16 5 Audio 2

Ergogenic Espresso: The Performance Benefits of Caffeine by Brian Zehetner – NHL/NBA/MLB/NFL Nutrition Consultant

Caffeine is, by far, the most consumed drug in the world. Millions of people yearn for their daily dose to generate some quick energy, and it certainly delivers. Improved mood, increased alertness, and delayed fatigue are just some of its far-reaching effects, and with only mild side effects (slight increases in heart rate and blood pressure). Athletes began to take notice of these effects and the potential for performance enhancement, and researchers were soon to follow. We now have plenty of studies examining caffeine as an ergogenic aid – whether it works, possible mechanisms, and the conditions that are ideal in order to optimize performance. This article will provide an overview of caffeine, its effects on your body, and the research completed on endurance athletes. You’ll be surprised and encouraged by the results!

THE SKINNY ON CAFFEINE Caffeine (a xanthine alkaloid) is classified as a central nervous system stimulant. It is found naturally in about 60 different plants, including coffee, tea, kola nut, guarana, mate, and cocoa. Caffeine is digested rapidly and absorbed through your small intestine, ultimately ending up in your liver to be metabolized. Here it is broken down into three separate types of active molecules. The first (paraxanthine) increases fat breakdown; the second (theobromine) dilates blood vessels and increases urine output; and the third (theophylline) relaxes smooth muscle within the bronchial tubes of your lungs. Before these three by-products can be excreted – through urine – more time must be spent to further metabolize them. The half-life of caffeine is approximately six hours, meaning that half of a given caffeine dose is still active in your body six hours after ingestion. However, this can vary depending on the person and circumstances. Caffeine has many mechanisms of action, but most of these stem from its role as an adenosine receptor antagonist. In other words, adenosine is a key, and its receptor is a lock. When the key fits into

the lock, it causes certain effects. However, caffeine blocks the key (adenosine) from fitting into the lock. This prevents adenosine from having its normal bodily effects, one of which is to regulate dopamine levels. Thus, as caffeine becomes available in the body, adenosine activity gradually declines, leading to a concomitant increase in dopamine activity. This increase in dopamine is the key step that causes the effects we associate with caffeine: strong stimulatory actions within the body. Graham et al. summed up caffeine’s effects in one of their reviews;1 they agreed that although adenosine receptor antagonism is the most widely supported mechanism of action, it couldn’t explain all of the observed responses within the body. Caffeine also increases epinephrine (adrenaline), which leads to a cascade of events via the sympathetic (fight or flight) nervous system, including, but not limited to, increased heart rate, increased diversion of blood to muscle tissue, and increased blood pressure. It also increases serotonin levels in the brain, resulting in positive mood changes. Other metabolic effects include enhanced muscular contraction, increased glycogen breakdown, and increased free fatty acid release from adipose (fat) tissue. Keep in mind, we are only scratching the surface in terms of the metabolic, physiological, and psychological effects caffeine has on the body.

DOES CAFFEINE AFFECT YOUR ENDURANCE PERFORMANCE? Without a doubt, caffeine does improve performance in endurance events, such as running and cycling. Costill and colleagues were the first to study caffeine and its potential in endurance activities.2 In one of their studies, nine cyclists exercised to exhaustion at 80% VO2max after consuming either decaffeinated coffee or coffee containing 330mg of caffeine 60 minutes prior to the start. Cyclists receiving the caffeine were able to perform for 90 minutes, while those receiving the decaf only rode for 75.5 minutes. This is significant because these were competitive cyclists, and a 15-minute difference in an actual event

would be nothing short of miraculous. Graham and Spriet obtained similar results when they evaluated the effect of a high caffeine dose during prolonged exercise.3 Seven competitive runners performed 4 exercise trials (two running and two cycling) at 85% VO2max to exhaustion. Subjects consumed either dextrose or caffeine at a dose of 9 mg/kg body weight one hour before exercise. Run times increased from 49 minutes in the placebo group to 71 minutes in the caffeine group, and cycling times improved from 39 minutes to 59 minutes when caffeine was used. Again, these results are very impressive, though we don’t exactly know how applicable they are to a real-world situation. It certainly is cause for excitement, and is one reason that the International Olympic Committee (IOC) banned caffeine prior to the 1972 Olympics and again from 1984 to 2004. However, because of its persistent use throughout the world in everyday life, caffeine now sits on the monitored list, which means it is no longer banned from competitions.

HOW CAFFEINE IMPROVES YOUR PERFORMANCE It’s clear that caffeine improves your endurance performance, but the real question is, how does it work? What mechanisms are at play that allow for these improvements? In Costill’s study, he found that fat oxidation was significantly higher in the caffeine group, which makes sense because, as mentioned above, we know that caffeine raises free fatty acid levels in your blood serum. Any increase in fat oxidation might spare muscle glycogen for more intense running later on, thereby improving endurance. (For more on glycogen and how it affects your running see 15.1 Jan/Feb ’06 p2.) He also found that perceived exertion ratings were much lower in the caffeine group, meaning that the cyclists thought the exercise task was much easier when ingesting caffeine. Graham and Spriet were able to show a glycogen-sparing effect in a study that involved eight subjects cycling at 80% VO2max to exhaustion.4 The subjects consumed either dextrose or caffeine at a

dose of 9 mg/kg body weight one hour before the start. When using caffeine, performance was, again, substantially improved, and they found that muscle glycogenolysis (the breakdown of glycogen to glucose) was decreased by 55% over the first 15 minutes of exercise. Therefore, the spare glycogen was available later in exercise, which coincided with a prolonged time to exhaustion. Obviously, the aforementioned studies seem to indicate that caffeine improves endurance performance by increasing your fat oxidation, which in turn slows glycogenolysis and allows your body to call upon muscle glycogen for an extended period of time. Unfortunately, for the sake of determining how caffeine improves your performance, recent studies have not been able to replicate the above findings. Graham et al. looked at leg metabolism after 10 male subjects performed one hour of exercise on two occasions at 70% VO2max after ingesting either placebo or caffeine.5 While caffeine ingestion did increase serum free fatty acid and glycerol concentrations, there were no differences in respiratory exchange ratio, leg glucose uptake, muscle glycogenolysis, or fatty acid uptake. They concluded that caffeine does not alter carbohydrate or fat metabolism during exercise – effectively unsolving the mystery of how caffeine improves performance. Laurent et al. also studied the effects of caffeine on muscle glycogen utilization.6 They had 20 glycogen-loaded subjects consume 6 mg/kg of placebo or caffeine 90 minutes prior to cycling for two hours at 65% VO2max. They found that serum free fatty acid concentrations increased and muscle glycogen content decreased similarly in both groups. However, they did find almost a doubling of beta-endorphin levels in the caffeine group. They concluded that caffeine does not exert a muscle glycogen-sparing effect, but that it may lower the threshold for beta-endorphin release. Beta-endorphins are thought to be released during vigorous exercise, producing an increased sense of wellbeing and relaxation, along with pain

reduction. These feelings are the essence of what some call the “runner’s high.” If the threshold for the release of these chemicals is lowered, perceived exertion may decrease. This means that, despite the stress of the activity, it might seem less difficult, resulting in improved performance. They hypothesize that this may be a potential mechanism for the performance improvements seen in endurance exercise studies. Graham wrote two excellent review articles about using caffeine as an ergogenic aid. When discussing how caffeine improves endurance performance, he concluded that it is unsupported and unlikely that increased fat oxidation and glycogen sparing is the prime ergogenic mechanism.7 He proposes that caffeine may work by creating a more favorable intracellular ionic environment in your muscles, helping to facilitate force production by the motor units.8 In other words, caffeine causes an increased release of calcium within your muscles, which is a crucial step in the process of muscular contraction. Stronger, more efficient muscle contractions should help improve performance in almost any type of physical activity. Another plausible explanation for improvement is the decreased perception of effort and altered mood states that have been noted in other studies. All in all, the mechanism of action is assumed to be multifactorial, and hopefully more research will expand our knowledge base even further.

WHAT IS OPTIMAL PROTOCOL WHEN USING CAFFEINE? Caffeine has been established as an effective ergogenic aid during endurance exercise, but we still need to clear up some important questions. How much caffeine is enough to affect performance, and when, and in what form, should it be taken? Researchers have been able to provide some answers – the findings are interesting. Graham and Spriet tried to determine the optimal dose of caffeine by having eight subjects avoid caffeine for 48 hours, and then ingest placebo or caffeine at doses of 3, 6 or 9 mg/kg.9

Afterward, the subjects ran at 85% VO2max until voluntary exhaustion. Endurance was enhanced with 3 and 6 mg/kg, but not with 9 mg/kg. Interestingly, the highest dose had the greatest effect on epinephrine (adrenaline), yet the least effect on performance. The authors couldn’t decipher the “optimal dosage,” yet they did conclude that the results didn’t support the idea that caffeine exerts its effect via catecholamines. Pasman et al. also investigated this “optimal dosage” issue.10 They had nine well-trained cyclists take 0, 5, 9 or 13mg/kg caffeine one hour prior to exercising to exhaustion at 80Wmax (Watt max – a measure of intensity). All caffeine doses improved performance in comparison to placebo, yet there were no differences between the three caffeine doses (47 minutes for placebo; and 58 minutes, 59 minutes, and 58 minutes for 5, 9, and 13 mg/kg, respectively). Even though no dose was clearly superior, this study is often referred to when addressing the optimal dose of caffeine, which is often set at approximately 6 mg/kg. For a 70 kg individual (154 lbs), this would be about 420 mgs of caffeine, or the equivalent of three to four strong cups of coffee. Other studies on caffeine have used doses close to this level with very good results, and through years of self-experimentation, both athletes and non-athletes have found that higher doses can potentially cause more side effects such as jitters, nervousness and gastrointestinal discomfort. (For more on gastrointestinal issues see 16.4 July/Aug ’07 p9.) Other researchers have tried to determine when caffeine should be taken in order to enhance performance. This issue resurfaced because many studies have used a bolus dose (one concentrated dose) one hour prior to exercise. But is this truly the best way to consume caffeine? And what about the sports nutrition products on the market that contain caffeine and are designed to be consumed during events? Conway and his colleagues addressed these issues when they evaluated the effect of a divided dose of caffeine on endurance cycling performance.11 Nine cyclists and

triathletes cycled for 90 minutes at 68% VO2max, followed by a self-paced time trial (equivalent to 80% VO2max for 30 minutes). Three different interventions were used: placebo 60 minutes before and again 45 minutes into exercise, caffeine (6 mg/kg) 60 minutes before and placebo 45 minutes into exercise, and a divided protocol with caffeine (3 mg/kg) 60 minutes before and again 45 minutes into exercise. The performance was no different between the two caffeine trials, indicating there is no performance advantage to either a bolus dose or a divided dose. An interesting side note, however, is that urinary concentration was lower post-exercise in the divided dose trial. This had realworld application when caffeine was on the IOC prohibited list because urinary concentration (12 ug/ml) was used as the benchmark for a positive doping test. Athletes could effectively lower their urinary concentration by dividing their doses over a period of time. (However, as mentioned earlier, caffeine is no longer on the IOC banned list.) Graham looked at one last variable that might alter the effect caffeine has on endurance performance. Does the form in which caffeine is delivered make a difference? Nine healthy adults ingested one of five different trials: caffeine capsules with water, placebo with water, decaffeinated coffee, decaffeinated coffee with caffeine added, or regular coffee.12 The caffeine dose was 4.45 mg/kg in all caffeine trials. After resting, subjects ran at 85% VO2max until voluntary exhaustion (about 32 minutes in the placebo and decaffeinated trials). The main finding here was that endurance only improved in the caffeine capsule trial, with no differences among the other four trials. The authors speculated that there must be some component of coffee that lessens the effect of the caffeine.

SO WHAT IS THE TAKE HOME MESSAGE? It seems that the more we know about caffeine, the more we know that we don’t know. As with all research, there’s plenty of conflicting evidence, but I think we can make some strong

assertions at this point: • Caffeine improves performance in endurance exercise, likely through a variety of systemic effects on your entire body. • A variety of caffeine doses have been found to be ergogenic, but in order to minimize side effects and maximize performance, 6 mg/kg (1 kg = 2.2 lbs) seems to be the gold standard dose. • Ingesting a bolus dose of caffeine one hour prior to an event works as well as divided doses during an event, though the bolus dose may be easier and more practical in real-world settings. • Caffeine tablets may be more effective than other sources of caffeine (coffee, soda, herbs) because of confounding factors and ingredients contained within these products. • Caffeine affects everyone differently, so as always, experiment with it during training to see how you respond.