Definition and System view

In short Caffeine blocks adenosine receptors (A1/A2A) in the CNS. Result: less “sleepiness signaling”, higher neuronal activation, partly more dopamine/noradrenaline downstream. In training it often lowers perceived effort (RPE), sharpens focus and can acutely improve performance and set quality.

• Primary effects: alertness, reaction time, attention; subjective fatigue ↓.
• Resistance training: sometimes more reps at the same RIR, higher bar speed, better set quality.
• Endurance: later fatigue, better pacing control.

Dosage — practical guardrails

For healthy, tolerant adults (training/performance context):

• Single vs total daily intake: keep single doses moderate; respect daily limits.
• Sensitivity varies: body mass, habit, genetics (CYP1A2/ADORA2A) & timing modulate effects.
• Minors: no performance-oriented caffeine dosing; no “pre-workout” use recommended for adolescents.

Timing and half-life

• Pre-workout: 30–60 min before the session works well (capsule/shot often faster than coffee).
• Half-life: roughly ~3–7 hours — late intake can impair sleep onset/quality.
• Cut-off: For most: avoid stimulants 6–8 hours before planned bedtime.

Sources and formats

• Coffee / espresso: variable content; ritual & taste, but imprecise dosing.
• Tea / matcha / guarana: often smoother kinetics; plus L-theanine (tea) can support “calm alertness”.
• Capsules / tablets / gums: precise dosing, fast uptake; ideal pre-workout.
• Energy drinks / pre-workouts: track the total dose & other stims (e.g., theacrine).

Tolerance and cycling

• Habituation: high daily use can blunt acute effects (subjectively).
• Cycling: 1–2 lighter weeks (low / no caffeine) may subjectively “reset” sensitivity.
• Use with intent: prioritize hard sessions / tests rather than “always max”.

Safety and typical pitfalls

• Sleep: sleep latency & deep sleep can suffer → respect cut-off.
• Heart / circulation / anxiety: palpitations, jitters, GI discomfort are possible — adjust dose.
• Pregnancy / lactation: medical guidance; common limit: ≤ 200 mg/day.
• Medication: interactions possible (e.g., some antibiotics, psychotropics) → consult your physician.
• Adolescents: avoid high doses; no recommendation for pre-workout use.
• Avoid daily stacking: coffee + energy drink + pre-workout can push beyond 400 mg/day quickly.
• Pure caffeine powders: do not “weigh out” (overdose risk). Prefer tablets/gums with clear mg labeling.

Common misconceptions

• “More caffeine = more performance.” No. Side-effects rise beyond a point; quality > quantity.
• “Morning coffee ruins cortisol.” Acute cortisol responses vary; overall stress, sleep & recovery matter more.
• “Same dose every day is optimal.” Purpose-driven timing (hard session vs daily life) is usually better.

Practice — quick checklist

• Heavy session planned? Test 3–4 mg/kg 30–60 min pre (start lower initially).
• Sleep issues? Maintain a 6–8 hour cut-off before planned bedtime.
• Tolerance? If effect fades: 7–14 days lower intake, then re-dose.

Further reading and resources

Notice: Descriptive information for orientation — not a treatment, diet or training prescription. Individual differences and possible contraindications apply.