Curvilinear Dose-Response Relationship of Carbohydrate (0-120 g.h-1) and Performance

SMITH, J. W., D. D. PASCOE, D. H. PASSE, B. C. RUBY, L. K. STEWART, L. B. BAKER, and J. J. ZACHWIEJA. Curvilinear Dose-Response Relationship of Carbohydrate (0-120 g.h(-1)) and Performance. Med. Sci. Sports Exerc., Vol. 45, No. 2, pp. 336-341, 2013. Background: There is a lack of consensus regarding the optimal range of carbohydrate (CHO) ingestion rates recommended for endurance athletes. Purpose: This study investigated the relationship between CHO dose and cycling time trial performance to identify an optimal range of CHO ingestion rates for endurance performance. Methods: Fifty-one cyclists and triathletes (28 +/- 7 yr, mean +/- SD) across four research sites completed four trials. Each trial consisted of a 2-h constant load ride at 95% of the workload that elicited a 4-mmol.L-1 blood lactate concentration immediately followed by a computer-simulated 20-km time trial, which subjects were asked to complete as quickly as possible. Twelve CHO electrolyte (18 mmol.L-1 Na, 3 mmol.L-1 K, and 11 mmol.L-1 Cl) beverages (three at each site) were tested in a double-blind manner, providing subjects 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, and 120 g CHO (1:1:1 glucose-fructose-maltodextrin) per hour during the 2-h constant load ride at a fluid intake rate of 1 L.h(-1). All subjects also consumed a noncaloric placebo on one counterbalanced test occasion. Data were natural log transformed, subjected to a mixed-model analysis, and are reported as adjusted treatment means. Results: We estimate incremental performance improvements of 1.0%, 2.0%, 3.0%, 4.0%, and 4.7% at 9, 19, 31, 48, and 78 g.h(-1), respectively, with diminishing performance enhancement seen at CHO levels 978 g.h(-1). Conclusions: CHO beverage ingestion and endurance (similar to 160 min) performance appear to be related in a curvilinear dose-response manner, with the best performance occurring with a CHO (1:1:1 glucose-fructose-maltodextrin) ingestion rate of 78 g.h(-1).