Here's an interesting study that runners who eschew carbrohydrate sports drinks might want to read.
Turns out, New Zealand researchers, in the journal Brain research, found that even just swishing the solution around in your mouth provides a wake-up call for the muscles. Presumably, late in a race, when you just can't swallow another cup of lemom lime Gatorade, just do like your dental hygienist says, rinse and spit.
Here's the abstract:
Brain Res. 2010 Apr 10. [Epub ahead of print]
Carbohydrate in the mouth immediately facilitates motor output.
Exercise Metabolism Laboratory, University of Auckland, Auckland, New Zealand.
The presence of carbohydrate in the mouth can immediately improve physical performance. How this occurs is not well understood. Here we used transcranial magnetic stimulation of primary motor cortex (M1) to investigate the effects of non-sweet carbohydrate on corticomotor excitability and voluntary force production. In Experiment 1, 16 participants performed a fatiguing isometric elbow flexion exercise for 30 minutes, and MEPs were recorded from the biceps brachii during maximal voluntary force (MVF) produced every two minutes. After 11 minutes participants drank a carbohydrate solution (CHO) or an energy-free placebo solution (PLA), in a double-blind, cross-over protocol. MEP amplitude increased by 30%, and MVF increased by 2%, immediately after carbohydrate ingestion. There was no relationship between the facilitation of MEP amplitude and plasma glucose or magnitude of fatigue. In a control experiment, 17 participants alternately mouth-rinsed CHO and PLA, in a randomized, double-blind protocol. Motor evoked potentials (MEPs) were recorded from right first dorsal interosseous at rest or during isometric contraction. MEP amplitude increased by 9% with CHO, when the muscle was voluntarily activated. In both experiments, there were no effects on silent period duration, indicating that MEP facilitation was not due to reduced inhibition within M1. This is the first demonstration that carbohydrate in the mouth immediately increases the excitability of the corticomotor pathway, prior to its ingestion. Afference from oral receptors is integrated with descending motor output, perhaps via nuclei in the brainstem. This novel form of sensorimotor integration facilitates corticomotor output to both fatigued and fresh muscle. Copyright © 2010 Elsevier B.V. All rights reserved.