Repeated high-intensity cycling performance is unaffected by timing of carbohydrate ingestion

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To determine whether carbohydrate feeding taken immediately before, early, or late in a series of high-intensity cycling exercises affected cycling performance 16 trained, male cyclists (> 6hr post-prandial) performed three, 4-km cycling time trials (TT1, TT2, TT3) separated by 15 min of active recovery on four separate occasions. Carbohydrate feeding (80g) was given either before TT1 (PRE1), before TT2 (PRE2), before TT3 (PRE3), or not at all (control, CTL). Treatment order was randomized. Sweet-placebo was given prior to the other time trials. Blood glucose concentration (BG) was measured before each trial. Mean power output (Pmean) and time to completion (TTC) were recorded. Pmean was higher in TT1 compared to TT2 (p=0.001) and TT3 (p=0.004) in all conditions, but no differences were observed between treatments. TTC was lower in TT1 compared to TT2 (p=0.01) but no other differences in TTC (within or between treatments) were observed. Within CTL and PRE1, BG did not differ between TT1, TT2, and TT3. In PRE2, BG was significantly higher in TT2 compared to TT1 (p=0.006), in TT3 compared to TT1 (p=0.001), and in TT3 compared to TT2 (p=0.01). In PRE3, BG was significantly higher in TT3 compared to TT1 and TT2 (p=0.001 for both). Given that performance was not influenced by the timing of carbohydrate ingestion, athletes engaging in repeated, high-intensity cycling exercise do not need to ingest carbohydrate prior to-, or between- exercise bouts; furthermore, athletes should refrain from ingesting carbohydrate between bouts if they wish to avoid a rise in BG.

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