What Is Circadian Rhythm?
Circadian rhythm is an approximately 24-hour biological clock that governs virtually all body functions — from sleep and wakefulness to hormone secretion, body temperature, digestion and physical performance. It is regulated by the suprachiasmatic nucleus (SCN) in the hypothalamus — a miniature brain region that responds directly to light through the eyes.
🦉 Chronotypes: Larks, Owls and Intermediates
| Chronotype | Share of population | Natural wake time | Peak time for sport | Sleep time |
|---|---|---|---|---|
| Lark (morning type) | ~15-20% | 5:00-6:30 | 8:00-12:00, second peak 14:00-16:00 | 21:00-22:00 |
| Intermediate type | ~60-70% | 6:30-8:00 | 10:00-14:00, second peak 16:00-18:00 | 22:00-23:30 |
| Owl (evening type) | ~15-20% | 8:00-10:00 | 14:00-18:00, sometimes later | 00:00-02:00 |
Important: Chronotype is partly genetically determined (PER3 gene), so "breaking" from an owl into a lark is very difficult and unnecessary. It is better to work with your chronotype rather than against it.
🏋️ Optimal Training Time by Circadian Rhythm
💪 Strength training
Muscle strength and power peak in the late afternoon (16:00-18:00), when body temperature is highest and the testosterone-to-cortisol ratio is optimal. There is evidence of greater strength in the evening than in the morning.
🏃 Endurance Sport
VO2max and endurance are also highest in the afternoon (14:00-18:00). Morning cardio may be 3-8% less effective, but with regular morning training, the body adapts.
🧘 Flexibility / Yoga
Flexibility is greatest in the evening (18:00-20:00), when the body is most warmed up. Morning stretching may be less effective and increase injury risk without a good warm-up.
🎯 Precision / Coordination Sport
Fine motor skills and reaction time are best in the morning (9:00-12:00) after full awakening. Tennis, shooting and darts reach their highest accuracy at this time.
📊 Hormonal Circadian Cycle — Important for Athletes
| Hormone | Peak | Lowest point | Practical relevance |
|---|---|---|---|
| Testosterone | 7:00-8:00 AM | 20:00-22:00 in the evening | Morning training is better for strength gains |
| Cortisol | 6:00-8:00 AM (waking response) | 00:00-04:00 at night | Morning cortisol — an energy source, not an enemy |
| Growth hormone | 22:00-02:00 (deep sleep) | During the day (between pulses) | Early sleep = more GH |
| Melatonin | 02:00-03:00 at night | During the day (near zero) | Darkness is essential for melatonin |
| Body temperature | 16:00-18:00 | 04:00-06:00 AM | Higher temp. = better physical performance |
✈️ Jet Lag and Athletic Performance
Travel across time zones is a major challenge for athletes. It is thought that traveling east (for example, from Europe to Asia) disrupts circadian rhythm more than traveling west. Recommendations:
- Westward (later time zone): Adaptation takes ~1 day per hour of difference. For the first 1-2 days after arrival, train easier.
- Eastward (earlier time zone): Adaptation is harder. Start changing your sleep time 2-3 days before the trip — go to bed 30 min. earlier each day.
- Light Strategy: After arrival, maximize your use of morning light (when traveling east) or evening light (when traveling west).
- Melatonin: 0.5-1 mg 30 min. before the desired sleep time in the new time zone.
🛒 Recommended Products for Circadian Rhythm
❓ Frequently Asked Questions
Can You Change Your Chronotype?
Partly yes, but it takes time. The main tools: light exposure at the right time (morning light for early birds, evening light for night owls), gradual shifting of the sleep schedule (±15-30 min. per week), strategic melatonin use, and avoiding caffeine after 14:00. A complete chronotype change can take 3-6 months.
What Should I Do If I Am Forced to Train in the Morning but I Am a Night Owl?
The main tip is lighting. Use bright light (a 10,000 lux light therapy lamp) for 20-30 min immediately after waking. This speeds up circadian rhythm adaptation. It is also important that the morning workout should include a good warm-up (15-20 min, not 5-10 min), because night owls need more time to "get going".
How Can I Tell If My Circadian Rhythm Is Healthy?
Signs of a healthy circadian rhythm: you fall asleep within 15-20 minutes, you wake up without an alarm at approximately the same time, you feel alert during the day without caffeine, and you have an energy surge in the morning and afternoon. If you constantly feel tired, your circadian rhythm may be out of balance.