INTRODUCTION
Caffeine is the most widely used, socially accepted whilst relatively inexpensive drug in the world. We commonly ingested caffeine in coffee, tea, soda, and energy drinks. Its ability to enhance muscular work has been apparent since the early 1900s (Astorino and Robertson 2010).
CAFFEINE is classified as part of the methylxanthine family of drugs and is also commonly consumed by athletes as an ergogenic aid (Mor et al, 2010) due to the fact that it typically increases endurance performance. Despite popular beliefs that caffeine is a diuretic because of such cause dehydration and hyperthermia, recent evidence shows that caffeine consumption does not result in water electrolyte imbalance, hyperthermia and reduced exercise heat tolerance (Armstrong et al 2007) It is important to correctly inform those involved to high level sports of its restrictions, by central bodies so they remain compliant to rules and regulations as well as gaining benefits from its ingestion.
HOW DOES CAFFEINE ENHANCE PERFORMANCE?
Ingested caffeine is quickly absorbed from the stomach and peaks in the blood in 1-2 hours and has the potential to affect all systems of the body, as it is absorbed by most tissue. The remaining caffeine is broken down in the liver and byproducts are excreted in urine. (ACSM)
At the cellular level, caffeine has proven to affect the translocation of calcium in muscle, promote an increase in cellular levels of cyclic AMP and cause a blockade of adenosine receptors in the central nervous system. The general systemic effect of caffeine is to cause central nervous system arousal, mobilisation of free fatty acids and other metabolites, and possibly enhance the contractile status of muscle (Powers and Dodd 1985)
Enhanced performance post caffeine ingestion, have been associated to increased wakefulness, and reduced pain perception for an increased force production during sub-maximal exercise. Tarnolopolsky (2008) found that the ergogenic effects of caffeine during endurance activities are mediated by partly enhanced contractile force, and a lowered sense of perceived exertion, which leads to an enhanced performance in sports and exercise (Burke et al, 2008)
Other explanations have become increasingly more convincing over time. For example, Mor et al (1998) found during their investigation of the effects of caffeine on tetraplegic patients that there was a reduction in fatigue of the central nervous system post caffeine ingestion. This shows that contrary to earlier beliefs, the effects of caffeine ingestion were not mediated by the sympathetic nervous system. Davis and Green (2009) agree that caffeine stimulates the CNS. Caffeine acts antagonistically on adenosine receptors thereby inhibiting the negative effects adenosine induces on neurotransmission, arousal and pain perception.
It might be suggested that, The hypoalgesic effects (http://en.wikipedia.org/wiki/Hypoalgesia) of caffeine can result in a dampened pain perception and blunted perceived exertion during exercise. This could potentially have favourable effects on negating decreased firing rates of motor units and possibly produce a more sustainable and forceful muscle contraction.
EFFECTS OF CAFFEINE AND EXERCISE/SPORT TYPE
The effects of caffeine upon different sports and exercise types (aerobic steady state vs anaerobic interval types) have created diverse view points, mainly because the experiments to date are so varied in terms of their methodologies. Burke (2008) believe that the direct effects on single events involving strength and power, such as lifts, throws, and sprints, are unclear.
EFFECTS OF CAFFEINE ON ENDURANCE SPORTS AND ACTIVITIES
There are many available studies which investigate the effects of caffeine on performance, duration and perceived exertion within endurance sports. There is certainly a myriad of evidence to suggest that caffeine can improve endurance performance.
Bridge and Jones (2006) assessed the effect of caffeine ingestion on 8km run performance in a field setting. During their randomised double blind cross over study, they identified a treatment effect for 8km run performance, where caffeine resulted in a mean improvement of 28.8s, in comparison to the placebo and no supplement group.
Interestingly Davis et al (2003) found that intracerebro-ventricular injections in rats increased run performance, whilst an adenosine injection reversed the effects of the caffeine injection. Meanwhile, the same authors found using the same experimental conditions but using an intraperitoneal injection did not incur the same effects. Studies to affirm these findings in humans would be most useful.
The effects of caffeine ingestion on high intensity time trial cycling performance in well trained subjects was investigated. Using a double blind within their study, McNaughton et al (2008) investigated six male middle aged cyclists who undertook three 1hr time trial performances with a control, placebo and caffeine. After resting for 60min subjects in the caffeine group were given a caffeine dose of 6mg.kg-1 body mass, the tests began after another 60 minutes of rest. results showed that the subjects in the caffeine group rode significantly further than the control or placebo group, the evidence from the tests showed that caffeine supplementation for training enhancement in cycling is beneficial.
Bruce et al (2000) investigated the enhancement of 2000-m rowing performance after caffeine ingestion in eight competitive rowers in a randomised double-blind crossover study. subjects performed three familiarisation trials of a 2000-m rowing test on an air-braked ergometer, followed by three experimental trials at 3 to 7 intervals, each 60minutes after ingesting caffeine (6 or 9 mg kg-1 body mass) or placebo. Trials were preceded by a standardised warm up. Plasma free fatty acid concentration before exercise was higher after caffeine ingestion, in comparison to the placebo group. Interestingly, Respiratory Exchange Ratio (RER) during the warm-up was also substantially lower with caffeine than with placebo. Both doses of caffeine had a similar ergogenic effect relative to placebo: although performance time decreased by a mean of 1.2% the corresponding increase in mean power was 2.7%. In conclusion, the testers proved that Ingestion of 6 or 9 mg-kg1 of caffeine produces a worthwhile enhancement of short-term endurance performance in a controlled laboratory setting.
EFFECTS OF CAFFEINE ON INTERVAL BASED, EXPLOSIVE TYPE SPORTS
Bell et al (2008) studied the effects of caffeine and ephedrine, separately and in combination during supra-maximal efforts during an anaerobic fitness test. (the MAOD test) Results showed that Ephedrine (E) increased power output during the early phase of the Wingate test, whereas Caffeine (C) increased time to exhaustion and O2 deficit during the maximal accumulated oxygen deficit (MAOD) test. It was found that C, E, and CE increased blood lactate, glucose, and catecholamine levels during this specific investigation. The authors concluded that improvement in anaerobic exercise performance is likely a result of both stimulation of the CNS by Ephedrine and skeletal muscle via Caffeine ingestion.
Mor et al (2010) investigated the effect of oral caffeine ingestion on intense intermittent exercise performance and muscle interstitial ion concentrations was examined. The study consisted of subjects using the leg extension intermittently with increasing the work demand (watts) over time with rest in between bouts.
In order to determine muscular fatigue they measured measured muscle interstitial K+ and Na. Interestingly, no differences in interstitial Na+were observed between the placebo group/non caffeine and the caffeine group. The testers affirmed that caffeine intake enhances fatigue resistance and reduces muscle interstitial K+ during intense intermittent exercise.
In a double blind, randomised cross over design, Stuart et al (2005) investigated the effects of caffeine in a performance test simulating the physical and skill demands of a rugby union game in nine competitive male rugby players ingested either caffeine (6 mg.kg(-1) body mass) or placebo (dextrose) 70 min before performing a rugby test. Each test consisted of seven circuits in each of two 40-min halves with a 10-min half-time rest. Each circuit included stations for measurement of sprint time (two straight-line and three agility sprints), power generation in two consecutive drives, and accuracy for passing balls rapidly. Samples were taken before ingestion of caffeine or placebo and then before testing, at half-time, and immediately after testing; samples were assayed chromatographically for caffeine and epinephrine concentrations. The effects of caffeine on mean performance over all 14 circuits were: sprint speeds, 0.5% through 2.9%; first-drive power, 5.0%; second-drive power, -1.2% and passing accuracy, 9.6%. Testers found that the enhancements in performance were mediated partly through a reduction of fatigue that developed throughout the test and partly by enhanced performance for some measures from the first circuit. Caffeine produced a 51% (+/-11%) increase in mean epinephrine concentration; correlations between individual changes in epinephrine concentration and changes in performance were mostly unclear, but there were some strong positive correlations with sprint speeds and a strong negative correlation with passing accuracy. The authors concluded that caffeine is likely to produce substantial enhancement of several aspects of high-intensity team-sport performance.
In summary it might be suggested that the reasons for the performance improvement within these interval based sports may be a direct positive effect of caffeine on muscle anaerobic energy provision and contraction or a central nervous component related to the sensation of effort.
HOW MUCH? WHEN? AND HOW?
Burke (2008) stipulates that performance benefits can be seen with moderate amounts (~3 mg.kg-1 body mass) of caffeine. Ingestion of 3 mg · kg−1 body mass 60 mins prior to an endurance event may reap benefits for performance.(Bridge and Jones 2006)
Ganio et al (2009) suggest that caffeine ingestion can be an effective ergogenic aid for endurance athletes when taken before and/or during exercise in moderate quantities (3-6 mg·kg-1 body mass).
According to some researchers in this field, abstaining from caffeine at least 7 days before use will give the greatest chance of optimising the ergogenic effect. Bruce et al (2000) suggest that Ingestion of 6 or 9 mg-kg1 of caffeine produces a worthwhile enhancement of short-term endurance performance in a controlled laboratory setting.
The ACSM are in agreement with the above, suggesting that ingestion of 3-9 mg of caffeine per kilogram (kg) of body weight one hour prior to exercise increased endurance running and cycling performance in the laboratory.
To put this into reality, ACSM reiterate that 3 mg per kg body weight equals approximately one mug or 2 regular size cups of drip-percolated coffee; and 9 mg/kg = approximately 3 mugs of 5-6 regular size cups of coffee.
Due to its stimulating effects on the nervous system, It is not advised that consumers ingest caffeine 1 hr before intending to sleep as it can cause disturbances during sleep. If caffeine is going to be considered for usage as an ergogenic aid then the athlete must first trial the drug before any major competition to ensure of no personal adverse effects from ingestion.
ATHLETES OF ALL LEVELS TO BE AWARE OF RESTRICTIONS
The odds of reaching the limit through normal caffeine ingestion are low, except where smaller volumes of coffee with very high caffeine concentrations are consumed. Therefore, an illegal urinary caffeine level makes it highly probable that the athlete deliberately took supplementary caffeine tablets or suppositories in an attempt to improve performance.
Nevertheless, It is strongly recommended that sports participants are aware of the restrictions of this drug, regardless of your level of sport. In Australia You can refer to the ASADA or WADA guidelines to get a better idea of the exact restrictions.
To give you an idea on the international scale, caffeine is a “controlled or restricted substance” as defined by the International Olympic Committee (IOC). These guideline stipulate that athletes are allowed up to 12 ug caffeine per millilitre of urine before it is considered illegal. The acceptable limit in sports sanctioned by the National Collegiate Athletic Association (NCAA) in the U.S. is 15 ug/ml urine.
These high urinary limits are to allow athletes to consume normal amounts of caffeine prior to competition. A large amount of caffeine can be ingested before reaching the “illegal” limit. For example, if a 70 kg person rapidly drank about 3-4 mugs, or 5-6 regular size cups of drip-percolated coffee (~9 mg/kg bw) one hour before exercise, exercised for 1-1.5 hours and then gave a urine sample, the urinary caffeine level would only approach the limit (12 ug/ml).
SUMMARY
In summary caffeine is proven to boost performance in sport and fitness across a range of activities and sports demanding energy derived from major pathways in the human body, aerobic and anaerobic.
Caffeine reduces sense of perceived exertion, reduces fatigue of the central nervous system, whilst also aiding force production which encompasses an enhanced performance due to these factors. Further studies are required to better interpret the range of protocols (timing and amount of doses) that produce benefits and the range of sports to which these may apply. Individual responses, the politics of sport, and the effects of caffeine on other goals, such as sleep, hydration, and refuelling, also should be considered by the authors who commit to testing this drug in sport. As a guideline 3-9mg per Kg of bodyweight 60minutes prior to exercise could help to enhance performance, however it is advisable to recognise that caffeine is still a drug therefore to tread with more caution if it has been consumed before.
REFERENCES
Armstrong, Lawrence .; Casa, Douglas.; Maresh, Carl; Ganio, Matthew: Caffeine, Fluid-Electrolyte Balance, Temperature Regulation, and Exercise-Heat Tolerance. Exercise and Sport Sciences Reviews 2007 - Volume 35 - Issue 3 - pp 135-140
Astorino TA, Roberson DW.J Strength Conditioning Research. Efficacy of acute caffeine ingestion for short-term high-intensity exercise performance: a systematic review.2010 Vol 24 (1)
Bell DG, Jacobs GI, Ellerington K.Effect of caffeine and ephedrine ingestion on anaerobic exercise performance. Med. Sci. Sports Exercise, 2001. Vol. 33,(8) pp. 1399–1403.
Bridge CA; Jones MA. The effect of caffeine ingestion on 8km run performance in a field setting.Journal of sports sciences (2006) Vol 24 (4)
Burke LM. Caffeine and sports performance.Applied Journal Physiology Nutritional Metabolism. 2008; Vol 33(6): pp1319-34.
Davis JK, Green JM.Caffeine and anaerobic performance: ergogenic value and mechanisms of action.Sports Med. 2009; 39(10):813-32.
Ganio, Matthew S; Klau, Jennifer F; Casa, Douglas J; Armstrong, Lawrence E; Maresh, Carl M. Effect of Caffeine on Sport-Specific Endurance Performance: A Systematic Review. Journal of Strength and Conditioning Research 2009. Vol 23 (1) pp 315-324
McNaughton LR, Lovell RJ, Siegler J, Midgley AW, Moore L, Bentley DJ.The effects of caffeine ingestion on time trial cycling performance.Int J Sports Physiol Perform. 2008 Jun;3(2):157-63
Stuart GR, Hopkins WG, Cook C, Cairns SP. Multiple effects of caffeine on simulated high-intensity team-sport performance. Med Sci Sports Exerc. 2005 Nov;37(11):1998-2005.
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