What is Freerunning sleep?
'''Freerunning sleep''' can be [[sleep]] which is not adjusted, ''entrained'', to the 24-hour [[cycle]] in nature. Sleep which is entrained to 24 hours but is not artificially regulated by alarm clocks etc. can also be called freerunning sleep. == Scientific experiments == [[Animal]]s which are kept in a [[laboratory]] for [[research]] in ''constant conditions'', that is in constant [[light]] or constant dark, will ''freerun''. They live by their built-in [[circadian rhythm]]s. Each [[day]] will be a little bit shorter or a little bit longer than 24 hours. It will be shorter if the animal's natural [[cycle]] is less than 24 hours long. The animals sleep and are active as usual, but their timing gets to be farther and farther off. [[Scientist]]s let the animals freerun and then do [[experiment]]s to see what sort of [[signal]]s are most effective at entraining them. They also experiment to see how long or short a cycle that animal can be entrained to. Some animals can be entrained to a 22-hour day, but they can not be entrained to a 20-hour day. Light is the most effective signal. Some animals are quite easily entrained by the timing of [[meal]]s. [[Exercise]] is a signal for some animals. [[Heat]] is not effective. Sometimes [[wikt:people|people]] stay in a laboratory for a few days in very low light without any [[knowledge]] of the [[time]]. Such experiments show that [[adult]]s, both older and younger, have a circadian cycle which is 24 hours and 11 minutes, on average. == People freerunning == === Illness === Some people have a condition, a [[circadian rhythm sleep disorder]], which makes them freerun all the time, even if they get out into daylight and eat regular meals. Many of these people are [[blind]], but some of them can see. They have a long circadian cycle and they do not entrain. Scientists do not yet know why. === Intentional freerunning === Some people believe they will be more [[health]]y if they do not sleep on a regular [[schedule]]. They try to go to [[bed]] only when t