Testosterone and Cycling: What Ultra-Endurance Training Does to Your Hormones

Introduction

As road cycling and ultra-endurance riding (such as 300K, 500K, and windbreak challenges) become increasingly popular in Taiwan, more and more male cyclists are asking: what effect does prolonged, high-intensity training have on hormones like testosterone? This question matters not only for athletic performance, but is also closely tied to muscle synthesis, bone health, mood, sexual function, and overall quality of life.

The Basic Functions of Testosterone

Testosterone is the primary male androgen, synthesized by the Leydig cells of the testes and regulated by the hypothalamic-pituitary-gonadal (HPG) axis.

Main functions of testosterone:

• Promotes muscle protein synthesis and increases muscle mass
• Maintains bone density
• Influences red blood cell production (indirectly affecting endurance)
• Regulates mood, motivation, and competitive behavior
• Maintains sexual function and reproductive health

Normal testosterone range for men (Taiwan clinical reference values):

• Morning (peak): 300–1,000 ng/dL
• Afternoon (trough): 200–700 ng/dL
• <300 ng/dL is considered low testosterone (Hypogonadism)

The Dual Effect of Cycling Training on Testosterone

Short-Term Effects (Acute Response)

After moderate-intensity cycling (60–80% VO2max), testosterone typically rises briefly (peaking 15–30 minutes post-exercise), a normal physiological response that helps trigger muscle repair and adaptation.

Long-Term Effects (Chronic Adaptation)

Hormonal Mechanisms Behind Ultra-Endurance Training

Hormonal Suppression from Energy Deficiency

When long-distance riding causes insufficient energy availability (calorie intake < calories expended minus exercise expenditure), the hypothalamus reduces secretion of gonadotropin-releasing hormone (GnRH), leading to declines in LH (luteinizing hormone) and FSH (follicle-stimulating hormone), which ultimately suppresses testosterone synthesis.

In men, this phenomenon is referred to as “Male Athlete Triad” or Relative Energy Deficiency in Sport (RED-S).

The Antagonistic Effect of Stress Hormones

Ultra-endurance cycling significantly raises cortisol (the stress hormone):

• Cortisol directly suppresses testosterone synthesis in the Leydig cells
• The testosterone-to-cortisol ratio (T/C ratio) is an important indicator for assessing overtraining
• A drop of more than 30% in the T/C ratio is one of the biochemical markers of Overtraining Syndrome

Local Effects of Saddle Pressure

As mentioned in a previous article, prolonged saddle pressure on the pudendal vessels may reduce blood flow to the testes. While research on its effect on baseline testosterone secretion is inconsistent, elevated scrotal temperature (caused by the insulating effect of the saddle and tight cycling shorts) has been shown to temporarily affect testicular function.

Research Data: Hormonal Changes in Ultra-Endurance Cycling

A study of Tour de France riders (a 21-day race) found that after the race:

• Total testosterone dropped by approximately 30–45%
• Cortisol remained elevated
• The T/C ratio declined significantly

However, after adequate recovery (3–4 weeks), testosterone fully returned to baseline levels. This indicates that the hormonal effects of ultra-endurance training are temporary, provided recovery is sufficient.

For amateur cyclists, a round-island tour (9–12 days) or an ultra-endurance challenge (such as 600K) may also produce similar temporary hormonal suppression, but recovery time is typically shorter (1–2 weeks).

When Should You See a Doctor?

The following symptoms may indicate a low testosterone problem and warrant hormone evaluation at a urology or endocrinology clinic:

• Chronic fatigue with slow recovery after training
• Low mood, loss of motivation (“losing your passion for cycling”)
• Continued decline in muscle mass with no strength gains
• Decreased bone density (signs of osteoporosis)
• Sexual function issues (erectile difficulty, reduced libido)

Testosterone blood testing is covered by Taiwan’s National Health Insurance and can be requested at a urology or family medicine clinic.

Practical Strategies for Maintaining Hormonal Health

Conclusion

The effect of cycling training on testosterone is not simply “good” or “bad” — it is a finely balanced system. Moderate training combined with adequate recovery allows you to enjoy the pleasure of riding while maintaining good hormonal health. If you experience persistent fatigue or recovery problems, don’t just “rest more” — actively seek medical evaluation to identify the underlying cause.

Related Reading

• Hormonal Response to High-Intensity Training: Testosterone, Cortisol, and Training Balance
• Hormonal Response to Cycling Training: The Relationship Between Testosterone, Cortisol, and Training Plans
• Does Exercise Really Build “Alpha Male Hormones”? A Complete Scientific and Practical Analysis of Exercise, Testosterone, and Men’s Health
• Low Testosterone Syndrome in Male Endurance Athletes: The Antagonism Between Training Volume, Cortisol, and Testosterone