Table 1.

PICOS criteria for the inclusion of crossover experimental designs in which the ingestion of caffeine was compared to a placebo in a single- or double-blind randomized manner. For inclusion, the study outcomes should be associated with endurance running performance.

Parameters	Inclusion	Exclusion	Extraction
P	Healthy runners	Participants of other sports disciplines or non-athletic population	Number of participants, gender, training level and experience, age, daily caffeine intake, and anthropometric characteristics
I	Caffeine	Caffeine intake in combination with other ergogenic aids	Dosage, the form of administration, and timing of ingestion
C	Placebo	Trials without a true placebo/control situation	Components, dosage, the form of administration
O	Endurance running performance	Any other form of endurance exercise different from running	Time to exhaustion trials and time trials
S	Single- or double-blind randomized controlled trials published in peer-reviewed journals	Systematic reviews, conference abstracts, graduate student dissertations, and editorials	Experimental design, date of publication