Reversal of fatigue during prolonged exercise by carbohydrate infusion or ingestion.
Seven cyclists exercised at 70% of maximal O2 uptake (VO2max) until fatigue (170 +/- 9 min) on three occasions, 1 wk apart. During these trials, plasma glucose declined from 5.0 +/- 0.1 to 3.1 +/- 0.1 mM (P less than 0.001) and respiratory exchange ratio (R) fell from 0.87 +/- 0.01 to 0.81 +/- 0.01 (P less than 0.001). After resting 20 min the subjects attempted to continue exercise either 1) after ingesting a placebo, 2) after ingesting glucose polymers (3 g/kg), or 3) when glucose was infused intravenously ("euglycemic clamp"). Placebo ingestion did not restore euglycemia or R. Plasma glucose increased (P less than 0.001) initially to approximately 5 mM and R rose (P less than 0.001) to approximately 0.83 with glucose infusion or carbohydrate ingestion. Plasma glucose and R then fell gradually to 3.9 +/- 0.3 mM and 0.81 +/- 0.01, respectively, after carbohydrate ingestion but were maintained at 5.1 +/- 0.1 mM and 0.83 +/- 0.01, respectively, by glucose infusion. Time to fatigue during this second exercise bout was significantly longer during the carbohydrate ingestion (26 +/- 4 min; P less than 0.05) or glucose infusion (43 +/- 5 min; P less than 0.01) trials compared with the placebo trial (10 +/- 1 min). Plasma insulin (approximately 10 microU/ml) and vastus lateralis muscle glycogen (approximately 40 mmol glucosyl U/kg) did not change during glucose infusion, with three-fourths of total carbohydrate oxidation during the second exercise bout accounted for by the euglycemic glucose infusion rate (1.13 +/- 0.08 g/min).(ABSTRACT TRUNCATED AT 250 WORDS)
Coggan
A R
AR
Department of Physical and Health Education, University of Texas, Austin 78712.
Coyle
E F
EF
D000284:Administration, Oral; D000328:Adult; D001786:Blood Glucose / Q000032:analysis; D005221:Fatigue / Q000628:therapy*; D005947:Glucose / Q000627:therapeutic use*; D006801:Humans; D007262:Infusions, Intravenous; D007328:Insulin / Q000097:blood; D007773:Lactates / Q000097:blood; D008297:Male; D010100:Oxygen / Q000502:physiology; D005082:Physical Exertion
D001786:Blood Glucose; D007328:Insulin; D007773:Lactates; D005947:Glucose; D010100:Oxygen