Exercise and fertility are more connected than I realised: yes, overtraining can genuinely mess with your cycle, and in some cases stop ovulation altogether. I found that out the hard way while we were trying to conceive, and it took me embarrassingly long to join the dots.
The Assumption I Started With (More Training, Better Body, Right?)
I'd always assumed exercise was one of those things you can't really overdo when it comes to fertility. Healthier body, healthier hormones, and it does belong on any list of natural ways to boost fertility, so that logic held fine right up until it didn't. A 2022 meta-analysis of prospective cohort studies found moderate activity had no negative effect on fertility, while high-intensity activity was associated with slightly lower odds of conceiving. The dose matters, and I was well past it.
To be honest, I was training six days a week at that point. Running, strength sessions, and the odd HIIT class thrown in because I felt guilty about taking a rest day.
I genuinely thought I was doing everything right.
Dr. Natalie Crawford has a genuinely clear explanation of the exercise and hormone link if you want to go deeper into it than I do here.
What Actually Counts as "Overtraining" for Your Cycle?
It isn't really about a number of hours a week. It's about whether your body is getting enough fuel and enough recovery to keep up with what you're asking of it.
Researchers do have a number for it, just not the one I was expecting. A 2003 study in the Journal of Clinical Endocrinology & Metabolism found that LH pulsing held up fine at an energy availability of 30 kcal per kg of lean body mass a day, and started coming apart below it. That's a lab measure rather than something you can work out over breakfast, but the point stands: what counts is what's left over after training.
The chain runs roughly like this: too much training on too little food or rest leads to your body reading that as a stress signal, which leads to your hormones quietly deprioritising ovulation, because from a survival standpoint it isn't a sensible moment to get pregnant.
A few things seem to matter more than the rest:
- Training volume relative to what you're actually eating. A calorie deficit on top of heavy training is a bigger red flag than the training on its own.
- Low body fat, which Cleveland Clinic lists alongside under-eating and hard training as a stressor that can shut a cycle down, and which travels with the usual low oestrogen symptoms.
- Recovery between sessions, rather than total weekly hours.
I didn't know any of that at the time. I just assumed more was better.
The Actual Medical Name for This (It's Bigger Than Just "Overtraining")
Once I actually went looking, it turned out to have a proper name: RED-S, short for Relative Energy Deficiency in Sport, and one more acronym for the TTC glossary nobody hands you at the start. The International Olympic Committee's consensus statement defines it as impaired physiological functioning caused by not eating enough to match how much you're training, and it lists menstrual function right alongside bone health, immune function and metabolic rate.
What surprised me is that RED-S grew out of an older, narrower term, "Female Athlete Triad." Researchers widened it because the underlying problem, not enough fuel for the amount of training, affects far more of the body than just periods and bone density, and affects men too, just differently.
I'm not repeating that to sound clinical. Seeing this was a real, named, studied condition rather than me being dramatic is what made me take it seriously.
The Real Signs I Ignored (Looking Back, They Were All There)
Looking back, I had two or three of these going on for a good few months before I paid any attention:
- Periods getting lighter, later, or stopping altogether
- Ovulation tests that never quite turned positive, even on the days my app said I should be in my fertile window
- Feeling wiped out all the time, not just normal post-workout tired
- Getting cold really easily, hands and feet especially
- Mood swings that felt bigger than usual
Most of that list turned out not to be random. A 2025 review in Physiological Research describes prolonged energy deficiency lowering your resting metabolic rate and your T3 thyroid hormone, which is roughly what being permanently cold and permanently tired feels like from the inside.
The one that finally got my attention was my period simply not turning up for two months. That's genuinely when I started reading around, and the NHS has a straightforward page on stopped or missed periods that lists intense exercise as one of the more common and reversible causes, alongside things like stress and low body weight.
👉 The bit that stuck with me: it isn't one bad week, it's your body reading a pattern over time and quietly deciding this isn't the moment for a pregnancy.
Why My Ovulation Tests Kept Confusing Me
This was the most frustrating part, and I didn't understand it until much later.
Ovulation predictor kits pick up a surge of luteinising hormone (LH) in your urine shortly before you ovulate, and University of Iowa Health Care's explainer on OPKs is a decent plain-language rundown of how that works. The catch is that LH is exactly what a sustained energy deficit interferes with. A 2023 Mayo Clinic Proceedings review puts it plainly: eating less and training more, past a certain threshold, disrupts LH pulsatility in women who were previously cycling normally.
So I wasn't imagining it. My tests weren't turning positive some months because there wasn't much of a surge there to find, not because I was using them wrong.
If your OPKs are consistently confusing and nothing else has changed, treat that as information rather than user error. It also makes the two week wait hard to read, because you're counting from a day you can't confirm happened.
What I Actually Changed
I didn't quit exercising, and looking back I could probably have been a bit less dramatic about the whole thing.
What actually helped was dropping to four sessions a week, taking a proper rest day, and just eating more, especially on training days. Nothing clever, mostly the boring fertility diet basics I'd been skipping past. Four sessions is also roughly where the NHS pitches it, at 150 minutes of moderate activity a week plus strength work on two days, spread across four or five days rather than crammed into six.
It wasn't about training less for the sake of it. It was about leaving my body enough spare capacity to bother ovulating again.
My cycle came back within about six weeks, which surprised me given how long it had been off. Cleveland Clinic puts the usual figure at three to six months, so I probably got off lightly rather than did anything especially right.
We were also leaning on the general advice on coping with TTC stress around that time, because the training was really only one part of a bigger stress picture for us.
When It's Worth Actually Seeing a Doctor
I'll be honest, I left this far longer than I should have before mentioning it to a doctor.
The NHS advice is to see a GP once you've missed three periods in a row, and I'd add that losing your period alongside real fatigue, hair changes or stress fractures is well past wait-and-see. A GP can run bloodwork and check your hormone levels instead of guessing from symptoms, and rule out causes that have nothing to do with exercise. Same goes for any period changes that don't fit your usual pattern.
The Endocrine Society's clinical guideline sets a similar bar, suggesting a proper work-up once cycles persistently run past 45 days or periods have been gone for three months. The bit I wish I'd known earlier is that the same guideline discourages using the pill purely to bring periods back or to protect bone density, because that treats the bleed rather than the energy deficit underneath it.
I mention it because I spent a while assuming it would sort itself out. In our case it did, but I got lucky with the timeline rather than managed it.
FAQ: Overtraining and Your Fertility
Can too much exercise really stop you ovulating?
Yes. It's a recognised thing, usually called exercise-related or hypothalamic amenorrhoea, where periods and ovulation stop because of the physical stress of hard training, generally alongside not eating enough to match it.
How much exercise is actually too much?
There isn't a single number that works for everyone. It comes down to the balance between how hard you're training and how well you're fuelling and recovering, so the same routine can be completely fine for one person and too much for someone else.
Will my cycle come back if I cut back on training?
For a lot of women it does, once training volume and food intake come back into balance, though how long that takes seems to vary a lot from person to person. If your periods have been away for a while, it's worth raising with a doctor rather than waiting it out.
Is RED-S the same as Female Athlete Triad?
They're related. RED-S is the newer and broader term that grew out of Female Athlete Triad, covering more of the body's systems than just periods and bone density, and recognising that men are affected too, just with different symptoms.
Can this happen even if I'm not a serious athlete?
Yes. RED-S and exercise-related amenorrhoea aren't limited to elite athletes. They're about the balance between training and fuelling, which a keen amateur can throw off just as easily as a professional, especially if what you're eating hasn't kept pace with a sudden jump in training.
This one has stayed with me because underneath it all it wasn't really about the exercise. It was about realising I'd been treating my body as something to optimise rather than something to listen to, which is a slightly bigger lesson than "do fewer HIIT classes." Matthew was patient about it in a way I probably didn't deserve, quietly encouraging the rest days I kept trying to skip while working on his own side of things. If you're in the middle of this, saying it out loud to your partner helps more than you'd think, and reading how backing off gently worked for someone else was oddly steadying.
Keep Reading: Helpful TTC Guides
Looking for more evidence-based support while you're trying to conceive? These guides go deeper on related questions:
