Exogenous carbohydrate oxidation during ultraendurance exercise

Abstract

The purposes of this study were: 1) to obtain a measure of exogenous carbohydrate (CHO(Exo)) oxidation and plasma glucose kinetics during 5 h of exercise; and 2) to compare CHO(Exo) following the ingestion of a glucose solution (Glu) or a glucose + fructose solution (2:1 ratio, Glu+Fru) during ultraendurance exercise. Eight well-trained subjects exercised three times for 5 h at 58% maximum O2 consumption while ingesting either Glu or Glu+Fru (both delivering 1.5 g/min CHO) or water. The CHO used had a naturally high 13C enrichment, and five subjects received a primed continuous intravenous [6,6-2H2]glucose infusion. CHO(Exo) rates following the ingestion of Glu leveled off after 120 min and peaked at 1.24 +/- 0.04 g/min. The ingestion of Glu+Fru resulted in a significantly higher peak rate of CHO(Exo) (1.40 +/- 0.08 g/min), a faster rate of increase in CHO(Exo), and an increase in the percentage of CHO(Exo) oxidized (65-77%). However, the rate of appearance and disappearance of Glu continued to increase during exercise, with no differences between trials. These data suggest an important role for gluconeogenesis during the later stages of exercise. Following the ingestion of Glu+Fru, cadence (rpm) was maintained, and the perception of stomach fullness was reduced relative to Glu. The ingestion of Glu+Fru increases CHO(Exo) compared with the ingestion of Glu alone, potentially through the oxidation of CHO(Exo) in the liver or through the conversion to, and oxidation of, lactate.

Factors Affecting Cadence Choice During Submaximal Cycling and Cadence Influence on Performance

“…42 A decrease in cadence with cycling duration has also been observed and is of unknown cause. [44][45][46][47][48] Perhaps the decrease in cadence has to do with fatigue of the neural networks constituting the central pattern generators or perhaps changed output from these. Another possibility is that peripheral fatigue affects freely chosen cadence.…”

Glycogen Persistence in Ultra Marathon Athletes after Six Hours of Exercise

“…Although there are studies in the scientific literature that have observed muscle metabolism behavior in ultra-prolonged exercise, [4,5]. In our research we decided to evaluate muscular metabolism performance under conditions never previously investigated.…”

“…This capture is particularly important since blood flow to active muscles can increase up to twenty fold during intense exercise [17]. Initially, this process probably prevents a critical reduction of intramuscular glycogen reserves, since it increases in the same way as glyconeogenic activity in the liver [5]. However, during ultra-prolonged exercise glycemic levels would be significantly reduced if it were not for the glucose/fatty-acids cycle modulation known as the "Randle Cycle", which increases fattyacid oxidation due to the increase in fatty-acids supply at the cellular level [18].…”

Sélection des substrats lors de l’exercice prolongé avec ingestion de glucides : études par traçage au 13C

“…La seconde raison est que les glucides exogènes, notamment le glucose et ses polymères, ont des effets ergogènes au cours de l'exercice prolongé . Burelle et al, 2006Burelle et al, , 1997Decombaz et al, 1985;Guezennec et al, 1989;Jandrain et al, 1993;Massicotte et al, 1994Massicotte et al, , 1986Massicotte et al, , 1989Massicotte et al, , 1990Slama et al, 1989), galactose (Burelle et al, 2006;Leijssen et al, 1995), saccharose Leese et al, 1996;Massicotte et al, 1996a), maltose (Hawley et al, 1992b), polymères de glucose (Guezennec et al, 1993(Guezennec et al, , 1989Jarvis et al, 1992;Johannsen et Sharp, 2007;Leese et al, 1996;Massicotte et al, 1989;Rehrer et al, 1992), triacylglycérols à chaîne moyenne (MCT) Satabin et al, 1987), ou à longue chaîne (LCT) (Satabin et al, 1987)], ou de mélanges de substrats exogènes [glucose + fructose Hulston et al, 2009;Jentjens et al, 2004b;Jeukendrup et al, 2006;Massicotte et al, 1996a;Riddell et al, 2001), glucose + saccharose (Jentjens et al, 2004c, glucose + fructose + saccharose (Jentjens et al, 2004a(Jentjens et al, , 2006, glucose + maltose (Jentjens et al, 2004c), glucose + lactate (Péronnet et al, 1997), glucose + MCT (Goedecke et al, 1999b;...…”