Carbohydrate ingestion and single muscle fiber glycogen metabolism during prolonged running in men

Aug 1, 1996Journal of applied physiology (Bethesda, Md. : 1985)

How Eating Carbohydrates Affects Energy Storage in Individual Muscle Fibers During Long Runs in Men

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Abstract

Running time to exhaustion was longer in the carbohydrate-electrolyte trial (132.4 ± 12.3 min) compared to the placebo trial (104.3 ± 8.6 min).

A 25% reduction in glycogen utilization in type I muscle fibers occurred during the carbohydrate-electrolyte trial compared to the placebo trial.
Glycogen levels in type I fibers were depleted at exhaustion in both trials, indicating the fibers were still reliant on glycogen as an energy source.
Muscle ATP and phosphocreatine concentrations were better maintained during the carbohydrate-electrolyte trial throughout the exercise.
Carbohydrate ingestion may enhance endurance capacity by supporting oxidative ATP production in type I fibers.

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The aim of this study was to examine the effect of carbohydrate (CHO) ingestion on glycogen degradation in type I and type II muscle fibers during prolonged running by using a quantitative biochemical method. To this end, eight male subjects ran at 70% maximal oxygen uptake to exhaustion on a motorized treadmill on two occasions, 1 wk apart. On each occasion, the subjects ingested 8 ml/kg body wt of either placebo (Pl) or a 5.5% CHO-electrolyte solution (CHO-E) immediately before the start of the run and 2 ml/kg body wt every 20 min thereafter. Needle biopsy samples were obtained from the vastus lateralis muscle before and after each trial and also at the time coinciding with Pl exhaustion in the CHO-E trial. Running time to exhaustion was longer (P < 0.01) in the CHO-E trial compared with the Pl trial (132.4 +/- 12.3 and 104.3 +/- 8.6 min, respectively). A 25% reduction in glycogen utilization in type I fibers only was observed in the CHO-E trial compared with the Pl trial (215.2 +/- 27.5 vs. 285.4 +/- 30.1 mmol/kg dry wt; P < 0.01). Furthermore, in the CHO-E trial, in contrast to the Pl trial, both muscle ATP and phosphocreatine concentrations were well maintained throughout exercise. Therefore, because in both the Pl and CHO-E trials the type I fibers were glycogen depleted at the point of exhaustion (31.6 +/- 10.3 and 28.1 +/- 7.1 mmol/kg dry wt, respectively), it is proposed that CHO ingestion improved endurance capacity by contributing to oxidative ATP production specifically in type I fibers and by doing so delayed the development of glycogen depletion in this fiber type.

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Carbohydrate ingestion and single muscle fiber glycogen metabolism during prolonged running in men

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