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Petteys, C L.1; Foster, C FACSM1; Brice, G1; Doberstein, S1; Porcari, J P. FACSM1

Medicine & Science in Sports & Exercise: May 2003 - Volume 35 - Issue 5 - p S298

1University of Wisconsin-La Crosse

(Sponsor: Carl Foster, FACSM)

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Early studies suggested that carbohydrate (CHO) ingestion shortly before endurance exercise may accelerate the rate of glycogen depletion, contribute to hypoglycemia and hasten fatigue. However, these studies have not used athletically meaningful outcomes, and have ignored the extensive warm-up often accomplished by athletes. This study evaluated the effect of 35 gm CHO consumption 30 min prior to a 40 km cycle time trial (TT).

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Well trained cyclists (n=10), habituated to TT, performed an intensive warm-up, ingested (in random order) either CHO or placebo, then performed TT. H2O was available ad libidum during TT. Outcomes were Time, Velocity, Power Output, HR, blood glucose (G) lactate (L), and rating of perceived exertion (RPE).

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There was no significant (p < 0.05) difference (CHO vs P) in Time (74.31 vs 74.29 min), mean Power Output (194 vs 199 Watts), mean Velocity (9.00vs 9.04 m*s-1), HR (145 vs 145 bpm), blood lactate (3.84 vs 4.02 mmol*1–1) or blood glucose (4.84 vs 4.63 mmol*1–1). There were significant trends (p < 0.1) for Power Output and Velocity to increase during the latter portion of the CHO trial. In support of this finding, there was a trend (p = 0.07) for RPE to be lower throughout the CHO trial (5.35 vs 5.74). G was significantly higher at the beginning of the CHO trial (6.66 vs 4.88 mmol*1–1) and decreased during the first 5 km. After this point, however, there was no difference in G between CHO vs P.

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The results suggest that pre-exercise feedings with CHO prior to TT is effectively neutral, which contradicts earlier studies using time to exhaustion rather than TT as an outcome measure. Trends within the data suggest that the ability to increase power output at the close of a TT may be facilitated by pre-exercise feedings.

©2003The American College of Sports Medicine