Your circadian rhythm is the part of your brain that tells every cell in the body when to be active and inactive. Circadian is a mouthful, so RISE calls it your energy schedule because it effectively predicts when your body is ready to perform or wants to rest. It's different for every person and shifts slowly — in some cases, up to an hour per day.
The clock inside your head dictates your energy cycles every day. The duration of the clock (chronotype) is determined by genetics and age, with the timing of the energy cycles changing daily based on your sleep and relative light exposure.
Understanding your circadian rhythm helps you listen to your body. You can sense and predict the right times to be active, rest, and sleep. RISE refers to your daily energy cycles as peaks and dips. The timing of these peaks and dips is unique to you based on your chronotype, but the primary sequence is the same for everyone.
Do you consider yourself a morning person or an evening person? This distinction is a basic indicator of your underlying circadian rhythm. It's called your chronotype, and we use it to define your preference for earlier or later sleep time and wake time. Society's daily clock is 24 hours, but if you are an evening (late) chronotype, the clock in your head is longer — if you're a morning (early) type, your clock is shorter than 24 hours.
For simplicity, we can group chronotypes into morning people and evening people. However, science measures them on a continuous scale. In a recent study, researchers found 351 genetic variations associated with being a morning person. Your exact chronotype is specific to your genetics, age, and exposure to environmental light. The Center for Environmental Therapeutics provides an online survey to help you find and understand your chronotype.
While your chronotype is set at birth, we all follow the same cycle of relative change to our circadian rhythm with age. You reach maximum lateness at around the age of 20 as it coincides with the end of adolescence. From that point forward, the clock in your head gets progressively shorter (earlier) as you get older.
Throughout life, the clock in our head is often at odds with our partners, children, friends, jobs, and society's clock. For example, the majority of university students experience a decrease in performance simply because their circadian rhythm is misaligned with their school schedule. The impact is real and triggered by a variety of life events at any age.
Life happens, we get misaligned, but by understanding our circadian rhythm and chronotypes, we can rediscover our natural rhythm to sleep, live, and adapt together.
Genetics and age are the major factors in determining chronotypes. However, behavior and environment can impact the timing of your energy cycles daily. If you've experienced jetlag you've felt an extreme case of circadian rhythm misalignment. Here are some of the daily inputs that can alter the timing of your melatonin window, energy peaks, and dips.
Many of us compensate for inflexible work schedules during the week by staying up later and sleeping later on the weekends. This behavior creates a phenomenon you feel on Monday morning called social jetlag. The result is a disruption in your circadian rhythm that affects sleep quality and psychological wellbeing.
Your circadian rhythm is composed of cycles of energy peaks and dips. The amount of sleep you are getting determines the height of the peaks and depth of the dips. So, the higher your sleep debt, the lower the dips feel. Low sleep debt optimizes the peaks. Your circadian rhythm tells your body when to sleep at night, and sleep debt determines your cognitive abilities during the day.
Light is by far the most significant input to shift your circadian rhythm. More light exposure in the morning means that you'll feel more alert sooner. More light exposure later in the day will also make you stay up later. You need darkness to help signal to your circadian rhythm to wind-down and start producing melatonin.
Your sleep times and associated light exposure are the primary signals to your circadian rhythm. RISE uses your recent sleep history data and some fancy algorithms to estimate your personal daily energy cycles.
The widely adopted framework scientists use for researching fatigue and performance is called the two-process model of sleep regulation — the interaction between sleep debt and circadian rhythm. We call this model the 2 Laws of Sleep and it's the scientific basis of RISE.