What did @barebyevelyn actually say?
The creator argues that "over exercising" — specifically daily long runs, CrossFit, and HIIT — disrupts the entire endocrine system, stressing "the adrenals, the thyroid, the ovaries," and eventually causing amenorrhea, hypothyroidism, and infertility. Her solution is cycle syncing: matching workout intensity to the four menstrual phases, with harder sessions in the follicular and ovulatory phases and gentler movement during menstruation and the luteal phase. She also says some clients should cut out formal exercise entirely for a period of time to "speed up their healing."
That is a lot of ground to cover in under three minutes. Some of it reflects real physiology. Some of it stretches well beyond what research actually supports.
Does the science back this up?
Partly. The link between excessive exercise and menstrual disruption is real and well-documented. The cycle syncing framework as a universal hormone fix is far less settled.
On the exercise side, the evidence is solid. Relative Energy Deficiency in Sport (RED-S), formerly called the Female Athlete Triad, shows clearly that chronic energy deficit from high training loads suppresses GnRH pulsatility, which in turn drops LH and FSH, leading to hypothalamic amenorrhea. Mountjoy et al. (2018, British Journal of Sports Medicine) laid this out comprehensively. Loucks et al. (2003, Exercise and Sport Sciences Reviews) showed that it is energy availability, not exercise volume alone, that drives these hormonal disruptions. That distinction matters and the creator skips it entirely.
On cycle syncing specifically, the data is thin. Sung et al. (2014, Journal of Sports Science and Medicine) found some performance variation across cycle phases, but effect sizes were small and inconsistent across individuals. A 2023 systematic review by McNulty et al. in Sports Medicine found limited evidence that cycle phase meaningfully affects exercise performance or recovery in most women. The idea that estrogen and progesterone fluctuations dictate energy levels in a predictable, actionable way for every woman is oversimplified.
What did they get wrong (or right)?
She gets the core warning right and then overshoots on the solution. Recommending that women doing daily high-volume intense training examine whether that load is sustainable is reasonable advice. Amenorrhea from under-fueled, over-trained states is a genuine clinical concern.
But saying "the female body is not designed for daily vigorous physical activity" is an overclaim with no real scientific basis. Female endurance athletes competing at elite levels regularly train at high volumes without hormonal disruption, because they fuel adequately. The problem is energy deficiency, not exercise itself. Framing vigorous movement as inherently harmful to women is misleading and frankly a bit patronizing.
The claim that HIIT and CrossFit "burn out your adrenals" leans on the widely popularized but poorly supported concept of adrenal fatigue. The Endocrine Society does not recognize adrenal fatigue as a medical diagnosis. Describing thyroid disruption as a consequence of hard workouts in otherwise healthy, well-fueled women is also not well supported by clinical evidence.
Her phase descriptions for the menstrual cycle are physiologically reasonable at a basic level. Estrogen does rise during the follicular phase and progesterone does rise during the luteal phase. That part is accurate.
What should you actually know?
If you have lost your period, are struggling with fertility, or have a confirmed thyroid condition, your exercise load and caloric intake are worth reviewing with an actual physician or registered dietitian, not a wellness coach on TikTok. Hypothalamic amenorrhea is a real condition that warrants clinical evaluation, including bloodwork, to rule out other causes before attributing it solely to exercise.
Cycle syncing your workouts is not harmful and some women find it useful for managing energy and recovery. But the evidence does not support it as a hormone-balancing intervention or a fertility treatment. If you enjoy lighter movement during your period and harder sessions mid-cycle, that is fine. Do not expect it to fix a hormonal disorder.
Anyone with amenorrhea, suspected thyroid dysfunction, or fertility concerns should be evaluated by a reproductive endocrinologist or OB-GYN. These are medical conditions. Adjusting your HIIT schedule is not a substitute for diagnosis and treatment.