Effect of an energy drink on physical and cognitive performance in trained cyclists
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This study investigated the effectiveness of an energy drink (ED) in enhancing cycling time-trial performance, and cognitive performance at rest, during moderate-intensity exercise, and after exercise. The protocol was double-blind, randomized, placebo-controlled, two-period, and within-subjects. The treatments were ED containing caffeine and carbohydrate, and a caffeine-free non-caloric flavored placebo beverage (PLA). Exercise performance was measured by time to finish a simulated 35 km time-trial course. Cognitive performance was measured by a Stroop task, a tapping task, a reaction time task, and an executive function task consisting of both tapping and reaction time. The effects of ED on blood markers were also assessed. Race performance was enhanced by an average of 3% when participants had ED compared to PLA without a difference in rating of perceived exertion (RPE). Performance was improved by ED even in participants that arrived to the lab with elevated blood caffeine concentrations. Both before and after the exercise, ED resulted in more taps per second in the tapping task. After receiving ED, plasma insulin spiked, there was a fall in free fatty acids (FFA) and blood glucose remained unchanged. Exercise onset caused a drop in blood glucose when participants consumed ED, though glucose returned to a level that was not different from PLA by 29 km into the race. FFA also increased as the exercise continued, and were not different from PLA by 23 km. ED elevated plasma caffeine levels. Epinephrine was elevated due to ED from 6 km to the end of the race. Norepinephrine was only elevated by ED at 6 km. At rest and throughout exercise ED caused elevated lactate concentrations. When participants consumed ED they sustained a greater VO₂ and heart rate throughout the race. In summary, ED enhanced exercise performance and simple movement time as assessed by the tap test before and after intense exercise. There was enough caffeine in ED to enhance physical performance without causing negative effects on cognitive function.