Gant, N., Stinear, C. M., & Byblow, W. D. (2009). Effects of carbohydrate ingestion on central fatigue. ACSM 56th Annual Meeting, Seattle, Washington. Presentation number 2296.

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This study examined the immediate and delayed influences of carbohydrate ingestion on voluntary drive and force production during fatiguing exercise. Right-handed males performed two separate bouts of a continuous isometric elbow flexion exercise at an intensity equivalent to 15% of maximal voluntary contraction force (15%MVC) for 30 minutes. Ss performed maximal voluntary contractions every two minutes during the 15%MVC exercise. At 60-second intervals throughout the 15%MVC task, and during each maximal voluntary contraction, transcranial magnetic stimulation was used to stimulate the contralateral hemisphere to elicit a motor evoked potential and silent period in the exercising biceps brachii. Force production and surface EMG of the biceps brachii were monitored continuously. Venous blood samples, heart rate and perceptual rating scales were collected every four minutes. After 11 minutes of exercise, a carbohydrate solution (0.4 g/kg BM) or an energy-free placebo solution were administered in a randomized crossover, double-blind fashion. Ss mouth-rinsed each solution for 15 seconds before swallowing.

Fatigue was confirmed by decreased force production at 15%MVC, decreased maximal voluntary contractions, increased superimposed twitch force, and increased silent periods in both trials. Comparisons between solutions were made in the period before feeding, following feeding (but before changes in plasma glucose), and alongside systemic glucose appearance. Immediately after carbohydrate ingestion, maximal voluntary contractions tended to be larger and silent period duration was shorter, suggesting an acute increase in voluntary drive. There were similar trends with subsequent plasma glucose inflection.

Implication. Carbohydrate ingestion improves maximal force production and the ability to generate voluntary drive during fatiguing exercise. These enhancements may occur before ingested carbohydrate is systemically available. [These findings provide insight into a signaling mechanism that regulates central drive according to substrate availability, both before and after glucose appearance in blood.]

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