Biological Rhythms

The basic time adaptation in biological rhythms is entrained, which means it is influenced by external cues. Other aspects of our biological rhythms are so influential that most of us adapt our activities to the time of day during which we function best. Some people are morning people, while others are night people. Morning people (sometimes called larks) wake up with lots of energy and perform their best work in the early hours of the day. Night people are sluggish in the morning and do their best work late in the day or in the evening. They are often called owls. Work environments in our society are not adjusted to these differences, though, and many people have to work at times when they are least likely to be productive.

An experiment that took place in New Mexico in 1989, when a woman spent 130 days in isolation in a cave that had no natural light, demonstrated how external cues affect our biological clocks. After six weeks, she was functioning within a 44 hour cycle of sleeping and wakefulness. Her perception of time was also compressed to a considerable degree. In other experiments, volunteers drifted into a 25-hour day, while others have experienced 50-hour days or irregular cyclical patterns.