Glucose-Fructose Enhances Performance versus Isocaloric, but Not Moderate, Glucose

Purpose: The effects of glucose-and-fructose (GF) coingestion on cycling time trial (TT) performance and physiological responses to exercise were examined under postprandial conditions. Methods: Eight trained male cyclists (age, 25 +/- 6 yr; height, 180 +/- 4 cm; weight, 77 +/- 9 kg; (V)over dotO(2max), 62 +/- 6 mL.kg(-1).min(-1)) completed the study. Subjects ingested either an artificially sweetened placebo (PL), a moderate-glucose beverage (MG, 1.03 g.min(-1)), a high-glucose beverage (HG, 1.55 g.min(-1)), or a GF beverage (1.55 g.min(-1), 2:1 ratio) during approximately 3 h of exercise, including 2 h of constant-load cycling (55% W-max, 195 +/- 17 W), immediately followed by a computer-simulated 30-km TT. Physiological responses ((V)over dot(E), (V)over dotO(2), RER, HR, blood glucose level, blood lactate level, and RPE) and incidences of gastrointestinal distress were assessed during early (15-20 min), middle (55-60 min), and late exercise (115-120 min) and during the TT. Magnitude-based qualitative inferences were used to evaluate differences between treatments. Results: In comparison with that in PL (52.9 +/- 3.7 min), TT performances were faster with GF (50.4 +/- 2.2 min, very likely benefit), MG (51.1 +/- 2.4 min, likely benefit), and HG (52.0 +/- 3.7 min, possible benefit). GF resulted in a likely improvement versus HG (3.0%) and an unclear effect relative to MG (1.2%). MG was possibly beneficial versus HG (1.8%). Few incidences of GI distress were reported in any trials. Conclusions: GF ingestion seems to enhance performance, relative to PL and HG. However, it is unclear whether GF improves performance versus moderate doses of glucose.