Table 1.

PICOS criteria for inclusion and exclusion studies.

Criteria	Inclusion Criteria	Exclusion Criteria
Population “P”	The sample must be composed of men and/or women trained athletes.	Participants receiving any type of medication or treatment; unhealthy individuals with gastrointestinal problems, with inflammatory and/or immunological pathologies, with musculoskeletal pathology. In general, individuals with chronic diseases.
	Individuals within the sample must be explicitly referred to as “trained athletes” in the manuscript or meet the criteria to be classified as “physically active” for exceeding the exercise recommendations of the American College of Sports Medicine (ACSM).
Intervention “I”	Include a supplementation intervention that should involve the use of melatonin in monotherapy, with clear information on dosage and duration of melatonin supplementation.	Administration together with other nutritional supplements.
Comparison “C”	Include either a placebo or control group (parallel group studies design) or experimental condition (cross-over studies design).	With other doses of melatonin, or with other nutritional supplements.
Outcomes “O”	Any parameter related to sports performance, and/or biomarkers related to health status, that reports on the bioavailability and adverse effects of melatonin.	None.
Study design “S”	Human intervention studies, randomized controlled trials, and/or randomized controlled crossover trials.	Observational studies and studies that used a targeted analytical approach.