¹³ C-labelled glucose-fructose show greater exogenous and whole-body CHO oxidation and lower O ₂ cost of running at 120 versus 60 and 90 g·h ⁻¹ in elite male marathoners

We used stable isotope methodology to evaluate exogenous rates of CHO oxidation in elite male marathoners. We report that 120 (maltodextrin:fructose ratio 1:1) g·h −1 CHO induces greater whole body and exogenous CHO oxidation compared with 60 (1:0)–90 (2:1) g·h −1 and reduces the O 2 cost of running. However, the performance implications of such doses remain to be determined. The prevalence of GI symptoms across the doses suggests targeted fueling practice and gut training is warranted.