Caffeine is a chemical commonly found in tea, coffee and energy drinks. Acute consumption has been found to improve physical performance in respect to:
· Aerobic performance (largest effect)
· Strength endurance (moderate effect)
· Maximal strength and power (smallest effect)
Optimal dose is considered to be:
· 3-6mg/kg
Caffeine can also be a cognitive enhance or ‘nootropic’ for some individuals but is highly variable between individuals. Some of the positive effects may be enhanced by co-ingestion of:
· L-theanine
· L-tyrosine
Some of the variability is explained by gene polymorphisms in
· CYP1A2 (liver enzyme responsible for metabolising caffeine)
· ADORA2A (gene that codes for the adenosine A2A receptor that caffeine binds to)
· COMT (enzyme that is involved in the metabolism of catecholamines e.g. dopamine, noradrenaline)

Dunn, A.L., Trivedi, M.H., Kampert, J.B., Clark, C.G. and Chambliss, H.O., 2005. Exercise treatment for depression: efficacy and dose response. American journal of preventive medicine, 28(1), pp.1-8.