Comparison of fructose and glucose ingestion before and during endurance cycling to exhaustion

Background. Pre-exercise and exercise ingestion of fructose and glucose dur ing cycling exercise were compared. Methods. Experimental design: Seventeen trained subjects ingested a placebo prior to and during a cycling test to exhaustion at 75% VO2max (control gr oup = CG). One week later, subjects were matched on exercise time to exhaus tion (ETE) and assigned to a fructose group (FG) or a glucose group (GG). S ubjects then performed a second cycling test to exhaustion, ingesting fruct ose or glucose doses. For all groups (CG, FG and GG), blood was drawn befor e and at timed intervals during exercise to determine glucose, lactate and free fatty acid (FFA) levels. Results. The ETE for CG was less than either FG (p<0.02) or GG (p<0.001) bu t FG and GG were similar, FG and GG did not show any differences in blood l actate or blood FFA during the ETE. However, CG FFA levels were higher than those of FG (p<0.02) prior to exercise. Conclusions. This study demonstrated that fructose and glucose are of equal value in prolonging ETE in endurance cycling. Ingesting fructose before an d during exercise apparently provided a more constant supply of glucose to be available to the working muscles. The more stable blood glucose levels w ith fructose ingestion may be beneficial in reducing perceived exhaustion, and thereby allowing for an enhancement in exercise performance.