Introduction
One of the earliest study on the effects of caffeine (CAF) and physical performance was proved by a researcher (Laties, 1964) who tested the effects of 500mg of CAF on work output using a ‘Mosso Ergometer’ and found that work output increased. However, that is only one of the many components that CAF may have an effect on. Other components include increased aerobic performance, strength and reaction time (T. Graham, 2001).This drug however, comes along with some adverse side effects such as dehydration and insomnia. Researchers found that caffeine did not negatively affect sports performance.
This substance was once banned by the IOC due to scientific findings which led to recommendation of ban from use in sport competition. The level deemed illegal was 12µg/mL which is around 600-800mg of caffeine (6-8 cups of brewed coffee). The ban, however has been lifted in 2004 as it is difficult to draw a line to what constitutes consumption of this drug to be of purely ‘doping’ in nature. What makes it even more difficult is that the use of this drug is widely accepted by the general population and more so, used by athletes today. Consumption of caffeine can be said to be normal as many of the food and drinks consumed contains as slight amount of this substance. This includes coffee, tea, chocolates and soft drinks. Caffeine composition may vary widely from one food source to another. An elevated level of this substance (> 70µmol/L) in the human body can be said to be normal.
The exact mechanism on how caffeine works as a performance booster is not clearly understood by scientists as CAF creates a chain of reactions to which is hard to pin-point exactly which starts first. These actions and reaction also occurs simultaneously. However, caffeine acts mainly as an adenosine receptor inhibitor and has an effect on various parts of the human body. This includes the brain, heart, skeletal muscle and adipocytes (Paluska, 2003). In relation, an increased in mobilization of free fatty acids (FFA), reduced reaction time and reduced fatigue are some of the mechanisms hypothesized to increase performance. An example of this is demonstrated by (T. Graham, 2001) where CAF stimulates secretion of adrenaline and thus creates secondary metabolic responses (e.g. increased blood circulation). This response can be from either neural (beginning from the brain) or cardiovascular changes affected by CAF. The fact that CAF may work as a placebo should not be dismissed (Brukner & Khan, 2007)
The purpose of this paper is to briefly review the use of caffeine with the goal of improving exercise performance. This includes the theory of mechanism involved, optimal dosage, time, method of consumption of CAF, and also the types of exercise caffeine plays a role on.
Caffeine as an ergogenic aid
Caffeine was and is still being widely used as an ergogenic aid to endurance performance. One study reported that improvements of up to 20% were seen in athletes who consumed caffeine 1-3 hours prior to exercise. (Douglas G. Bell & McLellan, 2002). The effects of caffeine on various aspects of exercise performance were studied by researchers. Most commonly, the effects of caffeine on endurance performance where the authors concluded that the question to ask is by what degree does caffeine induce performance increases instead of whether caffeine does improve performance.
It has also been proven that caffeine does improve power output in cycling where (Ivy et al., 2009) found an increase of 7.3% in power output over a 2 hour long cycle exercise period. Another study (E. M. R. Kovacs, J. H. C. H. Stegen, & F. Brouns, 1998) had similar findings in their study on trained athletes who consumed a carbohydrate and electrolyte solution with addition of caffeine. These authors found that there was a positive co-relation between ingestion of this solution (carbohydrate, electrolyte and caffeine) on power output in their testing protocol.
In a more functional test, a paper published was on the time difference in 100m swimming trials where the author found that there was significant difference in mean swim times between caffeine and placebo groups (Collomp, Anderson, & Fraser, 2000).
Other studies regarding power maximal power output were by (Anselme, Collomp, Mercier, Ahmaiedi, & Prefaut, 1992) who studied participants with CAF treatment on Wingate tests. These authors found that CAF treatment only affected performance in the 6s test and not the 30s test. There were no differences between the groups in relation to maximal anaerobic power generated and fatigue (Anselme et al., 1992).
The possible explanation to how caffeine increases athletic performance is through increased adrenaline and fat oxidation while sparing more limited sources of glycogen (Randle Effect). This theory was found by (Essig, Costill, & Van Handel, 1980)Plenty has changed since, most researchers only study the effects of caffeine and not the mechanism. With more recent data, the theory proposed by these authors may not be reliable/ valid even though plasma FFA levels were elevated. More recent studies suggest that this theory lacked evidence, yet these newer studies tend to be more descriptive rather than being critical with excluding measures of plasma caffeine and catecholamine levels. These two levels are crucial to Essig’s theory relating to glycogen sparing. Researchers also found that FFA uptake did not increase and led to respiratory exchange ratio (RER) to remain constant between both users and non-users of caffeine.
Consumption of Caffeine
There are various methods of CAF consumption (e.g. intravenous injection). However, the most conventional way is to consume orally. Caffeine is contained in many foods and beverages as mentioned above but this substance is also found in medications such as cough mixtures and weight loss products. Many sports drinks and gels are also marketed with caffeine as an additive to promote sales along with its ergogenic benefit.
Some, if not many gym-goers tend to turn to coffee or other caffeine rich sources for their caffeine dose before exercising. This may prove to be a good deed as researchers found that caffeinated coffee does increase exercise capacity especially in prolonged exercise (>30 minutes)
Caffeine in conjunction with other compounds
The effectiveness of caffeine may be increased or decreased if consumed in conjunction of other ergogenic aids (e.g. creatine). As caffeine inhibits various adenosine receptors, the body may not react naturally as it would to these substances without caffeine.
Several researchers (Eva M. R Kovacs et al., 1998) studied the effects of these sports (glucose + electrolyte) products with the caffeine additive. Their findings show that caffeine did not negatively co-relate with the sports drink containing either glucose and electrolytes or only glucose/electrolytes. These authors also found that the additive did not negatively affect performance and the utilization of glucose and electrolytes.
In contrast, one study (Vandenberghe et al., 1996) showed that caffeine negatively affected the utilization of creatine. 9 male volunteers participated in the study with Cr 0.5g/kg/day and 0.5g/kg/day + CAF 5mg/kg/day prescribed. The exercise protocol for their experiment was three consecutive isokinetic interval muscle contractions with 2 minute rest periods. Muscle ATP concentrations were reported to remain constant over the three experimental conditions. Phospho-creatine concentrations in muscle were increased in both groups by 10-23%. The researchers found that the creatine only treatment proved to be ergogenic but had zero co-relation towards performance when caffeine was included in the equation (creatine + caffeine). This information would be beneficial for bodybuilders who normally consume creatine and caffeine pre-training.
Caffeine was also reported to augment effects of non-steroidal anti-inflammatory drugs(NSAIDS) such as aspirin and ibuprofen (Sawynok & Yaksh, 1993). More research is required in this area for further clarification and confirmation as (Zhang et al., 1997) found contradictory results in their review on the same topic.
Prescription
(Pasman, Van Baak, & Jeukendrup, 1995) found that dosages as low as 3mg/kg bodyweight has shown to have a positive effect on aerobic performance. Findings from Bruce et al. and Kovacs et al. found ergogenic effects when CAF was prescribed with sports drinks. These researchers had confirmed that a dosage between 3 to 6mg/kg is optimal for improving performance.
The optimal method of consumption relates to timing if ingestion and dosage. There have been various studies done to answer the question on prescription. Two main approaches were used; 1) single dosage and 2) repetitive dosage. Data has shown that plasma concentrations of CAF may be elevated with a single dosage for up to several hours, repeated dosage of CAF may prove to be beneficial to those who are caffeine ‘intolerant’, experiencing severe symptoms of gastric irritation with large doses of this substance. Other than the following, repeated dosages would not be required.
Another paradigm of caffeine ingestion is whether dosage prescribed was absolute or relative. Many studies had prescribed a relative dosage (mg/kg bodyweight), this include studies done by (T. E. Graham & Spriet, 1995; Pasman et al., 1995)on high intensity (80-85%) aerobic exercise in male and female subjects. These researchers had 4 groups for treatment purposes with varying dosages (mg/kg). The general outcome for these studies is an increase in aerobic performance for dosages between 2.2mg/kg and 9mg/kg with or without mixing with sports drinks (Bruce, Anderson, & Fraser, 2000; E. M. R. Kovacs, J. Stegen, & F. Brouns, 1998). There were higher dosages prescribed but did not reap any further benefits.
Absolute dosages were also prescribed in some studies and although there were positive results, they may not be reliable as it is not a good indicator of the true requirement to increase caffeine plasma levels. The variance may be up to an excess of 20% of that is required in smaller bodied individuals (e.g. women vs. men) (T. Graham, 2001). Another limitation is that only (Eva M.R Kovacs et al., 1998) tested for the changes in caffeine plasma concentrations and found that exercise does not influence caffeine absorption.
In relation to timing of ingestion, (Nehlig, 1994; Weir, Noakes, & Myburgh, 1987) suggested that ingesting caffeine 3 hours prior to exercise is best as plasma free fatty acids (FFA) is optimal due to caffeine induced lipolysis. This finding however has limitations as this hypothesis has not been tested and proven.
Adverse effects of caffeine ingestion
Negative effects may arise from lower tolerance/higher sensitivity of caffeine. It is hard to set a clear limit or range of the amount of caffeine is to be ingested before reaching the point where adverse effects kick in. However, one source (Canada, 2007) recommended that no more than 400mg caffeine be ingested in a day.
From the same source, it was reported that the side effects of caffeine may be more acute (changes in behaviour) in children than in adults. If caffeine is taken in moderation, it may increase alertness and ability to concentrate. If the personal limit is exceeded, it could lead to acute insomnia, headaches irritability and nervousness.
Looking at the long term effects of caffeine includes 1) general toxicity leading to muscle tremors, nausea and irritability, 2) increased heart rate, cholesterol and blood pressure, 3) negative calcium balance leading to decreased bone density and increased risk of fractures, 4) behavioural changes including but not limited to anxiety and attentiveness, 5) effects on reproduction in women who are still in childbearing age and men.
Dehydration is a common concern amongst caffeine users especially those who participate in sport. A decrease of only even 2% of total plasma volume may hinder performance drastically. However, one study (T. E. Graham, Hibbert, & Sathasivam, 1998) reported that there were no differences in urine excretion between users and non-users and was highly reflected by total fluid ingestion. In matters relating to fluid balance, several authors found similar findings where there we no effects of caffeine on sweat rate, plasma volume and core temperature. These findings however only studied the acute effects of caffeine (around 1 hour after ingestion), while in a longer period post-ingestion caffeine works as a mild diuretic. This was reported by (30) over 4 hours and if exercise did take place, this diuretic effect of caffeine was over-ridden.
Urinary caffeine excretion was found to be a poor indicator of plasma caffeine concentration and urinary caffeine concentration is highly variable. This makes it difficult to prescribe dosages required if sporting competition lasts for several consecutive days. Repetitive dosages would ensure plasma concentration of caffeine is elevated for optimal ergogenic effects to take place (Dogulas. G Bell & McLellan, 2003). Caffeine excretion through urination is however an indicator of ingestion of caffeine. Urinary caffeine concentrations were between 1.9 and 2.5 µg/ml and was not close to the IOC limit of 12µg/L in a study (Eva M. R Kovacs et al., 1998) which prescribed between 2.1mg/kg and 4.5 mg/kg.
Another potential negative effect is dependency and increased tolerance towards this substance. Just as any drug, the body adapts to it and over a time period, requires more for the effects of the drugs to take place.
Conclusion
Ingestion of caffeine for purpose of exercise may pose both positive and negative effects for the consumer. However, recommendations for caffeine consumption should be made for athletes as it may give them an edge during training and competition. Although some studies reported no effects of caffeine on exercise performance, none of the studies in this review found a negative correlation on consumption of caffeine in regards to exercise performance (T. Graham, 2001). It can be said that participants of all sports requiring an expenditure of a relatively large amount of energy will benefit from caffeine ingestion. Caffeine however may hinder sporting performance in those requiring accuracy and a steady heart rate such as shooting and archery. There were no studies found in regards to these sports.
Several authors have proven that only a small amount of caffeine is required to promote ergogenic benefits (Bruce et al., 2000; T. E. Graham & Spriet, 1995; Eva M. R Kovacs et al., 1998; Pasman et al., 1995). These levels that are required for ergogenic benefit does not come close to the limit set by the IOC (12µg/mL).
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