Skip Navigation LinksHome > January 2008 - Volume 40 - Issue 1 > Carbohydrate Availability and Muscle Energy Metabolism durin...
Medicine & Science in Sports & Exercise:
doi: 10.1249/mss.0b013e3181586b2c
BASIC SCIENCES: Original Investigations

Carbohydrate Availability and Muscle Energy Metabolism during Intermittent Running

FOSKETT, ANDREW1; WILLIAMS, CLYDE2; BOOBIS, LESLIE3; TSINTZAS, KOSTAS4

Collapse Box

Abstract

Purpose: 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˙O2max 60.2 ± 1.6 mL·kg−1·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·kg−1 BM) and at 15-min intervals (3 mL·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 (~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·kg−1 DM·min−1) compared with the CHO-E trial (2.5 ± 0.7 mmol·kg−1 DM·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.

© 2008 American College of Sports Medicine

Login

Article Tools

Share

Search for Similar Articles
You may search for similar articles that contain these same keywords or you may modify the keyword list to augment your search.

Connect With Us