The hypotonic solution will, however, ensure high rates of gastric emptying (Rehrer et al, 1989a). The carbohydrate should be a glucose polymer, but the optimum chain length of the polymer has still to be determined (Moodley et al, 1991). Recent evidence suggests that, in theory at least, soluble startch may be
Effects of carbohydrate ingestion on plasma glucose levels (a) and on the rates of carbohydrate oxidation (b) and muscle glycogen utilization (c) during prolonged exercise at 70% V02max.
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Note. From “Muscle Glycogen Utilization During Prolonged Strenuous Exercise When Fed Carbohydrate” by E.F. Coyle, A.R. Coggan, M.K. Hemmert, and J.L. Ivy, 1986, Journal of Applied Physiology, 61, p. 167. Copyright 1986 by the American Physiological Society. Adapted by permission.
The best because it produces the fastest rates of muscle carbohydrate oxidation (Hawley et al, 1991).
Other Energy Sources
Other studies have shown that the ingestion of glycerol (Gleeson et al, 1986; J.M. Miller et al, 1983) or medium- or long-chain fatty acids (Ivy et al, 1980) during exercise is of no benefit, whereas the ingestion of alcohol is contraindicated because it impairs liver glucose production thereby increasing the risk that hypolgycemia will develop during prolonged exercise. Furthermore, alcohol per se cannot be utilized directly by muscle as a fuel; it must first be changed to acetaldehyde in the liver. Even then, acetaldehyde is a very inferior fuel, not nearly as effective as glucose, lactate, or free fatty acids. One study suggests that the ingestion of high-fat foods (e.g, almonds) delays the onset of the subjective feelings of fatigue during prolonged, low-intensity exercise (Arieli et al, 1985). Medium-chain triglycerides are oxidized during exercise but to a lesser extent than glucose (Satabin et al, 1987).