Female-endurance-athletes-hormones

People often admire female endurance athletes for their discipline. 

They get up early, take on long runs day after day, and keep going even when they’re tired. But behind the race results and training plans, many women are quietly facing hormone disruptions. 

The numbers speak for themselves. 

Research shows that up to 40% of female endurance athletes have menstrual problems, low estrogen, thyroid issues, or Relative Energy Deficiency in Sport (RED-S), even if they appear strong, lean, and healthy. 

These hormone changes affect more than just menstrual cycles. They also impact endurance, recovery, bone strength, mood, and long-term health. 

One challenge is that women can often keep going for a long time before problems show up. 

Many women continue training through small hormone changes for years before symptoms become obvious, such as constant tiredness, slower progress, injuries, irregular periods, or feeling like their body has changed. 

For female athletes, hormones are not a minor issue. They are central to how the body works. 

This guide looks at how endurance training affects women’s hormones, why estrogen and thyroid hormones react to training stress and energy levels, and how lab tests can spot early warning signs before burnout, injury, or long-term health problems develop. 

Feeling “off” but training looks fine on paper? The Access Labs Hormone Panel helps clinicians spot early shifts in estradiol, progesterone, thyroid, and cortisol before burnout or injury forces a reset. 

Key Takeaways 

• Up to 40% of female endurance athletes may experience hormone disruption tied to menstrual dysfunction, low estrogen, thyroid changes, or RED-S.
• Estrogen supports fuel use, recovery, and bone strength. When it drops, stress fracture risk rises, and endurance can suffer.
• Low energy availability can lower Free T3 while TSH stays “normal,” contributing to fatigue, slower recovery, and stalled progress.
• RED-S often looks like “normal training,” and lab markers can flag the pattern before a missed period or injury forces a reset.
• HRT can help in menopause or confirmed deficiency, but it doesn’t replace the need to correct fueling, stress, and training load in premenopausal athletes. 

Here's what you'll find in this article:

• The Physiology of Female Hormones in Endurance Training (and What the Latest Data Shows)
• The Estrogen Advantage, Until It Isn’t
• Thyroid, Cortisol, and Why You Feel Wiped All the Time
• RED-S and the Energy Deficit No One Talks About
• When (and When Not) to Consider HRT in Female Athletes
• Hormonal Resilience Is Performance Resilience 

The Physiology of Female Hormones in Endurance Training

Endurance training puts real pressure on a woman’s hormone system, especially a network called the hypothalamic–pituitary–ovarian axis, or HPO axis for short. 

Think of it as your body’s project manager for estrogen, progesterone, and your menstrual cycle. 

It’s incredibly sensitive to how much energy you’re taking in versus burning, how hard you’re training, how stressed you feel, and how well you’re sleeping. 

Even a small energy deficit can mess with the signals your brain sends to your ovaries, tweaking the hormones that keep your cycle regular and ovulation on track. 

This means you can train regularly, eat what seems like enough, follow all the advice, and your body may still quietly start conserving hormones. This often happens before your period becomes noticeably irregular. 

Research shows that endurance training can drop estrogen and progesterone levels by 25–30%, sometimes without you even realizing it. 

It’s a domino effect. When your body senses ongoing stress or a lack of fuel, it starts turning down the dial on multiple systems at once. That can include: 

• Lower estrogen production from your ovaries
• Slowed thyroid function, which lowers your metabolism
• Cortisol imbalances that make it harder to recover and bounce back 

The newer research helps explain why so many women feel “off” long before anything looks dramatic on the surface. 

In one study, 42% of female runners had low estradiol and progesterone across at least two consecutive cycles. Meaning nearly half were dealing with suppressed hormones even while training normally. 

Almost 1 in 5 showed measurable decreases in bone mineral density, and 1 in 5 elite athletes met the criteria for partial RED-S. 

What’s really telling is that functional testing of hormones like estradiol, LH, FSH, and thyroid markers can catch these patterns before your cycle actually stops. 

Losing your period is not the first sign of trouble. It’s often a late-stage sign. Lab work can reveal early hormone suppression and adaptation while you’re still training hard, still hitting your paces, and still thinking this is just what endurance training feels like. 

The Estrogen Advantage, Until It Isn’t

Healthy estradiol levels do much of the behind-the-scenes work that makes endurance training possible. They help your muscles store glycogen, keep blood flowing to working tissues, and make sure your bones can rebuild after each run or ride. 

When estrogen is at healthy levels, you can handle heavy training loads, recover between sessions, and your bones stay strong enough for high-impact activity. 

But estrogen is also one of the first things to decrease when the body senses it is using more energy than it is getting. 

If training load increases while energy intake drops, or if stress and lack of sleep add up, estradiol can go down. 

When this happens, the effects show up in not-so-favorable ways for endurance athletes: 

• Workouts feel harder than they used to

• Recovery gets slower

•  

  Mood gets flat

• Endurance starts to diminish, even if you’re doing “everything right” 

The bone piece is where it gets serious. 

In female athletes, low estrogen is linked to a three times higher risk of stress fractures. Bone repair and renewal cannot keep up with repeated impact. 

This is why functional clinicians get an early advantage by monitoring estradiol and progesterone to check ovarian output and ovulation patterns, and LH/FSH to spot hypothalamic suppression and signs of low energy. 

Do not wait until your period disappears. Or you’re sidelined with a stress fracture. It’s too late. The point is to catch this early so you can start training smarter, fuel better, and really recover. 

If training feels harder and recovery is slowing down, it’s worth checking what the hormones are doing behind the scenes. The Access Labs Hormone Panel helps clinicians measure estradiol, progesterone, and related markers so you can catch low estrogen early. 

Markers for Estrogen and Progesterone Evaluation

Thyroid, Cortisol, and the Fatigue Feedback Loop

When women who train hard start feeling exhausted, no matter how much they sleep, dragging through workouts, or taking forever to bounce back, the problem is often not motivation or fitness. 

It is usually a matter of physiology, especially the way thyroid hormones and cortisol interact under ongoing training stress. 

Your thyroid runs the show when it comes to metabolism, energy production, and body temperature regulation. 

Under normal circumstances, your body takes T4 (the inactive form) and converts it to T3 (the active form that actually fuels your cells). But when you’re dealing with chronic training stress, not eating enough, or running a calorie deficit for too long, that conversion process starts breaking down. 

Research on female endurance athletes who aren’t getting enough energy shows their T3 levels decrease, even when their TSH looks totally normal on paper. 

This is a protective response. The body slows metabolism to conserve energy when it senses there isn't enough. 

At the same time, cortisol levels often go up. 

In short bursts, cortisol is helpful. It mobilizes fuel and supports training. But when cortisol remains high for a long time, it can interfere with recovery, sleep, immune function, and thyroid function. 

High cortisol combined with low T3 creates a cycle in which athletes feel exhausted yet restless, struggle to recover, and see less progress from training. 

Without lab work, this pattern flies under the radar. Your weight might hold steady. You’re still getting your workouts done. But internally, your body has shifted into conservation mode. 

When fatigue lingers and progress stalls, thyroid markers can tell a different story than symptoms alone. The Access Labs Wellness Basic Panel includes key thyroid tests that help clinicians spot metabolic slowdown early, before exhaustion becomes your new normal. 

Biomarkers to Monitor Adrenal and Thyroid Recovery

RED-S and the Energy Deficit No One Talks About

RED-S (Relative Energy Deficiency in Sport) means that you’re not giving your body enough fuel to handle both your training and everything else it needs to do to function. 

For women who run, bike, or swim serious miles, RED-S rarely looks like crash dieting or dramatic weight loss. Instead, it’s a slow-building gap between training volume and consistent fueling. 

Over time, the body adapts by cutting back where it can. 

Hormone production slows down. Estrogen drops. Thyroid output reduces. Leptin falls, telling your brain energy is limited. Cortisol stays high to keep you moving. This doesn’t all crash at once, and your period doesn’t have to disappear right away for it to be happening. 

That’s exactly why RED-S gets missed so often. 

Research shows up to 60% of female endurance athletes have at least one RED-S-related biomarker, even though they’re still training and racing regularly. 

The fallout? Constant fatigue, getting sick more often, recovery that drags, low sex drive, cycles that go haywire, and stress injuries piling up, all because the body isn’t getting enough fuel to run the operation. 

Key Lab Markers to Detect RED-S

When (and When Not) to Consider HRT in Female Athletes

For women in menopause or those with confirmed estrogen deficiency that’s not caused by undereating or overtraining, HRT can bring back energy, stabilize mood, improve sleep, and protect bones. 

Here, the therapy replaces what the body has stopped making on its own. The aim is long-term health and staying functional in training. 

Things get trickier with younger endurance athletes who still get periods (or who used to). 

If low estrogen, cycle issues, or thyroid problems stem from not eating enough, RED-S, or relentless stress, slapping HRT on top won’t fix what’s broken underneath.  

Markers to Monitor Hormone Therapy

Hormonal Resilience Is Performance Resilience 

For female endurance athletes, hormonal changes are not just part of training. They are often the body’s early warning sign that training, recovery, and nutrition are out of balance. 

The tough part is that women can keep going for a long time while things slowly get worse. You can still run your miles, still show up, still look healthy, and still have low estrogen and progesterone, slow thyroid, and high cortisol without knowing it. By the time your period stops or a stress fracture happens, the problem has usually been building for a while. 

Functional lab tests can spot these patterns earlier. 

Tracking estradiol, progesterone, LH/FSH, thyroid markers (especially Free T3), cortisol, and energy markers like ferritin and leptin can help clinicians spot early signs before burnout becomes your normal. 

The solution is not to push harder. It is to adjust what you put in with better nutrition, smarter training plans, and real recovery. 

The real success is not just finishing the next race. 

It is building a body that can keep doing what it loves for years to come. 

If you want a clearer picture of what patient’s body is telling you, the Access Labs Hormone Panel provides comprehensive insight into estrogen, thyroid, cortisol, and energy-related markers. It gives clinicians the data they need to support sustainable training, recovery, and long-term health.

 

Disclaimer: Content on the Access Labs blog is for informational purposes only and reflects the views of individual contributors, not necessarily those of Access Medical Labs. We do not endorse specific treatments, products, or protocols. This content is not a substitute for professional medical advice. Always consult a qualified healthcare provider regarding any medical concerns.