Effects of preexercise feedings on endurance performance

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FOSTER, C., D. L. COSTILL, and W. J. FINK. Effects of Preexercise feedings on endurance performance. Med. Sci. Sports. Vol. 11, No. 1, pp. 1-5, 1979. Eight male and eight female students were studied during exercise to exhaustion on a bicycle ergometer at 80 and 100% of V̇o2max following the ingestion of water (W), 75 g of glucose (G) or a liquid meal (M) (10 g protein, 12.5 g fat, 15 g CHO). When compared to the endurance ride (80% V̇o2max) in the W treatment, endurance performance time was reduced by 19%, (p<.05) (53.2 to 43.2 min) as a result of the preexercise glucose feeding (Trial G). No difference in performance at 80% V̇o2max was found between the W and M trials. The preexercise feedings had no effect on exercise time to exhaustion at 100% V̇o2max. During the G and M trials at 80% V̇o2max, most of the subjects demonstrated a transient decline in serum glucose (<3.5 m M). After 30-40 min. of exercise, however, serum glucose returned to normal and was seldom low at the time of exhaustion. Serum free fatty acids (FFA) were depressed throughout the G trial. The results of these experiments indicate impaired lipid mobilization following CHO ingestion. The present data support our earlier findings (11) which demonstrate that glucose feedings 30-45 minutes before endurance exercise increase the rate of CHO oxidation and impede the mobilization of FFA, thereby reducing exercise time to exhaustion.


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