Biorhythms and Sport: The Circadian Biology of Performance, Chronotypes, and Synchronization of Training Cycles

1. Introduction and Relevance of the Topic

Biorhythms are cyclical changes in the intensity of biological processes that repeat over specific time intervals. In sports, the most important are circadian (daily) rhythms, which determine an athlete's peaks in strength, endurance, and reaction speed. Understanding biorhythms allows for aligning the training schedule with the body's natural cycles, significantly increasing workout effectiveness and accelerating recovery. This is not just a matter of wake-up time, but a deep physiological tuning of all systems—from body temperature to hormone levels.

The relevance of this topic stems from the modern lifestyle, which often contradicts natural rhythms (light pollution, shifting schedules). For an athlete, disrupted circadian rhythms lead to metabolic chaos, a decline in the anabolic background, and an increased risk of injury. Knowing one's chronotype ("owl" or "lark") and the ability to synchronize it with competition times can be a decisive advantage when the difference between gold and silver is measured in hundredths of a second.

Time is not just a number on a clock, but a biochemical window of opportunity for your body. Training in harmony with biorhythms means swimming with the current of your own biology.

2. History and Evolutionary Significance of Circadian Rhythms

Evolutionarily, the ability to anticipate changes in light and darkness provided a massive advantage. Organisms that could prepare their metabolism for activity or rest in advance survived better. Circadian rhythms are hardwired into our genetic code: approximately 15-20% of all genes in every cell of the body function on a daily cycle. The history of studying biorhythms has progressed from observations of plant leaf movements in the 18th century to the discovery of the molecular mechanisms of the clock, for which the Nobel Prize was awarded in 2017.

Jeffrey Hall, Michael Rosbash, and Michael Young identified the genes (Period, Timeless) that control the daily rhythm. In sports, this discovery explained why some athletes demonstrate incredible results in the morning, while others only in the evening. We realized that a "chronotype" is not a habit, but a genetically determined speed of the internal clock.

Today, we view biorhythms as the foundation of preventive medicine.

3. Anatomy of the Internal Clock: The SCN and Peripheral Oscillators

Anatomically, the primary control center for biorhythms is located in the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN receives information about light levels directly from special retinal cells (ipRGCs). This anatomical connection allows the brain to synchronize internal time with the external daylight cycle. The SCN acts as a conductor, sending signals to all other organs and tissues.

In addition to the central clock, there are peripheral oscillators—every cell in the muscles, liver, or heart has its own internal timing mechanism. Anatomically, these oscillators are synchronized by the SCN through hormonal signals and changes in body temperature. For the athlete, it is critically important that the central and peripheral clocks work in unison; desynchronosis (e.g., eating at night) leads to a drop in muscle performance.

Suprachiasmatic Nucleus (SCN)

The anatomical region of the brain that acts as the body's master clock, responding to the blue spectrum of light.

Peripheral Clocks

Genetic mechanisms within every muscle cell that anatomically regulate contraction force and the rate of protein synthesis depending on the time of day.

Biomechanical Mechanics: Biomechanically, biorhythms manifest in changes in tissue flexibility and viscosity.

4. Biochemistry of the Daily Cycle: The Cortisol and Melatonin Tandem

The biochemical foundation of biorhythms is the antagonism between cortisol and melatonin. Cortisol (the "awakening hormone") biochemically peaks in the morning, mobilizing energy and raising blood pressure to begin activity. Melatonin (the "night hormone") begins to be produced by the pineal gland in response to darkness, preparing the body for repair and sleep. Biochemically, these two hormones should never be high simultaneously.

During training, the biochemistry of biorhythms is modulated by the load. Evening workouts can temporarily increase body temperature and cortisol, biochemically delaying melatonin release. It is also important to consider testosterone rhythms; while the peak is usually in the morning, strength loads can create secondary peaks in the evening, promoting anabolism.

Biochemical adaptation of the athlete to biorhythms also includes nutrient rhythms.

5. Physiology of Performance: Strength, Endurance, and Time

Physiologically, the peak of muscle strength and power for most people falls between 16:00 and 19:00. During this time, the lungs function most efficiently and body temperature is at its maximum, which accelerates nerve impulse conduction. Cardiovascular physiology also supports this peak: cardiac stroke volume in the evening is typically higher than in the morning.

However, endurance and mental focus may have different physiological windows. Morning workouts (08:00-11:00) are ideal for cognitive work and learning complex technical elements, as the brain has high neuroplastic potential after sleep. The physiology of adaptation shows that the body is capable of "tuning" its peaks to regular training times: if you always train at 7 AM, your body will learn to mobilize resources precisely by that time.

• Reduced HRV: Heart rate variability drops when the sleep-wake regime is disrupted.
• Appetite Disturbance: Disruption of leptin and ghrelin rhythms leads to nighttime hunger and overeating.
• Daytime Sleepiness: Indicates that your biological energy peak does not coincide with your activity schedule.

You cannot change your genetic chronotype, but you can become a master at synchronizing your life with it. Working against biorhythms is working for exhaustion.

6. Progression in Rhythm Management: From Chaos to Chronodesign

Progression in sport is impossible without stable routines. At the first stage, progression consists of establishing regular sleep and wake times (with 30-minute precision). This is the stage of "grounding" the biological clock, letting the body know when to expect load and when to expect rest. Stability is the foundation upon which all other adaptation is built.

In the second stage, progression shifts to training chronodesign. The athlete learns to distribute loads according to their daily peaks: heavy squats in the evening, stretching and tactics in the morning. Progression here is measured by the quality of exercise execution and the speed of subjective recovery. This is the stage of transition from "I must train" to "I train at the best time for my body."

1. Sleep Stabilization Stage: Eliminating factors that disrupt rhythms (blue light, late dinner).
2. Chronotyping Stage: Identifying your performance peaks and moving key sessions to this time.
3. Competitive Synchronization Stage: Gradually shifting the regime 2 weeks before a start so that peak form coincides with the competition time.

7. Scientific Basis: Genetics of Chronotypes and Sports Records

The scientific base of chronobiology identifies several primary chronotypes based on the length of the PER3 gene. "Owls" have a shorter version of the gene, "larks" a longer one. Scientific studies have established that "larks" reach their strength peak approximately 5-6 hours after waking, while "owls" do so after 11-12 hours. This scientifically explains why the results of the same athlete can vary by 10-15% depending on the testing time.

Data regarding evening records are fascinating. Most world records in athletics and swimming were set precisely between 17:00 and 20:00, which scientifically correlates with the peak of body temperature and nervous system efficiency. This is scientific confirmation that the human body is biologically engineered for maximum power at the end of the day.

8. Synergy: Light, Temperature, and Meal Timing

Biorhythms work in synergy with three primary synchronizers (zeitgebers): light, food, and physical activity. Morning light synergizes with the cortisol peak, "launching" the day. Eating at consistent times synergizes with the liver's peripheral clocks, ensuring stable blood sugar levels. Training synergizes with body temperature, enhancing the hormetic effect of the load.

• Morning Sun + Protein Breakfast: Instantly synchronizes central and peripheral clocks, blocking residual melatonin and charging with energy.
• Evening Coolness + Melatonin: Lowering the air temperature in the bedroom synergizes with the body's natural cooling before sleep, deepening rest.
• Strength Training + Evening Carb-Loading: The evening strength peak allows for glycogen depletion, which is then perfectly replenished during dinner within the anabolic window.

9. Common Mistakes: Light Pollution and Nighttime Training

A major mistake is using gadgets before bed. The blue light of screens biochemically deceives the SCN, making it think it is daytime, which blocks melatonin and "breaks" the entire sleep architecture. Another mistake is intense training later than 21:00. This sharply raises body temperature and adrenaline, creating a "circadian conflict" where the body wants to sleep but is biochemically excited.

1. Chaotic Wake-up Times: A difference of more than 1 hour between weekdays and weekends causes "social jetlag," destabilizing the nervous system.
2. Eating Before Bed: Activating digestion at night synchronizes peripheral clocks with "daytime" mode while the SCN is certain it is night, leading to metabolic disruptions.
3. Training in Complete Darkness: The lack of light stimulus during activity prevents full mobilization of the body's resources.

10. FAQ: Questions and Answers

Can an "owl" be turned into a "lark"?

The genetic chronotype cannot be changed, but one's rhythm can be "shifted" by 1-2 hours through strict light hygiene and nutritional routines.

When is the best time for stretching?

In the evening (17:00-20:00), when body temperature is at its peak and tissues are anatomically most receptive to deformation without the risk of tears.

How does coffee affect biorhythms?

Coffee in the morning helps with awakening, but after 2:00 PM it can block adenosine receptors, shifting sleep time and disrupting the rhythm.

Is it harmful to train at night if I'm used to it?

It is possible, but physiologically it is wear and tear on the organism, as you are going against millions of years of evolution, which sooner or later will manifest as hormonal problems.

What is the "melatonin window"?

It is the time interval (usually 22:00-23:00) when melatonin levels rise most rapidly. If you miss this time, the next peak will not occur for another 90 minutes.