Why The Fittest Men In The Room Can Have The Lowest T

Male endurance athletes often look like they’ve optimized everything. Mileage. VO₂ max. Nutrition tracking. Recovery tools.  

But hormones tell a more complete story, one that many athletes and clinicians overlook.  

Behind the long runs and high training loads, many male endurance athletes show a consistent hormonal profile: lower testosterone and IGF-1, higher stress hormones, and thyroid shifts. 

Studies on low energy availability in men link these hormone shifts to reduced performance, bone stress, and metabolic strain, even in athletes who appear “fit” on paper.  

These markers shape endurance, recovery, bone density, motivation, and long-term metabolic health. They also influence clinical decisions around training load, nutrition planning, and when to consider further workup or hormone therapy. 

This is the hormonal conversation many male athletes are not having, and many clinicians are still catching up to. It needs to move into routine practice. 

This article builds upon our previous article, "Testosterone, IGF-1, and HRT: How Hormones Impact Endurance Training," focusing specifically on male physiology to provide insights for both practitioners and the athletes they coach. 

Comprehensive Hormone Panels at Access Medical Labs offer insights into hormone levels, which may help practitioners understand potential influences of training on hormones like testosterone, IGF-1, cortisol, and thyroid function. 

Key Takeaways 

• Low testosterone, reduced IGF-1, high cortisol, and thyroid shifts are common in male endurance athletes, particularly in athletes with energy intake that does not match their training demands, consistent with RED-S criteria.
• Chronic high-volume endurance training can lead to an “exercise hypogonadal” pattern (low testosterone with normal LH/FSH), where the priority is correcting training load, fueling, and sleep before considering hormone replacement therapy.
• IGF-1 and growth hormone provide insight into anabolic recovery capacity, while cortisol and DHEA-S help distinguish between everyday training stress and maladaptation and overtraining.
• HRT in male athletes is appropriate mainly for confirmed organic hypogonadism; it requires careful cardiovascular and safety screening and must comply with WADA/USADA rules to restore normal physiology rather than enhance performance.
• A testing roadmap establishes a baseline of hormones, enabling clinicians to pair subjective symptoms with objective data using Access Medical Labs panels 

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

• The Physiology Of Male Hormones In Endurance Training
• The Testosterone Paradox In Male Endurance Athletes
• IGF-1 And Growth Hormone For Recovery
• Cortisol, Energy Availability, And Overtraining
• When (And When Not) To Consider HRT In Male Athletes
• Male Endurance Athlete Testing Roadmap
• What This Means For Male Endurance Athletes 

The Physiology of Male Hormones In Endurance Training

Endurance training places continuous demands on the endocrine system. When fueling and recovery match the workload, hormone patterns in men tend to support performance.  

Testosterone helps maintain muscle repair and drive. IGF-1 supports tissue remodeling, and cortisol levels rise and then return to normal levels in line with training stress.  

With sustained high weekly volume and inconsistent energy intake, these systems begin to shift. 

The body begins to prioritize conservation over performance, a pattern observed in male endurance athletes.  

Research on RED-S in men links low energy availability with reduced testosterone, reductions in IGF-1, and disrupted thyroid activity when training stress consistently exceeds fueling needs. 

Testosterone, cortisol, IGF-1, and thyroid hormones all respond to endurance training; however, their responses do not occur in isolation.  

As mileage increases and recovery windows shrink, testosterone often trends downward, cortisol remains high for longer, and IGF-1 declines as the body attempts to reduce metabolic demands.  

Thyroid hormones follow the same conservation pattern. Free T3 commonly drops, even when TSH remains within range, indicating an adaptive response to prolonged stress and insufficient energy intake.  

These shifts are not outliers. They appear in endurance-focused cohorts, ranging from recreational runners to competitive athletes. 

RED-S in male athletes was historically underrecognized, but the data now show that men experience the same low-energy–driven hormonal changes long associated with female athletes. 

Reduced testosterone, a lower metabolic rate, and changes in bone turnover can occur even when weight, leanness, and outward performance metrics appear stable.  

This makes RED-S in men harder to identify without laboratory data, and easier to miss until symptoms such as fatigue, slower recovery, decreased motivation, or unexplained plateaus begin to surface. 

The result is a physiologic environment that may support short-term training blocks but undermines performance sustainability and health. 

Many male endurance athletes maintain the appearance of peak fitness while operating under a hormonal profile shaped by prolonged stress, under-fueling, and high training demands.

The Testosterone Paradox in Male Endurance Athletes 

In male endurance athletes, testosterone often moves in the opposite direction of what you would expect from someone who trains hard and appears metabolically healthy.  

Data show that long-term high volumes of aerobic training are associated with lower resting testosterone levels compared to non-athletic training, even when body composition and overall health appear robust. 

Proposed mechanisms center on long-term adaptation of the hypothalamic–pituitary–gonadal (HPG) axis. With endurance stress, the brain appears to reset its “set point” for testosterone, keeping androgen levels lower at rest while maintaining enough output to sustain training.  

Multiple studies describe men with reduced total testosterone but luteinizing hormone (LH) and follicle-stimulating hormone (FSH) values that are normal, suggesting a central adjustment rather than primary testicular failure. This pattern is often termed the “exercise hypogonadal male condition” or exercise-induced hypogonadism.  
 
On labs, this presents as low total testosterone with normal-range LH and FSH, stable prolactin, and no obvious structural pituitary disease.  

For some athletes, performance remains intact for a period of time. 

Over the course of months to years, however, symptoms begin to align with the numbers.  

Management strategies for hormone levels should be discussed with a healthcare provider to determine the best approach for individual needs.  

The first step is addressing the training and energy environment. That includes verifying caloric adequacy relative to training load, increasing carbohydrate availability around key sessions, and introducing planned lower-load weeks or blocks.  

As energy availability improves and cumulative stress is reduced, some athletes exhibit partial or complete normalization of testosterone levels without pharmacological intervention.  

The “testosterone paradox” in male endurance athletes is less about isolated gland failure and more about an endocrine system adapting to chronic training stress and, frequently, low energy availability.  

Lab testing that tracks total and free testosterone alongside LH, FSH, SHBG, and markers of energy status provides a means to distinguish primary hypogonadism from this exercise-related pattern and to design interventions that protect both current performance and future musculoskeletal and metabolic risk. 

Clinical Markers for Testosterone Evaluation

IGF-1 And Growth Hormone For Recovery

IGF-1 and growth hormone are key regulators of recovery in male endurance athletes. 

Growth hormone released during and after exercise stimulates hepatic IGF-1 production, and IGF-1 subsequently supports muscle protein synthesis, tissue repair, and the remodeling capacity of tissues after training. 

IGF-1 functions as a biomarker of anabolic recovery capacity. Low IGF-1 levels in a high-volume athlete can suggest limited recovery, inadequate fueling, or an accumulated workload, especially when accompanied by low testosterone or complaints of "feeling flat" or "not bouncing back." 

Low energy availability, insufficient protein intake, and micronutrient deficiencies can impair IGF-1, while interrupted sleep reduces growth hormone release and subsequently affects IGF-1 levels over time.  

Pairing IGF-1 with GH, testosterone, and cortisol helps move into targeted adjustments in training load, fueling, and sleep. 

Biomarkers To Monitor Recovery

Cortisol, Energy Availability, And Overtraining

Cortisol is one of the most informative and often misunderstood markers in male endurance athletes.  

In short bursts, it is adaptive. It mobilizes fuel, supports alertness, and helps the body respond to training stress.  

But with high mileage, repeated intensity sessions, or chronic low energy availability, cortisol begins to shift from an acute response to a sustained one. 

Studies in endurance athletes show that consistently high cortisol levels are associated with signs of maladaptation, including impaired recovery, reduced performance, and metabolic strain. 
 
This often looks like insomnia, irritability, difficulty completing once manageable sessions, or a performance decline despite increased effort. 

DHEA-S provides additional context. As an adrenal androgen, DHEA-S tends to fall when chronic stress is present, making the cortisol-to-DHEA-S relationship valuable for assessing overall adrenal balance.  

Combining cortisol with DHEA-S, testosterone, and IGF-1 enables a more comprehensive assessment of whether an athlete is adapting to the load or drifting toward overtraining. 

When (And When Not) To Consider HRT In Male Athletes 

Hormone replacement therapy (HRT), particularly testosterone replacement therapy (TRT), has a role in male athletes. Still, the bar for treatment should be high and grounded in hypogonadism rather than performance goals.  

Appropriate use cases include documented testosterone deficiency with symptoms and an identifiable organic cause (primary or secondary hypogonadism), and in some aging athletes with confirmed late-onset hypogonadism after reversible factors have been addressed.  

Data suggest that TRT aimed at restoring physiologic testosterone ranges does not increase overall cardiovascular event rates, although vigilance is still required.  

In the broader context of hormone therapy, Dr. Thierry Hertoghe, President of the International Hormone Society, summarizes the rationale: "In my experience, the most important cause of aging that we can treat is hormone deficiencies." 

By contrast, functional low testosterone related to overtraining, low energy availability, or short sleep is not an HRT-first scenario.  

In these athletes, training volume, fueling, sleep, and any underlying energy deficiency consistent with RED-S must be addressed before considering pharmacologic therapy.  

There are also limits. Exogenous testosterone and many other anabolic agents are prohibited at all times under the WADA Prohibited List (S1 Anabolic Agents), and peptide hormones and growth factors such as GH and IGF-1 fall under S2.  

Any athlete on these therapies while competing in a regulated sport must navigate Therapeutic Use Exemption (TUE) rules, and approvals for age-related or functional hypogonadism are uncommon.  

Cardiovascular risk, polycythemia, sleep apnea, prostate disease, and thrombosis risk also need systematic evaluation before starting or continuing TRT, in older athletes or those with existing cardiovascular disease.  

The objective is to achieve symptom relief and normalize validated biomarkers (testosterone, LH/FSH, hematocrit, PSA, and lipids).  

To hear a deeper discussion of how experts think about hormone therapy, aging, and risk–benefit decisions, you can watch the Access Labs webinar with Dr. Thierry Hertoghe.  

Male Endurance Athlete Testing Roadmap 

With the right testing plan, athletes can separate ‘this is just hard training’ from ‘my system needs help.’ This roadmap organizes the labs in sequence, allowing you to pinpoint issues, adjust your approach, and track performance over time. 

1. Establish the baseline

Before adjusting training, nutrition, or hormones, athletes need a clear snapshot of their internal physiology.  

A Comprehensive Male Hormone Panel establishes reference points for testosterone, estradiol, LH/FSH, SHBG, thyroid markers, and metabolic indicators. This becomes the comparator for all future testing and is essential before considering HRT. 

2. Assess the recovery stress 

Endurance athletes often train close to their upper limit. A paired cortisol and DHEA-S panel reveals how the adrenal system is responding to that load. Cortisol trends capture both acute and accumulated stress, while DHEA-S reflects longer-term adrenal output and resilience. 

3. Monitor anabolic markers 

To understand muscle repair capacity, adaptation, and training responsiveness, IGF-1 and growth hormone provide essential data. Low levels can indicate maladaptation, under-recovery, poor sleep, or nutrient insufficiency. 

4. Re-test after intervention  

Testing only matters if you track the response. After adjusting training load, nutrition, recovery strategies, or therapy, repeat labs reveal whether biomarkers are trending toward optimal ranges.  

Longitudinal data is the most reliable way to confirm whether interventions are working or if further investigation is needed. 

What This Means For Male Endurance Athletes 

For male endurance athletes, hormone data is central to understanding adaptation, recovery, and long-term health. 

This low-androgen, high-stress hormone picture can coexist with normal body composition and consistent training.  

Without lab data, these patterns can be easily missed or misattributed to “normal” training fatigue. 

The path forward is structured and data-driven: align hormone data with training, fueling, and recovery decisions, and re-test to confirm that changes are moving physiology in the right direction. 

Training load, nutrition, sleep, and RED-S require attention before pharmacological steps; HRT should be reserved for cases of defined hypogonadism to restore normal physiology. 

Access Medical Labs provides the Hormone Panels needed to support this approach in practice, from comprehensive hormone baselines to targeted markers like cortisol, DHEA-S, and IGF-1. 

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.

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