Carbohydrate metabolism during intense exercise when hyperglycemic.
The effects of hyperglycemia on muscle glycogen use and carbohydrate metabolism were evaluated in eight well-trained cyclists (average maximal O2 consumption 4.5 +/- 0.1 l/min) during 2 h of exercise at 73 +/- 2% of maximal O2 consumption. During the control trial (CT), plasma glucose concentration averaged 4.2 +/- 0.2 mM and plasma insulin remained between 6 and 9 microU/ml. During the hyperglycemic trial (HT), 20 g of glucose were infused intravenously after 8 min of exercise, after which a variable-rate infusion of 18% glucose was used to maintain plasma glucose at 10.8 +/- 0.4 mM throughout exercise. Plasma insulin remained low during the 1st h of HT, yet it increased significantly (to 16-24 microU/ml; P less than 0.05) during the 2nd h. The amount of muscle glycogen utilized in the vastus lateralis during exercise was similar during HT and CT (75 +/- 8 and 76 +/- 7 mmol/kg, respectively). As exercise duration increased, carbohydrate oxidation declined during CT but increased during HT. Consequently, after 2 h of exercise, carbohydrate oxidation was 40% higher during HT than during CT (P less than 0.01). The rate of glucose infusion required to maintain hyperglycemia (10 mM) remained very stable at 1.6 +/- 0.1 g/min during the 1st h. However, during the 2nd h of exercise, the rate of glucose infusion increased (P less than 0.01) to 2.6 +/- 0.1 g/min (37 mg.kg body wt-1.min-1) during the final 20 min of exercise. We conclude that hyperglycemia (i.e., 10 mM) in humans does not alter muscle glycogen use during 2 h of intense cycling.(ABSTRACT TRUNCATED AT 250 WORDS)
Coyle
E F
EF
Department of Kinesiology and Health, University of Texas, Austin 78712.
Hamilton
M T
MT
Alonso
J G
JG
Montain
S J
SJ
Ivy
J L
JL
D001786:Blood Glucose / Q000378:metabolism; D050260:Carbohydrate Metabolism; D015444:Exercise / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005947:Glucose / Q000008:administration & dosage; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D006943:Hyperglycemia / Q000378:metabolism*; D007328:Insulin / Q000097:blood; D007773:Lactates / Q000097:blood; D019344:Lactic Acid; D008297:Male; D009132:Muscles / Q000378:metabolism; D011659:Pulmonary Gas Exchange / Q000502:physiology
D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D007773:Lactates; D019344:Lactic Acid; D006003:Glycogen; D005947:Glucose