When it comes to fitness and sports performance, energy is key. Caffeine is largely becoming one of the most widely used central nervous system (CNS) stimulants in the world, as it may offer numerous pharmacological and physiological effects.1 According to the Institute of Medicine’s (IOM) book, “Caffeine for the Sustainment of Mental Task Performance: Formulations for Military Operations,” nearly 99% of caffeine is absorbed from the gastrointestinal (GI) tract within 45 minutes. Following absorption, caffeine is distributed throughout the body.
Once in the bloodstream, caffeine exerts numerous effects in the body, most notably, its ability to bind to adenosine receptors. Adenosine is a molecule involved in the biochemical pathways for energy transfer and signaling. It works like a depressant, slowing the body and making it drowsy. The IOM book noted caffeine is structurally similar to adenosine and thus binds in its place, blocking adenosine’s actions to signal relaxation and act as a depressant. Caffeine has also been shown to enhance the effects of natural stimulants such as norepinephrine,2 glutamate3 and dopamine.4
Caffeine is becoming a common substance in the diets of athletes and active consumers, appearing in energy drinks, sport bars and sport gels. While caffeine does not directly produce energy, it exerts other effects that may enhance exercise performance.
The energy for all activity in the body, including muscular activity, comes from the breakdown of sugar and fats, as well as stores of energy such as adenosine triphosphate (ATP) in the muscles themselves. ATP is an energy storage molecule that serves as the energy currency within the body. The hydrolysis of ATP provides energy to numerous body processes. In the context of sports performance, ATP is required for proper muscle contraction. As ATP is used up during exercise, it must be replaced by one of the various processes capable of producing ATP in the body.
One important mechanism for ATP synthesis is beta oxidation—the mobilization of fatty acids to create ATP within the body. Caffeine has shown promise in enhancing adipose tissue lipolysis, which results in free fatty acids (FFAs) being taken up and oxidized by contracting muscle. This increase in fatty acid oxidation spares muscle glycogen stores and may prolong work time to exhaustion (TTE).5 However, increased endurance performance with low doses of caffeine eliciting none of these metabolic changes6 suggests the ergogenic effect of caffeine may be mediated through the CNS and peripheral nervous system (PNS).
One study demonstrated caffeine’s antagonistic effect on adenosine receptors may be the most probable mechanism of action leading to enhanced athletic performance.7 Another study that injected caffeine directly into the brains of rodents linked caffeine to an ergogenic effect on running performance.8 The mechanisms of increased performance may be attributed to an increased central drive in the CNS as well as a decreased perception of effort and pain in the PNS, both of which may contribute to improved athletic performance.9
Editor’s Note: This article was excerpted from a longer piece. Click the following link to “Breakthroughs in sports nutrition RTD beverages" to access the digital magazine with this and additional content.
Madison Dorn specializes in the creation and management of content, with particular passion for the health/nutrition and fitness industries. In her free time, she enjoys working out and is a CrossFit Level One certified coach.
1 Cappelletti S et al. “Caffeine: Cognitive and Physical Performance Enhancer or Psychoactive Drug?” Curr Neuropharmacol. 2015;13(1):71-88.
2 Papadelis et al. “Effects of mental workload and caffeine on catecholamines and blood pressure compared to performance variations.” Brain Cogn. 2003;51(1):143-154.
3 John J et al. “Caffeine promotes glutamate and histamine release in the posterior hypothalamus.” Am J Physiol Regul Integr Comp Physiol. 2014;307(6):R701-R710.
4 Volkow N et al. “Caffeine increases striatal dopamine D2/D3 receptor availability in the human brain.” Transl Psychiatry. 2015;5(4):e549.
5 Costill D et al. “Effects of caffeine ingestion on metabolism and exercise performance.” Med Sci Sports. 1978;10(3):155-158.
6 Graham T and Spriet L. “Performance and metabolic responses to a high caffeine dose during prolonged exercise.” J Appl Physiol. 1991;71(6):2292-2298.
7 Fredholm B. “Adenosine, Adenosine Receptors and the Actions of Caffeine.” Pharmacol Toxicol. 1995;76(3):93-101.
8 Davis J et al. “Central nervous system effects of caffeine and adenosine on fatigue.” Am J Physiol Regul Integr Comp Physiol. 2003;284(2):R399-404.
9 Bowtell J et al. “Improved Exercise Tolerance with Caffeine Is Associated with Modulation of both Peripheral and Central Neural Processes in Human Participants.” Front Nutr. 2018;12(5):6.