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.

Dietary carbohydrate, muscle glycogen, and power output during rowing training

1991 ◽  
Vol 70 (4) ◽  
pp. 1500-1505 ◽  
Author(s):  
J. C. Simonsen ◽  
W. M. Sherman ◽  
D. R. Lamb ◽  
A. R. Dernbach ◽  
J. A. Doyle ◽  
...  
Keyword(s):  
Body Mass ◽  
Muscle Glycogen ◽  
Power Output ◽  
Glycogen Content ◽  
Dietary Carbohydrate ◽  
Mean Power ◽  
Muscle Glycogen Content ◽  
High Carbohydrate ◽  
Peak Vo2 ◽  
Mean Power Output

The belief that high-carbohydrate diets enhance training capacity (mean power output) has been extrapolated from studies that have varied dietary carbohydrate over a few days and measured muscle glycogen but did not assess power output during training. We hypothesized that a high-carbohydrate (HI) diet (10 g.kg body mass-1.day-1) would promote greater muscle glycogen content and greater mean power output during training than a moderate-carbohydrate (MOD) diet (5 g.kg body mass-1.day-1) over 4 wk of intense twice-daily rowing training. Dietary protein intake was 2 g.kg body mass-1.day-1, and fat intake was adjusted to maintain body mass. Twelve male and 10 female collegiate rowers were randomly assigned to the treatment groups. Training was 40 min at 70% peak O2 consumption (VO2) (A.M.) and either three 2,500-m time trials to assess power output or interval training at 70-90% peak VO2 (P.M.). Mean daily training was 65 min at 70% peak VO2 and 38 min at greater than or equal to 90% peak VO2. Mean muscle glycogen content increased 65% in the HI group (P less than 0.05) but remained constant at 119 mmol/kg in the MOD group over the 4 wk. Mean power output in time trials increased 10.7 and 1.6% after 4 wk in the HI and MOD groups, respectively (P less than 0.05). We conclude that a diet with 10 g carbohydrate.kg body mass-1.day-1 promotes greater muscle glycogen content and greater power output during training than a diet containing 5 g carbohydrate.kg body mass-1.day-1 over 4 wk of intense twice-daily rowing training.(ABSTRACT TRUNCATED AT 250 WORDS)

Variability in Power Output During Cycling in International Olympic-Distance Triathlon

2014 ◽  
Vol 9 (4) ◽  
pp. 732-734 ◽  
Author(s):  
Naroa Etxebarria ◽  
Shaun D’Auria ◽  
Judith M. Anson ◽  
David B. Pyne ◽  
Richard A. Ferguson
Keyword(s):  
Body Mass ◽  
Power Output ◽  
Coefficient Of Variation ◽  
Aerobic Power ◽  
Maximal Aerobic Power ◽  
Mean Power ◽  
Large Power ◽  
Elite Level ◽  
The Mean ◽  
Mean Power Output

Purpose:The patterns of power output in the ~1-h cycle section of Olympic-distance triathlon races are not well documented. Here the authors establish a typical cycling-race profile derived from several International Triathlon Union elite-level draftinglegal triathlon races.Methods:The authors collated 12 different race power profiles from elite male triathletes (N = 5, age 25 ± 5 y, body mass 65.5 ± 5.6 kg; mean ± SD) during 7 international races. Power output was recorded using SRM cranks and analyzed with proprietary software.Results:The mean power output was 252 ± 33 W, or 3.9 ± 0.5 W/kg in relative terms, with a coefficient of variation of 71% ± 13%. Normalized power (power output an athlete could sustain if intensity were maintained constant without any variability) for the entire cycle section was 291 ± 29 W, or 40 ± 13 W higher than the actual mean power output. There were 34 ± 14 peaks of power output above 600 W and ~18% time spent at >100% of maximal aerobic power.Conclusion:Cycling during Olympic-distance triathlon, characterized by frequent and large power variations including repeat supramaximal efforts, equates to a higher workload than cycling at constant power.

No Placebo Effect from Carbohydrate Intake during Prolonged Exercise

2009 ◽  
Vol 19 (3) ◽  
pp. 275-284 ◽  
Author(s):  
Carl J. Hulston ◽  
Asker E. Jeukendrup
Keyword(s):  
Placebo Effect ◽  
Prolonged Exercise ◽  
Time Trial ◽  
Cycling Performance ◽  
Plain Water ◽  
Mean Power ◽  
Flavored Water ◽  
Performance Times ◽  
Experimental Trials ◽  
Mean Power Output

The purpose of this study was to investigate the possibility of a placebo effect from carbohydrate (CHO) intake during prolonged exercise. Ten endurance-trained male cyclists performed 3 experimental trials consisting of 120 min of steady-state cycling at 61% VO2max followed by a time trial (TT) lasting approximately 60 min. During exercise participants ingested either plain water (WAT), artificially colored and flavored water (PLA), or a 6% carbohydrate-electrolyte solution (CES). PLA and CES were produced with identical color and taste. To investigate the possibility of a placebo effect from CHO intake, participants were told that both flavored solutions contained CHO and that the purpose of the study was to compare CHO drinks with water. Mean power output during TT was 218 ± 22 W in WAT, 219 ± 17 W in PLA, and 242 ± 27 W in CES. Performance times were 66.35 ± 6.15, 65.94 ± 5.56, and 59.69 ± 2.87 min for WAT, PLA, and CES, respectively. Therefore, CES ingestion enhanced TT performance by 11.3% compared with WAT (p < .05) and 10.6% compared with PLA (p < .05), with no difference between PLA and WAT. In conclusion, during a prolonged test of cycling performance, in which participants were not fully informed of the test conditions, there was no placebo effect when participants believed they had ingested CHO. In contrast, the real effect of CHO intake was a 10.6% improvement in TT cycling performance.

“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.

Physiological Profile of an Uphill Time Trial in Elite Cyclists

2018 ◽  
Vol 13 (3) ◽  
pp. 268-273 ◽  
Author(s):  
Ana B. Peinado ◽  
Nuria Romero-Parra ◽  
Miguel A. Rojo-Tirado ◽  
Rocío Cupeiro ◽  
Javier Butragueño ◽  
...  
Keyword(s):  
Power Output ◽  
Perceived Exertion ◽  
Lactate Concentration ◽  
Time Trial ◽  
Cycling Performance ◽  
Mean Power ◽  
Road Cycling ◽  
And Performance ◽  
Mean Power Output ◽  
Elite Cyclists

Context: While a number of studies have researched road-cycling performance, few have attempted to investigate the physiological response in field conditions. Purpose: To describe the physiological and performance profile of an uphill time trial (TT) frequently used in cycling competitions. Methods: Fourteen elite road cyclists (mean ± SD age 25 ± 6 y, height 174 ± 4.2 cm, body mass 64.4 ± 6.1 kg, fat mass 7.48% ± 2.82%) performed a graded exercise test to exhaustion to determine maximal parameters. They then completed a field-based uphill TT in a 9.2-km first-category mountain pass with a 7.1% slope. Oxygen uptake (VO2), power output, heart rate (HR), lactate concentration, and perceived-exertion variables were measured throughout the field-based test. Results: During the uphill TT, mean power output and velocity were 302 ± 7 W (4.2 ± 0.1 W/kg) and 18.7 ± 1.6 km/h, respectively. Mean VO2 and HR were 61.6 ± 2.0 mL · kg−1 · min−1 and 178 ± 2 beats/min, respectively. Values were significantly affected by the 1st, 2nd, 6th, and final kilometers (P < .05). Lactate concentration and perceived exertion were 10.87 ± 1.12 mmol/L and 19.1 ± 0.1, respectively, at the end of the test, being significantly different from baseline measures. Conclusion: The studied uphill TT is performed at 90% of maximum HR and VO2 and 70% of maximum power output. To the authors’ knowledge, this is the first study assessing cardiorespiratory parameters combined with measures of performance, perceived exertion, and biochemical variables during a field-based uphill TT in elite cyclists.

The Effects of Carbohydrate Loading on Muscle Glycogen Content and Cycling Performance

1995 ◽  
Vol 5 (1) ◽  
pp. 25-36 ◽  
Author(s):  
Laurie H.G. Rauch ◽  
Ian Rodger ◽  
Gary R. Wilson ◽  
Judy D. Belonje ◽  
Steven C. Dennis ◽  
...  
Keyword(s):  
Body Mass ◽  
Muscle Glycogen ◽  
Power Output ◽  
Glycogen Content ◽  
Potato Starch ◽  
Random Order ◽  
Cycling Performance ◽  
Muscle Glycogen Content ◽  
Glycogen Utilization ◽  
And Performance

This study compared the effects of supplementing the normal diets of 8 endurance-trained cyclists with additional carbohydrate (CHO), in the form of potato starch, for 3 days on muscle glycogen utilization and performance during a 3-hr cycle ride. On two occasions prior to the trial, the subjects ingested in random order either their normal CHO intake of 6.15 ± 0.23 g/kg body mass/day or a high-CHO diet of 10.52 ± 0.57 g/kg body mass/day. The trial consisted of 2 hr of cycling at ~75% ofwith five 60-s sprints at 100%at 20-min intervals, followed by a 60-min performance ride. Increasing CHO intake by 72 ± 9% for 3 days prior to the trial elevated preexercise muscle glycogen contents, improved power output, and extended the distance covered in 1 hr. Muscle glycogen contents were similar at the end of the 3-hr trial, indicating a greater utilization of glycogen when subjects were CHO loaded, which may have been responsible for their improved cycling performance.

Immersion with menthol improves recovery between 2 cycling exercises in hot and humid environment

2018 ◽  
Vol 43 (9) ◽  
pp. 902-908 ◽  
Author(s):  
Kévin Rinaldi ◽  
Than Tran Trong ◽  
Florence Riera ◽  
Katharina Appel ◽  
Olivier Hue
Keyword(s):  
Power Output ◽  
Perceived Exertion ◽  
Cold Water ◽  
Thermal Sensation ◽  
Water Immersion ◽  
Cycling Performance ◽  
Cold Water Immersion ◽  
Mean Power ◽  
Humid Environment ◽  
Mean Power Output

Endurance exercise performance is impaired in a hot and humid environment. This study compared the effects of cold water immersion, with (CMWI) and without (CWI) menthol, on the recovery of cycling performance. Eight heat-acclimatized cyclists (age, 24.1 ± 4.4 years; mass, 65.3 ± 5.2 kg) performed 2 randomized sessions, each consisting of a 20-min cycling trial (T1) followed by 10 min of immersion during recovery and then a second 20-min cycling trial (T2). Mean power output and perceived exertion (RPE) were recorded for both trials. Rectal (Trec) and skin temperatures were measured before and immediately after T1, immersion, and T2. Perceived thermal sensation (TS) and comfort were measured immediately after T1 and T2. Power output was significantly improved in T2 compared with T1 in the CMWI condition (+15.6%). Performance did not change in the CWI condition. After immersion, Trec was lower in CWI (–1.17 °C) than in CMWI (–0.6 °C). TS decreased significantly after immersion in both conditions. This decline was significantly more pronounced in CMWI (5.9 ± 1 to 3.6 ± 0.5) than in CWI (5.6 ± 0.9 to 4.4 ± 1.2). In CMWI, RPE was significantly higher in T1 (6.57 ± 0.9) than in T2 (5.14 ± 1.25). However, there was no difference in TC. This study suggests that menthol immersion probably (i) improves the performance of a repeated 20-min cycling bout, (ii) decreases TS, and (iii) impairs thermoregulation processes.

scholarly journals Effects of fasting and refeeding on the metabolic functions of the turtle Kinosternon scorpioides (Linnaeus, 1766) raised in captivity

2013 ◽  
Vol 33 (8) ◽  
pp. 1041-1044 ◽  
Author(s):  
Antonia S. Oliveira ◽  
Cinthia G. Candioto ◽  
Débora M.S. Santos ◽  
José G. Pereira ◽  
Alana L. Sousa ◽  
...  
Keyword(s):  
Blood Glucose ◽  
Food Deprivation ◽  
Muscle Glycogen ◽  
Blood Glucose Concentration ◽  
Liver Lipid ◽  
Liver Glycogen ◽  
In Captivity ◽  
Fasting And Refeeding ◽  
The One ◽  
Muscle Lipids

The metabolic responses of adult and young freshwater Kinosternon scorpioides turtles raised in captivity were evaluated. Two experiments were performed: a) blood metabolite changes caused by food deprivation, and b) liver and muscle glycogen and total lipid differences after fasting and refeeding. Blood glucose concentration of young animals was susceptible to food deprivation. In both groups this metabolite decreased after 30 days of fasting. Feeding for 15 days did not recover blood glucose. Total seric proteins were not affected by food deprivation. Fasting decreased blood urea nitrogen and the highest difference was found around 30 days. Uric acid increased in young animals after 60 days of fasting. Triacylglicerol decreased after 15 days of fasting and refeeding for 15 days recovered the pre-fasting levels. Free fatty acid plasma tended to increase around 15 days of fasting. Liver glycogen decreased at day 15 of fasting, being stable thereafter while muscle glycogen decreased at a slower rate. Total liver lipid stabilized after 30 days and then decreased 70% after 60 days of fasting. Muscle lipids remained stable throughout fasting. It could be concluded that fasting of Kinosternon scorpioides led to metabolic adaptations similar to the one reported from reptiles and fish.

Circadian rhythm in sensitivity of glucose metabolism to insulin in rat soleus muscle

1988 ◽  
Vol 255 (1) ◽  
pp. E41-E45 ◽  
Author(s):  
B. Leighton ◽  
J. M. Kowalchuk ◽  
R. A. Challiss ◽  
E. A. Newsholme
Keyword(s):  
Skeletal Muscle ◽  
Glucose Metabolism ◽  
Muscle Glycogen ◽  
Blood Glucose Concentration ◽  
Glycogen Synthesis ◽  
Liver Glycogen ◽  
Hepatic Glycogen ◽  
Feeding Period ◽  
Rat Soleus Muscle ◽  
Animal House

This study determined whether the sensitivity of glucose metabolism to insulin in skeletal muscle varies during a 24-h period. Soleus muscles were isolated from ad libitum-fed rats killed at 0900, 1600, 2100, and 0300. The animal house was illuminated between 0800 and 2000. The sensitivities of glycolysis (which is an excellent index of glucose transport) and glycogen synthesis to insulin were greatest in muscles isolated at 0900 and 2100. Marked decreases in sensitivities of both processes to insulin were observed in muscles isolated at 0300 and 1600, which are times halfway through the feeding and postabsorptive periods, respectively. Hence, this study demonstrates circadian changes in the sensitivity of glucose utilization by skeletal muscle to insulin, which may be important in control of blood glucose concentration. Glycogen levels in skeletal muscles were highest at 0300 and lowest at 2100; hepatic glycogen content reached a peak at 0900, and the lowest content was measured at 2100. The liver glycogen level was increased by only 15% midway into the feeding period (i.e., 0300). This suggests that muscle glycogen may act as a temporary store of glucose residues during the feeding period; it stores glycogen in the first half of the feeding period but during the second half some muscle glycogen is converted to lactate, which acts as a precursor for hepatic gluconeogenesis.

scholarly journals Reliability of a laboratory-based long sprint cycling test: applications of the smallest worthwhile changes in performance for repeated measures designs

2018 ◽  
Vol 20 (2) ◽  
pp. 201-210
Author(s):  
Rogério Santos de Oliveira Cruz ◽  
Rafael Alves de Aguiar ◽  
Tiago Turnes ◽  
Felipe Domingos Lisbôa ◽  
João Antônio Gesser Raimundo ◽  
...  
Keyword(s):  
Power Output ◽  
Repeated Measures ◽  
Intraclass Correlation ◽  
Cycling Performance ◽  
Systematic Change ◽  
Confidence Limits ◽  
Mean Power ◽  
Sprint Cycling ◽  
Repeated Measures Designs ◽  
Mean Power Output

The aims of the present study were to assess the reliability of long sprint cycling performance in a group of recreationally trained cyclists and to provide thresholds for changes in performance for this particular group of subjects in repeated measures designs through a scale of magnitudes. Repeatability of mean power output during a 1-min cycling time trial was assessed in a group of 15 recreationally trained cyclists (26 ± 5, years, 176 ± 5 cm, 78 ± 8 kg). They were tested on separate days, approximately one week apart. The test and retest values for the whole group of cyclists were 7.0 ± 0.5 W/kg and 6.9 ± 0.6 W/kg (systematic change and 90% confidence limits of -1.0% ± 1.1%). Our results indicated good test-retest reproducibility (typical error of 1.8%, 90% confidence limits of 1.4% to 2.6%; intraclass correlation coefficient of 0.96, confidence limits of 0.91 to 0.99), but suggested a reduction of mean power for the “slower” subjects on retest (-2.0%, 90% confidence limits of ±1.8%). If not monitored, this systematic decrease could interfere in results of studies utilizing groups with similar performance levels, particularly investigating strategies to improve performance in sprint cycling exercises around 1 min. The thresholds for moderate, large, very large and extremely large effects for mean power output on long sprint cycling performance are about 0.4%, 1.3%, 2.3%, 3.6%, and 5.8%, respectively.

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