The effect of fructose and maltodextrin vs glucose and maltodextrin formulated sports beverages on mountain-bike race performance : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Sport and Exercise Science at Massey University, Wellington, New Zealand
Background: Exogenous carbohydrate improves performance during prolonged high-intensity exercise. When ingested together, fructose and glucose polymers are oxidised at rates 1.5-1.7 higher than isocaloric glucose solutions. As fructose and glucose are transported across the intestine via different mechanisms, the capacity for exogenous-carbohydrate absorption is greater with composite carbohydrate mixtures. Therefore, since the effect of ingesting multi-transportable carbohydrate on field-based performance has to our knowledge not been investigated, we examined their effect on mountain bike race performance. Finishing time was expected to be substantially reduced when multi-transportable carbohydrates were ingested. Method: Ten; male (7) and female (3), mountain bikers aged 32.9 ± 8.7 years, weighing 68.8 ± 9.4 kg and training for at least 8 hours per week and racing regularly participated in a double-blind crossover study. Following a standardised training and diet regimen cyclists completed two Olympic-distance (target winning time of 2h 15m), cross-country mountain bike races during which they ingested either a 11.25% maltodextrin and fructose solution (MF) or an isocaloric, equi-volumetric, isosmotic control solution containing maltodextrin and glucose (MG). Performance times, ratings of perceived exertion, gastrointestinal discomfort and measurements of hydration status were recorded and compared. Data was analysed using appropriate mixed models in SAS. Results: Cyclists were 1.8% (2mins 31s) faster in MF compared to MG (90% confidence interval:±1.8%; 72% likelihood of a substantial benefit) The effect solution composition on the increase in time from the first the final lap (fatigue) was 9.7% (±2.8%) in MF and 10.7% (±2.8%) in MG; which corresponded to a 0.9% reduction (±3.5%; unclear) in the fatigue in MF. Abdominal cramps were reduced by 8.1% in MF relative to MG (±6.6%; likely benefit) and for every 1% change in abdominal cramp rating, lap time increased by 0.14% (±0.10%). There were no clear effects of MF on ratings of perceived exertion and hydration status compared with MG. Conclusion: Cross-country mountain bike race performance was substantially enhanced following ingestion of a maltodextrin and fructose solution. This outcome was related to reduced gastro-intestinal distress supporting the theory that solutions containing multiple-transportable carbohydrates increase the availability of carbohydrate for metabolism. Further investigation with a larger sample size is recommended to establish whether the performance effect is genuinely beneficial or trivial.