“Healthy” fitness equals low testosterone (and other health issues)

“But he’s so fit!”

“His heart rate is 40bpm!”

“He can run a mile close to 4 minutes!”

“He’s done over 10 marathons!”

“He is below 10% bodyfat!”

“How could something like that have happened to someone so fit and healthy?”

This is the typical reaction most people give when someone, who’s known for their status in “healthy” fitness, performance, and/or health starts to suffer.

Let’s redefine healthy fitness

Movement can be very beneficial in terms of promoting blood flow, improving insulin sensitivity, enhancing tissue oxygenation, CO2 production, synthesizing and releasing androgens, etc.

We are maximally healthy when we are euthyroid. A few measures for being euthyroid include, normal cholesterol (180-200), around 70-80bpm heart rate, around 98.6F (37C) core temperature during the day, proper and thorough digestion, fast transit time, well-formed stool that passes easily, good skin health, Achillies tendon reflex (R), lots of deep sleep during the night, mood stability during the day, etc.

What’s wrong with fitness?

Testosterone, cortisol and prolactin

It’s been known since the 70s that men who do endurance exercise have lower testosterone (R).

Hypogonadism is characterized by not just low testosterone but includes various other signs as well such as the absence or regression of secondary sex characteristics, anemia, muscle wasting, reduced bone mass or bone mineral density, oligospermia, and abdominal adiposity. Symptoms include sexual dysfunction (e.g., erectile dysfunction, reduced libido, diminished penile sensation, difficulty attaining orgasm, and reduced ejaculation), reduced energy, and stamina, depressed mood, increased irritability, difficulty concentrating, changes in cholesterol levels, anemia and osteoporosis. (R)

Although short-term, non-exhaustive endurance exercise can help to increase testosterone (a little) and not really increase cortisol, whereas prolonged exercise lowers testosterone and increases cortisol and prolactin (prolactin always increases during stress) (R).

Increased cortisol and prolactin both inhibits GnRH, LH and Leydig cell function, thus lowering testosterone levels.

Both endurance and resistance training can increase cortisol and prolactin if overdone. The prolactin release correlates with intensity, but there is a threshold. However, prolactin can continue to increase based on the duration of the intense exercise.

Other hormones that can also increase prolactin include estrogen, TRH, oxytocin, antidiuretic hormone, serotonin, histamine and angiotensin II (R).

Prolactin is negatively correlated with libido, erection quality and duration and vascular function. Acute elevations in prolactin can be helpful to reduce body temps (prevent overheating) and reduce inflammation, whereas long term elevations are detrimental.

The key characteristics and traits of “Exercise Hypogonadal Male Condition” (EHMC) as laid out by Hackney and associates were (R):

  • These men had testosterone levels at least 25% to 50% lower than expected for their age.
  • The lowered testosterone levels did not appear to be a transient phenomenon related to the acute stress-strain of exercise training.
  • The men were not experiencing a performance decrement or lack of motivation (i.e., overtrained).
  • They had not experienced a major bodyweight loss in recent months.
  • The men had a history of early involvement in sports resulting in them have many years of nearly daily exercise activity.
  • The modality of exercise and training most frequency associated involved high volume endurance activities such as running, triathlons, cycling cross-country skiing, and race walking.

Long duration exercise specifically is the culprit for lowering testosterone

In support of this model and the effect on reproductive function, Raichlen associates (122) found the Hadza, a hunter-gatherer population in northern Tanzania, where men accumulate nearly 2 h of moderate and vigorous physical activity daily, have testosterone concentrations roughly 50% lower to those in comparable North American men. Likewise, Trumble et al. found the Tsimane men, Bolivian foragers-farmers with high levels of daily physical activity, display similar testosterone reduction (30–35% lower) (123). Furthermore, generally resting testosterone is also lower among men in physically active non-industrial populations compared with those in less active, industrialized countries (124). Collectively these studies did not report their populations to be in high-stress situations (e.g., famine, warfare) or having insufficient food-caloric availability; hence, these hormonal changes seemed adaptive consequences of their lifestyle (121).” (R)

However, it should be pointed out that, as stated by Sansone and associates, “whether testosterone suppression is the result of a physiological adaptation to stress or an undesirable side effect of excessive training is a matter still open to debate” (R). 

The reason for this is because marathon runners with low T don’t necessarily display hypogonadal symptoms (R). I should just point out that most men are too shy/embarrassed to report hypogonadal symptoms and also, a lot of men think that not having morning wood or only having sex once or twice a month is completely normal.

Low energy as a cause of low testosterone

Often times men who do lots of cardio or train a lot are also conscious of how they look. They want to be lean. Thus they found calories and make sure they don’t overeat. Typically, calorie intake would range from 1500-2000. Low calorie intake has been shown to lower testosterone levels and slow the metabolism. This dietary stress is added on top of lots of cardio and stressful life. You need calories, especially carbs, to be able to tolerate/buffer stress.

The worse of all is if these men go on a low carb diet for additional “health” benefits and do their training fasted. Absolutely insane. Stress on top of stress times stress square stress.

Cut off values for calorie intake to prevent negative adaptions from lots of endurance exercise were: at risk = ≤30 kcal/kg lean body mass (LBM); moderate risk = 30–45 kcal/kg LBM; and no risk = ≥45 kcal/kg LBM (R).

High risk
Moderate risk
No risk
80kg male with 15% BF<2040 cal (68kg LBM)2040-3060 cal>3060 cal
100kg male with 15% BF <2550 cal (85kg LBM)2550-3825 cal>3825 cal

The main problem with endurance exercise (even in a well-fed state) is that it increases AMPK.

AMPK becomes elevated in a fasted/starved state and slows the metabolism. It upregulates fatty acids mobilization and oxidation and reduces glucose oxidation and also lowers testosterone and thyroid hormone production.

Elevated free fatty acids, mobilized through lipolysis, act as extracellular signaling molecules that modulate the production of chemokines and cytokines, and the synthesis of pro-inflammatory lipid-derived species (R, R).

AMPK also lowers LH, StAR, 3β-HSD and reduces Leydig cell function (R, R).

It’s often thought that you have to do fasting and cold water exposure and what not to increase the metabolism and brown tissue conversion and thermogenesis. But all you need is proper thyroid function. All the rest is more likely to have zero benefit and can even be detrimental.

Vidal-Puig and colleagues 1 now provide evidence that increases in metabolic rate induced by thyroid hormones involve inhibition of AMP-activated protein kinase (AMPK) in the hypothalamus (the key brain region that is known to regulate appetite, body temperature and circadian rhythms), thus triggering heat production in brown fat tissue via the sympathetic nervous system. … In the new study, Vidal-Puig and coworkers 1 initially made rats hyperthyroid by daily subcutaneous injections of T4. As expected, this caused elevation of plasma T3, and the rats gained less weight than controls, despite eating more. The rats also had increased mass of brown fat, a tissue that can increase energy expenditure via heat production from uncoupled mitochondria when stimulated by sympathetic nerves (non-shivering thermogenesis).” (R)

Other side effects of “healthy” endurance exercise.


Proper exercise is great for thyroid function, but this effect is highly individualized. Some people can do long bouts of exercise and not get any detrimental effects, whereas others can even do 20 min of exercise and get a negative response.

Thyroid hormone production is essential for every bodily function and if we suppress it long term, we’re setting ourselves up for trouble.

Training intensely can reduce thyroid function (R). “Short-duration, graded exercise (≤20 min) results in elevated blood TSH levels, as long as an intensity threshold of approximately ≥ 60% of maximal oxygen uptake (VO2max) or above the lactate threshold is achieved [5,6]. Interestingly, with this TSH elevation the expected increase in total and free T4 is seen, but total and free T3 become reduced [5].” (R)

And not just aerobic exercise, but anaerobic exercise as well, such as sprints, weights, or any other intense exercise.

Intensive anaerobic exercise (sometimes referred to as high-intensity interval training) increases fT4, fT3, and total T4 levels initially after the exercise, but by 12 h of recovery, fT3 was reduced and reverse T3 was increased, suggesting a reduced peripheral conversion of T4 to T3.” (R)

Keep in mind that not all HIIT programs are detrimental, but most HIIT programs do their “sprints” for too long, don’t give enough rest and also keeps the session going for too long.

However, this (acute) study below, looked at resistance training and T3 levels and found T3 to be increased significantly the night after training. They did 18 sets to failure. If such a workout is performed too frequently, that will also lead to suppression of the thyroid.

McMurray and associates did perform one criterial study looking at thyroids immediately afterward and 12 h into recovery (during the night) from intensive resistance exercise [16]. Hemoconcentration-induced transient but significant elevations in total T4 and T3 occurred immediately after exercise. During the night total T3, there was significant nocturnal elevation. These investigators proposed these changes were due to a thyroid-mediated increase in metabolism needed for tissue repairs and an increase in protein synthesis.” (R)

To optimize thyroid, you have to train smart. Train preferable heavy, in the 4-12 rep range, stay away from failure, rest about 3-5 min between sets, and don’t overdo the number of sets per muscle group. Learn your body to see how many sets you do best on.


Exercise-induced hypoglycemia is actually pretty common. Cortisol and adrenaline are secreted to prevent severe hypoglycemia, and then fatty acids are mobilized from adipose tissue. Doing endurance exercise chronically causes your body to adapt to this stress metabolism, burning fat instead of glucose. And some people think you just need to eat glucose to overcome it, but research in the keto sphere has shown that adding in carbs for a few days after doing keto for a while doesn’t restore proper glucose oxidation. With prolonged endurance exercise, you mimic a state of keto, thus causing the same kind of adaptions. Ketones can rescue the metabolism to a degree, but most people aren’t even producing enough ketones for this to occur. So they’re just stuck in the middle.

Twenty minutes of moderate-intensity aerobic exercise resulted in a significant fall in glycemia. However, one 10-second sprint at the end of the 20-minute aerobic exercise bout opposed a further fall in glycemia for 120 minutes, whereas in the absence of a sprint, glycemia decreased further after exercise.” (R) (at least in type 1 diabetics)

Even 20 min of low intensity exercise can be bad.

Our results suggest that repeated iatrogenic hypoglycemia leads to weight gainand that such weight gain is associated with a multifaceted deficit in metabolic regulation rather than to a chronic increase in caloric intake.” (R)

Most people when they get to their 40s and higher, start to struggle with mid-section fat. That is a clear sign of excess cortisol and reduced androgens. What’s worse is that these people will start to do more cardio and eat even less. Some people don’t necessarily get mid-section fat, but end up very scrawny (muscle wasting), weak and fragile.

Heart and vascular function

Exercise is generally thought to be cardioprotective, but when exposed to elevated free fatty acids, PUFAs, cortisol, prolactin, endotoxin, for too long (all of which are induced by endurance exercise), that will cause mitochondrial dysfunction, excess inflammation, and lead to cardiac pathologies.

Since Saltin and Stenburg58 suggested that prolonged exercise could impair intrinsic cardiac contractile function, a number of studies have addressed the phenomenon of ‘exercise-induced cardiac fatigue’.” (R)

endurance exercise may increase cardiovascular disease risk by reviewing the causes and incidence of exercise-related cardiac events, and the acute effects of exercise on cardiovascular function, the effect of exercise on cardiac biomarkers, including “myocardial” creatine kinase, cardiac troponins, and cardiac natriuretic peptides. This review also examines the effect of exercise on coronary atherosclerosis and calcification, the frequency of atrial fibrillation in aging athletes, and the possibility that exercise may be deleterious in individuals genetically predisposed to such cardiac abnormalities as long QT syndrome, right ventricular cardiomyopathy, and hypertrophic cardiomyopathy.” (R)

Over months to years of repetitive injury, this process, in some individuals, may lead to patchy myocardial fibrosis, particularly in the atria, interventricular septum, and right ventricle, creating a substrate for atrial and ventricular arrhythmias. Additionally, long-term excessive sustained exercise may be associated with coronary artery calcification, diastolic dysfunction, and large-artery wall stiffening.” (R)

In the longer term, some endurance athletes have an increased prevalence of coronary artery disease, myocardial fibrosis and arrhythmias. The inherent association between these ‘maladaptations’ and sudden cardiac death in the general population raises the question of whether endurance exercise could be detrimental for some individuals.” (R)

possible association between multiple splanchnic arterial aneurysms and long-distance running.” (R)

An unexpectedly high prevalence of myocardial fibrosis (50%) was observed in healthy, asymptomatic, lifelong veteran male athletes, compared with zero cases in age-matched veteran controls and young athletes.” (R)

Long distance running increase thrombogenic risk factors that increase blood clot risk that can lead to venous thromboembolism.” (R)

Prolonged shear stress induces platelet release, aggregation, and pro-inflammatory markers (ie, leukocytes, high sensitivity c-reactive protein), which in turn activate the clotting cascade.” (R)

The thing is that repetitive stress by endurance exercise causes histamine, serotonin and other inflammatory mediators to be released from platelets. They cause clotting, vascular permeability, spasms, inflammation, etc., which is definitely not good for long-term health.

It’s common to do mouth breathing during exercise. We blow off a lot of carbon dioxide (CO2) when we mouth breathe. Some of you might think that’s ok, since we’re producing a lot more during exercise. But we’re producing significantly less from fat oxidation compared to glucose oxidation and the oxygen requirements also go up a lot compared to glucose oxidation.

CO2 is anti-inflammatory, prevents glycation, promotes vasodilation and tissue oxygenation, and prevents the excess release of serotonin from platelets. More serotonin in the airway means more frequent infections and asthmatic symptoms, both of which are common amongst athletes.

Immune system and infections

As I just mentioned, more fatty acids oxidation means less CO2 and more serotonin. This predisposes people to weakened immune systems, asthmatic symptoms, airway inflammation and infections.

Heavily exercising endurance athletes experience extreme physiologic stress, which is associated with temporary immunodepression and higher risk of infection, particularly upper respiratory tract infections (URTI). Among macronutrients, the most effective approach to maintain immune function in athletes is to consume ≥6% carbohydrate during prolonged exercise.” (R)

Having carbs can help to prevent that drop in CO2 (not completely though) and minimize the side effects.

Together, our data suggest that, as a result of multi-organ interactions, RBER (repetitive bouts of exhaustive running) could cause a sustained inflammatory response for at least 24 h, resulting in tissue lesion and ultimately multiple organ dysfunction.” (R)


Here’s the good part. Gut problems are very common amongst athletes, or people that do endurance exercise. Runners’ diarrhea is one such symptom. The main thinking is that it’s food that causes the stomach upset, but it’s actually low blood sugar causing leaky gut and excess serotonin (R, R, R, R).

Fasted exercise is the worse (R). Stressful exercise in a low glycogen state is not some sort of “hormetic” stress that upregulates autophagy in a healthy way and promote longevity. It causes leaky gut, inflammation, elevates cortisol and adrenaline, causes pathological mitochondrial adaptions, excess serotonin, suppresses thyroid, etc.

It’s best to have some form of glucose and amino acids before training, such as fruit juice and EAAs.


I’m not trying to say you have to stop doing cardio or anything, but keep in mind that it can cause intestinal problems, suppress the immune system, cause insulin resistance (or glucose sparing state if you prefer), reduce testosterone and thyroid function and even lead to cardiac and vascular problems many years down the line. Hypothyroidism is related to low heart rate as is endurance exercise, and cardio is known to suppress thyroid function. So a low heart rate is not a good thing, it should raise eyebrows. Just things to keep in mind.

The main reason I wrote this article is to make people aware that cardio can have side effects. I’ve heard this far too often that people think if someone is very fit with a low heart rate and body fat, they are supposed to be very healthy. And it’s frequently those people that experience sudden health consequences.

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2 thoughts on ““Healthy” fitness equals low testosterone (and other health issues)”

  1. Aspirin inhibits mTor and activates AMPK, I assume you recommend aspirin, so why is it that fat metabolism is bad and mTor good? If AMPK is some (blanket) stress thing, why promote Aspirin? This is just downright incoherent and I could cite several other examples of this in your work. Promoting fruit as primary carb source because it stimulates insulin less, but insulin is a good thing. Stay lean, but not more lean than me, that is unhealthy. Mentions mitochondrial dysfunction, but promotes constant caloric excess or fructose for that matter! Fat burning bad, take mct. I’d like to be more polite but undoubtedly (hopefully) you must’ve found your own principles as weak and incoherent as I have, and yet you still promote them. I consider you a charlatan, because you are making people fat and incapable of exercise, and allowing perceived stressors to control their lives. You may have deluded yourself otherwise but I insist that you consider my points.

    Best wishes, Luke.

    • Hi Luke,
      Thanks for reading my content!
      I never said AMPK is bad overall. Increasing AMPK through fasting/glycogen depletion inhibits muscle protein synthesis, proper regeneration and shifts the balance more towards fatty acid oxidation. This is suboptimal for someone who is focused on gaining muscle, which I and my readers are interested in. Boosting AMPK also helps with proper glucose oxidation, but reducing overall glucose levels is suboptimal for our goals and can have deleterious health outcomes.

      As for your second point, highly insulinogenic foods can be problematic for some people, so for those that want to avoid insulin spikes and potentially hypoglycemia, a lower GI food such as fruit (high fructose food) might be a better option.

      “Stay lean, but not more lean than me, that is unhealthy.” Where did I say that? Now you’re just pulling stuff out of thin air. Many people are leaner than me and I’m happy for them. Nothing wrong with that.

      “Mentions mitochondrial dysfunction, but promotes constant caloric excess or fructose for that matter!” Where do I say people should overeat all the time, or just slam down fructose? If someone wants to build muscle, then a surplus is required. Also, show me a study that shows that fruit juice, honey or maple syrup is detrimental to the mitochondria. There is none. Only benefits.

      “Fat burning bad, take mct.” Excess fat burning at the expense of glucose oxidation is bad. MCT oil doesn’t interfere with the oxidation of glucose.

      “I’d like to be more polite but undoubtedly (hopefully) you must’ve found your own principles as weak and incoherent as I have, and yet you still promote them.” I’m flourishing on my own principles. I don’t recommend something I had or haven’t implemented myself. In fact, I’m in my best state of health yet thanks to my principles.

      “I consider you a charlatan, because you are making people fat and incapable of exercise, and allowing perceived stressors to control their lives.” Funny how you interpret things. I’m merely trying to bring awareness to the possibility of overtraining and the deleterious effects certain kinds of exercise can have on someone.


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