How it works
Caffeine's main action is blocking adenosine receptors in the brain. Adenosine builds up during wakefulness and exertion and promotes feelings of fatigue, so blocking it reduces perceived effort and pain and increases alertness. This means the same workload feels easier, or more work can be done at the same perceived effort. Caffeine may also enhance muscle fibre recruitment and calcium handling inside muscle. Its effects begin within 15–60 minutes and its half-life is roughly 3–6 hours, although genetics, pregnancy, smoking and some medications change this considerably.
What research supports
- Improves endurance performance in time trials and time-to-exhaustion tests
- Can improve muscular strength, power and repeated sprint performance
- Reduces perceived exertion and muscle pain during exercise
- Improves alertness, reaction time and concentration, especially when sleep deprived
- Low doses (around 1–3 mg/kg) can still be effective with fewer side effects for some people
Dosage
Typical research dose: 3–6 mg/kg of body weight, taken about 60 minutes before exercise. Lower doses of around 2–3 mg/kg are often effective. Doses of 9 mg/kg or more increase side effects without clear additional benefit. For healthy adults, many food safety agencies consider up to about 400 mg per day from all sources to be generally safe.
Timing
Take caffeine roughly 30–60 minutes before training or competition so blood levels peak at the right time. Chewing gum and some gels are absorbed faster. In long events, smaller doses later in the race may also help. Because caffeine can disrupt sleep for many hours, avoid it within about 6–8 hours of bedtime if evening training is followed by sleep, as poor sleep can outweigh any performance gain.
Side effects
- Sleep disruption, especially with afternoon or evening use
- Jitteriness, anxiety, raised heart rate and headache at higher doses
- Stomach upset and increased need to urinate in some people
- Withdrawal symptoms such as headache and fatigue if regular use stops abruptly
Cautions
- Pure caffeine powders and concentrated liquids are dangerous because a lethal amount can be measured out by mistake; avoid them
- People with heart rhythm problems, high blood pressure, anxiety disorders, or who are pregnant or breastfeeding should talk to a doctor about safe intake
- Caffeine interacts with some medications and stimulants; check with a pharmacist
- Pre-workout products often contain several stimulants at undisclosed doses; check labels and total caffeine from all sources
- Caffeine is not prohibited in sport but is on the WADA monitoring program; athletes subject to anti-doping rules should only use products certified by an independent third-party testing program for banned substances; certification lowers, but does not eliminate, the risk of contamination.
Food sources
Coffee, Tea, Cocoa and dark chocolate, Cola and energy drinks, Caffeinated gels and gum.