Caffeine as an ergogenic aid

Logistically speaking, caffeine is likely the most easily accessible, and most prevalent, ergogenic aid for recreational consumption. Caffeine is a stimulant that itself is non-caloric, and provides no energy in the form of carbohydrate, fat, or protein. Thus, its energetic effects are not derived from the caffeine molecule itself, but are a result of the processes the presence of caffeine generates. The most regarded physiological mechanism by which caffeine enhances one's performance is its ability to block, or inhibit the action of adenosine. (Ferré, Sergi.) Adenosine is a byproduct of ATP utilization that builds up during exercise. Adenosine has receptor sites in the brain that, when bound to adenosine, downregulate one's production of excitatory and stimulating neurotransmitters. As adenosine receptor saturation increases, one will have greater perception of fatigue, and desire to sleep. Under normal conditions adenosine will progressively saturate the adenosine receptor throughout the course of the day. During sleep, the adenosine molecules that are bound to the adenosine receptors will be recycled for other physiological functions, such as the regeneration of ATP. Caffeine also has the ability to bind to an adenosine receptor, but it does not produce any action. In essence, Caffeine inhibits adenosine from binding to the adenosine receptor, thus terminating the progresive development of fatigue. Due to the limited number of receptor sights, caffeine will bind to the available adenosine receptors and block the adenosine molecule from binding and promoting drowsiness and fatigue. One caveat to the process of adenosine inhibition is that adenosine production does not come to a standstill. One will continue to create adenosine as a byproduct of ATP utilization, however the adenosine molecule is unable to bind to its receptor to downregulate one's nervous system. Consequently, unbound adenosine levels accumulate during the period of time caffeine is inhibiting the adenosine receptor, and as caffeine metabolizes there is a high concentration of unbound adenosine molecules that have accumulated in the presence of caffeine. Additionally, caffeine will increase the secretion of catecholamines, most notably adrenaline. Catecholamines are hormones that serve a plethora of effects on our body, the predominant effect being an increased tolerance to pain, an increased awareness, and a priming effect on one's muscular system. We naturally secrete catecholamines in response to pain, and they play a pivotal role in decreasing one's perception of pain and fatigue during exercise. Furthermore, an increase in catecholamine stimulates a multitude of processes that prime one for a physical exertion. For example, catecholamines can bind to cell receptors that stimulate the release of calcium located inside the cell. Calcium subsequently binds to a receptor named Troponin C, which consequently alters the potential of a cell to allow for a muscle to shorten. (Guest, Nanci S., Kuo, Ivana Y) Furthermore, caffeine increases our fuel availability in the form of fatty acids, and glucose in our blood stream. (Institute of Medicine (US) Committee on Military Nutrition Research.) As mentioned, catecholamines upregulate a series of processes that prime an individual for a physical exertion. Catecholamines bind to receptor sites on adipose tissue and stimulate the release of fatty acids from adipose tissue to be mobilized, or released, into the bloodstream to make it readily available to the cell to create ATP. When fatty acids are available in unison with glucose, fatty acids can be used simultaneously alongside the available glucose for ATP production. Inevitably allowing for a certain degree of glucose preservation due to a reduced need to rely primarily on glucose for energy production during aerobic respiration. Due to the relative low intensity of endurance sports, athletes have available oxygen to undergo aerobic respiration. When energy needs increase to a level that surpasses our capacity to supply oxygen, we begin to metabolize glucose in order to fuel source anaerobic cellular respiration. Due to the duration of an endurance event, an athlete will typically have enough oxygen available to maintain a state of aerobic respiration. Anaerobic respiration allows an athlete to metabolize either carbohydrates or fatty acids to provide the energy needed for cellular respiration. Conversely, at the end of a race, in which an athlete would typically begin to sprint, an athlete loses the ability to consume enough oxygen to keep them in a state of aerobic respiration, inducing hypoxia, requiring cells to undergo anaerobic respiration. Glucose is the required fuel source for anaerobic respiration, and fatty acids cannot be used to fuel cellular respiration without the presence of oxygen. Caffeine is advantageous due to its ability to allow fatty acid metabolism during the earlier, aerobic, components of the race, thus allowing for the preservation of the glucose required for anaerobic respiration in the later components of an event.