Sleep Is Controlled By Circadian & Ultradian Rhythms

Biological Rhythms

Sleep is controlled by 2 basic biological rhythms

  • Circadian Rhythms – often referred to as your body clock which cycles in periods a little more than 24 hours. A fact that can cause problems as will be explained later.
  • Ultradian Rhythms – These are rhythms that cycle more frequently than 24 hours. The most relevant of which is your sleep cycle which lasts around 1.5 hours. It does vary with the individual and has been measured as lasting anywhere between 75 and 120 minutes.


Circadian Rhythms

Your natural body clock has a cycle that lasts longer than a day, so to stay synchronised it needs to be regularly reset. Sunlight and habitual daily routines of exercise and eating are the principle ways to do this. Getting up and going to sleep at a regular times is important. Dull as it may seem, routine is essential to your good health.

The circadian cycle is most evident in your body temperature. Contrary to what you may have thought, this fluctuates over the day and night and has a large effect on your body’s activity and consequently on sleep. Matching your daily routine to this temperature fluctuation is the single best way to reestablish a healthy sleep pattern. The 18 step program below has a number of suggestions based on this principle.



To understand ultradian rhythms you need to know a little about brain wave activity in the brain.

Brainwaves are the tiny electrical pulses, only a few millionths of a volt, which occur during various types of brain activity such as relaxing, learning, and thinking. Different brainwaves can occur at the same time in different parts of the brain.

They are recorded on an electroencephalograph (EEG) by placing electrodes directly onto the scalp.

Brainwaves are categorized according to their frequency, which is shown as hertz (Hz) – the number of times a wave occurs each second. The main categories are

There at least 6 categories of brain waves but we are only going to discuss the main 4 that are related to sleep. If you need more detail then please see the BrainWaves page.

Gamma 38 – 90Hz
Beta 14 – 37Hz
SMR 12 – 15Hz
Alpha 8 – 12Hz
Theta 4 – 7Hz
Delta 0.5 – 3Hz

Beta Waves Fully awake and alert.


Alpha Waves Relaxed or daydreaming. Generally associated with right-brain thinking activity.

Theta Waves These waves are associated with flashes of dreamlike imagery, inspiration, and your long-forgotten memories. It is common in deep states of meditation.


Delta Waves Long, slow, undulating waves. Delta is the slowest of all four brain wave frequencies. Most commonly associated with deep sleep, certain frequencies in the Delta range also trigger the release of Human Growth Hormone and so is beneficial for healing and regeneration.

delta waves



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