Regulation of fuel metabolism by preexercise muscle glycogen content and exercise intensity.
To date, the results of studies that have examined the effects of altering preexercise muscle glycogen content and exercise intensity on endogenous carbohydrate oxidation are equivocal. Differences in the training status of subjects between investigations may, in part, explain these inconsistent findings. Accordingly, we determined the relative effects of exercise intensity and carbohydrate availability on patterns of fuel utilization in the same subjects who performed a random order of four 60-min rides, two at 45% and two at 70% of peak O(2) uptake (Vo(2 peak)), after exercise-diet intervention to manipulate muscle glycogen content. Preexercise muscle glycogen content was 596 +/- 43 and 202 +/- 21 mmol/kg dry mass (P < 0.001) for high-glycogen (HG) and low-glycogen (LG) conditions, respectively. Respiratory exchange ratio was higher for HG than LG during exercise at both 45% (0.85 +/- 0.01 vs. 0.74 +/- 0.01; P < 0.001) and 70% (0.90 +/- 0.01 vs. 0.79 +/- 0.01; P < 0.001) of Vo(2 peak). The contribution of whole body muscle glycogen oxidation to energy expenditure differed between LG and HG for exercise at both 45% (5 +/- 2 vs. 45 +/- 5%; P < 0.001) and 70% (25 +/- 3 vs. 60 +/- 3%; P < 0.001) of Vo(2 peak). Yet, despite marked differences in preexercise muscle glycogen content and its subsequent utilization, rates of plasma glucose disappearance were similar under all conditions. We conclude that, in moderately trained individuals, muscle glycogen availability (low vs. high) does not influence rates of plasma glucose disposal during either low- or moderate-intensity exercise.
Exercise Metabolism Group, School of Medical Sciences, RMIT University, Bundoora, Victoria 3083, Australia.
Melissa J
MJ
Arkinstall
Clinton R
CR
Bruce
Sally A
SA
Clark
Caroline A
CA
Rickards
Louise M
LM
Burke
John A
JA
Hawley
D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D004040:Dietary Carbohydrates / Q000378:metabolism; D004041:Dietary Fats / Q000378:metabolism; D004734:Energy Metabolism / Q000502:physiology*; D004837:Epinephrine / Q000097:blood; D015444:Exercise / Q000502:physiology; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006003:Glycogen / Q000378:metabolism*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D007328:Insulin / Q000097:blood; D019344:Lactic Acid / Q000097:blood; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D009638:Norepinephrine / Q000097:blood; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*
D001786:Blood Glucose; D004040:Dietary Carbohydrates; D004041:Dietary Fats; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D019344:Lactic Acid; D006003:Glycogen; D010100:Oxygen; D009638:Norepinephrine; D004837:Epinephrine