How Overtraining Wrecks Your Hormones After 40 (It's Not Just Cortisol)

If your testosterone is low — or trending in the wrong direction — the instinct most athletes have is to ask how to increase it. That's understandable. But it's actually the second question you should be asking.

The first question is: what's suppressing it?

In athletes, and especially in masters athletes over 40, low testosterone is very rarely a primary hormonal failure. It's almost always a downstream consequence of something happening upstream in the physiological system. If you don't identify what that is, you're treating a symptom while the actual driver keeps running — and nothing you do to the number will hold.

This article gets into the specific mechanism of how training stress suppresses hormones, why it hits harder after 40 than it would have a decade ago, and what that tells us about how to actually fix it.

Prefer to watch? The full video is below — or keep reading for the expanded breakdown

The Stress-Hormone Relationship Most Athletes Have Never Had Explained

Your body has a fundamental hierarchy of priorities. Survival comes first. Everything else — including building muscle, adapting to training, and producing anabolic hormones like testosterone — comes after.

When your body detects sustained high physiological stress, it shifts resources toward immediate energy production and away from long-term functions. Recovery, tissue repair, reproductive hormone production, performance adaptation — all of these get downregulated when the stress signal is high enough or sustained long enough. This is orchestrated primarily through the HPA axis — the hypothalamic-pituitary-adrenal axis — which governs the cortisol response.

Here's the specific suppression pathway, because understanding it changes how you think about the intervention.

When the hypothalamus detects sustained stress, it signals the pituitary through corticotropin-releasing hormone (CRH). The pituitary responds by releasing ACTH, which drives cortisol production from the adrenal glands. Appropriate acute stress physiology so far.

But here's where the cascade becomes a problem for testosterone. The pituitary is also responsible for releasing LH — luteinizing hormone — the primary signal that drives testosterone production in both men and women. When cortisol is chronically elevated, it suppresses GnRH (gonadotropin-releasing hormone) from the hypothalamus. Less GnRH means less LH from the pituitary. Less LH means less testosterone production downstream. This is sometimes called functional hypogonadism — the gonads are capable of producing testosterone, but the upstream signal telling them to do so has been suppressed by the stress response.

And there's a second mechanism running simultaneously: cortisol and testosterone compete for shared precursor hormones in the adrenal pathway. So elevated cortisol doesn't just reduce the signal for testosterone production — it also competes for the raw materials.

Two distinct suppression mechanisms, operating at once. And both become more significant after 40, because baseline testosterone production is already declining — meaning you have less buffer to absorb that suppression before it becomes functionally significant.

The Four Drivers of Hormonal Suppression in Masters Athletes

1. Chronic Cortisol Elevation From Training Load

Short-term cortisol increases from hard sessions are normal and appropriate — that's acute stress physiology working correctly. The problem is when training load is high enough and recovery is insufficient enough that cortisol stays elevated between sessions rather than returning to baseline.

For masters athletes specifically, the threshold for this is lower than it was a decade ago. The same weekly training volume that the HPA axis absorbed at 32 may now be sufficient to chronically suppress the GnRH-LH-testosterone axis. This is a predictable consequence of the physiological changes that accompany aging — not a sign of weakness or declining capability. The distinction matters: you're not less capable of training hard. You're less capable of absorbing the cortisol consequences of training hard without adequate recovery. That's a meaningful and widely underappreciated difference.

2. Low Energy Availability

When caloric intake doesn't meet training demand, the hypothalamus detects an energy deficit and downregulates reproductive hormone production as a direct consequence. This is the RED-S mechanism — Relative Energy Deficiency in Sport — and it operates independently of training stress. An athlete who is both under-fueling and under-recovering is being hit by two separate suppression mechanisms simultaneously.

This is one of the most common findings in masters athletes specifically — because the body composition concerns that intensify in the fourth and fifth decades drive many athletes toward caloric restriction at exactly the stage of life when hormonal buffer is smallest. The hormonal consequences of under-fueling don't wait. They're operating continuously in the background while intake is insufficient.

3. Sleep Disruption

The majority of LH pulsatility — the hormonal signal that drives testosterone production — occurs during sleep, specifically during deep slow-wave sleep cycles. When sleep is shortened or fragmented, that LH signal is disrupted, and testosterone production drops as a direct downstream consequence.

This operates through a distinct mechanism from the cortisol-GnRH pathway above — meaning sleep disruption suppresses testosterone through its own independent channel, separate from and in addition to the training stress pathway. For masters athletes dealing with the sleep architecture changes that come with age, this is a compounding factor that frequently goes unaddressed because it's treated as an inevitable feature of aging rather than an addressable driver of hormonal suppression.

4. The Chronic Overtraining Hormonal Cascade

When training stress consistently exceeds recovery capacity over weeks and months, the HPA axis goes through a predictable progression.

In the early phase, cortisol is chronically elevated — the system is working overtime trying to manage a load it can't keep pace with. Testosterone suppression through the GnRH pathway is significant and ongoing.

In more advanced or prolonged cases, the HPA axis exhausts its output capacity. Cortisol becomes flattened and blunted — the system can no longer generate appropriate cortisol even when it should. At this stage, DHEA typically drops significantly as well.

DHEA deserves specific attention here, because it's one of the most commonly overlooked markers in this population. DHEA is not just a testosterone precursor — it's an anabolic hormone in its own right, with independent roles in tissue repair, immune regulation, and energy production. And unlike testosterone, which receives significant clinical attention, DHEA is frequently absent from standard hormone panels.

Critically for masters athletes: DHEA naturally declines with age even more rapidly and consistently than testosterone. Levels peak in the mid-20s and drop significantly through the 40s and 50s — often more dramatically than testosterone over the same period. Layer overtraining-driven cortisol elevation on top of that natural decline, and the adrenal pathway that's already producing less DHEA gets further diverted toward cortisol production. The clinical consequences — impaired tissue repair, reduced training tolerance, immune suppression, fatigue, mood changes — frequently get attributed to other causes because DHEA specifically isn't being measured.

The Thyroid Connection: One More Piece That Gets Missed

Chronic high cortisol impairs the conversion of T4 to the active T3 form of thyroid hormone in peripheral tissues. The thyroid produces T4 normally. TSH from the pituitary may look completely fine. But the active T3 that cells actually use is being generated at a reduced rate — and you don't see that unless Free T3 is specifically measured alongside TSH and Free T4.

For masters athletes, this matters because the symptoms of impaired T3 — fatigue, cold intolerance, slowed metabolism, weight changes, poor recovery, cognitive slowing — overlap significantly with the general picture of overtraining and low testosterone. They compound each other. Treating the testosterone piece without identifying impaired thyroid conversion means leaving a meaningful part of the physiological picture unaddressed, and wondering why progress is slower than it should be.

SHBG: Why Total Testosterone Can Look Acceptable While Functional Availability Is Low

Sex hormone-binding globulin (SHBG) can increase under conditions of chronic stress and low energy availability — and SHBG binds testosterone, rendering it biologically inactive. The free testosterone fraction — the portion actually available to tissue — is what drives the functional effects athletes care about.

An athlete can have total testosterone that falls within a "normal" reference range while free testosterone is meaningfully suppressed — because SHBG is binding a disproportionate share of what's available. This is why total testosterone alone is an insufficient picture, and why SHBG needs to be part of the panel. The pattern across all three — total testosterone, free testosterone, and SHBG — tells you something that no single marker does.

How This Presents Differently: Men vs. Women After 40

In men over 40, this cascade compounds natural andropause. Baseline testosterone is already declining, SHBG often rises with age which further reduces the free fraction, and the cortisol-to-testosterone ratio from training stress tips an already-challenged system further out of balance. The clinical picture — declining performance, loss of strength, poor recovery, reduced libido, mood changes, fatigue that doesn't respond to rest — gets attributed reflexively to aging when a meaningful part of it is the addressable suppression cascade described above.

In women over 40, the picture is more complex because it's occurring alongside the perimenopausal hormonal transition. Estrogen and progesterone are shifting dramatically, and testosterone — already lower in absolute terms — is often declining simultaneously. The overtraining-driven suppression of GnRH affects both the sex hormone pathways and the adrenal testosterone production that becomes increasingly important as ovarian production declines. Female masters athletes in perimenopause are particularly vulnerable to this cascade — and it's dramatically underdiagnosed because symptoms get attributed entirely to menopause rather than to the specific and addressable contribution of overtraining-driven hormonal suppression layered on top of it.

What to Actually Do

The intervention has to address the specific drivers rather than just the number — and for masters athletes, that requires more deliberate action than a younger athlete would need.

Reduce total stress load — training volume, intensity, and frequency — enough to create space for the HPA axis to recalibrate. For masters athletes, this is often a more aggressive reduction than feels comfortable, but the HPA axis at this stage of life doesn't respond to partial measures the way it might have at a younger age.

Correct energy availability immediately and consistently — adequate carbohydrates, total calories that genuinely match training demand, and protein in the range of 1.6 to 2.2 grams per kilogram. The hormonal consequences of under-fueling operate continuously; they don't pause while you get around to addressing them.

Protect sleep deliberately — because deep sleep is both when testosterone is produced and when the HPA axis recalibrates. Protecting sleep quality and duration is a direct hormonal intervention, not an ancillary wellness recommendation.

Support the dysregulated systems with targeted compounds:

• Magnesium glycinate or malate at 300 to 400 milligrams of elemental magnesium daily for nervous system regulation and sleep quality
• Omega-3 fatty acids at 2 to 4 grams of combined EPA and DHA for inflammation management and recovery
• Ashwagandha (KSM-66 or Sensoril) at 300 to 600 milligrams daily — with consistent clinical evidence for cortisol reduction and downstream improvements in testosterone through the HPA axis mechanism described above
• Rhodiola at 400 to 600 milligrams in the morning for stress resilience and mitochondrial function under physiological stress

The Testing Panel That Reveals the Full Picture

For masters athletes dealing with this hormonal pattern, the specific markers worth evaluating:

Multi-point salivary cortisol — four samples across the day — to map the full diurnal rhythm. Not whether cortisol is simply high or low, but what the pattern looks like: chronically elevated, blunted and flat, or inverted. Each pattern has different implications and requires a different intervention.

Total testosterone, free testosterone, and SHBG together — because free testosterone is often where the real suppression is visible while total testosterone still looks acceptable.

DHEA-S — the sulfated storage form, most accurately measured in blood — which is frequently depressed in overtrained masters athletes and consistently overlooked in standard panels.

Complete thyroid panel: TSH, Free T4, and Free T3 — because cortisol-driven impairment of T4-to-T3 conversion doesn't show up in TSH or T4 alone.

Ferritin — iron deficiency is extremely common in endurance athletes and directly affects energy production, compounding fatigue and recovery impairment across every other system involved.

Gut permeability markers — zonulin and anti-LPS antibody — because increased intestinal permeability drives systemic inflammation that compounds the hormonal suppression picture, and it's present far more commonly in endurance athletes than most practitioners appreciate. You can measure these, and a lot more on the Gut Zoomertest.

When you look at these markers together, you stop seeing isolated numbers and start reading a pattern. And the pattern — not any single value — is what tells you where the intervention actually needs to happen.

The Framing That Changes Everything

When testosterone is low after 40, the first question is always what's suppressing it — not just how to raise it. The suppression mechanism runs from chronic training stress through HPA axis dysregulation through GnRH suppression to reduced LH output to lowered testosterone production. It's a predictable, measurable, and largely addressable cascade — but it's running on top of a natural decline that means the buffer for tolerating that suppression is smaller than it was a decade ago.

Fix the upstream drivers. Support the dysregulated systems. Use lab testing to identify the specific pattern rather than guessing at which part of the cascade is most disrupted. And separate what's addressable from what's genuinely age-related — because that distinction is everything for a masters athlete who still has serious training ahead of them.

Dr. Jason Barker is a naturopathic doctor with over 20 years of clinical experience working with endurance athletes. He is a two-time Ironman finisher and the founder of Natural Athlete Clinic. For individualized hormone testing and performance-focused protocols for masters athletes, visit naturalathleteclinic.com.