Caffeine forms the base of the fitfam food pyramid. It is also the blood type of all Instahuns (myself included). The great Irish philosopher Rob Lipsett once said: “that’s what happens before you take pre-workout before a game”. But what did the Lipman mean by this iconic statement? This article will run through the basics of caffeine and its role in sports and exercise nutrition.

Caffeine: Who Is She?

Caffeine is the most widely consumed central nervous system (CNS) stimulant and psychoactive drug[1]. It is found in varying amounts in coffee, pre-workouts, energy drinks and certain soft drinks. Caffeine acts to enhance motor activity by interacting with adenosine receptors. Adenosine is produced from adenosine triphosphate (ATP, the “energy currency” of the cell) and has multiple functions in the body. Within the CNS, adenosine is involved in transporting signals from the brain to the rest of the body (neurotransmitter release) and is also involved in opening up blood vessels (vasodilation)[2]Adenosine is a sedative and promotes relaxation. By interfering with adenosine receptors, caffeine can act as an “adenosine antagonist”, increasing alertness[3].

Caffeine is highly soluble in fat, which allows it to rapidly cross the blood-brain barrier[1]. In addition, it is also water-soluble and is efficiently absorbed through the gastro-intestinal tract. This allows it to rapidly exert its effects on the body.

An instant coffee typically contains 80mg caffeine, as does a Red Bull.

Caffeine & Sports Performance

Caffeine is widely accepted as an effective ergogenic aid(performance enhancer). We are going to run through a few of the common effects of caffeine on performance.

Increased Alertness/Cognitive Performance

Caffeine is shown to acutely increase neuronal efficiency in the brain, even at low doses[4]. As we discussed earlier, caffeine can act to “reverse” the sedative effects of adenosine. This can promote feelings of wakefulness.

One study found a positive increase in cognitive performance from a dose as little as 12.5mg[5]. Recall from earlier that this is a fraction of the amount in coffee! Participants, regardless of habitual caffeine intake, improved their reaction time and information processing skills when a dose of caffeine was taken. Another study found that caffeine intake significantly lowered feelings of sedation and increased feelings of stimulation[6]. However, in this study, high doses of caffeine (450mg) reduced performance on memory tasks. This is potentially due to an “overstimulation effect”. This will be discussed further in the “dosage” section.

It is obviously a positive for the athlete to be alert and mentally functioning.

Fatigue Reduction

Caffeine is associated with a reduction in fatigue (potentially by interfering with those damn adenosine receptors again). This is widely accepted in literature, particularly in the context of endurance exercise.

A systematic review of caffeine intake and endurance performance found a positive association between caffeine intake and endurance times[7]. However, it must be noted there was huge variability in this exact impact. This is potentially due to a number of factors, including dose, body mass and timing of caffeine. One study found that caffeine improved aerobic endurance amongst soccer players, regardless of their usual intake[8]. Similarly, Cox et al[9], demonstrated an increased time to fatigue amongst endurance cyclists.

For resistance training, the literature is far less conclusive. Fatigue in resistance training tends to be measured in reps to failure. Some studies noted caffeine led to an increase in reps to failure[10]. Others found this effect was only seen in later sets[11].

Increased Aerobic Capacity

By delaying time to fatigue, caffeine is also associated with an increase in aerobic capacity.

Caffeine may also act to improve aerobic capacity by increasing the availability of free fatty acids[12]. You may recall from your PT course that fatty acids are a key energy source during endurance/aerobic activities. It must be noted that increasing the availability of fatty acids does not mean that you simply have to neck a Monster, sit on your arse and let science do the rest. You still need to do the work unfortunately. Making an energy source more available is great, but you still need to use the energy!

Literature has shown a positive correlation between improvements in VO2 max (how aerobic capacity is measured) and ingestion of a caffeinated beverage prior to training[13]. This is well-supported in literature[14].

The benefits of caffeine on anaerobic capacity are far less pronounced[14].

Increased Power Output

The direct effects of caffeine on power output are unclear. Older studies found caffeine to have no effect on the individuals’ power output during short-term exercise[15]. We must note that this study only sampled nine individuals, so we shouldn’t immediately take this as gospel. More recent studies, such as this 2019 study by Wilk et al[16] showed similar findings. Caffeine consumption prior to bench pressing did not significantly affect power output.

In contrast, one 2019 study concluded caffeine improved power output in several upper and lower body exercises[17]. A 2018 meta-analysis concluded caffeine had a significant ergogenic effect on muscle power and strength[18]. However, the authors do note that the evidence is limited in the field. Furthermore, as we will discuss in a later section, individual response to caffeine can differ hugely.

I would therefore say caffeine has a potential for increasing power input, but it requires further investigation.

Increased Training Volume/Capacity for Work

It is hypothesised that caffeine can lead to increased training volume and capacity for work. As we discussed in previous sections, caffeine has been shown to delay sympathetic responses. By delaying time to fatigue, and increasing alertness, it makes sense that caffeine consumption allows the athlete to carry out more work before feeling tired.

Considerations: Dose, Tolerance & Timing

It’s not all marathons and mental alertness, I’m afraid.

There are huge inter-individual differences in response to caffeine. As we discussed in an earlier section, caffeine is water and lipid soluble, which means it is rapidly absorbed and ready for use.

Caffeine is typically absorbed completely within 45 minutes of ingestion. For this reason, it is typically recommended to consume it 45 minutes prior to the event[19].

Depending on the method by which it is consumed, the time to impact may also vary. When caffeine in ingested in liquid form it is absorbed from the GI tract and distributed via water. Faster absorption occurs through caffeinated-gum, as it allows absorption through the oral mucosa[19].

European guidelines currently recommend a daily intake of less than 400mg[20]. This is not a blanket recommendation, and intake varies with cardiovascular conditions etc.

Caffeine “tolerance” is also well-documented in literature[5], whereby habitual intake dulls the effects of caffeine ingestion. Caffeine tolerance depends on genetics, body mass and habitual intake, amongst many other factors. Furthermore, a higher caffeine intake does not directly correlate with improved performance. Excessive consumption may lead to anxiety, insomnia, heart conditions and several other health complications. Therefore, caffeine intake must be carefully monitored in athletes.

We must also note that the majority of studies I referenced throughout this post only included trained men in their population. Females differ hugely in their makeup, hormonal levels and typical body mass. Each study also varied in its caffeine ingestion protocol, dose and timing.


In conclusion, the Lipman leaves us with more questions than answers. What happens when you take pre-workout before a game largely depends on the individual. In general, caffeine may:

  • Delay time to fatigue
  • Increase aerobic capacity
  • Increase overall training volume
  • Improve cognitive performance
  • Increase alertness

However, we must also note that these responses vary hugely between individuals, and therefore the case for individual caffeine intake is likely to be more beneficial than a blanket recommendation.


  1. Nehlig, A., Daval, J.L. (1992) ‘Caffeine and the central nervous system: Mechanisms of action, biochemical, metabolic and psychostimulant effects’, Brain Research Reviews. Available at:
  2. Sheth, S., Brito, R., Mukherjea, D., Rybak, L.P., Ramkumar, V. (2014) ‘Adenosine Receptors: Expression, Function and Regulation’, International Journal of Molecular Sciences. Available at:
  3.  Fisone, G., Borgkvist, A., Usiello, A. (2004) ‘Caffeine as a psychomotor stimulant: mechanism of action’, Cellular and Molecular Life Sciences. Available at:
  4.  Bendlin, B.B., Trouard, T.P., Ryan, L. (2007) ‘Caffeine attenuates practice effects in word stem completion as measured by fMRI BOLD signal’, Human Brain Mapping. Available at
  5. Smit, H.J., Rogers, P.J. (2000) ‘Effects of low dose of caffeine on cognitive performance, mood and thirst in low and higher caffeine consumers’, Psychopharmacology. Available at:
  6. Childs, E., de Wit, H. (2006) ‘Subjective, behavioural, and physiological effects of acute caffein in light, nondependent caffeine users’, Psychopharmacology. Available at:
  7. Ganio, M.S., Klau, J.F., Casa, D., Armstrong, L. (2008) ‘Effect of Caffeine on Sport-Specific Endurance Performance: A Systematic Review’, The Journal of Strength and Conditioning Research. Available at:
  8. Apostolidis, A., Mougios, V., Smilios, I., Rodosthenous, J,., Hadjicharalambous, M. (2019) ‘Caffeine Supplementation: Ergogenic in Both High and Low Caffeine Responders’, International Journal of Sports & Physiology Performance. Available at:
  9. Cox, G.R., Desbrow, B., Montgomery, P.G., Anderson, M.E., Bruce, C.R., Macrides, T.A., Martin, D.T., Moquin, A., Roberts, A., Hawley, J.A., Burke, L.M. (1985) ‘Effect of different protocols of caffeine intake on metabolism and endurance performance’, Journal of Applied Physiology. Available at:
  10. Da Silva, V.L., Messias, F.R., Zanchi, N.E., Gerlinger-Romero, F., Duncan, M.J., Gumaraes-Ferreira, L. (2015) ‘Effects of acute caffeine ingestion on resistance training performance and perceptual responses during repeated sets to failure’, Journal of Sports Medicine and Physical Fitness. Available at:
  11. Green, J.M., Wickwire, P.J., McLester, J.R., Gendle, S., Hudson, G., Pritchett, R.C., Laurent, C.M. (2007) ‘Effects of caffeine on repetitions to failure and ratings of perceived exertion during resistance training’, International Journal of Sports Physiology & Performance. Available at:,in%20a%20resistance%2Dtraining%20session.
  12. Acheson, K.J., Gremaud, G., Meirim, I., Montigon, F., Krebs, Y., Fay, L.B., Gay, L.J., Schneiter, P., Schindler, C., Tappy, L. (2004) ‘Metabolic effects of caffeine in humans: lipid oxidation or futile cycling?’, American Journal of Clinical Nutrition. Available at:
  13.  Smith, A.E., Fukuda, D.H., Kendall, K.L., Stout, J.R. (2010) ‘The effects of a pre-workout supplement containing caffeine, creatine and amino acids during three weeks of high-intensity exercises on aerobic and anaerobic performance’, Journal of the International Society of Sports Nutrition. Available at:
  14. Mielgo-Ayuso, J., Marques-Jiménez, D., Refoyo, I., Del Coso, J., León-Guereno, P., Calleja-González, J. (2019) ‘Effect of caffeine supplementation on sports performance based on differences between sexes: a systematic review’, Nutrients. Available at:
  15. Williams, J.H., Signorile, J.F., Barnes, W.S., Henrich, T.W. (1988) ‘Caffeine, Maximal Power Output and Fatigue’, British Journal of Sports Medicine. Available at:
  16.  Wilk, M., Filip, A., Krzysztofik, M., Maszczyck, A., Zajac, A. (2019) ‘The Acute Effect of Various Doses of Caffeine on Power Output and Velocity during the Bench Press Exercise among Athletes Habitually Using Caffeine’, Nutrients. Available at:
  17. Degrange, T.D., Jackson, W.A., Williams, T.D., Rogers, R.R., Marshall, M.R., Ballmann, C.G. (2019) ‘Acute Caffeine Ingestion Increases Velocity and Power in Upper and Lower Body Free-Weight Resistance Exercises’, International Journal of Exercise Science. Available at:
  18. Grgic, J., Trexler, E.T., Lazinica, B., Pedisic, Z. (2018) ‘Effects of caffeine intake on muscle strength and power: a systematic review and meta-analysis’, Journal of the International Society of Sports Nutrition. Available at:
  19. Institute of Medicine (2001) Caffeine for the Sustainment of Mental Task Performance. National Academies Press.
  20. European Food Safety Authority (2015) ‘Scientific Opinion on the Safety of Caffeine’. Available at:

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