The conditions during the Tokyo 2020 Olympic and Paralympic games are expected to be hot and humid, with wet bulb glob temperatures expected to be in excess of 28°C (Gerret et al., 2019). It is now accepted that use of multiple-transportable carbohydrates during exercise in the heat elicits an improvement in carbohydrate oxidation and endurance performance in comparison to ingestion of a single carbohydrate, with ingestion of water inferior to ingestion of either types of carbohydrate supplementation (Jentjens et al., 2005). A new carbohydrate beverage encapsulated in pectin-alginate hydrogel has started to be used by elite endurance athletes; however, there is little evidence to support the notion that they are superior to traditional maltodextrin-fructose drink alternatives available. Therefore, the purpose of this study was to compare whole body substrate oxidation, blood metabolic responses and cycle time trial performance in conditions expected during the Tokyo 2020 Olympic and Paralympic games while ingesting either an encapsulated maltodextrin-fructose drink or a nutrient matched non-encapsulated maltodextrin-fructose drink. 5 recreationally active subjects (3 males and 2 females, aged 23 ± 2.3 years, mass 76.0 ± 15 kg, height 164 ± 10 cm, VO2 max 51 ± 9.78 ml.kg-1.min-1) cycled at 45% VO2 max for 90 minutes and completed a following 15-minute time trial in 32°C heat at 70% humidity on 3 occasions (ingesting either water, maltodextrin-fructose-hydrogel or maltodextrin-fructose solution). At the start of exercise participants were provided with a 250ml bolus of water, maltodextrin-fructose (1.5g/min of carbohydrate) or maltodextrin-fructose hydrogel (1.5g/min of carbohydrate). After this, participants were provided with 145ml of the trial drink every 15 minutes. Whole body carbohydrate and fat oxidation was determined every 10 minutes during the protocol via indirect calorimetry and capillary blood samples were taken every 15 minutes to determine blood metabolites. The data obtained from the exercise trials are presented as mean values. Carbohydrate oxidation was higher during the hydrogel at 60-minute (1.84 ± 0.18 g/min) and 70-minute (1.99 ± 0.29 g/min) trials compared to water (1.27 ± 0.15 g/min and 1.3 ± 0.23 g/min, respectively; p < 0.05). Fat oxidation was lower during the hydrogel trial at the 60-minute (0.18 ± 0.09 g/min) and 70-minute (0.19 ± 0.07 g/min) time point compared to water (0.42 ± 0.19 and 0.45 ± 0.14 g/min, respectively; p < 0.05). The average blood glucose concentration over the 60-90 period in the hydrogel (5.74 ± 0.54 mmol/L) and maltodextrin-fructose (5.59 ± 0.28 mmol/L) trials was significantly (p < 0.05) higher compared with the water trial (4.52
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± 0.31 mmol/l). No difference was found in blood lactate concentration between the drink trials at any point during the 90-minute trial. There was no significant difference in work done (kj) between any of the drinks at any point during the 15-minute time trial. No difference was found between the hydrogel and maltodextrin-fructose trials for any of the parameters measured. Although the small sample sized caused a reduction in power of the study, the results of the study show that consumption of encapsulated carbohydrates does not alter whole body substrate oxidation, increase blood glucose availability or improve time trial performance when compared to a nutrient matched maltodextrin-fructose solution consumed during prolonged exercise in the heat.