Commercial sports drinks make many claims, such as giving athletes 'wings' (Red Bull GmbH, n.d.), "Seizing Every Advantage" (PepsiCo, 2013), or "Go Stronger for Longer" (Coca Cola Co., 2013). Red Bull's Energy Drink contains 320 mg of caffeine and 110g (11%) of sucrose and glucose per liter (Red Bull GmbH, n.d.). Gatorade Thirst Quencher contains 58.3 g (5.8%) of sucrose and dextrose per liter of beverage (PepsiCo., 2013) and Powerade contains 55.6 g (5.6%) of the artificial sweetener sucralose in the same volume (Coca Cola Co., 2013). This report will review what is known about caffeine and carbohydrate supplementation during intense physical exercise by reviewing three recent empirical studies addressing this issue.
Clarke et al. (2012)
Purpose: Both Red Bull's Energy Drink (Red Bull GmbH, n.d.) and Gatorade (Coca Cola Co., 2013) incorporate two different sugars into their drinks, which is probably based on research showing a sugar mix is absorbed through the gut faster than a single sugar (reviewed by Sawka et al., 2007). Clarke and colleagues (2012) tested this theory in well-conditioned soccer players who engaged in intense physical activity for 90 minutes. Methods: 11 male university soccer players between 25 and 29 years of age were enrolled in the study. After conducting experiments to establish baseline measurements, the soccer players engaged in a soccer treadmill simulation in an environmental chamber. Blood was drawn before the start of physical activity, after 45 minutes of activity (halftime), and at the end of another 45 minute soccer simulation task. The energy drinks were designed to taste exactly the same (blinded), except one had no carbohydrates (placebo), and the other two had glucose alone or glucose plus fructose. A total volume of 1.37 L. Of beverage was consumed at 6 equal intervals between time 0 and 75 minutes into the soccer simulation. Total carbohydrates consumed were 90.4 g or about 1 g per minute. Although a number of different metabolic measurements were taken, the most relevant to performance was an exercise-to-exhaustion treadmill test completed after the soccer simulation. Results: There was significant variability between participants in time-to-exhaustion scores, but were generally consistent for each individual whether consuming placebo, glucose, or glucose plus fructose. Statistically, there was no difference in time to exhaustion for the three drink formulations (p > 0.05); however, the high inter-individual variability masked a real effect. Soccer players consuming glucose did better compared to placebo and those consuming the sugar mix did better than those consuming glucose alone. Conclusions: Although the study was double-blinded to the sugar content of the drink mix, it could not be randomized because each athlete completed a session for each of the three conditions. In addition, the glucose plus fructose combination was the only sugar combination tested. The sample size was small and the use of a placebo was an appropriate control. The generalizability of the findings is very limited and would be relevant only to young, male, and very fit soccer players running on treadmills. Despite these limitations, these results are consistent with previous studies showing a slight, but significant improvement in athletic performance when consuming carbohydrates during prolonged exercise; an effect that was enhanced when more than one sugar was ingested.
Hulston and Jeukendrup (2008)
Purpose: Caffeine has been marketed as ergogenic and thus performance enhancing (Red Bull GmbH). Since carbohydrates were known to provide a measurable performance edge, Hulston and Jeukendrup (2008) examined the benefits of combining glucose supplementation with caffeine ingestion during intense physical exercise. Methods: The experimental subjects were 10 well-conditions endurance male cyclists between the ages of 20 and 34 who were caffeine users. The exercise task involved 105 minutes of steady state cycling at 62% VO2max on a stationary cycle, followed by a 45 minute time trial. The time trial consisted of completing a defined amount of work at their own pace. The ingestion of a placebo drink, glucose drink, or a glucose plus caffeine drink, was double-blinded and in a randomized order for each cyclist. These beverages were consumed only during the steady state phase of the exercise and in 15 minute intervals. Total volume consumed was 1.25 L, with or without 75 g (6.0%) glucose or 75 g glucose plus 375 mg of caffeine. A large number of metabolic measurements were made, but in terms of…