Coffee before lifting: real strength, or just a feeling of alertness?

The arms, and not the legs. Caffeine before exercise was tied to a small improvement in maximal upper-body strength and in explosive power, measured partly by vertical jump. In maximal lower-body strength there was no significant improvement. So the effect is not a uniform switch that raises every muscular performance.

Caffeine adds no energy. Adenosine builds up through the day and damps nerve activity, and caffeine binds the same receptors without activating them, so it blocks the feeling of tiredness.

Which means the effect should not be uniform. In a review of controlled trials there was a small improvement in maximal upper-body strength and in explosive power, measured partly by vertical jump.

In maximal lower-body strength there was no significant improvement. Explanations have been offered about differences in neural recruitment and about local fatigue, and none is agreed.

So a strong sense of arousal is no evidence that every muscle got stronger. All of this rests on a narrow sample: the number of studies behind each measure was small, most participants were young men, and the doses and the exercises varied between trials.