In the first part of our series about sleep, we looked at the importance of regular sleep and the underlying circadian rhythm. In addition to regularity and quality, the different stages of sleep and the resulting total sleep time also play a crucial role – if not the most important role.
What happens while we sleep?
While we sleep, we go through different stages of sleep, each with specific functions and properties. Some body functions, such as body temperature, frequency in breathing and cortical activity, reach their minimum values, others, such as the levels of certain hormones, reach their peak values at night. During sleep, the whole body is in a highly sensitive state, which needs to be protected and supported.
The most famous and important stages of sleep are deep sleep and REM sleep, which name is derived from the observation of extremely rapid eye movements (“Rapid Eye Movement”). The various sleep stages repeat themselves in the course of a night, but vary in length and frequency within the total sleep time. These stages are measured and classified based on the frequency of brain waves.
Deep sleep - the energizer
The first half of the night is dominated by two stages of deep sleep, with a short REM stage in between. Deep sleep is of particular importance for the regeneration, repair, and formation of new tissue – especially muscle tissue and the immune system. An increased protein synthesis is taking place. In this sleep stage, growth processes, physical processing of training stimuli and hence muscle development and fat reduction run at maximum speed.
REM sleep - the mental coach
The second half of the night is dominated by three or four REM stages, the length of which increases with the duration of the total time of sleep. In between, we fall into two stages of medium-deep sleep. REM sleep is particularly important for psychological recovery: We process the impressions of the day as well as emotions, and we internalize new learning such as motion sequences – hence it also makes us smarter!
When is the appropriate waking time?
During the transition into or out of REM sleep, waking up is easiest, because brain frequencies change and are therefore unstable, which marks the start or the end of a sleep cycle. This happens approximately every 70 to 100 minutes – on average every 90 minutes.
Waking up from deep sleep, however, is very difficult. Initially, we often cannot orient ourselves and fall asleep again immediately and we do not even remember having been awake. When we are woken up during deep sleep and stay awake, the effects are often felt for several more hours – if not throughout the day. For one, the recovery was incomplete. In addition, hormone levels during deep sleep do not fit the state of wakefulness, so this imbalance must first undergo a time-consuming regulation.
Waking up in the middle of a REM stage may have similar effects, because psychological recovery is incomplete. The hormone status during the morning REM stages resembles the waking stage more, which is why waking up from this sleep stage is much easier. Persistent lack of REM stages, however, may manifest itself in irritability, difficulty concentrating, and increased feeling of hunger and aggressiveness (urge).
What does this have to do with total sleep time?
None of the sleep stages should therefore be shortened or even revoked and certainly not over a longer period of time. To ensure this, however, a certain total sleep time is necessary so that the body can go through all stages of sleep to completion. Let us assume a 90-minute sleep cycle on average and the need for at least 4 sleep cycles per night. This would call for a minimum sleep time of 6 hours.
Is more sleep always better?
Although sleep times of 9 hours or more show positive effects on physical performance, life expectancy – paradoxically – decreases with 9 hours of sleep or more, and the risk of stroke, heart disease and diabetes even increases. This is caused by the permanently elevated levels of the sleep hormone melatonin, because long-term abnormalities of every hormone have an effect on the overall hormone status with corresponding consequences. Permanently higher melatonin levels are also the reason why people who sleep very much still feel ironically constantly tired and without energy. With 9 hours of sleep or more, effects on spiritual recovery are controversial.
How much sleep is enough?
The length of the sleep cycles varies from person to person and is also dependent on factors such as sleep routine and quality, which is why there is no generally accepted optimum amount of sleep. Nevertheless, for the above reasons, everyone should stay within normal range and aspire to have 6 to 9 hours of sleep. Those who fall into this sleep time range and still feel tired and exhausted, should check whether they can adjust their sleep duration a little more closely. Sleep Apps and Body Tracker can provide good reference points for the individual need to sleep.
Of course, not everyone can stick to the optimum sleep duration every night. This is not serious, because our body can easily compensate for small sleep infractions. Too little or too much sleep over an extended period of time, however, is definitely counterproductive and affects training, performance, concentration and overall health.