Each individual’s energy peaks occur at different times. Everyone knows a “morning person” that wakes up cheery and very energetic. Everyone also knows an “evening person” that can hardly get out of bed in the morning and tends to be sluggish for the first several hours of the day. For both, the tables turn late in the evening: Morning people can barely keep their eyes open, while evening people are full of energy.

Whether we are a morning person or an evening person is determined by our internal biological clock, called a circadian rhythm (from Latin circa dias, “about a day”). These rhythms derive from a complex system of internal pacemakers that regulate the timing of hundreds of biological behaviors and processes, including the sleep/wake cycle, growth, cell division, strength, moods and actions. They also affect our susceptibility to stress and illness. The scientific study of these biological rhythms is called chronobiology.

Most people are either moderate morning or evening types, others are neutral, and approximately 20 percent of the population fall into either “extreme” category.

There is little we can do to change some of the physiological aspects that are linked to distinct biological rhythms programmed into our genes. Circadian rhythms behave like an oscillator, causing daily fluctuations, with each cycle lasting for different amounts of time. We can, however, adjust physical and mental limits according to how we feel.

By mastering these rhythms, we can 
optimize our potential to manage stress and 
achieve peak performance. Maintaining a regular schedule, exposing ourselves to natural light in the morning, and avoiding blue light and screens in the late evening can help to balance our internal clock. In addition, it’s best to schedule the most challenging tasks for times when we have the most energy.