For an athlete, it seems to good to be true. A "sports supplement" that increases alertness, concentration, reaction time and focus while decreasing muscle fatigue or at least the perception of fatigue. It can even shorten recovery time after a game. HGH? EPO? Steroids? Nope, just a grande cup of Juan Valdez's Best, Liquid Lightning, Morning Mud, Wakey Juice, Mojo, Java, aka coffee.

Actually, the key ingredient is caffeine which has been studied repeatedly for its ergogenic (performance-enhancing) benefits in sports, both mentally and physically. Time after time, caffeine proves itself as a relatively safe, legal and inexpensive boost to an athlete.  Or does it?

If caffeine is such a clear cut performance enhancing supplement, why did the World Anti-Doping Agency (WADA), who also monitors this month's Beijing Olympics for the International Olympic Committee (IOC), first add caffeine to its banned substance list, only to remove it in 2004? At the time that it was placed on the banned list, the threshold for a positive caffeine test was set to a post-exercise urinary caffeine concentration of 12 µg/ml (about 3-4 cups of strong coffee).

However, more recent research has shown that caffeine has ergogenic effects at levels as low as the equivalent of 1-2 cups of coffee. So, it was hard for WADA to know where to draw the line between athletes just having a few morning cups of coffee/tea or maybe some chocolate bars and athletes that were intentionally consuming caffeine to increase their performance level. Even so, caffeine is still on the WADA monitoring list as a substance to screen for and watch for patterns of use.

Meanwhile, athletes are still convinced that caffeine helps them. In a recent survey from Liverpool John Moores University, 480 athletes were interviewed about their caffeine use. One third of track and field athletes and 60% of cyclists reported using caffeine specifically to give them a boost in competition. In addition, elite-level athletes interviewed were more likely to rely on caffeine than amateurs.

Dr. Neil Chester, co-leader of the study, commented about the confusion created by the WADA status change for caffeine, "There's been a lack of communication from WADA and there is a question about whether or not sporting authorities are condoning its use. Ultimately there is a need to clarify the use of caffeine within the present anti-doping legislation."

So, have athletes found a loophole to exploit that gives them an edge? Dr. Carrie Ruxton recently completed a literature survey to summarize 41 double-blind, placebo-controlled trials published over the past 15 years to establish what range of caffeine consumption would maximize benefits and minimize risk for cognitive function, mood, physical performance and hydration. The studies were divided into two categories, those that looked at the cognitive effects and those that looked at physical performance effects.

The results concluded that there was a significant improvement in cognitive functions like attention, reaction time and mental processing as well as physical benefits described as increased "time to exhaustion" and decreased "perception of fatigue" in cycling and running tests. Longer, endurance type exercise showed greater results than short-term needs for energy.

Given these results, how exactly does caffeine perform these wonderful tricks? Dr. Ruxton explains from the study, "Caffeine is believed to impact on mood and performance by inhibiting the binding of both adenosine and benzodiazepine receptor ligands to brain membranes. As these neurotransmitters are known to slow down brain activity, a blockade of their receptors lessens this effect."

Bottom line, the chemicals in your brain that would cause you to feel tired are blocked, giving you a feeling of ongoing alertness. Your body still needs the sleep, caffeine just delays the feeling of being tired.

As to the physiological benefits, caffeine has also been shown to stimulate the release of fat into the bloodstream. The early conclusion was that the increased free fatty acids in the blood would allow our muscles to use fat as fuel and spare glycogen (carbohydrates) allowing us to exercise longer. Another theory is that caffeine stimulates the central nervous system reducing our perception of effort so that we feel that we can continue at an increased pace for longer periods.

The discussion on glycogen has recently taken another interesting twist; caffeine's apparent ability to replenish glycogen (the body's primary fuel source) more rapidly after an intense workout. A team at the Garvan Institute for Medical Research has found that athletes who consumed a combination of carbohydrates and caffeine following an exhaustive exercise had 66% more glycogen in their muscles four hours later, compared to when they consumed carbohydrates alone. They asked cyclists to pedal to exhaustion in the lab, then gave them a drink that contained either carbohydrates with caffeine or just carbohydrates (the cyclists did not know which drink they were getting). They repeated the process 7-10 days later and reversed the groups.

Muscle biopsies and blood samples were tested for levels of glycogen after each trial period. The researchers did not have an explanation for the increased levels of glycogen resulting from the caffeine-spiked juice. One theory is the higher circulating blood glucose and plasma insulin levels caused by the caffeine were key factors.

In addition, caffeine may increase the activity of several signaling enzymes, including the calcium-dependent protein kinase and protein kinase B (also called Akt), which have roles in muscle glucose uptake during and after exercise.

So, before you start drinking the Starbucks by the gallon, here are some guidelines. You can consume 2-2.5 mg of caffeine per pound of body weight daily to achieve its ergogenic effects. This equates to 250-312 mg for a 125-pound woman and 360-450 mg for a 180-pound man. More is not better, as other research has shown a decline in benefit and an increase in caffeine's side effects beyond this level. One "grande" cup (16 oz.) of Starbucks coffee contains about 320-500 mg of caffeine, while a 12 oz. can of soda will provide 35-70 mg of caffeine. Maybe we'll see the ultimate sports drink soon, kind of like Monster meets Gatorade.

C. H. S. Ruxton (2008). The impact of caffeine on mood, cognitive function, performance and hydration: a review of benefits and risks Nutrition Bulletin, 33 (1), 15-25 DOI: 10.1111/j.1467-3010.2007.00665.x

N. Chester, N. Wojek (2008). Caffeine Consumption Amongst British Athletes Following Changes to the 2004 WADA Prohibited List International Journal of Sports Medicine, 29 (6), 524-528 DOI: 10.1055/s-2007-989231

D. J. Pedersen, S. J. Lessard, V. G. Coffey, E. G. Churchley, A. M. Wootton, T. Ng, M. J. Watt, J. A. Hawley (2008). High rates of muscle glycogen resynthesis after exhaustive exercise when carbohydrate is coingested with caffeine Journal of Applied Physiology, 105 (1), 7-13 DOI: 10.1152/japplphysiol.01121.2007