The promise of energy drinks is pretty irresistible push your body, work hard, sweat buckets, and if you need an extra boost, down a bottle or two of liquid fuel to drive you through the rest of your workout.
Makes sense, since the drinks provide your body with carbohydrates in the form of sugars the fuel that cells and tissues like muscle need to keep working. But exercise experts say that despite what you may think, energy drinks have no effect at all on your tired muscles. Instead, when your energy is petering out, a swig of an energy drink works on the brain to keep you inspired and motivated to push on. (Read "China Says 'Keep Out' to Coca-Cola.")
Researchers at the University of Birmingham and Manchester Metropolitan University report in the Journal of Physiology that sugary energy drinks activate reward and pleasure regions in the brain, a boost that can translate to better performance and one that does not occur with other artificially sweetened beverages. In the study, volunteers who got sugary energy drinks were able to complete a physical-training session 2% faster than those who got artificially sweetened drinks, and improved their mean power output as well.
"What we are suggesting is a central-governor model," says Ed Chambers, one of the study's co-authors and a researcher at the School of Sport and Exercise Sciences at the University of Birmingham. "Ultimately, the brain controls exercise performance by controlling the neural outflow to the exercising muscles."
Chambers decided to test this theory after a 2004 study found that energy drinks enhanced athletic performance even in short periods of physical activity. Intuitively, this makes sense, but physiologically, it doesn't. The human body is capable of generating enough fuel in the form of glucose to sustain itself, even in vigorous exercise, for about an hour. So in short periods of activity, energy drinks shouldn't have any effect on performance. Added carbs from drinks would be useful only after several hours of exertion, when the body starts to draw upon its stored glucose, known as glycogen, for energy. But the subjects in the study were showing improved times and greater power in sessions lasting 60 minutes or less. Were they experiencing a sugar rush from the beverages they were gulping?
To answer that question, Chambers gathered a couple of dozen competitive and recreational cyclists and put them on bikes in his lab. He asked one group to rinse with a sugar-based drink and another to rinse with an artificially sweetened drink. Then he took a third group of volunteers, asked each of them to rinse with the same solutions, and put them through an MRI scanner to see whether their brain reacted similarly to the two beverages.
To his surprise, they did not. The sugar-drinking volunteers showed activity in the reward and pleasure centers of the brain, while those drinking the artificially sweetened beverages did not. Chambers suspects that it's this activation of the brain that explains the enhanced performance effect of sugary energy drinks during short workouts. This theory is supported by other studies in which researchers infused carbohydrate sugar solutions directly into the body intravenously in those cases, subjects experienced no improvement in their physical performance.
Chambers' work supports the idea that the brain plays a critical role in pushing the body to achieve optimum performance. When the mouth tastes sugar, it may anticipate an influx of added fuel and therefore trigger the satisfaction and reward areas of the brain, in turn egging the body on to do more. At Loughborough University in Britain, Clyde Williams, emeritus professor of sports science, and his team found that distance runners on a treadmill selected faster running speeds after swishing with a sugared energy drink than with a placebo solution.
Other sports physiologists are currently studying how ingesting the sugared solution, as opposed to just rinsing with it, affects physical performance, and how the body responds to artificially sweetened drinks. The body may undergo a kind of metabolic letdown in anticipation of a sugar rush that never comes, which could affect performance. "In some ways, the body's reaction is to the 'promise' of an incoming carbohydrate load, so one wonders what happens when that promise is not fulfilled," says Williams.
So the next time you're pushing your body to its limits, remember that energy drinks could give you a boost in mind as well as body.