Caffeine – The World's Most Used Ergogenic Aid

Caffeine is a natural xanthine alkaloid found in over 60 plant species and is the most researched psychoactive substance in the world. As an adenosine receptor antagonist, it blocks fatigue, enhances focus, and improves athletic performance – with an impressive body of evidence.

Mechanism of Action: Adenosine Antagonism

Adenosine is a neurotransmitter that accumulates during wakeful activity and binds to A1 and A2A receptors → leading to drowsiness, reduced motivation, and slowed neuronal activity. Caffeine is structurally similar and competitively blocks these receptors:

A1 Receptor Blockade: Increases the release of acetylcholine, dopamine, noradrenaline, serotonin
A2A Receptor Blockade: Boosts dopamine release in the striatum → improved motivation, mood
Phosphodiesterase Inhibition (at high doses): Increases cAMP → fat mobilization, cardiac stimulation
Calcium Release from SR: At very high doses, relevant for muscle contraction

Proven Effects on Athletic Performance

Sport Area	Effect	Dosage	Level of Evidence
Endurance	+2–4% VO2max, prolonged time to exhaustion	3–6 mg/kg BW	Very High (A)
Strength/Power	+3–7% maximal strength, explosive power	3–6 mg/kg BW	High (B)
Cognition	Reaction time, attention, memory	100–200 mg	Very High (A)
Body Fat	+10–16% fat oxidation, slight thermogenic effect	3–6 mg/kg	Moderate (B)
Muscle Endurance	More repetitions to exhaustion	3–6 mg/kg BW	High (A/B)

Dosage and Timing

Purpose	Dose	Timing
General Focus/Alertness	100–200 mg	Morning, 90 min after waking
Pre-Workout (Strength/Endurance)	3–6 mg/kg BW (approx. 200–400 mg)	45–60 minutes before training
Maximum Cognitive Performance	100–200 mg + L-Theanine (2:1)	30 min before task
Night Shift/Sleep Deprivation	100–200 mg every 4–6h	Last dose 6h before sleep

Half-Life and Sleep

The half-life of caffeine in the average person is 5–6 hours (variance: 3–10h, depending on genetics, liver function, smoking, pregnancy). After 6 hours, ~50% is still active, after 12 hours, ~25% remains. Practical recommendation: last coffee no later than 6 hours before bedtime. If you have sleep problems, maintain an 8–10 hour gap.

Tolerance Development and Breaks

Regular caffeine consumption reduces its effect due to upregulation of adenosine receptors. Caffeine-sensitive effects can be maintained by a 10–14 day break (cycling) or by cyclical use (e.g., only on training days).

Side Effects of Overdose

Palpitations, hypertension (dose-dependent)
Anxiety, nervousness, tremors
GI discomfort (stomach irritation, diarrhea)
Sleep disturbances
Withdrawal headaches with abrupt cessation after regular consumption

Safe upper limit: 400 mg/day for adults (EFSA); 200 mg/day for pregnant women.

Frequently Asked Questions (FAQ)

Is caffeine on an empty stomach harmful?

Caffeine stimulates stomach acid production. For sensitive stomachs, coffee on an empty stomach can cause nausea. More tolerable: a small meal beforehand or buffered caffeine preparations.

Is caffeine a diuretic?

For occasional users, yes (mildly). Regular users develop tolerance to the diuretic effect. An espresso does not net dehydrate – the water contained in the coffee outweighs the diuretic effect.

Caffeine vs. Pre-Workout: Which is better?

Pure caffeine (caffeine tablets, caffeine capsules) has the advantage of precise dosage control. Pre-workout products contain caffeine plus synergists (beta-alanine, citrulline, L-tyrosine) – for most athletes, this is the superior option.