All about caffeine

Caffeine is probably  the most reliable ergogenic aid available, and can really improve athletic performance.


The primary mechanism is adenosine antagonism. Adenosine accumulates through the day and through a session, binding to central receptors and producing the sensation of fatigue. Caffeine occupies those receptors without activating them. Perceived effort drops, and you can work harder for the same energy cost. Secondary effects of caffeine on calcium handling in muscle and on motor units contribute, but the central effect does most of the work.

How strong is the evidence?

Grgic and colleagues ran an umbrella review of 21 meta-analyses drawn from eleven systematic reviews, and found caffeine improved performance across aerobic endurance, muscle strength, muscle endurance, power, jumping performance and exercise speed.¹ That breadth of effect is unusual and it's the main reason caffeine sits at the top of most supplement rankings.


The main issue with this study is that the underlying quality of evidence was graded as generally moderate, with some sections rated as  low and very low. Most of the participants across the literature were young men.¹


For strength and power specifically, Grgic's earlier meta-analysis of twenty studies found caffeine improved maximal strength and muscle power measured by vertical jump.² Both were statistically significant but small results.


One very interesting finding is the one that matters if you strike or grapple: caffeine significantly improved upper body strength but not lower body strength.² That result surprised the authors too.

Dose

Dose is where most people get it wrong. The ISSN position stand puts the effective range at 3–6 mg/kg, taken around 60 minutes before exercise.³ For an 80 kg athlete that's 240–480 mg. Above roughly 6 mg/kg the performance return flattens while the side effects — tremor, elevated heart rate, gastrointestinal upset, impaired fine motor control — keep climbing.


The bottom of the range is lower than most people think. The ISSN notes the minimum effective dose remains unclear but may be as low as 2 mg/kg.³ Spriet's review makes the case for doses under 3 mg/kg — around 200 mg — being ergogenic in some situations, and argues those low doses work through a different route: they don't alter whole-body physiological responses to exercise at all, but they do improve vigilance, alertness and mood, with few if any side effects.⁴ If caffeine is helping you at 200 mg, it's helping your head, not your muscles. More is not better; it's just more. For reference, a cup of filter coffee has 100-150 mg caffeine, and a 250 ml redbull has 80 mg caffeine.

Why it works better for some people

Individual response varies genetically. Womack and colleagues tested 35 trained male cyclists over a 40 km time trial at 6 mg/kg and found that variation in CYP1A2 — the enzyme handling the majority of caffeine metabolism — predicted the size of the ergogenic effect. AA homozygotes, the fast metabolisers, improved substantially more than C-allele carriers.⁵,⁶


The wider literature on CYP1A2 literature is inconsistent however: some studies find no genotype effect, and at least one has reported the opposite direction, so its a possible explanation but its not completely convincing.

Sleep

This is where timing of caffeine intake can cost you more than it returns. Drake and colleagues gave 400 mg at zero, three and six hours before habitual bedtime. All three timings significantly disrupted sleep relative to placebo — and even at the six-hour mark, objectively measured total sleep time fell by more than an hour.⁷


Study participants' own reports didn't reflect this. They lost over an hour of sleep and largely didn't notice. You cannot rely on how you feel to tell you whether your evening pre-workout is costing you.


Practical position:


  • 3 mg/kg is the sensible starting dose. Work up only if you need to.³

  • 60 minutes before, on an empty-ish stomach.

  • Nothing within six hours of bed. If you train in the evening and want to sleep, that rules out an afternoon pre-workout.⁷

  • Test it in training, never for the first time on competition day.


 

 

References

  1. Grgic J, Grgic I, Pickering C, Schoenfeld BJ, Bishop DJ, Pedisic Z. Wake up and smell the coffee: caffeine supplementation and exercise performance — an umbrella review of 21 published meta-analyses. Br J Sports Med. 2020;54(11):681–8.

  2. Grgic J, Trexler ET, Lazinica B, Pedisic Z. Effects of caffeine intake on muscle strength and power: a systematic review and meta-analysis. J Int Soc Sports Nutr. 2018;15:11.

  3. Guest NS, VanDusseldorp TA, Nelson MT, Grgic J, Schoenfeld BJ, Jenkins NDM, et al. International Society of Sports Nutrition position stand: caffeine and exercise performance. J Int Soc Sports Nutr. 2021;18(1):1.

  4. Spriet LL. Exercise and sport performance with low doses of caffeine. Sports Med. 2014;44(Suppl 2):S175–84.

  5. Womack CJ, Saunders MJ, Bechtel MK, Bolton DJ, Martin M, Luden ND, et al. The influence of a CYP1A2 polymorphism on the ergogenic effects of caffeine. J Int Soc Sports Nutr. 2012;9(1):7.

  6. Womack CJ, Saunders MJ, Bechtel MK, Bolton DJ, Martin M, Luden ND, et al. Erratum to: The influence of a CYP1A2 polymorphism on the ergogenic effects of caffeine. J Int Soc Sports Nutr. 2015;12:24.

  7. Drake C, Roehrs T, Shambroom J, Roth T. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. J Clin Sleep Med. 2013;9(11):1195–200.
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