Hormonal Responses to Running: Cortisol, Testosterone, and Training Adaptation

Introduction

“Running relieves stress”—almost everyone knows this phrase, but few understand the complex hormonal mechanisms behind it. Running doesn’t just improve your mood; it triggers a cascade of precise hormonal responses, and the balance of these hormones is exactly what determines whether training leads to progress or regression.

Among runners in Taiwan, overtraining is a frequently discussed yet often misunderstood issue. Many runners assume fatigue means “not training enough,” unaware that hormonal imbalance is the real core of the problem.

Major Hormonal Responses Triggered by Running

Cortisol: The Double-Edged Sword of Training

Cortisol is a stress hormone secreted by the adrenal cortex and plays a key role in running:

Acute Benefits (Normal Short-Term Responses):

• Mobilizes glycogen and fat to provide energy for running
• Anti-inflammatory effects (short-term), allowing runners to continue exercising while fatigued
• Raises blood sugar, supporting brain and muscle function

Chronic Problems (Harms of Prolonged Elevation):

• Muscle protein breakdown (muscle loss)
• Suppresses the immune system (the reason runners “catch colds constantly”)
• Disrupts sleep quality (can’t sleep even when exhausted)
• Suppresses testosterone secretion (affecting recovery and muscle synthesis)

Cortisol rises during running and gradually decreases after exercise. The problem is: if training volume is excessive or recovery is insufficient, cortisol remains chronically elevated, entering the hormonal pattern of “overtraining syndrome.”

Testosterone: The Fuel for Recovery

Testosterone exists in both male and female runners (with lower concentrations in women) and is a key hormone promoting muscle repair, bone strengthening, and red blood cell production:

• After moderate exercise: Testosterone rises briefly (especially after resistance training)
• After overtraining: Testosterone continuously declines, and its ratio to cortisol (T:C ratio) drops
• The T:C ratio is one of the most commonly used hormonal indicators for assessing overtraining

Growth Hormone (GH) and Insulin-Like Growth Factor (IGF-1)

Growth hormone and IGF-1 are anabolic hormones that promote muscle and bone repair:

• Running (especially high-intensity intervals) can significantly stimulate growth hormone secretion
• The peak of secretion occurs during deep sleep (not during exercise itself)
• Sleep deprivation directly reduces GH secretion—this is the hormonal reason for “training without progress”

Adrenaline and Noradrenaline (Catecholamines)

In the early stages of running, catecholamines are secreted in large amounts, triggering the “runner’s high feeling”:

• Increased heart rate, vasoconstriction, and elevated blood sugar
• Enhanced brain alertness, which is part of why running “improves mood”
• Chronically elevated levels are one of the early signals of overtraining

Endorphins and the “Runner’s High”

Many Taiwanese runners are drawn to road running because of the occasional “Runner’s High”—a feeling of euphoria and freedom from fatigue. The traditional view attributes this to endorphins (β-Endorphin), but recent research points to another important player:

• Endocannabinoids: Such as anandamide, which have been found to rise significantly after running, and their euphoric effects are more direct than those of endorphins
• These two work together after long-distance running (60–90 minutes or more) to produce the runner’s high experience

Hormonal Balance and the Menstrual Cycle (Female Runners)

Female runners in Taiwan need to pay special attention to “Exercise-Related Menstrual Dysfunction”:

• When training volume is excessive and energy intake is insufficient, the hypothalamic-pituitary-ovarian axis is disrupted
• Estrogen and progesterone decline, leading to irregular or absent menstruation
• Chronic low estrogen status accelerates bone loss, forming the “Female Athlete Triad”

If the menstrual cycle exceeds 45 days or stops for more than 3 months, training volume should be temporarily reduced and medical evaluation sought.

Hormonal Signals of Overtraining Syndrome

Hormonal characteristics of Overtraining Syndrome (OTS):

• Chronically elevated cortisol (can be assessed via morning salivary cortisol testing)
• Declining testosterone (reduced T:C ratio)
• Persistently low resting HRV (parasympathetic inhibition)
• Mildly decreased thyroid hormone (T3) (reduced metabolic rate)

Common non-hormonal symptoms include: prolonged fatigue, plateaued or declining performance, low mood, recurrent colds, and reduced sleep quality.

Practical Recommendations

• The “less is more” philosophy: Training supercompensation doesn’t occur during the run itself, but after adequate recovery. Training without sufficient recovery merely accumulates fatigue rather than adaptation.
• Monitor resting heart rate: Measure your resting heart rate every morning before getting out of bed. If it is 5–7 beats per minute above baseline for 3 consecutive days, it is an early signal of elevated hormonal stress.
• Protect your sleep: 7–9 hours of sleep per night is a prerequisite for growth hormone secretion and a necessary environment for cortisol to decline normally.
• Avoid prolonged low-calorie diets: Strictly restricting food intake while training heavily is the fastest path to hormonal imbalance.
• Schedule deload weeks appropriately: Every 4–6 weeks, arrange a week with training volume reduced by 20–40% to allow the hormonal system to reset its balance.

Conclusion

The hormonal responses triggered by running represent an ongoing, precise dialogue between the body and training stress. The dynamic balance between cortisol and testosterone determines whether your training is building up or breaking down your body. By learning to listen to this hormonal conversation—through appropriate training volume, sufficient sleep, and balanced nutrition—you can ensure that every training investment yields tangible physiological progress.

Related Reading

• Hormonal Responses to Cycling Training: The Relationship Between Testosterone, Cortisol, and Training Plans
• Hormonal Responses to High-Intensity Training: Testosterone, Cortisol, and Training Balance
• A Complete Guide to Exercise and Hormones: Testosterone, Cortisol, and Growth Hormone—Understanding Your Endocrine Signals
• Swimming and Stress Hormones: Balancing Training Volume and Cortisol