When it comes to fitness and sports performance, energy is key. Caffeine is becoming primarily one of the most widely used central nervous system (CNS) stimulants in the world, as it can offer numerous pharmacological and physiological effects.1 According to the Institute of Medicine (IOM) book, “Caffeine for Maintaining Mental Duty: Formulations for Military Operations,” almost 99% of caffeine is absorbed from the gastrointestinal tract (GI) within 45 minutes. After absorption, caffeine is distributed throughout the body.
Once it has entered the bloodstream, caffeine exerts numerous effects on the body, most notably its ability to bind to adenosine receptors. Adenosine is a molecule involved in biochemical pathways for energy transfer and signaling. It works like a depressant, slowing down the body and making it drowsy. The IOM book noted that caffeine is structurally similar to adenosine and thus binds in place, blocking the actions of adenosine to signal relaxation and act as a depression. Caffeine has also been shown to increase 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, sports bars and sports gels. While caffeine does not directly produce energy, it exerts other effects that can enhance exercise performance.
Energy for all activity in the body, including muscle activity, comes from the breakdown of sugar and fats, as well as from energy reserves such as adenosine triphosphate (ATP) in the muscles themselves. ATP is an energy storage molecule that serves as an energy coin within the body. ATP hydrolysis provides energy for many body processes. In the context of athletic performance, ATP is required for proper muscle contraction. Since ATP is used during exercise, it must be replaced by one of the various processes capable of producing ATP in the body.
An important mechanism for the synthesis of ATP is beta oxidation – the mobilization of fatty acids to create ATP within the body. Caffeine has shown promise in increasing adipose tissue lipolysis, which results in the uptake and oxidation of free fatty acids (FFAs) by contracting muscle. This increase in fatty acid oxidation saves muscle glycogen stores and can extend working time to exhaustion (TTE).5 However, increasing endurance performance with low doses of caffeine that do not cause any of these metabolic changes6 suggests that the ergogenic effect of caffeine may be mediated through the CNS and peripheral nervous system (PNS).
One study showed the antagonistic effect of caffeine on adenosine receptors may be the most likely mechanism of action leading to increased athletic performance.7 Another study that injected caffeine directly into rodent brains linked caffeine to an ergogenic effect on running performance.8 Performance enhancement mechanisms can be attributed to an increase in central stimulus in the CNS, as well as a reduced perception of effort and pain in the PNS, both of which can contribute to improved athletic performance.9
Editor’s note: This article is taken from a longer section. Click the link below for “Advances in Sports Food Drinks” to access the digital magazine with this and additional content.
Madison Dorn specializes in content creation and management, with a particular passion for the health / nutrition and fitness industries. In her spare time, she enjoys working out and is a certified CrossFit Level One trainer.
1 Cappelletti S et al. “Caffeine: Cognitive and Physical Performance Enhancer or Psychoactive Drugs?” Curr Neuropharmacol. 2015; 13 (1): 71-88.
2 Papadelis et al. “Effects of mental load and caffeine on catecholamines and blood pressure compared to performance variations.” Cognition of the brain. 2003; 51 (1): 143-154.
3 John J et al. “Caffeine stimulates the release of glutamate and histamine in the posterior hypothalamus.” Am J Physiol Regul Integr Comp Fiziol. 2014; 307 (6): R701-R710.
4 Volkow N et al. “Caffeine increases the availability of striatal D2 / D3 dopamine receptors in the human brain.” Psychiatry Transl. 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 dose of caffeine during prolonged exercise.” J Appl Physiology. 1991; 71 (6): 2292-2298.
7 Fredholm B. “Adenosine, adenosine receptors and caffeine actions.” Pharmacol ToxicolMe 1995; 76 (3): 93-101.
8 Davis J et al. “Effects of the central nervous system on caffeine and adenosine on fatigue.” Am J Physiol Regul Integr Comp Fiziol. 2003; 284 (2): R399-404.
9 Bowtell J et al. “Improving exercise tolerance with caffeine is associated with modulation of peripheral and central nervous processes in human participants.” Front Nutr. 2018; 12 (5): 6.