PerimenopauseMenopause transition
The years of fluctuating hormones before periods stop for good.
Perimenopause is the transitional phase before the menopause, when ovarian function becomes erratic and hormone levels fluctuate rather than simply declining. It commonly lasts several years and typically begins in the mid forties, though it can start earlier.
Menopause itself is a single point defined retrospectively: twelve consecutive months without a period. Everything before that point is perimenopause, and everything after is postmenopause, which is a distinction that matters because the symptoms cluster in the transition rather than after it.
The fluctuation is the reason it is difficult. Oestrogen swings rather than falls steadily, which produces hot flushes, night sweats, disrupted sleep, mood and concentration changes, cycle irregularity, and shifts in training recovery and body composition, often before periods become obviously abnormal.
UK guidance identifies it clinically in people aged 45 and over from symptoms and cycle changes, explicitly without blood tests, because fluctuating hormones make single results unreliable. An FSH test is suggested only below 45, and it is often unhelpful even then.
That guidance matters practically, because a normal blood test is routinely used to dismiss symptoms that are entirely consistent with perimenopause.
Training implications are real and mostly indirect. Disrupted sleep and altered recovery affect what you can tolerate, and bone loss accelerates around this time, which makes heavy resistance and impact training more valuable rather than less.
In practice, symptoms are the diagnosis in the 45 and over group, hormone therapy is the most effective treatment for vasomotor symptoms, and both belong in a conversation with a GP rather than with a supplement aisle.