Fate of exogenous glucose during exercise of different intensities in humans

Abstract

The extent to which an oral load of glucose is absorbed from the gut and oxidized during prolonged exercise is a matter of controversy. Four healthy volunteers, 18-28 yr, were submitted on 4 different days to a 105-min treadmill exercise at 22, 39, 51, and 64% of their individual VO2max. After 15 min adaptation to exercise, they received orally 100 g naturally labeled [13C]glucose. Oxidation of the exogenous glucose was followed by 13CO2 measurements in the expired air; total carbohydrate and lipid oxidation were evaluated by indirect calorimetry. Between 22 and 51% VO2 max, total carbohydrate, lipid oxidation, and exogenous glucose oxidation were linearly correlated with the relative work load (r = 0.81; P less than 0.01). Between 51 and 64% VO2 max, exogenous glucose oxidation and lipid oxidation tended to level off, whereas endogenous carbohydrate oxidation was markedly enhanced. The lesser contribution of exogenous glucose during the most intense exercise might be due to a decrease in the oxidation in the muscles or to a lesser availability of this exogenous glucose.

Time-course effects of endurance training on fat oxidation in sedentary elderly people

“…This could be related to the greater dependance of muscle on glucose for energy release during intensive training. 34 Another interesting ®nding in this study is the decrease in fat oxidation between the 7th and 14th week of training. This was observed under standardised conditions (controlled light-activity programme and composition of food intake, neutral daily energy balance) and occurred despite a 3% increase in FFM.…”

“…This situation is known to stimulate carbohydrate metabolism at the expense of FFA oxidation. 34 Moreover, it is well known that endurance training improves insulin sensitivity in young adults as well as in elderly people 35,36 and improved insulin action has been associated with a higher glucose uptake at the muscle level. 35 Moreover, under hyperinsulinaemic hyperglycaemic conditions, insulin andaor glucose have been shown to inhibit fat oxidation by controlling the rate of long chain FFA entrance into the mitochondria.…”

Fuel kinetics during intense running and cycling when fed carbohydrate

“…In order to determine the effect of exercise intensity on ingested CHO oxidation Pirnay et al (1982), examined four different exercise intensities At higher (> 70% V02max) exercise intensities, the oxidation of ingested CHO are not known. In theory, high exercise intensities reduce ingested CHO oxidation by slowing splanchnic blood flow and intestinal absorption (Barclay and Turnberg 1987;Maughan et al 1990;Williams et al 1964).…”

“…7 It was only after the late 1970's and early 1980's that 13c and 14c labelling techniques were used to calculate rates of ingested CHO oxidation during exercise (Lefebvre et al 1975;Lefebvre et al 1979;Pirnay et al 1977aPirnay et al , 1977bPirnay et al , 1982Jandrain et al 1984Jandrain et al , 1989Krzentowski et al 1984;Massicotte et al 1986Massicotte et al , 1989Massicotte et al , 1990Pallikarakis et al 1986;Peronnet et al 1990;Hawley et al 1992a;Moodley et al 1992). Such studies were, on the whole performed on cyclists, possibly because it is easier to take blood from a cyclist on a stationary ergometer that from a runner on a treadmill.…”

Effects of ingesting [13C]glucose early or late into cold exposure on substrate utilization

“…Using isotopic methodologies, combined with indirect calorimetry, this latter study also showed that exogenous glucose oxidation peaked and reached a plateau at a rate of ϳ195 mg/min at the lower ingestion rate of 400 mg/min. Interestingly, this oxidation rate was one-third less than what is found during exercise eliciting a similar metabolic rate (28). Glucose ingestion also modified the utilization of endogenous glycogen reserves.…”