Can Endurance Training Kill Testosterone?

Exercise is good for you, endurance, HIIT and strength. Most of the people I asked do sports because they want to be healthy. But we know that too much of a good thing can be a bad thing. Endurance training is no exception! Especially when it affects your sex life. Endurance athletes especially have a tendency to favor quantity over quality, which can hurt their health. Example? Reduced testosterone.

In my coaching I work with different types of athletes and by now, when a 30+ y.o. man tells me he has trouble losing belly fat despite eating relatively clean and exercising regularly, I can  pretty safely guess he favors endurance sports.

Is it because endurance exercise causes fat storage? No. But excessive endurance training can cause hormonal issues in some men, that cause them to experience excessive tiredness, resistance to weight loss, low libido and even infertility. We spoke about it in depth with Matt on podcast.

How does endurance training affect libido?

Exercise, while bringing many physiological and mental benefits, is also catabolic (breaks down muscle) and causes stress to your body (cortisol). Endurance exercise does this to a greater extent than strength training or HIIT.

Acute stress is beneficial for your body. It is a signal for it to adapt. But if you don’t recover well in between your training sessions, negative effects start to creep in. Your body gets more stress than it can handle and starts breaking down. One of the first systems that go is the reproductive system as it is not essential for your survival. 

How much endurance training is too much?

While women respond to hormonal disbalances quickly, men do not and symptoms like erectile dysfunction appears later.

Symptoms of testosterone deficiency in adult men include:

  • Reduced body and facial hair
  • Loss of muscle mass
  • Low libido, impotence, small testicles, reduced sperm count and infertility
  • Increased breast size
  • Hot flashes
  • Irritability, poor concentration, and depression
  • Loss of body hair
  • Brittle bones and an increased risk of fracture

Unfortunately, there is not a definite answer to how much endurance exercise causes health issues. Some men can tolerate much more activity than others and most amateur athletes get injured before they fall into hormonal disbalances.

These studies revealed that high PA intensities ranging 60%-80% the maximal oxygen uptake (VO2 max) or only 80% VO2 max for, at least, 30 min resulted in statistically significant higher cortisol levels compared with resting control situations.

More highly trained individuals typically have a higher intensity threshold necessary to provoke an increase in cortisol.

We also need to consider things like nutrition (vit. D, energy balance…) and life stressors (having a newborn causes a substantial testosterone to drop in men).

Things need to be considered in the big picture. Life stress and training stress add up. Your nutrition status plays a role as well and your genetics underline all of it.

We can measure how stressed out our body is by looking at total and free testosterone.

For example in this study they looked at well-trained endurance athletes and compared their testosterone levels to average men. Endurance athletes had lower levels of total and free testosterone. Men in the study were training about 6.6 days a week on average, 68 minutes per session on average with a ~34min 10k PR and 167min marathon PR, and had been training this way for at least the past 12 months

But what if you can’t have your hormones panel done?

I found that resting heart rate can be a guide. We, endurance athletes take pride in low resting heart rates. What I observed in myself is that when I had rHR below 40, I was well trained but that is also when I experienced negative consequences, like non-existent libido, feeling cold often, loss of muscle mass. 

When I reduced my endurance training for several months, my libido increased and I stopped feeling cold. My rHR was in the low to mid 40′ range.

Should you reduce your endurance training?

Unless you are experiencing negative effects mentioned above, you might not need to reduce your training.

The more I know, the more I favor substituting endurance for higher intensity and strength training.

There are other benefits of exercise

Benefits of exercise go beyond physical adaptations and can be achieved through running, cycling, or lifting weights.

Running boosts self-esteem, and research shows that people who exercise have more positive body image and feel more desirable and confident in the bedroom. “They feel good in their bodies,” said Ian Kerner, a sex therapist in New York City. “They’re really able to translate that into sex where they feel free and comfortable and to a greater extent uninhibited.”

Last Update: 9.9.2020

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