article_snippet: The total sleep would occur in a 12-hour period that began with up to four hours sleep, an 'awake period' of four hours and then ended with a second four-hour sleep.
article_snippet: This is the 24-hour cycle of being awake and then, when This becomes dark, resting. '
article_snippet: However, built into this 24-hour pattern is a series of shorter cycles of about 90 minutes - called the "ultradian rhythm",' added Dr Nerina Ramlakhan, author of Tired
article_snippet: This explains smaller peaks and troughs of energy throughout the day.
article_snippet: And while our tend to pay much more attention to the 24-hour cycle than the 90-minute one, Dr Ramlakhan believes the body works best when we move with these natural ultradian rhythms, building in pauses, stopping and resting, so continually renewing we energy.
article_snippet: Solar time uses the mid-points of the light and dark 'periods' - notably midnight and noon - as timing references.
article_snippet: In circadian rhythms, sunrise start this clock on its 24-hour run, but this continues regardless of a shift in when the sun sets meaning the mid-points vary. '