Table 1.

Population, intervention, comparator, outcomes and study design (PICOS) criteria

Population	Healthy women aged 18–40 years were considered for inclusion in this study. No restrictions on activity level or training status were placed
Intervention	All participants were required to take an OCP, either habitually or experimentally. “Habitual” was defined as OCP use prior to the commencement of the study and not for the purposes of the study. “Experimentally” was defined as starting OCP use for the purposes of the study. All forms of OCPs were considered for use within this review
Comparator	Four broad types of comparisons were considered: (1) Between group comparison of habitual OCP users to naturally menstruating women. Women were phase matched in two ways for this comparison: (i) OCP withdrawal versus the early follicular phase of the menstrual cycle and (ii) OCP consumption versus all other phases of the menstrual cycle except for the early follicular phase; (2) within group comparison of OCP consumption with the hormone-free withdrawal phase; (3) comparison of active OCP use with non-use (e.g ., within-group comparison of women who were habitual users or non-users who stopped/started taking OCP for the purpose of the study); (4) randomised controlled trials of OCPs versus placebo intake ( e.g ., between group comparison of naturally menstruating women who were randomly assigned to either an OCP or placebo pill)
Outcomes	The primary outcome was to determine any differences in exercise performance, based on the comparisons described above. ‘Exercise performance’ referred to outcomes stemming from: workload, time to completion and exhaustion, mean, peak outputs, rate of production and decline and maximum oxygen uptake (a full list of considered outcomes can be found in Table 2). Although maximum oxygen uptake is not a performance test, this physiology-based outcome was included as it is widely used as an indicator of performance and is often used to describe the fitness of participants. Different exercise outcomes, broadly categorised as endurance and strength were considered. All exercise outcomes were extracted, and effect size duplication of multiple outcomes from the same test accounted for within the statistical analysis, as described in Sect. 2.4
Study design	Any study design that included the information described above was considered for inclusion

OCP oral contraceptive pill