Caffeine is one of the most researched legal sport enhancing supplements in recent decades. However, its underlying mechanism complexity and lack of consistent research findings has led to misleading information being spread regarding its effect as an ergogenic aid. So what is caffeine and how does it work in the body to heighten performance?
What is caffeine?
Caffeine (also known as 1, 3, 7-trimethylxanthine) is a stimulant substance found naturally occurring in various foods (e.g. chocolate) and drinks (e.g. coffee), and is classed as a psychoactive drug. Although it is safe and legal to consume in certain quantities, caffeine was previously on the international olympic committee (IOC) and world anti doping agency (WADA) banned substance list until 2000 and 2004 respectively (Stear et al., 2010). However, whilst having been removed, these organisations still control and monitor the use of caffeine in extreme doses (urinary caffeine levels >12μg/mL).
Caffeine acts as a stimulant to the central nervous system in the body, increasing levels of alertness and reducing perceived levels of tiredness. The magnitude of these effects depends mostly on your tolerance towards the drug; however, other variables such as age, overall health and body mass can contribute to your response to a certain amount of caffeine. Caffeine is commonly used within the general population as a means to improve mental attention and reduce fatigue, but within the athlete population, caffeine has demonstrated some significant ergogenic effects within a range of sports. To provide a few examples, this can include:
- Increased time to exhaustion in endurance events, with research demonstrating this effect in running (Graham & Sathasivam, 1998), cycling (Ivy et al., 1979), and a reduced time to completion in triathlon (Potgieter et al., 2021).
- Improvements in sprint times for high intensity sports including cycling (Glaister et al, 2012), Rugby (Stuart et al., 2005), American football (Gwacham & Wagner, 2021)
- Improvements in power produced during strength exercises (For a meta-analysis, see Warren et al., 2010)
Theories behind why caffeine works as an ergogenic aid:
The reasons behind why caffeine works as an ergogenic aid is not fully understood, but the theories are classified into three main areas:
- Metabolic system: One reason why caffeine works as a performance enhancing aid is through the increased fat oxidation, and thus sparing CHO (carbohydrate) oxidation. This aspect is particularly important in endurance sports. Research has shown that intake of caffeine intake spares glycogen use during the first 15 minutes, while increasing intramuscular triglycerides (Intramuscular fat) during the first 30 minutes (Maughan, 2000). Sprite & Dyke (1996) suggested that the mechanism behind the increase in fat oxidation can be explained through the Randle cycle (Randle et al., 1963). This refers to increased fatty acid accessibility to the muscle, increasing acetyl-coenzyme A in the muscle; which in turn inhibits glucose action and muscle glucose oxidation (Maughan, 2000). The effects of caffeine intake on the metabolic systems is mostly evident in long-term endurance exercise (See Collado-Mateo et al., 2020), but there has been some evidence that it may benefit short, anaerobic performance (Jackman et al., 1996).
- Ion handling in skeletal muscles: Increased calcium (Ca2+) release during exercise and increased sodium (NA+), potassium (K+) and ATPase activity is a result of methylxanthines (a substance found in coffee) levels in the body after ingestion of caffeine. All these factors help maintain a superior membrane potential in contracting muscles, which may contribute to increased skeletal force production (Lindinger et al., 1993). However, this mechanism is not fully understood, and more research needs to be done in the area to conclude a relationship between caffeine and changed in ion handling in the body. (For more research, see Rosser et al, 2009). [For more information on the mechanics of muscle contractions, see here]
- Central effects of caffeine: Some research has suggested that all the ergogenic effects of caffeine is due to the effects it has on the CNS (central nervous system) (e.g. increased mood, alertness and reduced fatigue). And although there is no way to measure the effect caffeine has on the central and peripheral systems, the ability of caffeine to delay fatigue and lower perceived exertion of exercises been linked to the central fatigue hypothesis. The central fatigue hypothesis suggests “an exercise-induced increase in extracellular serotonin concentrations in several brain regions contributed to the development of fatigue during prolonged exercise” (Meeusen et al., 2006), and research has demonstrated caffeine can delay fatigue in the CNS, partly by blocking adenosine receptors (Davis et al, 2003).
Myths surrounding the intake of coffee:
- Caffeine leads to dehydration: FALSE. Caffeine is a diuretic (a substance that increases the amount of water expelled by the body) and because of this, speculation has been made encompassing the poor level of hydration maintained during exercise through the intake of caffeine. However, in a meta-analysis by Graham (2001), no evidence was found to suggest caffeine ingestion leads to dehydration. This finding is backed up by studies which assessed physiological changes in the body after the ingestion of caffeine, also finding that no changes in sweat loss and plasma loss during exercise, suggesting no dehydrating effect of caffeine (Gordon et al., 1982; Falk et al., 1990).
- High carbohydrate diets reverse the oxidation of fat during exercise, increasing reliance on carbohydrates as fuel and reducing time to exhaustion: MOSTLY FALSE. A high carbohydrate diet has been shown to have no effect on the ergogenic effects of caffeine (Sprite, 1995), and more importantly it has been demonstrated that post-exercise consumption of caffeine with carbohydrates improves subsequent high-intensity performance and capacity (Taylor et al., 2021).
- You should intake caffeine just before a workout: FALSE. Research has shown that it can take around 30 minutes for the ergogenic effects of caffeine to become prominent (Moreno, 2016)
Considerations when using caffeine in elite sport- Caffeine and its link to doping:
Although caffeine is no longer a banned substance in the realm of elite sport, like previously stated, extreme doses are still considered doping. Therefore, athletes should be aware of using caffeine to its fullest potential, without reaching the levels considered doping. According to a document published by NCAA, consuming caffeine in excess of 600-800mg can lead to an athlete to test positive. This level of caffeine equates to “6-8 cups of coffee around 2 hours before exercise”. Although this paper was published in the USA, it still goes that these levels of caffeine are still regarded as doping according to the IOC and WADA.
Proper intake of caffeine:
So, what is the correct way to intake caffeine to optimise athletic performance?
Studies have shown that 3mg/kg of caffeine would be sufficient to reach the optimal benefits in performance. No dose-response relationship has been demonstrated with doses above this, meaning that any more than 3mg/kg would have no additional benefit (Kreider et al., 2000). For an individual weighing 65kg, this would equate to 195mg caffeine, which is the same as about 2 espressos. In the case of low-duartion sports, this dose should be taken about an hour before exercise. However, during very long endurance events, this dose can be taken in multiple doses during the event (e.g. 3 doses of 65mg throughout the event), or all of it at the beginning of the event. Furthermore, to get the greatest benefit from this caffeine ingestion, it is suggested that you refrain from intaking caffeine two days before to cleanse the body of caffeine, magnifying the effect of the intake of caffeine before the exercise bout.
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