Ovarian hormones shift substrate metabolism across the cycle (oestrogen→fat oxidation/glycogen sparing), but the effect is E/P-ratio-dependent and easily overridden by nutrition
Key Findings
The literature is split: as many studies find endurance performance varies between menstrual phases as find no difference.
Comparing the luteal rise in oestrogen (E) relative to progesterone (P) — the E/P ratio — across those studies suggests endurance performance may be improved mid-luteal vs early-follicular only when the mid-luteal E/P ratio is high; the ratio, not the phase label, drives any effect.
The late follicular phase (pre-ovulatory oestrogen surge, suppressed progesterone) tends to improve a cycling time trial — the authors call for future studies to include it.
Oestrogen tends to promote glucose availability and uptake into type I fibres, spare muscle glycogen during exercise and (not yet supported by human tracer studies) raise free-fatty-acid availability and oxidation; progesterone often acts antagonistically. Oestrogen's stimulation of AMPK may explain many of these actions.
High luteal oestrogen augments muscle-glycogen storage capacity, BUT a carbo-loading diet super-compensates glycogen in the early-follicular phase to luteal values — diet overrides the hormonal difference; energy demand and nutritional status are confounders, especially for carbohydrate metabolism.
Both hormones suppress gluconeogenic output during exercise → inadequate energy replacement may compromise the latter stages of ultra-long events; supplementing with protein during exercise may be more relevant when progesterone is elevated (progesterone promotes, oestrogen suppresses protein catabolism).
Practical Application
Narrative review (2010): menstrual-phase effects on endurance performance are inconsistent; where they appear they track a high luteal oestrogen:progesterone ratio, and the metabolic differences (glycogen sparing, storage) are overridden by carbohydrate loading — fuelling, not phase, is the lever.
Treat cycle-related substrate shifts as small and nutrition-sensitive: robust carbohydrate fuelling neutralises most phase differences — prioritise fuelling, not phase.
For very long/ultra sessions, ensure sufficient exogenous energy regardless of phase; when progesterone is high (mid-luteal), some protein during exercise is the review's suggestion.
Don't promise a "fat-burning phase" — the fat-oxidation effect of oestrogen is not yet confirmed by human tracer studies, is ratio-dependent and swamped by diet/training status.
Limitations
2010 narrative review, mechanistic emphasis; performance magnitudes modest/uncertain; metabolic differences don't reliably become performance differences.
The fat-oxidation claim for oestrogen rests on animal/indirect-calorimetry data — the abstract itself says it is "not as yet supported by human tracer studies".
How this entry was checked and changed
Why this level
regraded 2026-09-27 from B–C: narrative review without systematic method (rubric: C+)
Content correction 2026-09-27
Level "B–C" -> C+ per rubric (narrative review). Added from the abstract: the split literature, the late-follicular cycling-TT observation, the AMPK note, and the caveat that oestrogen's fat-oxidation effect lacks human tracer support (the entry presented it as established). Lead rewritten to the review's own conclusion. Sport line set to "cycling, running".
Cross-references to duplicate stubs repointed to their canonical entries (REF-526->REF-335); the stubs were emptied on 2026-09-27.