Table 3.

Proposed menstrual cycle phase definitions based on hormonal profiles (see Fig. 4)

Recommendation	Rationale (intended to…)	Pro	Con
Phase 1: indicated by the onset of bleeding until day 5 Oestrogen and progesterone levels are low	Capture the lowest concentrations of oestrogen and progesterone	Easy to determine due to obvious physical cue (i.e., bloody discharge)	Can be difficult to predict in those with variable cycle length therefore requiring reactive testing sessions (i.e., participant alerting the researcher on day 1 of bleeding and then both parties having availability for testing within the next 4 days)
Phase 2: occurs in the 14–26 h prior to ovulation and the LH surge Oestrogen higher than during phase 1, 3 and 4 and progesterone higher than during phase 1, but lower than 6.36 nmol·L−1	Capture the highest oestrogen concentration, while progesterone remains low	Enables the biggest difference between oestrogen and progesterone to be investigated	Difficult to predict without daily blood samples for the determination of oestrogen and progesterone
Phase 3: indicated by a positive urinary ovulation kit and lasts 24–36 h Oestrogen higher than phase 1 but lower than phase 2 and 4 and progesterone higher than phase 1 but lower than 6.4 nmol·L−1	Capture a medium oestrogen concentration, while progesterone remains low	Easy to establish due to the positive LH surge captured by the ovulation kit	Relies on having multiple ovulation kits available for each participant (cost) and requires reactive testing sessions (i.e., participant alerting the researcher to the positive result and then both parties having availability for testing within the next 24–36 h)
Phase 4: + 7 days after ovulation has been confirmed Oestrogen higher than phase 1 and 3 but lower than phase 2 and progesterone > 16 nmol·L−1	Capture the highest concentration of progesterone and a high concentration of oestrogen	Easy to establish in those with eumenorrheic cycles as it typically occurs within 7 days of confirmed ovulation	Relies on the confirmation of ovulation

LH luteinising hormone

These recommendations have been developed using information from the following sources: McGovern et al. [69]; Tsampoukos et al. [70]; Janse de Jonge et al. [48]; Elliott-Sale et al. [71]. The phases described in Table 3 are referred to as number (i.e., 1–4), rather than names (i.e., follicular, ovulatory and luteal), to reduce the misidentification or mislabelling of phases. This should ensure that phases are described based on quantifiable metrics rather than ambiguous terms. In order to draw comparisons with previous literature the following matches can be used: phase 1 with the ‘early follicular’ phase; phase 2 with the ‘late follicular’ phase; phase 3 with the ‘ovulatory’ phase; and phase 4 with the ‘mid-luteal’ phase. To date, no consensus has been reached within sport and exercise science on the nomenclature used to describe menstrual cycle phases and their corresponding hormonal profiles