Caffeine and Physical Performance

Caffeine is the most widely consumed psychoactive substance in the world and occurs naturally in dozens of plant species, including coffee, tea, and cocoa. Caffeine and its health effects have been a topic of study for a long time and continue to be a dietary compound of public health concern, as indicated by extensive research. At the same time, caffeine has become ubiquitous in the sports world, where there is great interest in better understanding the impact of caffeine on exercise performance.

Although the action of caffeine on the central nervous system (CNS) is widely accepted as the main mechanism by which caffeine alters performance, several mechanisms have been proposed to explain caffeine's ergogenic effects, including increased availability of myofibrillar calcium, optimized exercise metabolism and substrate availability, as well as CNS stimulation. 

Caffeine also appears to have some direct effects on muscle that may contribute to its ergogenicity. The most likely pathway by which caffeine may benefit muscle contraction is through the mobilization of calcium ions (Ca2+), which facilitates force production by each motor unit. Fatigue caused by the gradual reduction of Ca2+ release after exercise may be mitigated following caffeine ingestion. Similarly, caffeine may function, in part, peripherally by increasing sodium/potassium pump (Na+/K+) activity to potentially enhance the excitation-contraction coupling necessary for muscle contraction.

Caffeine seems to exert its effects at various sites in the body, but the most robust evidence suggests that the primary target is the CNS, which is now widely accepted as the main mechanism by which caffeine alters mental and physical performance. Caffeine is believed to exert its effects on the CNS through the antagonism of adenosine receptors, leading to increases in neurotransmitter release, motor unit firing rates, and pain suppression.

Adenosine is involved in numerous processes and pathways and plays a crucial role as a homeostatic regulator and neuromodulator in the nervous system. The main known effects of adenosine are to decrease the concentration of CNS neurotransmitters, including serotonin, dopamine, acetylcholine, norepinephrine, and glutamate. Caffeine, which has a molecular structure similar to adenosine, binds to adenosine receptors upon ingestion and thus increases the concentration of these neurotransmitters. This results in positive effects on mood, alertness, focus, and wakefulness in most, but not all individuals.

Upon critical evaluation of the available literature to date, the position of the International Society of Sports Nutrition (ISSN) regarding caffeine intake is the following:

1. Caffeine supplementation has been shown to improve various aspects of exercise performance in many, but not all studies. The small to moderate benefits of caffeine use include, but are not limited to: muscular endurance, movement speed, muscular strength, running, jumping, and throwing performance, as well as a wide range of sport-specific aerobic and anaerobic actions.
2. Aerobic endurance seems to be the form of exercise with the most consistent moderate to large benefit from caffeine use, although the magnitude of its effects differs among individuals.
3. Caffeine has been consistently shown to enhance exercise performance when consumed in doses of 3 to 6 mg/kg of body mass. Very high doses of caffeine (e.g., 9 mg/kg) are associated with a high incidence of side effects and do not appear to be necessary to elicit an ergogenic effect.
4. The most commonly used timing for caffeine supplementation is 60 minutes before exercise. The ideal timing for caffeine intake likely depends on the source of caffeine. For example, compared to caffeine capsules, caffeine gums may require a shorter waiting time from consumption to the start of exercise.
5. Caffeine seems to enhance physical performance in both trained and untrained individuals.
6. Interindividual differences in performance in sports and exercise, as well as adverse effects on sleep or feelings of anxiety following caffeine intake, may be attributed to genetic variation associated with caffeine metabolism and physical and psychological response. Other factors, such as habitual caffeine intake, may also play a role in the variation of response among individuals.
7. Caffeine has been shown to be ergogenic for cognitive function, including attention and vigilance, in most individuals.
8. Caffeine may improve cognitive and physical performance in some individuals under sleep deprivation conditions.
9. The use of caffeine combined with resistance exercise in heat and at altitude is well-supported when dosages vary from 3 to 6 mg/kg and 4 to 6 mg/kg, respectively.
10. Alternative sources of caffeine, such as caffeine gum, energy gels, and chews, have been shown to enhance performance, especially in aerobic exercise.
11. Energy drinks and pre-workout supplements containing caffeine have been shown to improve anaerobic and aerobic performance.

In summary, caffeine supplementation has been shown to improve many aspects of exercise, including prolonged aerobic activities and high-intensity, short-duration exercises. Caffeine at recommended doses does not appear to significantly affect hydration. Individuals should also be aware of the side effects associated with caffeine intake, such as sleep disturbances and anxiety, which are generally linearly dependent on the dose.

Reference: Guest NS, VanDusseldorp TA, Nelson MT, Grgic J, Schoenfeld BJ, Jenkins NDM, Arent SM, Antonio J, Stout JR, Trexler ET, Smith-Ryan AE, Goldstein ER, Kalman DS, Campbell BI. International society of sports nutrition position stand: caffeine and exercise performance. J Int Soc Sports Nutr. 2021 Jan 2;18(1):1. doi: 10.1186/s12970-020-00383-4. PMID: 33388079; PMCID: PMC7777221.