Caffeine & Stimulants Simulator

Caffeine is the most widely studied legal ergogenic aid in endurance sports. At doses of 3–6 mg/kg body weight, it reduces perceived exertion and improves endurance performance by 2–4%. This tool models caffeine pharmacokinetics — absorption, peak plasma concentration (~45 minutes post-ingestion), and elimination (half-life ~5 hours) — to help you time doses for optimal benefit during a race. It also accounts for habitual caffeine intake, which attenuates the acute ergogenic response by approximately 30%.

Frequently asked questions

How much caffeine should I take before a marathon?

The evidence-based dose is 3–6 mg/kg body weight, taken 45–60 minutes before the start. For a 70 kg runner, that is 210–420 mg — roughly equivalent to 1–2 strong coffees. Higher doses (>6 mg/kg) increase GI distress and anxiety without additional performance benefit.

Does daily coffee habit reduce the race-day caffeine benefit?

Yes. Habitual caffeine intake above ~300 mg/day (about 1.5 strong coffees) attenuates the acute ergogenic response by approximately 30%. Some athletes reduce intake in the 1–2 weeks before a race to partially restore sensitivity, though evidence on this "wash-out" strategy is mixed.

When does caffeine peak in the bloodstream?

Caffeine reaches peak plasma concentration approximately 45 minutes after oral ingestion. The half-life is roughly 5 hours, meaning half the caffeine is still active 5 hours later. For a 4-hour marathon, a single pre-race dose provides meaningful levels throughout the race.

Sources

  • Southward et al. (2018). The effect of acute caffeine ingestion on endurance performance: a systematic review and meta-analysis. Sports Medicine.
  • Pickering & Kiely (2019). Are the current guidelines on caffeine use in sport optimal? International Journal of Sport Nutrition and Exercise Metabolism.
  • Beaumont et al. (2017). Chronic effects of dietary caffeine on adaptations to exercise training. European Journal of Applied Physiology.

Related glossary terms

  • Caffeine
  • Caffeine Habituation
  • Dose-Response
  • Ergogenic Aid
  • Pharmacokinetics (PK)
  • CNS (Central Nervous System)
  • GI Distress