Potential mechanisms

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Caffeine’s ergogenic effects were once thought to be explained by caffeine’s stimulation of free fatty acid oxidation and, as a result, sparing of muscle glycogen42, however several other mechanisms are now also under investigation.

Endurance exercise

Any suggested improvement in sports performance is strongest for endurance sports. Research and reviews conclude that caffeine affects endurance performance largely through its antagonist effect on the adenosine receptors in the brain i.e. via a pathway that leads to an increased production of adrenalin, which stimulates energy production and improves blood flow to the muscles and heart6. Caffeine modulates central fatigue and influences ratings of perceived exertion, perceived pain and levels of vigour, all of which may lead to performance improvements6.

Fig. 1 Illustration of caffeine binding to the adenosine receptor, which may enhance the central nervous system6

Short-term high-intensity exercise

For short-term anaerobic exercise, the fatty acid oxidation and glycogen sparing is not a realistic model for the mechanism behind performance improvement because, for example, the time frames do not fit. A 2009 review on anaerobic mechanisms of action discussed current options and demonstrated that it is not yet clear how caffeine improves short-term high-intensity exercise performance15.

Some of the areas under investigation include: lactic acid, blood glucose, potassium – for peripheral mechanisms; caffeine as an adenosine antagonist, pain perception and ratings of perceived exertion – for a central mechanism. This caffeine-related central model is the most promising to date.

It is interesting that the models for the mechanisms of action to explain the benefits of caffeine for performance in both types of exercise – endurance and short-term, high- intensity – seem to be moving in the same direction21-23. As a consequence the recommendations for sports people also show more and more similarities21-23.

Genetic variability

Researchers have suggested that the impact of caffeine consumption on performance may differ between individuals, possibly mediated by polymorphisms within two genes, CYP1A2 and ADORA2A, as well as environmental factors. A clearer understanding of the factors underpinning inter-individual variation may facilitate customisation of caffeine ingestion guidelines, specific to an individual’s biology, history, and competitive situation43.

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