Caffeine

Caffeine is the only legal, cheap, over-the-counter compound that reliably makes you better at almost every kind of exercise. Endurance, sprints, maximal strength, reaction time, perceived effort — the effect appears across all of them.

It is also the supplement most likely to quietly cost you more than it gives, because the thing it interferes with is sleep, and sleep is where training adaptation actually happens.

The dose that works

Three to six milligrams per kilogram of body weight, 45 to 60 minutes before you train.

For an 80 kg lifter that is 240 to 480 mg. A standard pre-workout scoop is usually 200 to 300 mg; a strong home-brewed coffee is 100 to 150 mg; an espresso is about 65 mg.

The ceiling matters as much as the floor. Above 6 mg/kg the performance benefit stops improving, while anxiety, tremor and heart rate keep climbing. Doses at 9 mg/kg perform no better than 3 mg/kg and feel considerably worse. There is no reward for going harder here.

What it actually improves

Caffeine blocks adenosine receptors. Adenosine accumulates through the day and through a session, and one of the things it does is tell you that you are tired. Block the receptor and the fatigue signal is quieter.

That mechanism explains the pattern in the data. The largest effects show up in endurance work and in anything where perceived exertion is what makes you stop. Effects on one-rep-max strength are real but smaller. Effects on muscular endurance — more reps at a given load — sit in between and are the ones most lifters will actually notice.

It does not make you stronger. It makes the same effort feel more manageable, and you do more work as a result.

Timing, and why the form matters

Capsules and powders peak in the blood at roughly 45 to 60 minutes. That is the standard pre-workout timing and it is what most of the research uses.

Coffee is a little faster. Caffeinated gum is much faster — closer to 10 to 20 minutes — because a portion is absorbed through the mouth rather than the gut, which is why it turns up in team sports where the warm-up window is short.

Coffee works. The position stand on coffee specifically found comparable benefits to anhydrous caffeine when the dose is matched. The catch is that matching the dose is genuinely hard: the caffeine in a cup varies by bean, roast, grind and method, easily two-fold. If you want precision, use a capsule.

Tolerance is less of a problem than you think

The standard advice is to cycle off caffeine to restore sensitivity. The evidence is thinner than the advice.

Habitual consumers still get a performance benefit. It is somewhat blunted compared to non-consumers, but it does not disappear, and the deloading protocols that have been tested produce modest resensitisation at the cost of several days of headaches and flat training.

If you are drinking 600 mg a day and escalating, that is worth addressing. If you are at 200 mg before training, leave it alone.

The part that actually costs you

Caffeine’s half-life is around five hours, and considerably longer in some people depending on how fast they metabolise it.

Take 300 mg at 4pm and roughly 150 mg is still circulating at 9pm. You will probably fall asleep. You will get less deep sleep, and you will not necessarily notice — the subjective experience of caffeine-disrupted sleep is much better than the objective measurement of it.

For an evening trainer this is the whole calculation. A pre-workout at 6pm buys you a slightly better session and takes a bite out of the recovery that session depends on. Either train earlier, or accept a worse session and better sleep, or use a much smaller dose.

A reasonable rule: nothing caffeinated within eight hours of bed.

Who should be careful

Anyone with high blood pressure or a cardiac arrhythmia should agree a limit with a doctor rather than a supplement label. Pregnancy guidance is generally 200 mg a day total. Anyone prone to anxiety will usually find the useful dose sits at the bottom of the range or below it.

And read the label on anything sold as pre-workout. Stacking a 300 mg scoop onto two coffees is how people end up at 600 mg without deciding to.

Side effects and who should skip it

• Sleep disruption is the real cost. Caffeine has a half-life of roughly five hours, so a 200 mg afternoon dose still has 100 mg circulating at bedtime — and the sleep you lose costs more than the session gained.
• Anxiety, jitters and a raised heart rate, mostly at doses above 6 mg/kg. Effect on performance does not improve above that dose, so there is nothing to gain by pushing through it.
• Withdrawal headaches and fatigue for two to five days if a habitual intake stops abruptly. Taper rather than quit if you are cycling off.
• People with hypertension, cardiac arrhythmias, or who are pregnant should set their limit with a clinician, not with a pre-workout label.