Carbohydrate availability and muscle energy metabolism during intermittent running.
OBJECTIVE
To examine the influence of ingesting a carbohydrate-electrolyte (CHO-E) solution on muscle glycogen use and intermittent running capacity after consumption of a carbohydrate (CHO)-rich diet.


METHODS
Six male volunteers (mean +/- SD: age 22.7 +/- 3.4 yr; body mass (BM) 75.0 +/- 4.3 kg; V O2 max 60.2 +/- 1.6 mL x kg(-1) x min(-1)) performed two trials separated by 14 d in a randomized, crossover design. Subjects consumed either a 6.4% CHO-E solution or a placebo (PLA) in a double-blind fashion immediately before each trial (8 mL x kg(-1) BM) and at 15-min intervals (3 mL x kg(-1) BM) during intermittent high-intensity running to fatigue performed after CHO loading for 2 d. Muscle biopsy samples were obtained before exercise, after 90 min of exercise, and at fatigue.


RESULTS
Subjects ran longer in the CHO-E trial (158.0 +/- 28.4 min) compared with the PLA trial (131.0 +/- 19.7 min; P < 0.05). There were no differences in muscle glycogen use for the first 90 min of exercise (approximately 2 mmol of glucosyl units per kilogram of dry matter (DM) per minute). However, there was a trend for a greater use in the PLA trial after 90 min (4.2 +/- 2.8 mmol x kg(-1) DM x min(-1)) compared with the CHO-E trial (2.5 +/- 0.7 mmol x kg(-1) DM x min(-1); P = 0.10). Plasma glucose concentrations were higher at fatigue in the CHO-E than in the PLA trial (P < 0.001).


CONCLUSIONS
These results suggest that CHO-E ingestion improves endurance capacity during intermittent high-intensity running in subjects with high preexercise muscle glycogen concentrations. The greater endurance capacity cannot be explained solely by differences in muscle glycogen, and it may actually be a consequence of the higher plasma glucose concentration towards the end of exercise that provided a sustained source of CHO for muscle metabolism and for the central nervous system.
Foskett
Andrew
A
Institute of Food, Nutrition and Human Health, Massey University, Auckland, New Zealand. a.foskett@massey.ac.nz
Williams
Clyde
C
Boobis
Leslie
L
Tsintzas
Kostas
K
D000328:Adult; D004040:Dietary Carbohydrates / Q000008:administration & dosage; D004734:Energy Metabolism / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D017079:Exercise Tolerance / Q000502:physiology*; D005221:Fatigue / Q000503:physiopathology*; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*; D012420:Running / Q000502:physiology*; D013997:Time Factors
D004040:Dietary Carbohydrates; D006003:Glycogen