Fuel selection and cycling endurance performance with ingestion of [13C]glucose: evidence for a carbohydrate dose response

2010 ◽  
Vol 108 (6) ◽  
pp. 1520-1529 ◽  
Author(s):  
JohnEric W. Smith ◽  
Jeffrey J. Zachwieja ◽  
François Péronnet ◽  
Dennis H. Passe ◽  
Denis Massicotte ◽  
...  
Keyword(s):  
Muscle Glycogen ◽  
Ingestion Rate ◽  
Time Trial ◽  
Endurance Performance ◽  
Dependent Manner ◽  
Mean Power ◽  
Exogenous Glucose ◽  
Fuel Selection ◽  
Tracer Techniques ◽  
Glucose Ingestion

Endurance performance and fuel selection while ingesting glucose (15, 30, and 60 g/h) was studied in 12 cyclists during a 2-h constant-load ride [∼77% peak O2 uptake] followed by a 20-km time trial. Total fat and carbohydrate (CHO) oxidation and oxidation of exogenous glucose, plasma glucose, glucose released from the liver, and muscle glycogen were computed using indirect respiratory calorimetry and tracer techniques. Relative to placebo (210 ± 36 W), glucose ingestion increased the time trial mean power output (%improvement, 90% confidence limits: 7.4, 1.4 to 13.4 for 15 g/h; 8.3, 1.4 to 15.2 for 30 g/h; and 10.7, 1.8 to 19.6 for 60 g/h glucose ingested; effect size = 0.46). With 60 g/h glucose, mean power was 2.3, 0.4 to 4.2% higher, and 3.1, 0.5 to 5.7% higher than with 30 and 15 g/h, respectively, suggesting a relationship between the dose of glucose ingested and improvements in endurance performance. Exogenous glucose oxidation increased with ingestion rate (0.17 ± 0.04, 0.33 ± 0.04, and 0.52 ± 0.09 g/min for 15, 30, and 60 g/h glucose), but endogenous CHO oxidation was reduced only with 30 and 60 g/h due to the progressive inhibition of glucose released from the liver (probably related to higher plasma insulin concentration) with increasing ingestion rate without evidence for muscle glycogen sparing. Thus ingestion of glucose at low rates improved cycling time trial performance in a dose-dependent manner. This was associated with a small increase in CHO oxidation without any reduction in muscle glycogen utilization.

“Live high–train low” using normobaric hypoxia: a double-blinded, placebo-controlled study

2012 ◽  
Vol 112 (1) ◽  
pp. 106-117 ◽  
Author(s):  
Christoph Siebenmann ◽  
Paul Robach ◽  
Robert A. Jacobs ◽  
Peter Rasmussen ◽  
Nikolai Nordsborg ◽  
...  
Keyword(s):  
Placebo Effect ◽  
Time Trial ◽  
Endurance Performance ◽  
Normobaric Hypoxia ◽  
Controlled Study ◽  
Mean Power ◽  
Physiological Variables ◽  
Weekly Training ◽  
Double Blinded ◽  
Mean Power Output

The combination of living at altitude and training near sea level [live high–train low (LHTL)] may improve performance of endurance athletes. However, to date, no study can rule out a potential placebo effect as at least part of the explanation, especially for performance measures. With the use of a placebo-controlled, double-blinded design, we tested the hypothesis that LHTL-related improvements in endurance performance are mediated through physiological mechanisms and not through a placebo effect. Sixteen endurance cyclists trained for 8 wk at low altitude (<1,200 m). After a 2-wk lead-in period, athletes spent 16 h/day for the following 4 wk in rooms flushed with either normal air (placebo group, n = 6) or normobaric hypoxia, corresponding to an altitude of 3,000 m (LHTL group, n = 10). Physiological investigations were performed twice during the lead-in period, after 3 and 4 wk during the LHTL intervention, and again, 1 and 2 wk after the LHTL intervention. Questionnaires revealed that subjects were unaware of group classification. Weekly training effort was similar between groups. Hb mass, maximal oxygen uptake (VO2) in normoxia, and at a simulated altitude of 2,500 m and mean power output in a simulated, 26.15-km time trial remained unchanged in both groups throughout the study. Exercise economy (i.e., VO2 measured at 200 W) did not change during the LHTL intervention and was never significantly different between groups. In conclusion, 4 wk of LHTL, using 16 h/day of normobaric hypoxia, did not improve endurance performance or any of the measured, associated physiological variables.

A Comparative Analysis Between the Effects of Galactose and Glucose Supplementation on Endurance Performance

2012 ◽  
Vol 22 (1) ◽  
pp. 24-30 ◽  
Author(s):  
Paul W. Macdermid ◽  
Stephen Stannard ◽  
Dean Rankin ◽  
David Shillington
Keyword(s):  
Perceived Exertion ◽  
Time Trial ◽  
Endurance Performance ◽  
Cycling Performance ◽  
Rating Of Perceived Exertion ◽  
Work Intensity ◽  
Mean Power ◽  
Beneficial Effects ◽  
Main Effect ◽  
Performance Trial

Purpose:To determine beneficial effects of short-term galactose (GAL) supplementation over a 50:50 glucose–maltodextrin (GLUC) equivalent on self-paced endurance cycling performance.Methods:On 2 separate occasions, subjects performed a 100-km self-paced time trial (randomized and balanced order). This was interspersed with four 1-km and four 4-km maximal efforts reflecting the physical requirements of racing. Before each trial 38 ± 3 g of GAL or GLUC was ingested in a 6% concentrate fluid form 1 hr preexercise and then during exercise at a rate of 37 ± 3 g/hr. Performance variables were recorded for all 1- and 4-km efforts, all interspersed intervals, and the total 100-km distance. Noninvasive indicators of work intensity (heart rate [HR] and rating of perceived exertion) were also recorded.Results:Times taken to complete the 100-km performance trial were 8,298 ± 502 and 8,509 ± 578 s (p = .132), with mean power outputs of 271 ± 37 and 256 ± 45 W (p = .200), for GAL and GLUC, respectively. Mean HR did not differ (GAL 157 ± 7 and GLUC 157 ± 7 beats/min, p = .886). A main effect of carbohydrate (CHO) type on time to complete 4-km efforts occurred, with no CHO Type × Effort Order interaction observed. No main effect of CHO type or interaction of CHO Type × Sequential Order occurred for 1-km efforts.Conclusion:A 6% GAL drink does not enhance performance time during a self-paced cycling performance trial in highly trained endurance cyclists compared with a formula typically used by endurance athletes but may improve the ability to produce intermediate self-paced efforts.

Diet and Training in the Week Before Competition

2001 ◽  
Vol 26 (S1) ◽  
pp. S56-S63 ◽  
Author(s):  
Bente Kiens
Keyword(s):  
Muscle Glycogen ◽  
Exercise Performance ◽  
Time Trial ◽  
Endurance Performance ◽  
Strenuous Exercise ◽  
Dietary Regimen ◽  
Carbohydrate Loading ◽  
Exercise Muscle ◽  
Exercise Induced ◽  
Glycogen Stores

For many years athletes have used carbohydrate loading to enhance endurance performance. This practice has been based on findings demonstrating that 1) exercise induced depletion of the muscle glycogen stores followed by the intake of a carbohydrate rich diet, resulted in muscle glycogen stores above normal values and 2) that the pre-exercise muscle glycogen content was the main determinant of the capacity to perform strenuous exercise to exhaustion. Lately it has been speculated whether a period of a high fat diet, followed by carbohydrate loading to restore or increase muscle glycogen levels above normal, would be of further advantage for exercise performance. From the discussed data it emerges, however, that varying periods offat adaptation followed by a carbohydrate rich diet prior to exercise is of no benefit for exercise performance. Despite an increased fat oxidation and a concomitant decrease in carbohydrate oxidation during submaximal exercise, no benefit in a subsequent time trial appeared. Data suggest that this dietary regimen impairs the ability to utilise carbohydrates.

scholarly journals Effects of carbohydrate availability on sustained shivering I. Oxidation of plasma glucose, muscle glycogen, and proteins

2004 ◽  
Vol 96 (1) ◽  
pp. 32-40 ◽  
Author(s):  
François Haman ◽  
François Péronnet ◽  
Glen P. Kenny ◽  
Éric Doucet ◽  
Denis Massicotte ◽  
...  
Keyword(s):  
Heat Production ◽  
Plasma Glucose ◽  
Indirect Calorimetry ◽  
Muscle Glycogen ◽  
Glucose Oxidation ◽  
Fuel Selection ◽  
Glucose Ingestion ◽  
Diet And Exercise ◽  
Tracer Methods ◽  
A Minor

Carbohydrates (CHO) can play an important thermogenic role during shivering, but the effect of their availability on the use of other oxidative fuels is unclear. Using indirect calorimetry and tracer methods ([U-13C]glucose ingestion), we have determined the specific contributions of plasma glucose, muscle glycogen, proteins, and lipids to total heat production (Ḣprod) in men exposed to cold for 2-h (liquid-conditioned suit perfused with 10°C water). Measurements were made after low-CHO diet and exercise (Lo) and high-CHO diet without exercise (Hi). The size of CHO reserves had no effect on Ḣprod but a major impact on fuel selection before and during shivering. In the cold, a complete shift from lipid oxidation for Lo (53, 28, and 19% Ḣprod for lipids, CHO, and proteins, respectively) to CHO-based metabolism for Hi (23, 65, and 12% Ḣprod for lipids, CHO, and proteins, respectively) was observed. Plasma glucose oxidation remains a minor fuel under all conditions (<13% Ḣprod), falling to 7% Ḣprod for Lo. Therefore, adjusting plasma glucose oxidation to compensate for changes in muscle glycogen oxidation is not a strategy used for maintaining heat production. Instead, proteins and lipids share responsibility for this compensation. We conclude that humans can show remarkable flexibility in oxidative fuel selection to ensure that heat production is not compromised during sustained cold exposure.

Use of 13C substrates for metabolic studies in exercise: methodological considerations

1990 ◽  
Vol 69 (3) ◽  
pp. 1047-1052 ◽  
Author(s):  
F. Peronnet ◽  
D. Massicotte ◽  
G. Brisson ◽  
C. Hillaire-Marcel
Keyword(s):  
Isotopic Composition ◽  
Prolonged Exercise ◽  
Substrate Oxidation ◽  
O2 Uptake ◽  
Common Mistake ◽  
Exogenous Glucose ◽  
Exogenous Substrate ◽  
Glucose Ingestion ◽  
Endogenous Substrates ◽  
Methodological Considerations

The purpose of this study is to outline a common mistake made when the rate of oxidation of exogenous substrates during prolonged exercise is computed using 13C naturally labeled substrates. The equation proposed and commonly used in the computation does not take into account that exercise and/or exogenous substrate ingestion modifies the composition of the mixture of endogenous substrates oxidized and, consequently, the isotopic composition of CO2 arising from oxidation of endogenous substrates. The recovery of 13C and the amount of exogenous substrate oxidized are thus overestimated. An adequate procedure for the computation of exogenous substrate oxidation taking into account changes in isotopic composition of CO2 arising from oxidation of endogenous substrates is suggested. Results from a pilot experiment (4 subjects) using this procedure indicate that over 2 h of exercise (66% of maximal O2 uptake), with ingestion of 60 g of glucose, 39 +/- 4 g of glucose were oxidized. Estimates made without taking into account changes in isotopic composition of CO2 arising from oxidation of endogenous substrates range between 70 +/- 8 and 44 +/- 3 g depending on 1) the isotopic composition of exogenous glucose and 2) the isotopic composition of expired CO2 taken as reference (rest or exercise without glucose ingestion). These observations suggest that results from previous studies of exogenous substrate oxidation during exercise using 13C labeling should be used with caution.

Carbohydrate loading failed to improve 100-km cycling performance in a placebo-controlled trial

2000 ◽  
Vol 88 (4) ◽  
pp. 1284-1290 ◽  
Author(s):  
Louise M. Burke ◽  
John A. Hawley ◽  
Elske J. Schabort ◽  
Alan St Clair Gibson ◽  
Iñigo Mujika ◽  
...  
Keyword(s):  
Body Mass ◽  
Muscle Glycogen ◽  
Blood Glucose Concentration ◽  
Controlled Trial ◽  
Liver Glycogen ◽  
Cycling Performance ◽  
Controlled Study ◽  
Mean Power ◽  
Road Racing ◽  
Mean Power Output

We evaluated the effect of carbohydrate (CHO) loading on cycling performance that was designed to be similar to the demands of competitive road racing. Seven well-trained cyclists performed two 100-km time trials (TTs) on separate occasions, 3 days after either a CHO-loading (9 g CHO ⋅ kg body mass− 1 ⋅ day− 1) or placebo-controlled moderate-CHO diet (6 g CHO ⋅ kg body mass− 1 ⋅ day− 1). A CHO breakfast (2 g CHO/kg body mass) was consumed 2 h before each TT, and a CHO drink (1 g CHO ⋅ kg.body mass− 1 ⋅ h− 1) was consumed during the TTs to optimize CHO availability. The 100-km TT was interspersed with four 4-km and five 1-km sprints. CHO loading significantly increased muscle glycogen concentrations (572 ± 107 vs. 485 ± 128 mmol/kg dry wt for CHO loading and placebo, respectively; P < 0.05). Total muscle glycogen utilization did not differ between trials, nor did time to complete the TTs (147.5 ± 10.0 and 149.1 ± 11.0 min; P = 0.4) or the mean power output during the TTs (259 ± 40 and 253 ± 40 W, P = 0.4). This placebo-controlled study shows that CHO loading did not improve performance of a 100-km cycling TT during which CHO was consumed. By preventing any fall in blood glucose concentration, CHO ingestion during exercise may offset any detrimental effects on performance of lower preexercise muscle and liver glycogen concentrations. Alternatively, part of the reported benefit of CHO loading on subsequent athletic performance could have resulted from a placebo effect.

scholarly journals Relationship Between the Critical Power Test and a 20-min Functional Threshold Power Test in Cycling

2021 ◽  
Vol 11 ◽  
Author(s):  
Bettina Karsten ◽  
Luca Petrigna ◽  
Andreas Klose ◽  
Antonino Bianco ◽  
Nathan Townsend ◽  
...  
Keyword(s):  
Critical Power ◽  
Pearson Correlation ◽  
Time Trial ◽  
Peak Oxygen Consumption ◽  
Threshold Power ◽  
Strong Correlations ◽  
Mean Power ◽  
Power Test ◽  
Paired Samples ◽  
The Mean

To investigate the agreement between critical power (CP) and functional threshold power (FTP), 17 trained cyclists and triathletes (mean ± SD: age 31 ± 9 years, body mass 80 ± 10 kg, maximal aerobic power 350 ± 56 W, peak oxygen consumption 51 ± 10 mL⋅min–1⋅kg–1) performed a maximal incremental ramp test, a single-visit CP test and a 20-min time trial (TT) test in randomized order on three different days. CP was determined using a time-trial (TT) protocol of three durations (12, 7, and 3 min) interspersed by 30 min passive rest. FTP was calculated as 95% of 20-min mean power achieved during the TT. Differences between means were examined using magnitude-based inferences and a paired-samples t-test. Effect sizes are reported as Cohen’s d. Agreement between CP and FTP was assessed using the 95% limits of agreement (LoA) method and Pearson correlation coefficient. There was a 91.7% probability that CP (256 ± 50 W) was higher than FTP (249 ± 44 W). Indeed, CP was significantly higher compared to FTP (P = 0.041) which was associated with a trivial effect size (d = 0.04). The mean bias between CP and FTP was 7 ± 13 W and LoA were −19 to 33 W. Even though strong correlations exist between CP and FTP (r = 0.969; P &lt; 0.001), the chance of meaningful differences in terms of performance (1% smallest worthwhile change), were greater than 90%. With relatively large ranges for LoA between variables, these values generally should not be used interchangeably. Caution should consequently be exercised when choosing between FTP and CP for the purposes of performance analysis.

scholarly journals Does caffeine supplementation alter energy contribution during a work-based ~30 min cycling time-trial?

2020 ◽  
Vol 34 (3) ◽  
pp. 471-481
Author(s):  
Gabriel Barreto ◽  
Rafael Pires da Silva ◽  
Guilherme Yamaguchi ◽  
Luana Farias de Oliveira ◽  
Vitor de Salles Painelli ◽  
...  
Keyword(s):  
Perceived Exertion ◽  
Lactate Concentration ◽  
Blood Lactate Concentration ◽  
Time Trial ◽  
Energy System ◽  
Energy Contribution ◽  
Mean Power ◽  
Double Blind ◽  
Cycling Time Trial ◽  
Cycling Time

Caffeine has been shown to increase anaerobic energy contribution during short-duration cycling time-trials (TT) though no information exists on whether caffeine alters energy contribution during more prolonged, aerobic type TTs. The aim of this study was to determine the effects of caffeine supplementation on longer and predominantly aerobic exercise. Fifteen recreationally-trained male cyclists (age 38±8 y, height 1.76±0.07 m, body mass 72.9±7.7 kg) performed a ~30 min cycling TT following either 6 mg·kg-1BM caffeine (CAF) or placebo (PLA) supplementation, and one control (CON) session without supplementation, in a double- -blind, randomised, counterbalance and cross-over design. Mean power output (MPO) was recorded as the outcome measure. Respiratory values were measured throughout exercise for the determination of energy system contribution. Data were analysed using mixed-models. CAF improved mean MPO compared to CON (P=0.01), and a trend towards an improvement compared to PLA (P=0.07); there was no difference in MPO at any timepoint throughout the exercise between conditions. There was a main effect of Condition (P=0.04) and Time (P<0.0001) on blood lactate concentration, which tended to be higher in CAF vs. both PLA and CON (Condition effect, both P=0.07). Ratings of perceived exertion increased over time (P<0.0001), with no effect of Condition or interaction (both P>0.05). Glycolytic energy contribution was increased in CAF compared to CON and PLA (both P<0.05), but not aerobic or ATP-CP (both P>0.05). CAF improved aerobic TT performance compared to CON, which could be explained by increased glycolytic energy contribution.

Carbohydrate-Loading during the Follicular Phase of the Menstrual Cycle: Effects on Muscle Glycogen and Exercise Performance

2001 ◽  
Vol 11 (4) ◽  
pp. 430-441 ◽  
Author(s):  
D.R. Paul ◽  
S.M. Mulroy ◽  
J.A. Horner ◽  
K.A. Jacobs ◽  
D.R. Lamb
Keyword(s):  
Menstrual Cycle ◽  
Lean Body Mass ◽  
Muscle Glycogen ◽  
Time Trial ◽  
Follicular Phase ◽  
High Carbohydrate Diet ◽  
Carbohydrate Diet ◽  
High Carbohydrate ◽  
Experimental Trial ◽  
Carbohydrate Loading

The effects of employing a high-carbohydrate diet (carbohydrate-loading) to increase glycogen storage in skeletal muscle are not well established in female athletes. On 4 occasions—2 familiarization trials and 2 experimental trials—6 well-trained female subjects completed 6 × 15-min continuous intervals of cycling (12 min at 72% V̇O2max, 1 min at maximal effort, and 2 min at 50% V̇O2max), followed by a time trial 15 min later. The women consumed their habitual diets (HD; 6–7 g carbohydrate/kg lean body mass) for 3 days after the second familiarization trial and before the first experimental trial. During the 3 days following the first experimental trial, the subjects consumed a high-carbohydrate diet (CD; 9–10 g carbohydrate/kg lean body mass) prior to the second experimental trial. Mean (±SEM) pre-exercise muscle glycogen concentrations were greater after CD versus HD (171.9 ± 8.7 vs. 131.4 ± 10.3 mmol/kg wet weight, P < 0.003). Although 4 of the 6 subjects improved their time-trial performance after CD, mean performance for the time trial was not significantly different between diets (HD: 763.9 ± 35.6 s; CD: 752.9 ± 30.1 s). Thus, female cyclists can increase their muscle glycogen stores after a carbohydrate-loading diet during the follicular phase of the menstrual cycle, but we found no compelling evidence of a dietary effect on performance of a cycling time trial performed after 90 min of moderate-intensity exercise.

scholarly journals The Ingestion of 39 or 64 g·hr−1 of Carbohydrate is Equally Effective at Improving Endurance Exercise Performance in Cyclists

2015 ◽  
Vol 25 (3) ◽  
pp. 285-292 ◽  
Author(s):  
Michael L. Newell ◽  
Angus M. Hunter ◽  
Claire Lawrence ◽  
Kevin D. Tipton ◽  
Stuart D. R. Galloway
Keyword(s):  
Power Output ◽  
Statistical Significance ◽  
Time Trial ◽  
Cycling Performance ◽  
Constant Load ◽  
Peak Power Output ◽  
Task Completion ◽  
Intake Rate ◽  
Mean Power ◽  
Pacing Strategy

In an investigator-blind, randomized cross-over design, male cyclists (mean± SD) age 34.0 (± 10.2) years, body mass 74.6 (±7.9) kg, stature 178.3 (±8.0) cm, peak power output (PPO) 393 (±36) W, and VO2max 62 (±9) ml·kg−1min−1 training for more than 6 hr/wk for more than 3y (n = 20) completed four experimental trials. Each trial consisted of a 2-hr constant load ride at 95% of lactate threshold (185 ± 25W) then a work-matched time trial task (~30min at 70% of PPO). Three commercially available carbohydrate (CHO) beverages, plus a control (water), were administered during the 2-hr ride providing 0, 20, 39, or 64g·hr−1 of CHO at a fluid intake rate of 1L·hr−1. Performance was assessed by time to complete the time trial task, mean power output sustained, and pacing strategy used. Mean task completion time (min:sec ± SD) for 39g·hr−1 (34:19.5 ± 03:07.1, p = .006) and 64g·hr−1 (34:11.3 ± 03:08.5 p = .004) of CHO were significantly faster than control (37:01.9 ± 05:35.0). The mean percentage improvement from control was −6.1% (95% CI: −11.3 to −1.0) and −6.5% (95% CI: −11.7 to −1.4) in the 39 and 64g·hr−1 trials respectively. The 20g·hr−1 (35:17.6 ± 04:16.3) treatment did not reach statistical significance compared with control (p = .126) despite a mean improvement of −3.7% (95% CI −8.8−1.5%). No further differences between CHO trials were reported. No interaction between CHO dose and pacing strategy occurred. 39 and 64g·hr−1 of CHO were similarly effective at improving endurance cycling performance compared with a 0g·hr−1 control in our trained cyclists.

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