽  
Oxidative Capacity ◽  
Running Economy ◽  
Male Rats ◽  
Time To Exhaustion ◽  
O2 Consumption ◽  
Vo2 Max ◽  
Running Performance ◽  
And Performance

Before the start and after 4, 8, and 12 wk of a treadmill training program male rats were randomly selected and tested for running performance, maximum O2 consumption (VO2 max), running economy (VO2 submax), and skeletal muscle oxidative capacity (QO2). Data were compared with values from untrained weight-matched control rats. Maximum running time to exhaustion increased significantly (P less than 0.01) by 4 wk and again at 12 wk (P less than 0.01). Submaximal running endurance increased by 120 (4 wk), 320 (8 wk), and 372% (12 wk) (P less than 0.01). VO2 max was increased only at 12 wk (86.0 +/- 2.7 vs. 75.5 +/- 1.9 ml O2.kg-1.min-1); VO2 submax was decreased at 4 and 8 wk but not at 12 wk. Soleus QO2 was unchanged after 4 wk of training and increased by 50% at 8 wk and by 77% at 12 wk. This study is the first to show a dissociation in both the time course and the magnitude of longitudinal changes in VO2 max, VO2 submax, QO2, and maximal and submaximal running performance. We conclude that factors other than those measured explain the improvement in running performance that resulted from endurance training in these rats.

scholarly journals Effects of D-allulose on glucose tolerance and insulin response to a standard oral sucrose load: results of a prospective, randomized, crossover study

2021 ◽  
Vol 9 (1) ◽  
pp. e001939
Author(s):  
Francesco Franchi ◽  
Dmitry M Yaranov ◽  
Fabiana Rollini ◽  
Andrea Rivas ◽  
Jose Rivas Rios ◽  
...  
Keyword(s):  
Crossover Study ◽  
Plasma Glucose ◽  
Large Scale ◽  
Insulin Response ◽  
Mean Difference ◽  
Dietary Guidelines ◽  
Sugar Intake ◽  
Time Points ◽  
Insulin Levels ◽  
Dose Dependent

IntroductionCurrent dietary guidelines recommend limiting sugar intake for the prevention of diabetes mellitus (DM). Reduction in sugar intake may require sugar substitutes. Among these, D-allulose is a non-calorie rare monosaccharide with 70% sweetness of sucrose, which has shown anti-DM effects in Asian populations. However, there is limited data on the effects of D-allulose in other populations, including Westerners.Research design and methodsThis was a prospective, randomized, double-blind, placebo-controlled, crossover study conducted in 30 subjects without DM. Study participants were given a standard oral (50 g) sucrose load and randomized to placebo or escalating doses of D-allulose (2.5, 5.0, 7.5, 10.0 g). Subjects crossed-over to the alternate study treatment after 7–14 days of wash out. Plasma glucose and insulin levels were measured at five time points: before and at 30, 60, 90 and 120 min after ingestion.ResultsD-allulose was associated with a dose-dependent reduction of plasma glucose at 30 min compared with placebo. In particular, glucose was significantly lower with the 7.5 g (mean difference: 11; 95% CI 3 to 19; p=0.005) and 10 g (mean difference: 12; 95% CI 4 to 20; p=0.002) doses. Although glucose was not reduced at the other time points, there was a dose-dependent reduction in glucose excursion compared with placebo, which was significant with the 10 g dose (p=0.023). Accordingly, at 30 min D-allulose was associated with a trend towards lower insulin levels compared with placebo, which was significant with the 10 g dose (mean difference: 14; 95% CI 4 to 25; p=0.006). D-allulose did not reduce insulin at any other time point, but there was a significant dose-dependent reduction in insulin excursion compared with placebo (p=0.028), which was significant with the 10 g dose (p=0.002).ConclusionsThis is the largest study assessing the effects of D-allulose in Westerners demonstrating an early dose-dependent reduction in plasma glucose and insulin levels as well as decreased postprandial glucose and insulin excursion in subjects without DM. These pilot observations set the basis for large-scale investigations to support the anti-DM effects of D-allulose.Trial registration numberNCT02714413.

Electrically-induced quadriceps fatigue in the contralateral leg impairs ipsilateral knee extensors performance

2021 ◽  
Author(s):  
Fabio Giuseppe Laginestra ◽  
Markus Amann ◽  
Emine Kirmizi ◽  
Gaia Giuriato ◽  
Chiara Barbi ◽  
...  
Keyword(s):  
Muscle Activation ◽  
Central Fatigue ◽  
Endurance Performance ◽  
Voluntary Exercise ◽  
Peripheral Fatigue ◽  
Knee Extensors ◽  
Motor Drive ◽  
Time To Exhaustion ◽  
Crossover Effect ◽  
The Impact

Muscle fatigue induced by voluntary exercise, which requires central motor drive, causes central fatigue that impairs endurance performance of a different, non-fatigued muscle. This study investigated the impact of quadriceps fatigue induced by electrically-induced (no central motor drive) contractions on single-leg knee-extension (KE) performance of the subsequently exercising ipsilateral quadriceps. On two separate occasions, eight males completed constant-load (85% of maximal power-output) KE exercise to exhaustion. In a counterbalanced manner, subjects performed the KE exercise with no pre-existing quadriceps fatigue in the contralateral leg on one day (No-PreF), while on the other day, the same KE exercise was repeated following electrically-induced quadriceps fatigue in the contralateral leg (PreF). Quadriceps fatigue was assessed by evaluating pre- to post-exercise changes in potentiated twitch force (ΔQtw,pot; peripheral-fatigue), and voluntary muscle activation (ΔVA; central-fatigue). As reflected by the 57±11% reduction in electrically-evoked pulse force, the electrically-induced fatigue protocol caused significant knee-extensors fatigue. KE endurance time to exhaustion was shorter during PreF compared to No-PreF (4.6±1.2 vs 7.7±2.4 min; p<0.01). While ΔQtw,pot was significantly larger in No-PreF compared to PreF (-60% vs -52%, p<0.05), ΔVA was greater in PreF (-14% vs -10%, p<0.05). Taken together, electrically-induced quadriceps fatigue in the contralateral leg limits KE endurance performance and the development of peripheral fatigue in the ipsilateral leg. These findings support the hypothesis that the crossover-effect of central fatigue is mainly mediated by group III/IV muscle afferent feedback and suggest that impairments associated with central motor drive may only play a minor role in this phenomenon.

Effect of menstrual cycle phase on carbohydrate supplementation during prolonged exercise to fatigue

2000 ◽  
Vol 88 (2) ◽  
pp. 690-697 ◽  
Author(s):  
Stephen P. Bailey ◽  
Cristine M. Zacher ◽  
Karen D. Mittleman
Keyword(s):  
Fatty Acids ◽  
Menstrual Cycle ◽  
Prolonged Exercise ◽  
Cycle Phase ◽  
Time To Exhaustion ◽  
Menstrual Cycle Phase ◽  
Exercise Time ◽  
Carbohydrate Supplementation ◽  
Plasma Tyrosine ◽  
Placebo Drink

The effects of menstrual cycle phase and carbohydrate (CHO) supplementation were investigated during prolonged exercise. Nine healthy, moderately trained women cycled at 70% peak O2 consumption until exhaustion. Two trials were completed during the follicular (Fol) and luteal (Lut) phases of the menstrual cycle. Subjects consumed 0.6 g CHO ⋅ kg body wt− 1 ⋅ h− 1(5 ml/kg of a 6% CHO solution every 30 min beginning at min 30 of exercise) or a placebo drink (Pl) during exercise. Time to exhaustion during CHO increased from Pl values ( P < 0.05) by 14.4 ± 8.5 (Fol) and 11.4 ± 7.1% (Lut); no differences were observed between menstrual cycle phases. CHO attenuated ( P < 0.05) the decrease in plasma glucose and insulin and the increase in plasma free fatty acids, tryptophan, epinephrine, and cortisol observed during Pl for both phases. Plasma alanine, glutamine, proline, and isoleucine were lower ( P < 0.05) in Lut than in Fol phase. CHO resulted in lower ( P < 0.05) plasma tyrosine, valine, leucine, isoleucine, and phenylalanine. These results indicate that the menstrual cycle phase does not alter the effects of CHO supplementation on performance and plasma levels of related substrates during prolonged exercise.

Variability of Time to Exhaustion During Submaximal Exercise

1995 ◽  
Vol 20 (1) ◽  
pp. 39-51 ◽  
Author(s):  
Tom M. McLellan ◽  
Stephen S. Cheung ◽  
Ira Jacobs
Keyword(s):  
Sample Size ◽  
Dependent Measure ◽  
Time Of Day ◽  
Submaximal Exercise ◽  
Time To Exhaustion ◽  
Final Test ◽  
Exercise Time ◽  
Coefficients Of Variation ◽  
Post Hoc ◽  
Average Fitness

Exercise time to exhaustion (TE) is commonly used to evaluate the success or failure of such treatments as endurance training programs or nutritional supplements. The present study determined the variability of TE during submaximal exercise at 80% [Formula: see text]. Fifteen males performed cycle exercise to exhaustion on five occasions at the same time of day with a minimum of 72 hrs between sessions. There was no difference in TE (0.1 > p > 0.05) among the trials, with values ranging from 14.4 ± 1.1 min for Test 1 to 18.2 ± 2.4 min during the final test. Substantial variability in TE over the five trials was observed among subjects with coefficients of variation (CV) ranging from 2.8 to 31.4%. Subjects were divided into two groups using the median CV for TE. For the low CV group (n = 8), TE was significantly increased during Test 3 (14.9 ± 1.3 min) compared with Test 1 (12.8 ± 1.0 min) and Test 5 (12.5 ± 1.2 min). For the high CV group (n = 7), TE was increased during Test 5 (24.7 ± 3.7 min) compared with the other tests (18.5 ± 2.2 min). CV for [Formula: see text], [Formula: see text], pH, [Formula: see text], and rectal temperature were less than 5% and did not differ between groups. Post hoc power calculations revealed that if all subjects were considered as one group, sample size would have to increase to 40 to increase the power to 0.8. Due to the variability in TE that may be observed with males of average fitness, it is concluded that TE should not be the only dependent measure used to evaluate treatment effects during submaximal exercise. Key words: coefficient of variation, blood lactate, sample size, power

Niacin supplementation impairs exercise performance

2021 ◽  
Author(s):  
Greggory R. Davis ◽  
Arnold G. Nelson
Keyword(s):  
Body Weight ◽  
Resistance Exercise ◽  
Aerobic Exercise ◽  
Exercise Performance ◽  
Respiratory Exchange Ratio ◽  
Time To Exhaustion ◽  
Total Work ◽  
Cycling Exercise ◽  
Exercise Time ◽  
Performance Effects

Abstract. Several pre-workout supplements contain niacin, although the exercise performance effects of niacin are poorly understood. The purpose of the present study was to examine the performance effects of niacin versus caffeine as a pre-workout supplement. Twenty-five untrained males were recruited to complete three identical ramped aerobic cycling exercise trials. Participants were administered caffeine (CA) at 5 mg/kg body weight, 1000 mg niacin (NI), or a methylcelluloce placebo (PL) supplement prior to each trial. NI treatment induced significantly higher respiratory exchange ratio (RER) during exercise compared to the CA treatment, but not the PL treatment (PL=0.87±0.08, NI=0.91±0.08, CA=0.87±0.08; p=0.02). Similarly, exercise time to exhaustion (in minutes) was significantly different between the NI treatment and the CA treatment, but not the PL treatment (PL=27.45±4.47, NI=26.30±4.91, CA=28.76±4.86; p<0.01). Habitual caffeine use (p=0.16), habitual aerobic exercise (p=0.60), and habitual resistance exercise (p=0.10) did not significantly affect RER. Similarly, habitual caffeine use (p=0.72), habitual aerobic exercise (p=0.08), and habitual resistance exercise (p=0.39) did not significantly affect total work performed. The elevated RER and decreased time to exhaustion in the NI treatment suggests limited lipid availability during exercise and impaired exercise performance.

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