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Researchers have known for years thatcaffeine has a positive effect on endurance, and that the longer you
exercise, the more profound that effect becomes. Taken beforehand, a standard 200 milligram 1mg) dose of
caffeine - exactly what you'd get from one tablet of Vivarin or Maximum Strength No Doz - can extend your
time to fatigue by approximatelyl5 minutes after an hour of exercise.
But if you think caffeine is interchangeable with a hot cup of Joe, it's time to wake up and smell the coffee. According to a new study (T.E. Graham et al., "Metabolic and exercise endurance effects of coffee and caffeine ingestion," Journal of Applied Physiology, 85:883-89, 1998), performance-enhancing benefits evaporate sometime between the moment coffee beans are harvested and the time the java gets poured into your mug. On five different occasions, the researchers administered caffeine to nine young adults, who then ran to exhaustion. The subjects took either a caffeine capsule with water, a placebo with water, regular coffee, decaffeinated coffee, or decaf with a caffeine capsule. The caffeine capsules produced the expected increases in both endurance and epinephrine secretion, but the coffee produced no performance enhancement whatsoever.
The researchers first guessed that the body absorbs coffee differently from caffeine pills, but an analysis of blood samples revealed identical concentrations of caffeine. The team then suspected that the various forms of caffeine were metabolized differently, but those concentrations were also identical. "Coffee is a very complex organic solution comprising hundreds of compounds, and some of these must interact in a way that cancels out the normal effects we see from pure caffeine," says researcher Terry Graham, PHD.
Setting aside the coffee issue for a moment how does caffeine boost endurance? Conventional wisdom has held that caffeine promotes fat metabolism and thus spares carbohydrate for use as energy later in a workout. However, newer research suggests that the endurance benefits from caffeine may relate more to its direct action on the contractile properties of skeletal muscle than to its effects on metabolism and hormones - or that the contractile changes trigger those metabolic and hormonal changes.
As for caffeine's effect on weight training, the jury is still out. Caffeine has been shown to boost anaerobic endurance in cyclists, and one study did find that subjects squatted more weight when given caffeine beforehand. Other studies haven't shown a similar effect of caffeine on muscle- force production in humans, but the possibilities are intriguing.
For an endurance boost says Graham, a safe efficacious dose is 1.4mg per pound of bodyweight. For a 150-pound person, that translates into about 210 mg. Because caffeine is readily absorbed by the gut and peak blood levels are reached 30-60 minutes after consumption, most athletes take it an hour or so before an activity.