The Performance Effect of Early Versus Late Carbohydrate Feedings During Prolonged Exercise
Matt Heesch Medicine & Science in Sports & Exercise Volume 45, May 2013, Supplement 1 5S, p 126
Ingesting carbohydrate during prolonged exercise can increase time to fatigue and improve time trial performance at the end of exercise. However, the optimal timing of carbohydrate ingestion has not been conclusively established.
PURPOSE: To determine how the timing of isoenergetic carbohydrate feedings during prolonged cycling affects performance in a subsequent 10 km cycling time trial.
METHODS: Recreationally trained male cyclists (n = 8, age 34.5 ± 8.3 y, mass 80.0 ± 6.3 kg, 16.0 ± 3.8% body fat, VO2 peak 4.54 ± 0.42 L • min-1) completed four experimental trials consisting of cycling continuously for two hours at 60% of VO2 peak, followed immediately by a self-paced 10 km time trial. Participants received 250 mL of beverage every 15 minutes during the two hour exercise. The four conditions included no carbohydrate ingestion (PP), early carbohydrate ingestion (CP), late carbohydrate ingestion (PC), or carbohydrate ingestion throughout (CC). Trials were completed in a randomized, counterbalanced order. All trials in which carbohydrate was ingested were isoenergetic. Blood samples were obtained at 0, 60, and 120 minutes of cycling as well as at the conclusion of the time trial.
RESULTS: 10 km time trial time to completion was faster in trials CC (17.70 ± 0.52 min) and PC (17.60 ± 0.62 min) as compared to trial PP (18.13 ± 0.52 min, p = 0.028 and p = 0.007, respectively) while trial CP (17.85 ± 0.58 min) was not different from trial PP (p = 0.178). After 60 minutes of cycling, serum glucose concentrations were higher in trials CC (6.72 ± 0.18 mM) and CP (6.76 ± 0.19 mM) when compared to trial PP (5.92 ± 0.15 mM, p = 0.027 and p = 0.009, respectively) as well as higher in CP compared to PC (6.08 ± 0.18 mM, p = 0.046). After 120 minutes of cycling, serum glucose concentrations were higher in trials CC (6.60 ± 0.20 mM) and PC (6.58 ± 0.33 mM) than in trials PP (5.52 ± 0.17 mM, p = 0.015 and p = 0.016, respectively) and CP (5.55 ± 0.22 mM, p = 0.016 and p = 0.014, respectively).
CONCLUSION: These data indicate that carbohydrate ingestion late during exercise (CC and PC) can improve subsequent 10 km time trial performance while early ingestion (CP) does not.
