Chronotype research began with the identification of "clock genes" — particularly PER3 — which regulate your circadian rhythm at the molecular level. A longer PER3 gene variant correlates with morning preference (Lion), while shorter variants correlate with evening preference (Wolf).

Dr. Michael Breus expanded the traditional two-type (morning lark / night owl) model into four chronotypes: Lion, Bear, Wolf, and Dolphin. This framework more accurately captures the spectrum of human sleep-wake patterns and has practical implications for scheduling every aspect of performance.

Research published in Chronobiology International demonstrates that aligning training, nutrition, and cognitive demands with your chronotype can improve performance by 10-26%. Cold and heat exposure timing is especially important — cortisol, testosterone, and growth hormone responses vary significantly based on time of day and chronotype.