The ingestion of protein with a maltodextrin and fructose beverage on substrate utilisation and exercise performance
The study investigated the ingestion of maltodextrin, fructose and protein on exogenous carbohydrate oxidation (CHOEXO) and exercise performance. Seven trained cyclists/triathletes (VO2max: 59.20 ± 9.00 ml •kg-1•min-1) performed three exercise trials consisting of 150 minutes cycling at 50 % Wmax (160 ± 11 W), followed by a 60 km time trial (TT). One of three beverages were randomly assigned during each trial and consumed at 15 minute intervals: (1) 0.84 g•min-1 maltodextrin + 0.52 g•min-1 fructose + 0.34 g•min-1 protein (MD+F+P), (2) 1.10 g•min-1 maltodextrin + 0.60 g•min-1 fructose (MD+F) or (3) 1.70 g•min-1 maltodextrin (MD). CHOEXO and fuel utilisation were assessed via measurement of expired air 13C content and indirect calorimetry, respectively. Mean total CHO oxidation (CHOTOT) rates were 2.35 ± 0.18, 2.76 ± 0.08 and 2.61 ± 0.17 gmin-1 with MD, MD+F, MD+F+P, respectively, although not significantly different. Peak CHOEXO rates with MD+F were significant greater by 41.4 % (P=0.001) and 45.4 % (P=0.0001) compared to MD+F+P and MD, respectively (1.57 ± 0.22 g•min-1, 1.11 ± 0.08 g•min-1 and 1.08 ± 0.11 g•min-1, respectively). Performance times were 2.2 % and 5.0 % faster with MD+F compared to MD+F+P and MD, respectively, however were not statistically significant. Ingestion of a MD-fructose-protein commercial sports beverage significantly reduced peak and mean CHOEXO rates compared to MD+F, but did not significantly influence CHOTOT. The addition of protein to a MD+F beverage did not enhance performance times.