Glucose but not fructose ingestion improves endurance cycling performance despite similar neuromuscular fatigue at exhaustion.

PURPOSE: This study investigated the neuromuscular differences between glucose (GLU) and fructose (FRU) ingestion on central and peripheral fatigue development and blood glucose responses during endurance cycling to failure. METHODS: Seven young, recreationally active participants (4 males, 3 females) completed a randomized, single-blinded crossover study involving three conditions: GLU, FRU, and placebo (PLA) ingestion. Participants cycled at an intensity set at their maximal lactate steady state until task failure while consuming PLA, or 60 g/h of GLU or FRU. Heart rate and ratings of perceived exertion (RPE) were assessed every 5 min whereas neuromuscular function of the knee extensors and capillary blood glucose and lactate were assessed every 20 min. RESULTS: GLU ingestion significantly increased time to task failure (~ 25%) compared to PLA (p < 0.05), whereas FRU showed no difference from PLA. Blood glucose levels increased with GLU ingestion compared to PLA (GLU: + 0.63 ± 0.96 mmol/L; PLA: -0.64 ± 0.38 mmol/L; p < 0.05), with no difference in FRU ingestion (-0.15 ± 0.53 mmol/L) versus PLA at a matched time to task failure. Despite these differences, no significant differences were observed among conditions at a matched time to task failure for fatigue-induced changes in MVC torque, voluntary activation, or indices of peripheral fatigue (i.e., 10 Hz, 50 Hz, and Δ10:50 Hz torque ratio). Furthermore, blood lactate, heart rate, and RPE increased similarly across all conditions. CONCLUSIONS: These findings suggest that GLU, but not FRU, ingestion enhances endurance performance primarily through improved blood glucose maintenance rather than by the attenuation of neuromuscular fatigue.