As a sleep researcher who focuses on how sleep affects elite athlete, I have studied the effects of travel and disrupted sleep on athletes for many years. The combination of cross-country travel and athletic performance is not pretty. Travel and circadian timing matter.

Are you a lark, someone who likes being up and active in the early morning? Or are you a night owl, someone who tends to wake later and perhaps gains energy and focus as the day progresses, someone who likes to work (and play) in the evening hours?

People with delayed sleep phase feel sleepy much later in the night and need to sleep in to get sufficient sleep. As a result, they often suffer the effects of chronic lack of sleep, since most people have commitmernts to fulfill -- such as being in school or at work -- in the morning.

In our modern society of too-late work hours and too much time in front of computer screens, we are listening to our social clocks more than our physiological clocks, causing a greater sleep gap, known as social jetlag.

Ingrained in all of us is a natural instinct for continuity in our sleeping and waking schedule each day -- our circadian rhythms. While we can choose to ignore this need for continuity by working at night or sleeping late into the day, it carries consequences.