The average length of a movie is 90 minutes. And that doesn't seem to be an accident. If you ask the experts on these things, they'll tell you that many of the functions of your body and brain are set to operate in cycles of roughly 90 minutes each. And going with the flow of biorhythms helps you maintain motivation and attention for whatever the task at hand.
We humans, like all other animals, live in a world that is marked most basically and most invariably by cycles of day and night. This external fact of life has its counterpart in our bodies; somewhere in the dawn of time these fundamental rhythms were etched into our brains, so that we would be organized in synchrony with our environment.
How the brain does this is through an elaborate system of signals kicked off by light. Light strikes our eyes, certain nerve cells in our eyes detect the wavelengths of natural light, they signal the brain, and the brain sends messages to virtually every system of the body to rev up or ramp down. By virtue of this control center, among others, the performance of bodily systems is coordinated one with the other.
Like the world around us, our biological clocks are set to tick in cycles of approximately 24 hours. We are designed to sleep and wake in cycles of roughly 24 hours, otherwise known as our basic circadian rhythm.
Study after study has shown that we function best physiologically and psychologically when our internal cycles are well-synchronized with those of the external world. If we mess up our sleep and wake patterns, for example, we feel out of sorts. Mood suffers. Alertness wanes and concentration falters. Memory gets shoddy. And performance on important tasks takes a dive. You don't feel coherent, may not even be able to speak coherently.
Physical well being suffers too. The immune system is compromised, leading to higher likelihood of a cold or flu. Hormones are in disarray, stomach problems arise. These are common complaints among those doing shift work, experiencing jet lag and suffering insomnia.
Many of the body's major systems run on circadian rhythms. Cardiovascular activity has a circadian pattern, as does body temperature, metabolic functions and liver and kidney function.
Yet, it is increasingly common for people to override basic biorhythms and ignore the biological signals for sleep. Stimulation is available around the clock in the form of the internet, to name just one attraction.
According to Dr. Roseanne Armitage, an expert on sleep at the University of Michigan, the sleep patterns of Americans are getting worse, increasingly out of phase with the natural rhythm. People are staying up later than ever and it's happening at a progressively younger age.
Interestingly, she points out, the less people sleep, the more they get depressed. And the worsening of sleep among Americans has been accompanied by real increases in the incidence of clinical depression.
In addition to the body rhythms set to the day, there are other body rhythms occurring in cycles of shorter duration, often multiple times during the day. These are known as ultradian rhythms. With these, too, biological and psychological alertness and performance are very strongly correlated to the synchronization of your actions with the body's natural patterns.
Perhaps the best-known of the ultradian rhythms are the dream cycles of sleep. Researchers have long known that we cycle through deepening states of sleep until we fall into dream sleep, commonly known as REM sleep, for the rapid eye movements that occur as we dream. Within a night, we complete roughly five cycles of REM sleep. Disturbance of these sleep cycles interferes with mood regulation and leads to depression.
According to Dr. Armitage, our bodies are similarly set for performance of most tasks in 90-minute cycles. Every 90 minutes, she believes, we need to take a mental break because otherwise our concentration, memory and learning ability start fading.
Staying in tune with your body's cycles puts you in line to achieve peak performance. Failure to synchronize your patterns of activity and stimulation with your body's natural circadian and ultradian rhythms puts a stress on the system.
The most reliable way to set your body clock is to schedule exposure to natural light in the early morning. It allows you to fall asleep at night. The corollary is to avoid bright light at night. And avoid computer usage at night.