Why testosterone and cortisol alone are not the full story

Both hormones are relevant to training, but both are hard to read from a single result. They follow a daily rhythm: cortisol peaks roughly 30 minutes after waking and then declines, while testosterone is highest on waking and falls through the day.1Hard exercise shifts them further. After exhaustive endurance exercise, cortisol rises and free testosterone falls, and levels typically take 48 to 72 hours to return to baseline, although recovery time varies considerably between individuals and with the type of session.2 A reading taken at the wrong time of day, or in the days after a big session, can look abnormal when nothing is wrong.

The testosterone-to-cortisol ratio is often described as a way to tell whether training and recovery are in balance. International consensus statements are clear that no single hormonal measure, including this ratio, can diagnose overtraining in an individual athlete.3,4A reduced free testosterone-to-cortisol ratio is often seen alongside overtraining, but as an associated finding rather than a diagnostic test.4 Across groups of athletes, a rising ratio over a training block may be associated with positive adaptation.5 That is a population-level pattern, and it has not been prospectively validated as a tool for interpreting one person's result. It is best read alongside how you actually feel and perform, not as a verdict on its own.

There is also a common misreading worth naming. A low testosterone result in a training athlete is not always a problem with the testes. Low energy availability, meaning too little fuel for the training load, can lower testosterone in male athletes.6–8That distinction changes what you do about it. What a basic hormone snapshot does not cover is everything happening around those two hormones: iron status, thyroid function, inflammation, cardiovascular and metabolic markers, and how well you are fuelled.

Iron and ferritin: the most common nutrient issue in athletes

Ferritin is the protein that stores iron, and blood ferritin is the usual indirect measure of iron reserves. Iron deficiency is described as the most common nutrient deficiency in athletes. International studies estimate it affects roughly 15–35% of female athletes and 5–11% of male athletes.9–12These estimates depend heavily on the ferritin cut-off used. A meta-analysis of collegiate athletes that used a higher threshold (ferritin below 50 μg/L) found a pooled prevalence of around 54%.12 Comparable Australian athlete data are limited, so these figures come from overseas cohorts.

The causes are multifactorial. They include menstrual blood loss, losses through sweat and the gut, the breakdown of red blood cells under repeated foot strike, and a rise in the hormone hepcidin after exercise. Hepcidin peaks around three to six hours after a session and temporarily reduces how much iron the gut absorbs.10,13,14How much each of these contributes varies from person to person, and they have not been definitively ranked.10

For performance, two situations are worth separating. Where iron deficiency has progressed to anaemia, restoring iron reliably improves performance by restoring the blood's oxygen-carrying capacity.15,16 Where iron stores are low but haemoglobin is normal, the evidence is mixed. About half of trials show a performance benefit from supplementation, mostly those in athletes with ferritin at or below 20 μg/L, and half show none.15,16 A recent randomised controlled trial in iron-deficient, non-anaemic women found improvements in running economy and fatigue with intravenous iron, but no change in peak aerobic capacity (VO2peak).17 One commentary re-analysing the trial data has suggested the benefit may shrink gradually as baseline ferritin rises, rather than stopping at a fixed cut-off. This is the author's interpretation rather than an established finding.18 Treat low ferritin without anaemia as worth investigating with a practitioner, not as a settled explanation for fatigue.

One interpretation trap: ferritin also rises in response to inflammation. A normal-looking ferritin does not always rule out low iron stores, which is why it is usually read alongside an inflammatory marker and a full blood count.10None of these sit in a basic hormone panel.

Thyroid function: relevant when there is a reason to look

Thyroid hormones regulate metabolic rate. An underactive thyroid can cause fatigue, weight change and reduced exercise tolerance, which overlap with ordinary training fatigue.19,20 Two caveats matter. Overt thyroid disease is uncommon in young, otherwise healthy adults, and current guidelines do not support routine thyroid screening in people without symptoms. Testing is best reserved for those with symptoms or recognised risk factors, such as autoimmune disease or a family history.19,21,22No athlete-specific prevalence data are available. Second, under-fuelling can lower the thyroid hormone T3, so an unusual thyroid result in a hard-training athlete may reflect energy availability rather than thyroid disease.6,8 Results are best interpreted by a practitioner who knows your training context.

Fuelling: the explanation that is easiest to overlook

Taking in less energy than training demands, over weeks to months, is known as relative energy deficiency in sport (REDs). It can lower reproductive hormones, including testosterone, reduce T3 and lower bone mineral density.6,7These effects are increasingly recognised in men as well as women.6–8 In one study of male Olympic-level athletes with low resting metabolic rate, a quarter had subclinical low testosterone.8 REDs is also linked to more frequent illness, although the evidence for that specific outcome is more indirect.23

This matters for testing because low energy availability can shift several of the results above at once. If fatigue and stalled performance are the reason for testing, fuelling is worth reviewing alongside the bloods, ideally with a sports dietitian or sports physician.

Inflammation and recovery markers

Markers such as creatine kinase and C-reactive protein (CRP) reflect muscle damage and the body's inflammatory response. CRP rises after hard exercise, typically peaking around 24 hours later, then settles with recovery.24

Using these markers to fine-tune an individual's training is a different matter. There are no validated individual thresholds that indicate readiness to train; only group-level trends have been described.3,4Where they are useful is context: an inflammatory marker that stays elevated with no recent hard session is a reason to look for another cause, rather than write the fatigue off as training.

Cardiovascular and metabolic markers

For most people, the cardiovascular benefits of regular exercise far outweigh its risks.25Being fit does not make standard markers such as cholesterol and blood glucose irrelevant, though. They sit alongside the hormone picture, not instead of it, and are most useful tracked over time. One area deserves careful description. In men who have done long-term, high-volume endurance training, studies report higher coronary artery calcium scores than in less active men.25–28 This has not been shown in female masters endurance athletes.27 The plaque in athletes tends to be more calcified and stable. Higher fitness partly offsets the risk linked to a high calcium score, but does not remove it.25,27,28 Atrial fibrillation, an irregular heart rhythm, also appears more common in highly trained endurance men after many years of training. One narrative review of observational studies puts the increase at roughly three to five times; this figure has not been confirmed by a meta-analysis and is best read as an approximate estimate. Absolute risk remains low, and the relationship with training volume appears U-shaped.26 These findings apply to a specific group, male masters endurance athletes, and are a reason for an individual conversation with a doctor rather than a general concern.

Matching the panel to the question you are asking

Not every athlete needs the same panel. The right starting point depends on what you are trying to understand.

• A general hormone snapshot. Testosterone, cortisol and related markers, as a first check or periodic monitoring point. The Sports Hormone Check covers this. • A fuller hormone picture. Testosterone, free testosterone, SHBG, LH and FSH together, useful where a basic panel has raised a question worth following up. The Advanced Male Sports Hormone Test covers this. • The broader male hormone picture beyond training. Relevant where symptoms extend into general wellbeing, libido or mood rather than training performance alone. The Comprehensive Male Hormone Test covers this. • Iron, thyroid, inflammation, cardiovascular and hormone markers together. For athletes who want these systems covered in one order, with results reviewed by a practitioner. The Men's Platinum Health Test covers this. • The same panel plus genetic markers. Research shows that genetic variation can influence athletic traits such as endurance, strength and injury susceptibility, with links reported for variants including ACTN3 and ACE. Each variant tends to have a small effect, and genetic results alone cannot predict how an individual will perform, recover or get injured.29–33 Some variants in collagen genes such as COL1A1 and COL5A1 have been associated with tendon and ligament injury risk, and variants in inflammation genes such as IL6 with recovery.34,35 Hormones may play a part too. Oestrogen influences collagen synthesis and the stiffness of tendons and ligaments, and this is one proposed explanation for differences in injury risk between women and men, although it has not been established as the cause.36,37 Clinical and functional testing is needed to understand how much these factors are actually playing out for you. The Men's Platinum Health & DNA Test covers this. • The broadest picture: blood, functional and genetic markers together. Iron, hormone, thyroid, inflammation, metabolic and electrolyte markers alongside the genetic markers above. The panel also includes functional markers such as urinary organic acids. Organic acid testing is an established tool for diagnosing inherited metabolic disorders.38 For athletes, these markers are best treated as exploratory. The Precision Athlete Blueprint covers this.

A hormone-only check answers a narrower question than most athletes have. If fatigue, recovery or performance are the reason for testing, the explanation often sits outside a basic hormone panel: iron, inflammation and fuelling among them, with thyroid worth checking when symptoms or risk factors point that way.

Testing without a GP referral

All of the tests above can be ordered online without a GP referral, collected at a partner collection centre, and reviewed through the online dashboard once a NATA-accredited laboratory has processed the results. The Athletic Performance & Recovery hub groups the full range in one place. This article is for general information and does not replace advice from a qualified health practitioner. Always discuss test results with a GP, sports physician or other treating practitioner.