A sleep doctor says 4 types of animals represent how people sleep - and these are the ideal daily routines for each

When it comes to health and productivity, it's not just about what you do - eating right, exercising, and working hard - it's also about when you do it.

Chronobiology is the study of internal clocks, how they differ among people, and how you can adjust your daily schedule to suit your unique biological rhythm. Each person's rhythm, or chronotype, is different.

According to psychologist and sleep specialist Dr. Michael Breus, there are four chronotypes, which he labels dolphins, lions, bears, and wolves. Roughly half the population is made up of bears; the rest is split among dolphins, lions, and wolves.

Breus' website includes a diagnostic quiz readers can take to try to identify their chronotype.

In Breus' book "The Power of When," he outlines the ideal daily routine for each chronotype. Below, you'll find the highlights of those schedules.

Keep in mind that it's virtually impossible to have a perfect day every day, so make the changes you realistically can.

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