Theory 29/Menstrual cycle/Progression phase
Phase Length Is Luteal Fixed
The claim
Follicular phase length varies while luteal length is set by the ratio of corpus luteum lifespan to luteolytic sensitivity, so cycle variability comes from one phase.
01Mechanism
The luteal phase has a fixed clock; variability arises before ovulation.
02Prediction
Variability should be concentrated in the follicular phase.
03Refutation
Equal variability in both phases would remove the fixed clock.