Caffeine acts through multiple mechanisms by acting on receptors and channels in the cell membrane as well as acting on calcium and cyclic AMP pathways. The principal mode of action is as an agonist at adenosine receptors in the brain as its structure is similar to adenosine. This results increased activity of dopamine. Caffeine also increases release of acetylcholine in the prefrontal nucleus resulting in increased wakefulness and locomotor activity. Caffeine also increases levels of epinephrine and adrenaline as well as levels of serotonin, resulting n positive changes in mood.
Caffeine is a competitive inhibitor of cAMP-phosphodiesterase thus resulting in an increase in cAMP in cells. Thus caffeine intensifies and prolongs the effect of epinephrine. This also increases activation of protein kinase A which is important in glucose syntheses.
Metabolites of caffeine contribute to caffeine’s effects. Theobromine is a vasodilator and increases oxygen and nutrient flow to the brain and to the muscles. Theophylline acts as a smooth muscle relaxant and acts to relax the bronchioles and is a chronotrope and inotrope affecting an increase in heart rate and efficiency. The third metabolite, paraxanthine, increases lipolysis which releases glycerol and fatty acids into the blood to be used as a fuel by muscles.
So in plain words what this means for the athlete is that caffeine in moderate amounts improves alertness, and increases the use of fat as fuel. At the same time, caffeine opens the bronchioles and improves cardiac efficiency. Caffeine use can thus spare glycogen which is the principal fuel for muscles. This means that exercise can be prolonged as glycogen is the principal fuel for muscles. In fact, caffeine has been shown to decrease glycogen utilization by as much as 50%. Thus more glycogen is available at the later stages of exercise. Subjects of experimental studies were able to exercise longer before exhaustion would occur by enhancing the use of fat as fuel and preserving glycogen. The critical period when glycogen sparing occurs is during the first 15 minutes of exercise. Pre-race caffeine may thus be beneficial in a longer a race.
There is some controversy surrounding the lifted ban since caffeine does have some ergogenic properties but it can also be dangerous if abused. Back to running the marathon: caffeine can help you run it faster, but only if done correctly, so let’s talk about who can benefit from caffeine and how it can be properly used.
Notes to consider:
Caffeine is often mistakenly classified as a diuretic. Diuresis (elimination of water from the body) can complicate an individual’s water balance, which determines how efficient he/she will perform by decreasing stroke volume and the amount of blood delivered with each heart beat. However, research performed on trained athletes has NOT FOUND caffeine to cause a diuretic effect. See Diuretic Effects of Caffeine for more details.