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  • 1
    Electronic Resource
    Electronic Resource
    Fuel utilisation during prolonged low-to-moderate intensity exercise when ingesting water or carbohydrate (1995)
    Springer
    Pflügers Archiv 430 (1995), S. 971-977 
    Details
    ISSN: 1432-2013
    Keywords: Glucose turnover and oxidation ; Fat oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Previously, we examined the effects of carbohydrate (CHO) ingestion on glucose kinetics during exercise at 70% of maximum O2 uptake ( $$\dot V$$ O2,max). Here we repeat those studies in heavier cyclists (n=6 per group) cycling for 3 h at a similar absolute O2 uptake but at a lower (55% of $$\dot V$$ O2,max) relative exercise intensity. During exercise, the cyclists were infused with a 2-3H-glucose tracer and ingested U-14C glucoselabelled solutions of either flavoured water (H2O) or 10 g/100 ml glucose polymer, at a rate of 600 ml/h. Two subjects in the H2O trial fatigued after 2.5 h of exercise. Their rates of glucose appearance (R a) declined from 2.9±0.6 to 2.0±0.1 mmol/min (mean ± SEM) and, as their plasma glucose concentration [Glu] declined from 4.7±0.2 to below 3.5±0.2 mM, their rates of glucose oxidation (R ox) and fat oxidation plateaued at 2.7±0.4 and 1.7±0.1 mmol/min respectively. In contrast, all subjects completed the CHO trial. Although CHO ingestion during exercise reduced the final endogenousR a from 3.4±0.6 to 0.9±0.3 mmol/min at the end of exercise, it increased totalR a to 5.5±0.5 mmol/min (P〈0.05). A higher totalR a with CHO ingestion raised [Glu] from 4.3±0.3 to 5.3±0.1 mM and acceleratedR ox from 3.5±0.2 to 5.9±0.2 mmol/min after 180 min of exercise (P〈0.05). The increased contribution to total energy production from glucose oxidation (34±1 vs. 20±1 %) decreased energy production from fat oxidation from 51±2 to 40±5% (P=0.08) and produced patterns of glucose, muscle glycogen (plus lactate) and fat utilisation similar to those during exercise at 70% of ( $$\dot V$$ O2,max). Thus, CHO ingestion is necessary to sustain even prolonged, low to moderate intensity exercise and when ingested, it suppresses the higher relative rates of fat oxidation usually observed at exercise intensities less than 60% of $$\dot V$$ O2,max.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01837411
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  • 2
    Electronic Resource
    Electronic Resource
    Fuel metabolism during ultra-endurance exercise (1998)
    Springer
    Pflügers Archiv 436 (1998), S. 211-219 
    Details
    ISSN: 1432-2013
    Keywords: Key words Glucose and lactate oxidation and interconversion ; Carbohydrate utilisation ; Fat oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Cyclists either ingested 300 ml 100 g/l U-[14C] glucose solution every 30 min during 6 h rides at 55% of VO2max (n=6) or they consumed unlabelled glucose and were infused with U-[14C] lactate (n=5). Maintenance of euglycaemia limited rises in circulating free fatty acids, noradrenaline and adrenaline concentrations to 0.9±0.1 mM, 27±4 nM and 2.0±0.5 nM, respectively, and sustained the oxidation of glucose and lactate. As muscle glycogen oxidation declined from 100±13 to 71±9 μmol/min/kg in the last 3 h of exercise, glucose and lactate oxidation and interconversion rates remained at approximately 60 and 50 and at about 4 and 5 μmol/min/kg, respectively. Continued high rates of carbohydrate oxidation led to a total oxidation of around 270 g glucose, 130 g plasma lactate and 530 g muscle glycogen. Oxidation of some 530 g of muscle glycogen far exceeded the predicted (about 250 g) initial glycogen content of the active muscles and suggested that there must have been a considerable diffusion of unlabelled lactate from glycogen breakdown in inactive muscle fibres to adjacent active muscle fibres via the interstitial fluid that did not equilibrate with 14C lactate in the circulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050624
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  • 3
    Electronic Resource
    Electronic Resource
    Carbohydrate ingestion and muscle glycogen depletion during marathon and ultramarathon racing (1988)
    Springer
    European journal of applied physiology 57 (1988), S. 482-489 
    Details
    ISSN: 1439-6327
    Keywords: Carbohydrates ; Ultramarathon ; Glycogen ; Fructose ; Performance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Two studies were undertaken to characterize the effects of carbohydrate ingestion on fuel/hormone response to exercise and muscle glycogen utilization during prolonged competitive exercise. In study 1, eighteen subjects were divided into three groups, matched for maximum oxygen consumption ( $$\dot V_{{\text{O}}_{{\text{2 max}}} } $$ ) and blood lactate turnpoint. All subjects underwent a 3-day carbohydrate (CHO) depletion phase, followed by 3 days of CHO loading (500–600 g·day−1). During the race, the groups drank either 2% glucose (G), 8% glucose polymer (GP), or 8% fructose (F). Muscle biopsies were performed before and after the race and venous blood was sampled before and at regular intervals during the race. In study 2, eighteen subjects divided into 2 matched groups ingested either a 4% G or 10% GP solution during a 56 km race. Despite significantly greater CHO ingestion by GP and F in study 1 and by GP in study 2, blood glucose, free fatty acids and insulin concentrations, muscle glycogen utilization and running performance were not different between groups. These studies show (i) that hypoglycaemia is uncommon in athletes competing in races of up to 56 km provided they CHO-load before and ingest a minimum of 10 g CHO·h−1 during competition; (ii) that neither the amount (10 g vs 40 g·h−1) nor the type of carbohydrate (G vs GP vs F) has any effect on the extent of muscle glycogen depletion or running performance in matched subjects racing over distances up to 56 km.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00417997
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  • 4
    Electronic Resource
    Electronic Resource
    Dose-related elevations in venous pH with citrate ingestion do not alter 40-km cycling time-trial performance (2000)
    Springer
    European journal of applied physiology 83 (2000), S. 320-327 
    Details
    ISSN: 1439-6327
    Keywords: Key words Buffer ; Lactate ; Performance ; pH ; Sodium citrate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004210000264
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