Caffeine is the most consumed stimulant, which is socially acceptable in the world, with approximately 90% of the adult population consuming caffeine each day. It is rapidly absorbed through the gastoinestinal tract into the bloodstream, reaching peak concentrations in approximately one hour. Caffeine works in the central and peripheral nervous systems as it is a potent antagonist of adenosine receptors, which means it blocks their function. This allows there to be a release of excitatory neurotransmitters, which can be the cause of the behavioral effects induced by caffeine.
Caffeine has been shown to have positive influences on various physiological systems in the human body. The most well known effects are how it can affect a person’s alertness and cognition. The most likely reason the majority of people consume caffeine, generally as coffee or tea, is because it increased feelings of alertness, ability to concentrate, and mental energy. And people are well-served to believe this, as studies have shown caffeine to act as a central nervous system stimulant.
Studies have demonstrated that in individuals who are well rested, doses of 30-300mg of caffeine can improve vigilance and reaction times. Also, if a person is a habitual consumer of coffee, studies show that they perform better on tests of cognitive performance, “such as reaction time and visuo-spatial reasoning.” These proposed effects of increased mental alertness, vigilance, and improved reaction times are parameters that are appealing to athletes to help improve their performance.
There have been studies demonstrating the performance-enhancing effects of caffeine over a variety of types of physical activities. The International Society of Sports Nutrition has taken a position stand on this statement: “Caffeine is effective for enhancing sport performance in trained athletes when consumed in low-to-moderate dosages (~3-6 mg/kg) and overall does not result in further enhancement in performance when consumed in higher dosages (≥ 9 mg/kg).” However, this is where the discussion becomes more controversial. This is because there is not a consensus of how caffeine can cause there to be an increase in athletic performance and there are many studies with conflicting data.
The most stated reason as to why caffeine can cause in increase in athletic performance is because it is an ergogenic aid; meaning that it is a substance that can help to enhance energy production. Caffeine can act in a way in which it can initially spare the use of glycogen in the body. Glycogen is a primary way our bodies store sugar and it acts as the principle fuel that our muscles use to work. A secondary source of fuel our bodies can utilize is our body fat. Caffeine is believed to work by mobilizing body fat to be broken down into fuel, so that muscles will use this fuel first before they start to use their glycogen stores. This will then cause a delay in the body using its glycogen stores and the thought is this will help prolong the time a person can exercise. This is the reasoning behind why “caffeine is ergogenic for sustained maximal endurance exercise, and has been shown to be highly effective for time-trial performance.” In other words, caffeine may be beneficial to the endurance athlete as it can help to provide an athlete with fuel for their muscles to a greater period of time.
Apart for the way our body may change the way it utilizes fuel, there may also be other effects of caffeine to improve athletic performance. A study has demonstrated that there is an increase in contractile force of the muscles when an athlete is at sub-maximal exertion. This is due to enhanced function at the molecular level that causes an increase in calcium that is available to the muscle cells to induce their contraction. Another study demonstrated an almost 2-fold increase in the amount of endorphin concentrations in the blood when caffeine was ingested before exercise. Endorphins can improve athletic performance by decreasing the perception of pain and to promote euphoria, sometimes this is referred to as the ‘runner’s high.’ Although this can happen in individuals who do not use caffeine, when caffeine is used it can cause these effects to occur earlier in the activity by lowering the threshold required for the endorphin release.
The data has shown that caffeine use before endurance athletics may have a beneficial effect, its effect on strength-power performance or anaerobic activities (sprinting) are more unknown. There have been many conflicting studies in this area and there is no consensus agreement on caffeine’s effect in this area of athletic performance.
Chase King, MS-IV
David Carfagno, D.O., C.A.Q.S.M.
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