Glycogen, the muscle's primary fuel source during exercise, is replenished more rapidly when athletes ingest both carbohydrate and caffeine after rigorous exercise, thus improving their performance.
The researchers found that athletes who ingested caffeine with carbohydrate had 66% more glycogen in their muscles four hours after finishing intense, glycogen-depleting exercise, compared to when they consumed carbohydrate alone.
"If you have 66% more fuel for the next day's training or competition, there is absolutely no question you will go farther or faster," said Dr. Hawley, the study's senior author.
Despite coffee, caffeine is also present in common foods and beverages, including, tea, chocolate and cola drinks.
The study involved seven well-trained endurance cyclists, wherein they were asked to ride a cycle ergometer until exhaustion, and then consume a low-carbohydrate dinner before going home.
The study was conducted in four sessions. This exercise reduced the athletes' muscle glycogen stores prior to the experimental trial.
The athletes did not eat again until the next day for the second session, when they again cycled until exhaustion. The participants were given a drink that contained carbohydrate alone or carbohydrate plus caffeine and rested in the laboratory for four hours. Both the processes were repeated 7-10 days later.
The researchers found that one hour after exercise, muscle glycogen levels had been refilled to the same extent whether or not the athlete had the drink containing carbohydrate and caffeine or carbohydrate only.
However, four hours after exercise, the drink containing caffeine resulted in 66% higher glycogen levels compared to the carbohydrate-only drink and caffeinated drink resulted in higher levels of blood glucose and plasma insulin.
Several signalling proteins believed to play a role in glucose transport into the muscle also elevated to a greater extent after the athletes ingested the carbohydrate-plus-caffeine drink, compared to the carbohydrate-only drink.
However, the researchers warned that athletes who want to incorporate caffeine into their workouts should experiment during training sessions well in advance of an important competition to find out what works for them.
From the July 7, 2008, Prepared Foods e-Flash