Caffeine is a drug that has reached social acceptance in many different forms including pills, drinks, supplements and foods. Caffeine is rapidly and nearly completely absorbed, and its actions last for five to six hours. Caffeine’s ability to enhance the senses and produce alertness can become a feeling that we depend on to get through the day. In fact, some people may become so dependent on their caffeine that if they miss their morning “cup of joe,” they experience withdrawal symptoms of fatigue, headaches and flu-like symptoms.
Caffeine is heavily used in sports-nutrition products intended for fat loss and pre-workout stimulation. There are numerous studies that suggest that caffeine can improve sports performance and endurance.1,2 Studies suggest that a moderate dose of 3 milligrams per kilogram of bodyweight is an adequate dose to experience performance-enhancing benefits. In a 70-kilogram or a 154-pound man, 3 milligrams per kilogram is only 210 milligrams of caffeine. Interestingly, despite performance enhancement, very little metabolic changes occur at this dose.
Muscle stores glucose in the form of glycogen to act as an immediate source of energy before mobilizing fats. Glycogen is spared in moderate exercise after ingestion of caffeine at 5 to 9 milligrams per kilogram of bodyweight. The exact mechanism through which this occurs is still unclear, but may consist of a more rapid mobilization of fats to use as an energy source. There is little evidence to support a metabolic component like this for enhancing performance at a low caffeine dose (3 mg/kg). Thus, it appears that alterations in muscle metabolism alone cannot fully explain the ergogenic effect of caffeine during endurance exercise in low doses. [To put this into perspective, 3 mg per kg body weight of caffeine is equivalent to approximately 2 cups (~8 oz.) of coffee; and 9 mg/kg = approximately 5-6 regular size cups of coffee.]
INCREASED PERFORMANCE AND ENERGY DRINKS
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