scholarly journals Effects of carbohydrate ingestion before and during exercise on glucose kinetics and performance

2000 ◽  
Vol 89 (6) ◽  
pp. 2220-2226 ◽  
Author(s):  
Mark A. Febbraio ◽  
Alison Chiu ◽  
Damien J. Angus ◽  
Melissa J. Arkinstall ◽  
John A. Hawley
Keyword(s):  
Plasma Glucose ◽  
Glucose Concentration ◽  
Peak Power ◽  
Glucose Oxidation ◽  
Time Trial ◽  
Peak Power Output ◽  
Glucose Kinetics ◽  
Carbohydrate Ingestion ◽  
Total Fat ◽  
And Performance

We investigated the effect of carbohydrate (CHO) ingestion before and during exercise and in combination on glucose kinetics, metabolism and performance in seven trained men, who cycled for 120 min (SS) at ∼63% of peak power output, followed by a 7 kJ/kg body wt time trial (TT). On four separate occasions, subjects received either a placebo beverage before and during SS (PP); placebo 30 min before and 2 g/kg body wt of CHO in a 6.4% CHO solution throughout SS (PC); 2 g/kg body wt of CHO in a 25.7% CHO beverage 30 min before and placebo throughout SS (CP); or 2 g/kg body wt of CHO in a 25.7% CHO beverage 30 min before and 2 g/kg of CHO in a 6.4% CHO solution throughout SS (CC). Ingestion of CC and CP markedly (>8 mM) increased plasma glucose concentration ([glucose]) compared with PP and PC (5 mM). However, plasma [glucose] fell rapidly at the onset of SS so that after 80 min it was similar (6 mM) between all treatments. After this time, plasma [glucose] declined in both PP and CP ( P < 0.05) but was well maintained in both CC and PC. Ingestion of CC and CP increased rates of glucose appearance (Ra) and disappearance (Rd) compared with PP and PC at the onset of, and early during, SS ( P < 0.05). However, late in SS, both glucose Ra and Rd were higher in CC and PC compared with other trials ( P < 0.05). Although calculated rates of glucose oxidation were different when comparing the four trials ( P < 0.05), total CHO oxidation and total fat oxidation were similar. Despite this, TT was improved in CC and PC compared with PP ( P < 0.05). We conclude that 1) preexercise ingestion of CHO improves performance only when CHO ingestion is maintained throughout exercise, and 2) ingestion of CHO during 120 min of cycling improves subsequent TT performance.

Effects of Shoe Cleat Position on Physiology and Performance of Competitive Cyclists

2009 ◽  
Vol 4 (4) ◽  
pp. 517-523 ◽  
Author(s):  
Carl D. Paton
Keyword(s):  
Oxygen Consumption ◽  
Steady State ◽  
Power Output ◽  
Peak Power ◽  
Time Trial ◽  
Peak Power Output ◽  
Maximum Oxygen Consumption ◽  
Competitive Cyclists ◽  
And Performance ◽  
Foot Position

Purpose:Aerobic economy is an important factor that affects the performance of competitive cyclists. It has been suggested that placing the foot more anteriorly on the bicycle pedals may improve economy over the traditional foot position by improving pedaling efficiency. The current study examines the effects of changing the anterior-posterior pedal foot position on the physiology and performance of well-trained cyclists.Methods:In a crossover study, 10 competitive cyclists completed two maximal incremental and two submaximal tests in either their preferred (control) or a forward (arch) foot position. Maximum oxygen consumption and peak power output were determined from the incremental tests for both foot positions. On two further occasions, cyclists also completed a two-part 60-min submaximal test that required them to maintain a constant power output (equivalent to 60% of their incremental peak power) for 30 min, during which respiratory and blood lactate samples were taken at predetermined intervals. Thereafter, subjects completed a 30-min self-paced maximal effort time trial.Results:Relative to the control, the mean changes (±90% confidence limits) in the arch condition were as follows: maximum oxygen consumption, -0.5% (±2.0%); incremental peak power output, -0.8% (±1.3%); steady-state oxygen consumption at 60%, -2.4% (±1.1%); steady-state heart rate 60%, 0.4% (±1.7%); lactate concentration 60%, 8.7% (±14.4%); and mean time trial power, -1.5% (±2.9%).Conclusions:We conclude that there was no substantial physiological or performance advantage in this group using an arch-cleat shoe position in comparison with a cyclist’s normal preferred condition.

scholarly journals Preexercise Cycling Protocol Alters Pacing Behavior in Competitive Time Trials

2020 ◽  
Vol 15 (9) ◽  
pp. 1303-1308
Author(s):  
Marco J. Konings ◽  
Florentina J. Hettinga
Keyword(s):  
Power Output ◽  
Repeated Measures ◽  
Peak Power ◽  
Perceived Exertion ◽  
Time Trial ◽  
Cycle Ergometer ◽  
Peak Power Output ◽  
Experimental Conditions ◽  
And Performance ◽  
The Impact

Purpose: The behavior of an opponent has been shown to alter pacing and performance. To advance our understanding of the impact of perceptual stimuli such as an opponent on pacing and performance, this study examined the effect of a preexercise cycling protocol on exercise regulation with and without an opponent. Methods: Twelve trained cyclists performed 4 experimental, self-paced 4-km time-trial conditions on an advanced cycle ergometer in a randomized, counterbalanced order. Participants started the time trial in rested state (RS) or performed a 10-min cycling protocol at 67% peak power output (CP) before the time trial. During the time trials, participants had to ride alone (NO) or against a virtual opponent (OP). The experimental conditions were (1) RS-NO, (2) RS-OP, (3) CP-NO, and (4) CP-OP. Repeated-measures analyses of variance (P < .05) were used to examine differences in pacing and performance in terms of power output. Results: A faster pace was adopted in the first kilometer during RS-OP (318 [72] W) compared with RS-NO (291 [81] W; P = .03), leading to an improved finishing time during RS-OP compared with RS-NO (P = .046). No differences in either pacing or performance were found between CP-NO and CP-OP. Conclusions: The evoked response by the opponent to adopt a faster initial pace in the 4-km time trial disappeared when cyclists had to perform a preceding cycling protocol. The outcomes of this study highlight that perceived exertion alters the responsiveness to perceptual stimuli of cyclists during competition.

Prevalence of Hypoglycemia Following Pre-exercise Carbohydrate Ingestion Is Not Accompanied by Higher Insulin Sensitivity

2002 ◽  
Vol 12 (4) ◽  
pp. 398-413 ◽  
Author(s):  
Roy L.P.G. Jentjens ◽  
Asker E. Jeukendrup
Keyword(s):  
Insulin Sensitivity ◽  
Plasma Glucose ◽  
Glucose Tolerance Test ◽  
Time Trial ◽  
Tolerance Test ◽  
Cycle Ergometer ◽  
Submaximal Exercise ◽  
Oral Glucose ◽  
Carbohydrate Ingestion ◽  
Carbohydrate Feeding

Pre-exercise carbohydrate feeding may result in rebound hypoglycemia in some but not all athletes. The aim of the present study was to examine whether insulin sensitivity in athletes who develop rebound hypoglycemia is higher compared with those who do not show rebound hypoglycemia. Twenty trained athletes (V̇O2max of 61.8 ± 1.4 ml · kg−1 · min−1) performed an exercise trial on a cycle ergometer. Forty-five minutes before the start of exercise, subjects consumed 500 ml of a beverage containing 75 g of glucose. The exercise trial consisted of · 20 min of submaximal exercise at 74 ± 1% V̇O2max immediately followed by a time trial. Based upon the plasma glucose nadir reached during submaximal exercise, subjects were assigned to a Hypo group (<3.5 mmol/L) and a Non-hypo group (≥3.5 mmol/L). An oral glucose tolerance test was performed to obtain an index of insulin sensitivity (ISI). The plasma glucose nadir during submaximal exercise was significantly lower (p < .01) in the Hypo-group (n = 10) compared with the Non-hypo group (n = 10) (2.7 ± 0.1 vs. 4.1 ± 0.2 mmol/L, respectively). No difference was found in ISI between the Hypo and the Non-hypo group (3.7 ± 0.4 vs. 3.8 ± 0.5, respectively). The present results suggest that insulin sensitivity does not play an important role in the occurrence of rebound hypoglycemia.

Cycling Efficiency and Performance Following Short-Term Training Using Uncoupled Cranks

2009 ◽  
Vol 4 (1) ◽  
pp. 18-28 ◽  
Author(s):  
Andrew D. Williams ◽  
Isaac Selva Raj ◽  
Kristie L. Stucas ◽  
James W. Fell ◽  
Diana Dickenson ◽  
...  
Keyword(s):  
Lactate Threshold ◽  
Performance Enhancement ◽  
Average Power ◽  
Time Trial ◽  
Mechanical Efficiency ◽  
Cycling Performance ◽  
Peak Power Output ◽  
Gross Efficiency ◽  
And Performance ◽  
Study Participants

Objectives:Uncoupled cycling cranks are designed to remove the ability of one leg to assist the other during the cycling action. It has been suggested that training with this type of crank can increase mechanical efficiency. However, whether these improvements can confer performance enhancement in already well-trained cyclists has not been reported.Method:Fourteen well-trained cyclists (13 males, 1 female; 32.4 ± 8.8 y; 74.5 ± 10.3 kg; Vo2max 60.6 ± 5.5 mL·kg−1·min−1; mean ± SD) participated in this study. Participants were randomized to training on a stationary bicycle using either an uncoupled (n = 7) or traditional crank (n = 7) system. Training involved 1-h sessions, 3 days per week for 6 weeks, and at a heart rate equivalent to 70% of peak power output (PPO) substituted into the training schedule in place of other training. Vo2max, lactate threshold, gross efficiency, and cycling performance were measured before and following the training intervention. Pre- and post testing was conducted using traditional cranks.Results:No differences were observed between the groups for changes in Vo2max, lactate threshold, gross efficiency, or average power maintained during a 30-minute time trial.Conclusion:Our results indicate that 6 weeks (18 sessions) of training using an uncoupled crank system does not result in changes in any physiological or performance measures in well-trained cyclists.

Reliability of Physiological Attributes and Their Association With Stochastic Cycling Performance

2014 ◽  
Vol 9 (2) ◽  
pp. 309-315 ◽  
Author(s):  
Gregory T. Levin ◽  
Paul B. Laursen ◽  
Chris R. Abbiss
Keyword(s):  
Power Output ◽  
Ventilatory Threshold ◽  
Intraclass Correlation ◽  
Time Trial ◽  
Cycling Performance ◽  
Peak Power Output ◽  
Cycling Time Trial ◽  
Physiological Variables ◽  
Physiological Attributes ◽  
And Performance

Purpose:To assess the reliability of a 5-min-stage graded exercise test (GXT) and determine the association between physiological attributes and performance over stochastic cycling trials of varying distance.Methods:Twenty-eight well-trained male cyclists performed 2 GXTs and either a 30-km (n = 17) or a 100-km stochastic cycling time trial (n = 9). Stochastic cycling trials included periods of high-intensity efforts for durations of 250 m, 1 km, or 4 km depending on the test being performing.Results:Maximal physiological attributes were found to be extremely reliable (maximal oxygen uptake [VO2max]: coefficient of variation [CV] 3.0%, intraclass correlation coefficient [ICC] .911; peak power output [PPO]: CV 3.0%, ICC .913), but a greater variability was found in ventilatory thresholds and economy. All physiological variables measured during the GXT, except economy at 200 W, were correlated with 30-km cycling performance. Power output during the 250-m and 1-km efforts of the 30-km trial were correlated with VO2max, PPO, and the power output at the second ventilatory threshold (r = .58–.82). PPO was the only physiological attributed measured during the GXT to be correlated with performance during the 100-km cycling trial (r = .64).Conclusions:Many physiological variables from a reliable GXT were associated with performance over shorter (30-km) but not longer (100-km) stochastic cycling trials.

scholarly journals The effect of acute dark chocolate consumption on carbohydrate metabolism and performance during rest and exercise

2014 ◽  
Vol 39 (2) ◽  
pp. 173-182 ◽  
Author(s):  
Trent Stellingwerff ◽  
Jean-Philippe Godin ◽  
Chieh J. Chou ◽  
Dominik Grathwohl ◽  
Alastair B. Ross ◽  
...  
Keyword(s):  
Carbohydrate Metabolism ◽  
Plasma Glucose ◽  
Time Trial ◽  
Peak Oxygen Uptake ◽  
Dark Chocolate ◽  
Trial Effect ◽  
Tracer Techniques ◽  
And Performance ◽  
The Impact ◽  
Rest And Exercise

Consumption of cocoa-enriched dark chocolate (DC) has been shown to alter glucose and insulin concentration during rest and exercise compared with cocoa-depleted control (CON). However, the impact of DC consumption on exercise metabolism and performance is uncertain. Therefore, we investigated carbohydrate metabolism via stable isotope tracer techniques during exercise after subjects ingested either DC or CON. Sixteen overnight-fasted male cyclists performed a single-blinded, randomized, crossover design trial, after consuming either DC or CON at 2 h prior to 2.5 h of steady-state (SS) exercise (∼45% peak oxygen uptake). This was followed by an ∼15-min time-trial (TT) and 60 min of recovery. [6,6-2H2]Glucose and [U-13C]glucose were infused during SS to assess glucose rate of appearance (Ra) and disappearance (Rd). After DC consumption, plasma (−)-glucose and insulin concentrations were significantly (p < 0.001) elevated throughout vs. CON. During SS, there was no difference in [6,6-2H2]glucose Ra between treatments, but towards the end of SS (last 60 min) there was a ∼16% decrease in Rd in DC vs. CON (p < 0.05). Accordingly, after DC there was an ∼18% significant decrease in plasma glucose oxidation (trial effect; p = 0.032), and an ∼15% increase in tracer-derived muscle glycogen utilization (p = 0.045) late during SS exercise. The higher blood glucose concentrations during exercise and recovery after DC consumption coincided with high concentrations of epicatechin and (or) theobromine. In summary, DC consumption altered muscle carbohydrate partitioning, between muscle glucose uptake and glycogen oxidation, but did not effect cycling TT performance.

A Carbohydrate Ingestion Intervention in an Elite Athlete Who Follows a Low-Carbohydrate High-Fat Diet

2018 ◽  
Vol 13 (7) ◽  
pp. 957-960 ◽  
Author(s):  
Christopher C. Webster ◽  
Jeroen Swart ◽  
Timothy D. Noakes ◽  
James A. Smith
Keyword(s):  
High Intensity ◽  
Time Trial ◽  
Endurance Performance ◽  
High Fat ◽  
Carbohydrate Ingestion ◽  
High Intensity Training ◽  
Low Carbohydrate ◽  
Elite Level ◽  
And Performance ◽  
Intensity Training

This case study documents the performance of an elite-level, exceptionally well-fat-adapted endurance athlete as he reintroduced carbohydrate (CHO) ingestion during high-intensity training. He had followed a strict low-CHO high-fat (LCHF) diet for 2 y, during which he ate approximately 80 g of CHO per day and trained and raced while ingesting only water. While following this diet, he earned numerous podium finishes in triathlons of various distances. However, he approached the authors to test whether CHO supplementation during exercise would further increase his high-intensity performance without affecting his fat adaptation. This 7-wk n = 1 investigation included a 4-wk habitual LCHF diet phase during which he drank only water during training and performance trials and a 3-wk habitual diet plus CHO ingestion phase (LCHF + CHO) during which he followed his usual LCHF diet but ingested 60 g/h CHO during 8 high-intensity training sessions and performance trials. After each phase, rates of fat oxidation and 30-s sprint, 4-min sprint, 20-km time trial (TT), and 100-km TT performances were measured. Compared with LCHF, 20-km TT time improved by 2.8% after LCHF + CHO, which would be a large difference in competition. There was no change in 30-s sprint power, a small improvement in 4-min sprint power (1.6%), and a small reduction in 100-km TT time (1.1%). The authors conclude that CHO ingestion during exercise was likely beneficial for this fat-adapted athlete during high-intensity endurance-type exercise (4–30 min) but likely did not benefit his short-sprint or prolonged endurance performance.

A Comparison of Different Prerace Warm-Up Strategies on 1-km Cycling Time-Trial Performance

2020 ◽  
Vol 15 (8) ◽  
pp. 1109-1116
Author(s):  
Mathias T. Vangsoe ◽  
Jonas K. Nielsen ◽  
Carl D. Paton
Keyword(s):  
Blood Lactate ◽  
Power Output ◽  
Peak Power ◽  
Lactate Concentration ◽  
Blood Lactate Concentration ◽  
Time Trial ◽  
Peak Power Output ◽  
Warm Up ◽  
Performance Time ◽  
Competitive Cyclists

Purpose: Ischemic preconditioning (IPC) and postactivation potentiation (PAP) are warm-up strategies proposed to improve high-intensity sporting performance. However, only few studies have investigated the benefits of these strategies compared with an appropriate control (CON) or an athlete-selected (SELF) warm-up protocol. Therefore, this study examined the effects of 4 different warm-up routines on 1-km time-trial (TT) performance with competitive cyclists. Methods: In a randomized crossover study, 12 well-trained cyclists (age 32 [10] y, mass 77.7 [4.6] kg, peak power output 1141 [61] W) performed 4 different warm-up strategies—(CON) 17 minutes CON only, (SELF) a self-determined warm-up, (IPC) IPC + CON, or (PAP) CON + PAP—prior to completing a maximal-effort 1-km TT. Performance time and power, quadriceps electromyograms, muscle oxygen saturation (SmO2), and blood lactate were measured to determine differences between trials. Results: There were no significant differences (P > .05) in 1-km performance time between CON (76.9 [5.2] s), SELF (77.3 [6.0] s), IPC (77.0 [5.5] s), or PAP (77.3 [5.9] s) protocols. Furthermore, there were no significant differences in mean or peak power output between trials. Finally, electromyogram activity, SmO2, and recovery blood lactate concentration were not different between conditions. Conclusions: Adding IPC or PAP protocols to a short CON warm-up appears to provide no additional benefit to 1-km TT performance with well-trained cyclists and is therefore not recommended. Furthermore, additional IPC and PAP protocols had no effect on electromyograms and SmO2 values during the TT or peak lactate concentration during recovery.

Training Prescription Guided by Heart-Rate Variability in Cycling

2019 ◽  
Vol 14 (1) ◽  
pp. 23-32 ◽  
Author(s):  
Alejandro Javaloyes ◽  
Jose Manuel Sarabia ◽  
Robert Patrick Lamberts ◽  
Manuel Moya-Ramon
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
Oxygen Uptake ◽  
Power Output ◽  
Maximal Oxygen Uptake ◽  
Peak Power ◽  
Performance Enhancement ◽  
Time Trial ◽  
Peak Power Output ◽  
Road Cycling

Purpose: Road cycling is a sport with extreme physiological demands. Therefore, there is a need to find new strategies to improve performance. Heart-rate variability (HRV) has been suggested as an effective alternative for prescribing training load against predefined training programs. The purpose of this study was to examine the effect of training prescription based on HRV in road cycling performance. Methods: Seventeen well-trained cyclists participated in this study. After an initial evaluation week, cyclists performed 4 baseline weeks of standardized training to establish their resting HRV. Then, cyclists were divided into 2 groups, an HRV-guided group and a traditional periodization group, and they carried out 8 training weeks. Cyclists performed 2 evaluation weeks, after and before a training week. During the evaluation weeks, cyclists performed a graded exercise test to assess maximal oxygen uptake, peak power output, and ventilatory thresholds with their corresponding power output (VT1, VT2, WVT1, and WVT2, respectively) and a 40-min simulated time trial. Results: The HRV-guided group improved peak power output (5.1% [4.5%]; P = .024), WVT2 (13.9% [8.8%]; P = .004), and 40-min all-out time trial (7.3% [4.5%]; P = .005). Maximal oxygen uptake and WVT1 remained similar. The traditional periodization group did not improve significantly after the training week. There were no differences between groups. However, magnitude-based inference analysis showed likely beneficial and possibly beneficial effects for the HRV-guided group instead of the traditional periodization group in 40-min all-out time trial and peak power output, respectively. Conclusion: Daily training prescription based on HRV could result in a better performance enhancement than a traditional periodization in well-trained cyclists.

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