Graded Carbohydrate Ingestion up to 120 g·h−1 Attenuates the Reduction in Critical Power Following 3 h of Moderate-Intensity Exercise in a Dose-Dependent Manner

Abstract

This study examined the effects of graded carbohydrate (CHO) ingestion at rates of 0 (water only), 60 and 120 g·h−1 (1:0.8 ratio of maltodextrin-to-fructose) on changes in critical power following 3-h of moderate-intensity cycling in endurance-trained cyclists/triathletes (n = 16; V̇O2max 51.8 ± 6.8 mL·kg−1·min−1). Following a standardized 24-h CHO loading protocol (8 g·kg−1) and pre-exercise meal (2 g·kg−1), participants completed a 3-min critical power (CP) test, with end-test power (EP) and work done above EP used as estimates of CP and W′, respectively, in a non-fatigued state and after 3-h of cycling at 95% gas exchange threshold (‘fatigued’ state). CP was significantly reduced (p < 0.001) after the 3-h exercise in all experimental conditions (water: 236 ± 30 W; 60 g·h−1: 257 ± 28 W; 120 g·h−1: 266 ± 29 W) compared to the non-fatigued state (277 ± 27 W). However, this reduction in CP was attenuated with increasing CHO intake during exercise in a dose-dependent manner, such that CP after 3-h was greater in the 120 g·h−1 vs. 60 g·h−1 vs. water condition (p < 0.05). W′ declined over time, with no differences between fatigued conditions (p > 0.05). Mean whole-body CHO oxidation rates were significantly higher (p < 0.001) with increasing CHO intake (water: 1.84 ± 0.28; 60 g·h−1: 2.16 ± 0.15; 120 g·h−1: 2.31 ± 0.14 g·min−1). These data suggest that CHO ingestion at 120 g·h−1 limits the reduction in CP following prolonged moderate-intensity cycling, with no effect on W′. These findings demonstrate that the boundary between heavy- and severe-intensity exercise shifts under fatigue, with CHO availability possibly acting as a key modulator of endurance durability.