Whether you need extra energy to finish an ultramarathon or just to get out the door for a 5K, stimulant supplements abound. They are available as pills, and are also added to a variety of beverages, making them versatile, portable and accessible. Caffeine and guarana are two very common stimulants, and both are legal -- to a point -- for use in sports. They've been shown to delay fatigue in endurance exercise, but they also have potentially serious side effects that bear consideration.
Caffeine and Guarana
Caffeine and guarana are two sides of the same coin. Caffeine is an alkaloid that produces a fight-or-flight response in the body, the effects of which are perceived as increased energy. Caffeine is also the active ingredient in guarana, a paste made from the seeds of a South American plant. So when you are discussing the ergogenic effects of guarana, you are actually discussing caffeine. Sports drinks and supplements frequently contain both, however -- the caffeine listed on the Supplement Facts is caffeine that is added separately, not the caffeine content of the guarana.
Short-Term
The fight-or-flight response produced by caffeine from any source is part of what makes it helpful for endurance athletes. Essentially, you are taking advantage of the "flight" part of the response. Your stroke volume increases, your airways widen to allow more oxygen in, your blood pressure increases and blood flow is diverted to the limbs. This makes oxygen more available to your muscles, and allows for stronger, quicker contractions. All of these reactions may help you perform better in the beginning of the event, but it's the long-term effects that help endurance.
Long-Term
During endurance exercise, your body uses glycogen for fuel. When glycogen runs out, exhaustion sets in. Caffeine helps prolong your glycogen stores by encouraging your body to burn stored fat as fuel, saving the glycogen for later. This all takes place early in the exercise -- according to Dr. Mark Jenkins of SportsMed Web, you may use as much as 50 percent less glycogen during the first 15 minutes. But this leaves larger stores intact for the rest of the event, delaying the point of exhaustion.
Caution
Taking guarana and caffeine separately may be risky, because you may inadvertently ingest too much caffeine, but beverages and supplements that contain both are generally safe unless you are caffeine-sensitive, pregnant or nursing, or taking other stimulant medications or supplements. Caffeine is a diuretic, and can lead to dehydration, especially during endurance sports. Caffeine can cause side effects such as nervousness, tremors, headache and nausea, and your body builds up a tolerance over time. The International Olympic Committee allows caffeine only up to 12 mcg per mL of urine, and the National Collegiate Athletic Association allows it only up to 15 mcg per mL of urine. Athletes exceeding the limits may be banned.
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