Sleep as the Most Important Form of Recovery
Ferenc Soma Kovács, All-American middle-distance runner
Biohacking and Elite Sports – A Shared Goal, Different Paths
We hear from countless sources that an adequate quantity and quality of sleep is indispensable for elite athletes. In the 2020s, we also constantly encounter so-called “biohackers” across social media platforms. This trendy English loanword refers to curious and highly motivated individuals who tirelessly optimize their training, nutrition, and recovery, while reducing or completely eliminating environmental and internal factors that may harm their health. Most often, they pursue these practices in order to slow biological aging and preserve their health and overall quality of life.
Although elite athletes are sometimes exposed to levels of physical load and intensity that may even be detrimental to their health and well-being, their goals in the realm of recovery fully align with those of biohackers: to maximize the body’s self-healing and self-cleansing processes.
Brian Johnson and the Question of Optimized Sleep
Perhaps the most well-known biohacker today is the American entrepreneur Brian Johnson, whose primary goal is to live 150 healthy years on this planet. To achieve this, Brian follows an ascetic lifestyle and makes use of modern medical technologies. I have personally been following the experiments he conducts on his own body for roughly four years, along with their results. His experiences and insights related to sleep inspired me to explore the topic more deeply. The key findings of my research are presented in the article below.
The Evolutionary Paradox of Sleep – Why Do We Spend One-Third of Our Lives Resting?
Despite the vast number of complex medical studies conducted on sleep, one of the greatest mysteries of human physiology remains: why do we spend roughly one-third of our lives asleep? From an evolutionary perspective, time spent asleep—unconscious and unaware—is clearly disadvantageous, as it makes us vulnerable and exposed to predators.
At the same time, numerous clinical studies have demonstrated that insufficient sleep contributes to tumor growth and weakens the immune system. For now, we can conclude that although humans appear to sleep an extraordinary amount of time, this is necessary—because inadequate sleep ultimately leads to systemic “malfunction” of the body.
The Biological Functions of Sleep and Their Relevance to Sports Physiology
Building on the previous discussion, current sleep science (somnology) offers the following, though still inconclusive, explanation for why we sleep. First, the body’s metabolism slows down during sleep, meaning the organism uses less energy, and the remaining energy is redirected toward cellular energy restoration. Second, growth hormones are released during sleep, which repair cells and tissues damaged throughout the day. Third, the body restores balance and reduces excessive inflammatory responses.
This latter process naturally occurs in the daily lives of most endurance athletes. Eccentric muscle contractions induced by downhill running, VO₂max efforts, or sustained performance at race pace all generate oxidative stress for the athlete. In response to this oxidative stress, the body sends immune cells to the muscle tissue to clear away damaged cells. These immune cells ultimately catalyze the adaptive processes.
Brain Regeneration and the Glymphatic System
Sleep researchers unanimously agree that of all our organs, the brain has the greatest need for restorative nighttime sleep. On the one hand, this is because learning processes and memory consolidation occur during the REM (rapid eye movement) phase. During this stage, the brain summarizes and organizes the knowledge acquired during the day, and some suggest that our dreams are abstract projections of this information processing.
On the other hand, the brain produces a significant amount of metabolic waste during the day, which can only be cleared through the process of sleep. It may sound surprising at first, but although the brain accounts for only about two percent of our body weight, it is responsible for twenty percent of the body’s oxygen consumption and sixty percent of glucose utilization.
Although it may seem paradoxical, the lymphatic system does not permeate the brain—the organ with the highest metabolic rate in the body. Instead, the removal of metabolic waste from the brain is performed by the so-called glymphatic system. In practice, this process works as follows: neurons in the brain compress like a sponge, expelling toxins and other metabolic byproducts into the intercellular space.
The Cognitive and Physiological Consequences of Sleep Deprivation
Problems arise when this self-cleansing process does not occur properly each night. According to experts, cognitive performance after 18 hours of wakefulness declines to a level comparable to having a blood alcohol concentration of 0.05%. A full day of sleep deprivation can equate to the impairment caused by a 0.10% blood alcohol level.
Objective Measurement of Sleep – Practical Metrics and Their Interpretation
After understanding why we sleep and what biological processes occur in the body during sleep, let us now take a look at the parameters that can be easily measured and analyzed at home, providing the most accurate picture of our sleep quality. The Polar Loop proves to be an excellent companion for monitoring restorative sleep.
Total Sleep Time:
Sleep duration is detected from the moment the device first senses that you have entered stage one non-REM sleep. It continues until you wake up, get out of bed, and begin your daily activities.
Sleep Structure:
The device is capable of identifying which stage of sleep you are currently in (light, deep, REM). It also summarizes interruptions and indicates whether you completed full sleep cycles during the night.
Heart Rate Variability (HRV):
HRV refers to the variation in time intervals between individual heartbeats. These intervals are naturally variable. Higher HRV levels indicate better autonomic nervous system regulation and balanced interaction between the sympathetic (“fight or flight”) and parasympathetic (“rest and digest”) branches.
Oxygen Saturation (SpO₂):
Knowing your oxygen saturation may help signal certain conditions, such as chronic fatigue, overtraining, or the possibility of obstructive sleep apnea. Since the Polar Loop does not measure peripheral oxygen saturation, this parameter must be assessed with another device, such as another Polar watch or a standard medical pulse oximeter.
Movement Detection:
In the case of the Polar Loop, wrist movement is detected through the built-in 3D accelerometer. This can help determine whether someone is sleeping restlessly and may indirectly provide insight into REM sleep quality, which is typically accompanied by sleep paralysis (absence of muscle movement).
Finally, I would like to highlight a few important Polar Loop features.
Sleep and Internal Rhythm:
The body’s internal biological rhythm determines when you naturally feel sleepy or alert. On the graph, the purple lines represent the so-called “sleep window” — the period during which your body is biologically prepared for sleep. The blue bars, on the other hand, represent your actual sleep rhythm. Synchronizing the two naturally enables better sleep quality. This metric can be particularly useful for elite athletes who frequently travel across time zones.
Sleep Gate:
This predicts the time when your body is biologically ready to fall asleep. However, your internal rhythm does not always align with your daily obligations. Therefore, the so-called “sleep gate” time does not always coincide with your ideal bedtime in practice.
Sleep Gate Recognizability:
On many occasions, an elite athlete’s bedtime differs from previous evenings. This irregularity significantly affects the monthly average of bedtimes, which in turn results in a less consistent calculation of the sleep gate. To address this issue, Polar introduced the Sleep Gate Recognizability scale (ranging from one to three), which indicates the statistical variability of your sleep gate values. I recommend relying on the sleep gate’s suggested bedtime only when the Sleep Gate Recognizability score reaches 3/3.
Sleep Score (1–100):
A composite value that condenses both the quantity and quality of your sleep into a single numerical score.
Training Insight Supported by Polar
Sleep tracking, HRV monitoring, and internal rhythm analysis are part of how we approach recovery at DTC.
If you’re interested in exploring Polar devices, you can use our partner code POLARDTC15 for 15% off selected products.
References
Johnson, B. (2024, October 10). How I fixed my terrible sleep. Blueprint.
Naganawa, S., Taoka, T., Ito, R., & Kawamura, M. (2024). The glymphatic system in humans: Investigations with magnetic resonance imaging. Investigative Radiology, 59(1), 1–12.
Williamson, A. M., & Feyer, A. (2000). Moderate sleep deprivation produces impairments in cognitive and motor performance equivalent to legally prescribed levels of alcohol intoxication. Occupational and Environmental Medicine, 57(10), 649–655.