Caffeine

Overview: 

Caffeine is a naturally occurring compound found primarily in coffee beans, but has been extracted from certain teas or beans. It is a mild central nervous system stimulant meaning it can alleviate fatigue and drowsiness, making it useful in daily life and is the most used stimulant compound in the world. It is regarded as safe in doses that do not exceed 400 mg per day by the FDA, but this also depends on each individual's weight. In recent years, caffeine has been even more widely used as an exercise enhancing supplement, with substantial research to support it.

Simple: 

Caffeine is a stimulant that acts on the central nervous system creating a wide range of positive effects on performance, including one-repetition maxes, isometric and isokinetic strength, muscular endurance, power, velocity, throwing, jumping, and sprinting. It has been shown that safe doses range from 3-6 mg/kg of body-weight and most resistance training bodybuilders would get a moderate-large effect in that range. Looking at the center of that range (4.5mg/kg), that equated to a 180lb person ingesting ~367mg of caffeine. Convert your body-weight from lbs to kg, and then multiply by your decided ratio of mg/kg to find your optimal dose. This range also minimizes side effects that are apparent in high doses, that affect sleep cycles, and induce heart palpitations and irregular heart rate. It seems habitual use may not highly affect the positive effects of this compound, but more research is needed to fully determine the effect of habitual use of caffeine on performance.

Complex:

Caffeine is a widely used psychoactive stimulant that has an interesting mechanism of action. Instead of it actually making you more “energized,” it may make you feel that way because it conversely keeps you from feeling the effects of tiredness or fatigue [1]. This is because it has the ability to cross the blood brain barrier, and block what's called the adenosine receptors, or the regulatory receptors for sleep cycles. By blocking these, it effectively blocks any normal adenosine (sleep) molecules from binding to these slots, which would typically make you feel the effects of tiredness as molecules of adenosine build up in the brain over the course of the day. As this blocking effect wears off however and caffeine levels are depleted, this could allow for the dreaded “crash,” if you were already very “tired” before, as all the adenosine is now built up and ready to bind at the same time.

Now let's go into some literature going over why this matters to a common athlete or bodybuilder. In a full review in sports medicine, it indicates that caffeine not only reverses fatigue, but it has ergogenic (enhanced physical performance) effects on the body and skeletal muscle. Through extensive research it has been found to positively impact one-repetition maxes, isometric and isokinetic strength, muscular endurance, power in resistance training, and velocity. Some evidence from this review points to the ability of caffeine to enhance the adaptations of strength training increasing gains in strength. Although this is true, habitual use, or becoming tolerant to caffeine's effects modulates caffeine's effects on resistance training, leading to less of a benefit in the described areas. In addition, jumping and throwing, and sprinting were also reported to be benefitted by caffeine intake by a significant amount. Caffeine seems to have moderate-large benefits in aerobic endurance (resistance training and shorter bouts of exercise) comparatively to longer endurance bouts. This study indicates that minimal effects are seen at 2 mg/kg of bodyweight of caffeine, but 3-6 mg/kg seem to be the sweet spot, decreasing incidence of side effects which are apparent at doses up to 9 mg/kg. The review also demonstrates that optimal timing of caffeine before exercise is around 60 minutes beforehand, but the type of caffeine source may affect this. For example, the use of caffeine chewing gum may increase the rate of absorption compared to the ingestion of caffeine through energy drinks or powders/capsules [2].

An important side effect of caffeine is a developed tolerance to this compound. A study in 2020 explored the effect of caffeine on low caffeine users, and moderate to high caffeine users, particularly how habitual use affects resistance training. The study evaluated low caffeine and high caffeine subjects on the following criteria: movement velocity, power, and muscular endurance via the bench press. Contrary to some previous notions, in this specific study, they found no ergogenic difference in the exercises performed, possibly indicating that caffeine may not be affected by habitual use, although more research is needed, as there is still some conflicting data on this area of study [3]. 

Side effects are also common with ingestion of high doses of caffeine. The most prevalent was tachycardia/heart palpitations and negative effects of sleep onset with athletes using doses exceeding the recommended limit. This study shows that these side effects can occur both after exercise, but also at least 24 hours after ingestion with caffeine's long half-life being 4-6 hours. This study supports previous studies, suggesting 3 mg/kg of bodyweight may be the safest dose, while providing a high ergogenic effect [4].

1. Evans J, Richards JR, Battisti AS. Caffeine. 2024 May 29. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan–. PMID: 30137774.
2. 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.
3. Grgic, J. and Mikulic, P. (2021), Acute effects of caffeine supplementation on resistance exercise, jumping, and Wingate performance: no influence of habitual caffeine intake. European Journal of Sport Science, 21: 1165-1175. https://doi.org/10.1080/17461391.2020.1817155
4. de Souza, J.G., Del Coso, J., Fonseca, F.d. et al. Risk or benefit? Side effects of caffeine supplementation in sport: a systematic review. Eur J Nutr 61, 3823–3834 (2022). https://doi.org/10.1007/s00394-022-02874-3