Polyphasic sleep is a theory regarding sleep patterns. First coined by psychologist J.S.Szymanksi, the concept of polyphasic sleep has to do with establishing a pattern of multiple sessions of sleep during any given twenty-four hour period. This is in contrast to the concept of biphasic sleep, which addresses the idea of one extended period of sleep during the same time frame.
The theory of polyphasic sleep has to do with engaging in a daily schedule that allows for sleeping small amounts throughout the course of the day and evening hours, rather than setting aside a block of eight hours for a long session of sleep. This approach of segmented sleep is understood by proponents to be especially beneficial for people who are dealing with sleep disorders or who have recently experienced a health or life crisis that makes it difficult to sleep for more than a short time. By building in multiple sleep sessions throughout the day, the body learns to adapt to this approach and is able to utilize these shorter sleep periods to greater advantage.
Some proponents of polyphasic sleep see the approach as a means of compensating short term when external factors make it difficult to set aside a full eight hours for sleeping. Others see polyphasic sleep as a viable sleep alternative that can be utilized long term. The usual line of thinking is that the body requires an average of eight hours of accumulated sleep time during a twenty-four hour period. As long as an individual is able to achieve this goal, it does not matter if the sleep is obtained in multiple naps or in one long session.
Critics of polyphasic sleep sometimes note that while napping in addition to a full night of rest can be helpful when the individual is recuperating from illness or other factors, the napping is not a substitute. The basic thought process is that the body has to enter into an adaptive state to slip into the right phase to achieve a deep recuperative sleep. This most often is accomplished by an extended period of sleeping. Shorter naps are not understood to provide this level of deep sleep, and thus will not provide the same level of refreshment and rejuvenation that extended sleep can provide.